ALBERT

Notes: The mechanics of “springy” or “hard elastic” row-crystallized polymers were investigated. It was found that their unique tensile and physical properties could be explained by adhesive fracture mechanics and simple beam deflection. The deformed lamellae had an apparent negligible modulus of flexural rigidity. An adhesive failure model was designed which duplicated all the tensile characteristics of springy polymers, including constant lateral contraction, critical stress, peel stress, rehealing, energetic elasticity, and cyclic strain behavior. The ideal relative density change as a function of strain was found to be the same for all springy polymers. Dynamic infrared analysis showed that the molecular orientation decreased during the deformation of springy polypropylene films. The latter is due to the deflection of lamellae. Rehealing was accompanied by a time-dependent reversal of orientation. The enthalpic elasticity is derived from the strain energy of the lamellar network.

Notes: Samples of two helically wound monofilaments were used as experimental models to check the theoretical expression for light scattering from helixes. A method of estimating the pitch and tilt of the helixes was outlined and the results were compared with measurements from microscopy. The agreement was satisfactory. Layer line streaking and splitting was observed and explained in terms of irregularity of the helical parameters. Samples of several helically wound monofilaments were also prepared and their scattering patterns were compared with those from native and regenerated cellulosic fibers.

Notes: Dynamic loss modulus curves have been determined over a temperature range beginning at liquid nitrogen temperature for poly-α-olefin polymers containing various ring structures, i.e., phenyl, cyclohexyl, cyclopentyl, and naphthyl, in the side chain. Glass transition and appropriate secondary relaxation temperatures were observed for each polymer. Separation of each pendant ring structure from the main backbone chain by successive additions of methylene units results in lower glass-transition temperatures. Comparison of polymers with similar side chains and different ring structures shows that the respective glass-transition temperatures decrease in the order naphthyl 〉 cyclohexyl 〉 phenyl 〉 cyclopentyl. Secondary relaxation peaks were obtained at about -150°C for polymers containing the cyclohexyl and cyclopentyl rings. A similar peak was observed for the polymer possessing a phenyl ring separated from the main chain backbone by two methylene units. The comparable polymer containing the naphthyl ring structure exhibited a broad secondary relaxation peak centered at -20°C. The polymers possessing cyclohexyl rings separated from the main chain backbone by one or two methylene units had an additional low temperature peak at -80°C. The molecular mechanism associated with this relaxation may be related to intramolecular transformations of the cyclohexyl ring between its “chair-chair” conformations.

Notes: Tensile deformation of poly(methyl methacrylate) carried out under hydrostatic pressures up to 4 kbar has shown that the pressure-transmitting fluid (silicone oil) strongly affects the mechanical properties of this polymer. Unsealed specimens fractured in a brittle manner at almost the same strain of 5% in the whole pressure range examined, while specimens sealed with Teflon tape and rubber showed a brittle to ductile transition at only 0.25 kbar. At this pressure, the craze initiation and shear band initiation stresses were found to become equal. The pressure dependence of the shear band initiation stress could be expressed well with a “nonlinear” pressure-dependent von Mises criterion and the onset of the shear banding was proved to relate to the enthalpy energy density stored in the specimen. The combination of the nonlinear pressure-dependent von Mises criterion and the enthaply energy density concept enabled us to predict the pressure dependence of Young's modulus.

Notes: Styrene-acrylonitrile (St-AN) copolymers of three compositions - 27.4 mole-% (SA1); 38.5 mole-% (SA2); and 47.5 mole-% (SA3) acrylonitrile - and styrene-methyl methacrylate (St-MMA) copolymer (SM) of 46.5 mole-% methyl methacrylate were prepared by bulk polymerization at 60°C with benzoyl peroxide as the initiator, and were then fractionated. The molecular weights of unfractionated and fractionated samples were determined by light scattering in a number of solvents. The [η] versus M̄w relations at 30°C were established for SA1, SA2, SM, and polystyrene (PSt) in ethyl acetate (EAc), dimethyl formamide (DMF), and γ-butyrolactone (γ-BL), and for SA3 in methyl ethyl ketone (MEK), DMF, and γ-BL. Second virial coefficients A2 and the Huggins constant were determined. From values of A2 and the exponent a of the Mark-Houwink relation it is seen that the solvent power for samples SA1, SA2, and PSt is in the order EAc 〈 γ-BL 〈 DMF, while for sample SA3 the solvent power is in the order MEK 〈 γ-BL 〈 DMF. The solvent power decreases with an increase in AN content. The solvent power of the three solvents used for SM copolymer sample is practically the same within experimental errors. From the a values it is concluded that in a given solvent the copolymer chains are more extended than the corresponding homopolymers.

Notes: The dielectric relaxation behavior of three sodium polyphosphates with different but low degrees of polymerization in aqueous solution (without salt) has been investigated between 8 kHz and 100 MHz. The highest molecular weight sample (DP 338) exhibits two dispersion regions as is generally observed with synthetic polyelectrolytes at higher degrees of polymerization and is interpreted, according to the theory of van der Touw and Mandel, by attributing a certain flexibility to the polymer chain. The experimentally determined relaxation time of the high-frequency dispersion is in fair agreement with the theoretically calculated value. For the lowest molecular weight sample (DP 112) the experimental results can best be described by a single dispersion curve pointing to a rigid, more or less stretched, conformation of the polyion in agreement with theoretical predictions. For the sample of intermediate molecular weight (DP 198) the situation is borderline as it is possible to describe the relaxation behavior by either one or two dispersion regions; it is, however, concluded from an analysis of the dielectric results that the average conformation is rather extended, but not completely rigid.

Notes: Samples of an S-B-S three block copolymer exhibiting a lamellar morphology have been prepared, in which the macrolattice formed from the segregated amorphous is uniformly oriented throughout the sample volume. The associated optical anisotropy has been studied in the unswollen state and in the presence of preferential solvents for the polybutadiene phase. The results obtained are consistent with form birefringence being the dominant contribution to the observed birefringence. There is a small contribution from a slight molecular orientation, corresponding to polystyrene chains perpendicular to the lamellar surfaces. The form birefringence is appropriately modified when the sample is in the swollen state by molecular orientation produced in the polybutadiene, due to the anisotropic dimensional changes in the sample. The implication of the results as regards the nature of the polybutadiene phase is also discussed.

Notes: The photoconductivity of poly(N-acryloylcarbazole) (PACz), with the pendant carbazolyl group only a short distance from the skeletal chain of the polymer but separated from it by a carbonyl group, is investigated and compared with that of poly(N-vinylcarbazole) (PVCz). There is no significant difference between PACz and PVCz in the temperature, light intensity, and spectral dependences of the photocurrent. The photoconductivity of PACz, however, is much inferior to that of PVCz and even to that of poly(N-carbazolylethylvinylether), a representative vinyl polymer with pendant carbazolyl groups far from the skeletal chain. The poor photoconductivity of PACz is discussed in relation to the intensity of the electronic interaction between neighboring carbazolyl groups in the polymer chain and to singlet exciton migration. It is attributed mainly to an extremely low efficiency of extrinsic carrier generation via a singlet exciton, which is due to the poor electron-donating character and the extremely short lifetime of a singlet exciton in the presence of the carbonyl group.

Notes: The thermal degradation of polyoxymethylene produced by the solid-state polymerization of trioxane crystals has been studied. Changes in small-angle and wide-angle x-ray patterns, weight loss, and density have been measured in specimens heated in air at 175°C, 185°C, and 195°C. The polyoxymethylene contained material in two different crystallographic orientations, which behaved differently. Material in the so-called “twin” orientation melted preferentially at 185°C and 195°C, and at 185°C resolidified on cooling in parallel to the main orientation, in a lamellar structure. At 195°C, randomly oriented material was produced on resolidification. At 175°C, there was no evidence of melting or the formation of a lamellar structure, but the twin material was preferentially degraded so that only material in the main orientation remained after a time of 1500 min. The more rapid loss by degradation of the twin material was attributed to its having a lower molecular weight than the material in the main orientation.

Notes: A wide-angle x-ray method has been developed by which quantitative structural information can be obtained on nylon-6 yarns. To this end, experimental equatorial diffractometer scans measured in transmission were fitted to a mathematical model describing the profiles as the envelopes of three bell-shaped functions. Four different models were investigated using, respectively, Gauss, Lorentz (Cauchy), Logistic, and Pearson-VII functions. The last model, which can be regarded as a generalized Lorentz function, gave the best fit. On the basis of a statistical analysis of the results of well-separated x-ray peaks, two parameters could be fixed. Another reduction of the number of parameters was achieved by interrelating the peak areas of the two outer reflections. These reductions widened the applicability of a computer program based on the aforementioned model to highly overlapping x-ray peaks. So the whole variety of x-ray scans, which can be obtained from nylon-6 yarns made under widely varying process conditions, can be well described. The fitting procedures provide unique solutions and hence objectively determined parameters.

Notes: The kinetics of formation of a swollen surface layer by diffusion of liquid solvent into solid poly(vinyl chloride) in the glassy state has been studied. The apparent Fickian diffusion coefficients of cyclohexanone, cyclopentanone, tetrahydropyrane, 1,2-dichloroethane, N,N-dimethyl-formamide, and monohalogen derivatives of benzene in PVC is calculated with the use of Crank's model for discontinuous change of diffusion coefficient with concentration. It is found that the apparent activation energy for diffusion is in the range 6-17 kcal/mole and is dependent on the polarity of the solvent molecule.

Notes: Persistent polarization in poly(vinylidene fluoride) thermoelectrets prepared under high electric field has been studied by measurements of depolarization and pyroelectricity. Various polarizations are examined in detail; the polarizations related to a characteristic molecular motion near 60°C and the polarizing temperature are not responsible for the major piezoelectric effect in β-form electrets. The piezoelectricity is attributed to a polarization appearing near the melting temperature. The persistent polarization corresponding to d31 of 2 × 10-11 coul/N is about 5 × 10-6 coul/cm2. The pyroelectricity of β-form electrets is linearly correlated with the piezoelectricity.

Notes: Three transitions have been found with peaks at 130°C (α), 88°C (β), and -65°C (γ), by mechanical relaxation techniques for a quick-quenched sample of an alternating copolymer of ethylene and chlorotrifluoroethylene. The intensity of the α transition was found to increase with an increase in crystalline content. It was observed at 150°C by infrared and x-ray diffraction techniques and by mechanical relaxation spectra on an annealed sample. X-ray diffraction and dichroic infrared measurements were conducted on oriented specimens as a function of temperature. These data showed that the β transition was accompanied by a change in lateral bonding distances in the crystalline phase and a conformational change attributed to an “unkinking” of the molecular chain. The β transition was found to be related to the amorphous phase and the onset of the β peak corresponded to the transition at 35°C found by infrared techniques and previously by a torsional modulus method. It was tentatively assigned to the glass transition. A more definitive assignment of the β transition would depend on a detailed structural analysis of the γ transition. The γ peak was not studied in detail in the present work.

Notes: Neutron transmission of polydimethylsiloxane has been measured as a function of neutron wavelength in the range 4-10 Å, at room temperature. Scattering cross sections per hydrogen atom have been obtained and the slope (12.2 ± 0.2) barns/Å has been derived. Comparison with calibration curves relating the slope to the barrier hindering internal rotation as well as comparison with calculated neutron cross sections using the Krieger-Nelkin formalism for different dynamical situations indicates practically free rotation of CH3 groups about their C3 symmetry axes.

Notes: We report flow birefringence observations of polyethylene oxide solutions in a four roll mill where the flow field in the central region of the mill approximates well to that of pure shearing flow. When flow birefringence is observed it is seen to be highly localized within a region close to the “outgoing” asymptotic plane of flow. The phenomenon can be explained in terms of the flow birefringence corresponding to high extension of some polymer chains where the localization is caused by the chains requiring sufficient time in the flow field to become extended. This explanation has important consequences in all “persistently extensional flows” and can explain the origin of previously published results of localized flow birefringence observed for polyethylene solutions in axial compression and axial extensional flows.

Notes: Dynamic viscoelastic properties of block copolymers of styrene with butadiene or isoprene are consistent with the growth of a diffuse interphase or interlayer as block lengths decrease. Under the conditions of the present study the interlayer does not lead to a secondary loss maximum between the two domain glass transitions. The pattern of shifts of the loss maxima characteristic of the domain Tg's suggests strongly that the interlayer composition profile must be asymmetric with an average volume composition rich in styrene. Typical block polymer viscoelastic behavior is observed even beyond the point at which the interlayer attains 100% of the polymer volume. Such block polymers no longer contain compositionally pure phases, but are visualized as retaining a residual domain structure in which composition fluctuates between ever narrowing limits as blocks become shorter, approaching homogeneity and the mechanical behavior of random copolymers.

Notes: The influence of thermal history on the morphology of bulk-crystallized isotactic polystyrene was investigated. Results from x-ray diffraction (both wide- and small-angle), DSC experiments, and electron microscope observations, were combined to define the influence of thermal history on the fold surface free energy σe. lamellar thickness, and crystallite perfection. The increase of the melting point with crystallization temperature is not only the consequence of an increase in lamellar thickness, but also of marked decrease of σe. Annealing above the crystallization temperature results in a fast reorganization to a more stable structure, as reflected in an increase in melting point. This reorganization, depending on the crystallization temperature, involves an increase in lamellar thickness, a decrease of σe, and eventually an increase in crystallite perfection.

Notes: This paper discusses the applicability of three melting equations to the melting temperature and its pressure dependence in polymer crystals. The equations considered are the empirical Simon equation and two semiempirical equations, the Lindemann equation and the anharmonic potential barrier equation (APB equation). It was found that although the Simon equation fits melting curves of polymeric solids well, it is merely an interpolation and extrapolation formula. There appears to be no correspondence between theoretical and experimental values of the exponent in the Simon equation. With regard to the melting temperature at atmospheric pressure, the APB and Lindemann equations perform equally well. Using the value 3.5 for the universal Grüneisen constant, it is shown that TM0 (Lindemann) = 1.07 TM0 (APB). On the other hand, the different physical arguments behind the two approaches lead to a very different behavior at high pressures. For the predicated initial change of melting temperature with increasing pressure a ratio close to 5:1 is obtained between the APB and the Lindemann equation. For high-density polyethylene the Lindemann equation yields a melting temperature of 470°K when θ3 = 112°K given by Wunderlich is substituted for the Debye temperature. The observed melting temperature 405°K Corresponds to a Debye temperature of 107°K. The increase of the melting temperature with pressure for high-density polyethylene is predicted as 31°K/kbar by the Lindemann equation as compared with 23°K/kbar found by experiment.

Notes: The dynamic modulus, G′, and viscosity, η′, in the melt were determined for styrene ionomers containing up to 7.7 mole-% sodium methacrylate in the frequency range of 10-2 to 40 rad/sec, at various temperatures. The same parameters were determined for the methyl ester of these ionomers, as well as for some acid samples. It was found that in the temperature range studied the time-temperature superposition principle was applicable to the salts as well as to the esters and acids. Furthermore, it was found that the shapes of the G′ versus ω plots for the three types of polymers were identical for a particular molecular weight and comonomer concentration, and independent of whether the sample was in the acid, ester, or salt form. The temperatures required to achieve superposition were, however, quite different. This temperature difference, ΔT (between the salt and the ester), was found to be a function of the ion concentration, c. The shape of the plot of ΔT versus c suggests that the structure of the ionic aggregates changes in the range of 4-5 mole-% of ions.

Notes: Pulsed NMR T1, T2, and T1ρ measurements are reported for poly(vinylidine fluoride) (PVF2). The results demonstrate clearly the presence of four relaxation processes, three amorphous and one crystalline. The α relaxation is undoubtedly a crystalline one, while β and γ are both amorphous, in agreement with earlier conclusions from dielectric and dynamic mechanical measurements. The fourth relaxation (β′) observed initially in the mechanical measurements of Kakutani, but undetected in dielectric experiments, has been confirmed in our results and the process is described by an activation energy of 15.1 kcl/mole. Motion of folds on the surface of crystal lamellae is deemed to be the responsible mechanism for the β′ relaxation. Two models have been considered in the interpretation of the α process; rotation of crystalline chains in the vicinity of defects and rotational oscillation of restricted amplitude of all crystalline chains about the main chain axes. Rotation of amorphous chains is a possible mechanism for the γ process while motions of a general nature are responsible for the β relaxation. Our experimental results again indicate that spin diffusion plays an important role in the overall NMR response of the polymer.

Notes: Combined measurements of quenching and fluorescence polarization corroborate the results previously obtained by the polarized fluorescence anisotropy decay technique and, more especially, confirm the form of the proposed orientation autocorrelation function. The use of this method to determine the mean relaxation time of the relaxation time distribution is also explained.

Notes: Changes in dynamic mechanical properties of cellophane films due either to fungal attack or to hydrochloric acid hydrolysis have been measured. It appears that damage caused by cellulase enzymes that are released from a fungal overgrowth is localized in noncrystalline regions. These effects include a substantial reduction in elastic modulus, a reduction in temperature at which relaxation processes involving chain segmental mobility occur, and a broadening of loss tangent peaks due to segmental mobility and to rotations of methylol groups. Comparing results obtained from cellulase hydrolysis with those obtained from acid hydrolysis, it is clear that enryme attack proceeds by a characteristic and selective process. Implications regarding the embrittlement often seen to accompany biodegradation are discussed.

Notes: Hydrophobic-hydrophilic water-soluble block copolymers were prepared by “living” anionic polymerization. They consist of a polystyrene block and a polyethylene oxide block. From data on solution viscosity and high-resolution NMR in water, the molecular dimensions of the two-blocks copolymers are found similar to that of polyethylene glycols of the same molecular weight in the same solvent. These block copolymers exhibit microphase separation.

Notes: Emf measurements have been used to study the activity and the extent of sodium ion binding to several polyelectrolytes, poly(styrenesulfonate) (PSS), poly(2-acrylamido-2-methylpropanesulfonate) (PAMS), poly(3-methacryloyloxypropane-1-sulfonate) (PMOS), and copoly[(N-t-butylacrylamide)-(2-acrylamido-2-methylpropanesulfonate)] (NB-AMS) (mole ratio 3.8:1). The activity coefficient of sodium ion in Na-PAMS and Na-PMOS without added salt is found to be in the range from 0.1 to 0.3 and is insensitive to changes in polymer concentration. However, it increases with increasing concentration of the added salt.The extent of sodium ion binding at a given sodium ion concentration, as estimated from the activity data for some sodium and tetrabutylammonium (TBA) salts, decreases in the order Na-PAMS ≍ Na-PMOS 〉 TBA-PAMS 〉 TBA-(NB-AMS). This indicates that a significant portion of the binding is attributed to the binding of TBA+ ions. Also compared are the results of ion binding in Na-PAMS and Na-PSS as a function of ionic strength. At low ionic strength (〈1.0M), the order of binding strength is Na-PAMS 〉 Na-PSS, while the order is reversed at high ionic strength (〉1.0M). This finding is in good agreement with data obtained by dilatometry and viscometry.

Notes: The influence of the thermal history on the morphology and mechanical behavior of PET was studied. The degree of crystallinity (density measurements) and the morphological structure (electron microscopy and small-angle x-ray diffraction) depend on the crystallization temperature. The viscoelastic parameters obtained from the modulus-temperature curves are mainly determined by the morphology of the samples. The glass-transition temperature, Ti, is a function of the crystallinity and the crystallization temperature. It is maximum for a crystallinity between 0.34 and 0.39 for a sample crystallized isothermally between 120 and 150°C. This dependence on crystallization conditions is ascribed to the conformation of the amorphous chain segments between the crystalline lamellae as well as the concentration and the molecular weight of the polymer material rejected during isothermal crystallization. Both factors are supposed to be temperature-dependent.The value of the rubbery modulus is a function of both the volume concentration of the crystalline lamellae and the structure of the interlamellar amorphous regions (chain folds, tie molecules, chain ends, and segregated low molecular weight material). Annealing above the crystallization temperature of isothermally crystallized samples has a marked influence on their morphology and mechanical behavior. The morphological structure and the viscoelastic properties of annealed PET samples are completely different from those obtained with samples isothermally crystallized at the same temperature.

Notes: Depolarization ratios ρ of the Raman bands due to CH3 stretching at 2907 cm-1 and the Si—O skeletal mode at 491 cm-1 have been measured in polydimethylsiloxane gum as a function of temperature from 100°C to -45°C. Below 0°C the changes in p have been interpreted in terms of the formation of helical regions in the gum. The enthalpy of helix formation ΔH has been determined as 3200 ± 600 cal/mole. An upper limit on the entropy change, ΔS, of 16 ± 3 e.u./mole and minimum values of helix content at different temperatures have been found. The Raman spectrum of crystalline polydimethylsiloxane is presented.

Notes: The gas permeability and diffusion time lag may exhibit varying degrees of pressure dependence for glassy polymers. The sorption isotherm appears to consist of contributions from both Langmuir and Henry's law terms in such systems. This “dual sorption” theory advanced in the literature pictures gas held by the Langmuir mode as being completely immobilized. In the present paper, this model is extended to accommodate different degrees of partial immobilization of gas sorbed by this mode using two different formulations. One uses a transport expression based on concentration gradients while the other is based on chemical potential gradients. The predictions are that: (1) total immobilization results in a constant permeability with a time lag which strongly decreases with pressure; (2) no immobilization results in a constant time lag with a permeability which decreases strongly with pressure; and (3) incomplete immobilization results in both the permeability and time lag decreasing with pressure but neither as strongly as in the other limiting cases. The differences which may arise by the two formulations of the model are discussed.

Notes: Polychloroprene [CCl=CH—CH2—CH2—]x of approximately 95% trans-1,4 stereochemical structure was prepared by low-temperature emulsion polymerization. Fractions, obtained by liquid-liquid precipitations were studied in toluene solutions at 30°C by viscometry and osmometry. In addition, force-temperature measurements were carried out on networks of the polymer in the amorphous state. The results obtained on the polymer solutions indicate that the unperturbed dimensions of trans-1,4-polychloroprene are essentially the same as those of trans-1,4-polybutadiene of the same molecular weight. This observation, that substitution of a relatively large Cl atom for one of the methine H atoms in the trans-1,4-polybutadiene repeat unit has little effect on the chain dimensions, suggests that this increase in substituent size is offset by the fact that the length of a C—Cl bond is very much greater than that of a C—H bond. The results obtained on the polymer networks indicate that the unperturbed dimensions of trans-1,4-polychloroprene decrease significantly with increasing temperature, as has also been reported for both trans-1,4-polybutadiene and trans-1,4-polyisoprene.

Notes: The stable packings of polyethylene chains were investigated by intermolecular potential energy calculations based on various chain-assembly models. The structures of the two crystal modifications of polyethylene (i.e., orthorhombic and the monoclinic), together with their cell constants and the setting angles, were well reproduced. The packing modes of polymethylene chains found in various alkane derivatives were also explained by the energy minima of the chain-assembly models. In these calculations, several sets of potential functions were tried and three sets of functions were found to reproduce conformations of single polymer chains, the cell constants of polyethylene at low temperature, and those at room temperature.

Notes: Truncated, six-sided single crystals of a 10-16 linear polyester were grown from dilute solution in hexanol, deposited onto Mylar film, and uniaxially deformed at room temperature. For elongations below 10%, the crystals deform uniformly; however, above 20% elongation many cracks spanned by fibrils of 300 Å diameter develop approximately normal to the applied stress direction. Depending on the position of the crystal relative to the draw direction, lateral buckling pleats and cleavage cracks can also occur. Collapse of the nonplanar crystals onto the substrate with a resulting nonuniform adherence of the crystal influences the deformation. The deformation morphology is compared to that of truncated sixfold sector polyethylene crystals. Most notably, in contrast to polyethylene, {010} fold sectors do not deform differently from {110} fold sectors and phase boundaries between {110} and {010} fold sectors do not fracture easily.

Notes: The melting behavior of samples of oriented low-density polyethylene is examined as a function of annealing temperature and time, subsequent heat treatment, and irradiation dose. Three types of endotherm are identified which are attributed to primary melting of the lamellae, to melting of the products of reorganization during the scan, and to melting of material crystallized during cooling from the original annealing temperature. Irradiation was found to suppress the refolding which normally occurs when a sample is heated above its annealing temperature, but also produces an increase in melting point. The behavior of similar samples prepared from high-density polyethylene is briefly considered.

Notes: A study is reported of the anisotropic swelling behavior of “single crystal” samples of an S-B-S two-phase copolymer, Kraton K102, on imbibing a selective swelling agent. This material consists of a hexagonal array of polystyrene cylinders in a matrix of polybutadiene. Initially the material expands reversibly, perpendicular to the cylinders. Low-angle x-ray studies show that this corresponds to expansion of the hexagonal lattice and indicates lateral expansion of the matrix material. Birefringence changes can be broadly ascribed to the changes in form birefringence.Subsequently, irreversible expansion occurs along the rod direction. x-ray diffraction studies combined with electron microscopy indicate a transformation of the cylindrical microstructure into a more complex arrangement. This often appears to be an arrangement of spheres, packed on a hexagonal or square lattice, but this cannot completely account for the x-ray results. Some micrographs suggest the existence of a more complex network of the polystyrene microphase units.

Notes: The concepts of fracture mechanics have been used to analyze the fracture toughness of polycarbonate in terms of the polymer relaxation properties. By considering the temperature rise at the tip of a growing crack; a model is proposed which describes the viscoelastic energy loss in the fracture process. The model was used to predict the fracture toughness of polycarbonate as a function of test temperature.

Notes: Experimental observations are reported of the behavior of solutions between two rotating parallel rollers where the form of the flow field between corotating rollers corresponds to that of a col which has nonorthogonal asymptotes. The obliquity of the asymptotes of the flow gives a direct measure of the relative magnitude of the constituent pure shear and rotational components of the flow field.Flow birefringence observations of polyethylene oxide solutions between the corotating rollers show that molecular orientation is limited to a highly localized region near the “outgoing” asymptotic sheet of the flow field in accordance with the predictions of a “persistent extensional flow” analysis presented. Counterrotating rollers show no flow birefringence also as expected.The behavior of polymer solutions and Newtonian fluids are compared. With increasing strain rate using corotating rollers the obliquity of the asymptotes of the flow remains constant for the Newtonian fluid but changes significantly for the polymer solution.

Notes: The room-temperature tensile mechanical properties and fracture topographies of polycarbonate are reported as a function of strain rate, sample preparation, and thermal history above and below Tg. The bulk physical structural changes produced by various thermal treatments were monitored by density, yield stress, and differential scanning calorimetry observations. Ordered regions do not form in bulk polycarbonate at or below 145°C. The changes produced in the mechanical properties of polycarbonate on annealing below Tg, relative to a quenched or 145°C equilibrium-state glass, are caused by liquidlike packing changes in free volume. In room-temperature tensile a 125°C-6 day annealed glass exhibits transitional behavior from shear free volume, such as quenched and 145°C equilibrium-state glasses, this transition occurs at higher strain rates. Polycarbonate embrittles as a result of the cessation of shear yielding and reversion to a crazing failure mode with a corresponding decrease in molecular flow and energy to failure.Density measurements indicate that ordered regions do start to grow immediately above 145°C in bulk polycarbonate. This phenomenon allows precrystalline and/or crystalline entities to grow below the bulk Tg in thin films and on the free surfaces of thick films where mobility restrictions are less severe than in the bulk. From bright-field transmission electron micrographs of thin films and carbon-platinum surface replicas of etched thick films it is suggested that the observed spherical precrystalline structures are aggregates of 50-60 Å ordered molecular do mains.

Notes: Dimensional changes in nylon 6 film on absorption and desorption of water were studied as functions of time and the amount of absorbed water. For absorption, a plot of film expansion versus the square root of time was sigmoidal in the initial region and did not coincide with the sorption curve: the latter was linear in the same region. This behavior is very similar to that reported for nylon 6 fiber by Kunzman. A theoretical analysis based on certain assumptions about the molecular state of nylon 6 gave good agreement with experimental results. By this analysis it was shown that the characteristic swelling behavior arises from instantaneous relaxation of the polymer molecules and is not connected with a time lag between water absorption and expansion of the polymer, as Kunzman proposed.

Notes: A procedure is described to include the effect of depolarization of the originally plane-polarized incident light beam as it passes through a thin polymer sample on the intensity of multiple light scattering. The multiple scattering gives rise to “polarization scrambling” in which, for example, Hv scattering measurements involve multiple scattered rays which may have undergone some Vv scattering. These phenomena reduce the angular dependence of scattering since large intensities originally occurring at small values of θ are rescattered so as to enhance intensities at other angles. Correction factors for both Hv and Vv scattering are presented.

Notes: The interaction of unlike polymer molecules (components 2 and 4) in a ternary solution can be regarded as selective exclusion or desorption of one polymer by another. A relation is derived between the coefficient of selective sorption and the interaction parameters A24 and A244 which are analogs of the second and third virial coefficients. The ratio between the apparent light-scattering molecular weight and the true value for a polymer solute in a ternary system with one component of a binary solvent polymeric is more involved than in a ternary system in which both solvent components are of low molecular weight. Under certain conditions, the introduction of polymer component 2 into a dilute solution of polymer component 4 may lead to a decrease in the total intensity of scattered light.

Notes: The effects of combined pressure and temperature on the mechanical behavior of polypropylene have been studied. Tests were conducted in tension and compression superimposed on various hydrostatic pressures up to 7 kbar at temperatures of 20, 50, and 75°C. The experimental data have been analyzed in view of molecular and continuum approaches.It has been observed that the Young's modulus and the yield strength in both tension and compression increased significantly with increasing pressure at all temperatures studied. However, the rate of increase of the Young's modulus undergoes abrupt change about the glass-transition pressure (Pg). The Pg is linearly dependent on the test temperature and the pressure coefficient of the Tg is estimated, from Pg versus temperature relations, to be about 18°C/kbar for the polypropylene samples of this study. Pressure dependence of the yield stress is described by a generalized Eyring theory incorporating pressure effects and two flow mechanisms, the α- and the β-relaxation processes. The theory predicts a bilinear dependence of the yield stress of polypropylene on hydrostatic pressure as observed in the tests.The paper also described a method of healing stress whitening in polypropylene by a combination of shear stress and hydrostatic pressure.

Notes: The similarity of the π-electron backbones of the polyenes and the polydiacetylenes suggests an analogy between these two fully conjugated, linear polymers. The extent of the analogy is discussed through the examination of a series of model compounds: the polyenes and the polyenynes. The optical band gaps and the polarizabilities of polyenynes are compared to those of the polyenes and to the predictions of a modified free-electron model. It is concluded that the chain-dependent electronic properties of the polyenes may be extrapolated with some confidence to the polydiacetylenes.

Notes: Diffusion coefficients of cellodextrin alditols from DP 1 to 5 in 0.32 molar NaOH are found to be 22% less than in water. Slightly lower diffusion rates and higher friction coefficients and Einstein-Stokes hydrodynamic radii are also reported for the alditols as compared to cellodextrins in water. Considered as ellipsoids based on diffusion rates, the length-to-width ratio for the alditols, only slightly greater than for the cellodextrins in water, increase by about 100% in alkali. A similar increase in axial ratio is shown for cellodextrins in the highly alkaline solvent cadoxene as for the alditols in alkali. It is suggested that creation of the large frictional envelope occurs in alkali prior to complexing with the common cellulose solvents in which complexing with copper, cadmium, and iron in divalent from are involved. The possible nature of the enlarged frictional domain is discussed.

Notes: Sequence lengths of stereochemical additions in vinyl polymers are described in terms of the number average lengths of like configurational placements. Under these circumstances, a pure syndiotactic polymer has a number average sequence length of 1.0; a polymer with 50:50 meso, racemic additions has a number average sequence length of 2.0 and polymers with more meso than racemic additions have number average sequence lengths greater than 2. Amorphous and crystalline polypropylenes and an amorphous polystyrene are examined using 13C NMR as examples of the applicability of the average sequence length method. The results appear to be accurate for amorphous and semicrystalline polymers but limitations are present when this method is applied to highly stereoregular vinyl polymers containing predominantly isotactic sequences.

Notes: This paper deals with the formation of crazes that may be caused by an external load on glassy polymers wetted with kerosene. First, the orientation of crazes has been determined when applying a uniaxial tension to a specimen of cold-rolled polyvinyl chloride sheet at various angles to the rolling direction. The critical stress for craze initiation in poly(methyl methacrylate) and polyvinyl chloride rods has been investigated under combined tension-torsion loading. It is shown that: (1) in an anisotropic, as well as an isotropic polymer, the direction of crazes is perpendicular to that of the maximum strain calculated by taking into account the internal stress due to rolling; and (2) under the action of a crazing agent, crazing may occur even under the pure torsional load, i.e., in the absence of dilatational stress.

Notes: After annealing at low temperature, linear polyethylene displays an unusual feature in its specific heat curve. On heating, a maximum is observed just above the annealing temperature. The magnitude of this excess specific heat is dependent on the initial level of crystallinity and the temperature and time of annealing. The maximum does not reappear on subsequent cooling followed by rapid heating and represents the formation and disappearance of an unstable structure. These results can be interpreted as a crystallization-melting phenomenon and are consistent with the wide-angle x-ray diffraction patterns. The optimum effects are observed in the β-region (-50°C to 0°C) and could possibly lead to complications in interpreting other phenomena in this temperature range.

Notes: A model for the interpretation of homogeneous nucleation data for chain molecules is presented. The two surface energies σs and σe are related to interchain and intrachain bonding. Surface energies calculated from experimental data on n-alkanes from octane to dotriacontane and polyethylene agree with estimated values. The results are discussed in relation to surface energies measured from spherulite growth rates in polymers but these values are not known with sufficient reliability to provide a good basis for comparison.

Notes: Dielectric measurements, differential thermal analyses, and density measurements are reported on concentrated solutions of polyvinylchloride in tetrahydrofuran. The relaxation processes observed between 80 and 400°K have been classified into four types. From the analysis of experimental data, the primary process at the highest temperature and the process at the lowest temperature are assigned, respectively, to segmental motion of the polymer and motion of the solvent. Activation plots for the primary process conform to the Vogel-Tamman equation. The dielectric glass-transition temperature T'g (defined as the temperature at which the dielectric relaxation time is 100 sec) determined with this equation agrees well with the glass-transition temperature Tg from thermal analysis. Therefore, Tg can be represented by an expression of the form \documentclass{article}\pagestyle{empty}\begin{document}$$ T_g = T_0 + B/(A + 3) $$\end{document} The parameters of the Vogel-Tamman equation A and B are nearly independent of concentration, whereas To depends strongly on concentration. The dipole moment per monomeric unit calculated from the experimental data changes with concentration and exhibits steep increments around 30% and 90% by weight. The width of the distribution of the relaxation time also increases with the concentration. The results were compared with those for the system polystyrene-toluene studies in the same way.

Notes: A study was made of the dielectric relaxation in polyethylenes rendered dielectrically active through oxidation (0.5-1.7 carbonyls/1000 CH2) and chlorination (14-22 Cl/1000 CH2). Both linear and branched polymers were studied. All of the relaxations between the melt and -196° were studied in the frequency range 10 Hz to 10kHz (100 kHz in the chlorinated samples). In the linear samples a wide range of crystallinities was studied (55% in quenched specimens to 95% in extended-chain specimens obtained by crystallization at 5 kbar). As is consistent with its being a crystalline process, the α peak was found to discontinously disappear on melting of the samples and reappear on recrystallizing on cooling. The disappearance of the smaller crystals before the larger ones appeared to be evident in the isothermal loss versus frequency curves. The relaxation strength of the α process increases with crystallinity. The measured relaxation strength is less than that expected on the basis of direct proportionality to the crystalline fraction with full contribution of all dipoles in the crystalline material. However, the intensity is not sufficiently low for the process to be interpreted in terms of reorientation of localized conformational defects in the crystal. The variation of intensity with crystallinity is best interpreted in terms of full participation of crystalline dipoles but with selective partitioning of both carbonyls and chlorines favoring the amorphous domains. A strong correlation of the α loss peak location (Tmax at constant frequency or log fmax at constant T) with crystallinity for both carbonyl and chlorine containing polymers was found. This variation is interpreted in terms of chain rotations in the crystal where the activation free energy depends on crystal thickness. The dependence of log fmax and Tmax on lamellar thickness as well as a comparison with the loss peaks of ketones dissolved in parafins indicates that the chain rotation is not rigid and is accompanied by twisting as the rotation propagates through the crystal. In agreement with previous studies the β process is found to be strong only in the branched polymers but can be detected in the chlorinated linear polymer. The β process was resolved from the α in the branched samples by curve fitting and its activation parameters determined. The γ relaxation peak in oxidized polymers including its high asymmetry (low-temperature tail) and increasing εmax with increasing frequency and temperature when plotted isochronally can be interpreted in terms of a simple nearly symmetrical relaxation time spectrum that narrows with increasing temperature. No increase in relaxation strength with temperature was found. The chlorinated polymers behave similarly but appear to have some Boltzmann enhancement (450-750 cal/mole) of relaxation strength with temperature. The dependence of relaxation strength on crystallinity indicates that the process is an amorphous one. Further, no evidence of relaxation peak shape changes with crystallinity that could be interpreted in terms of a crystalline component in addition to the amorphous one was found. The comparison of the γ relaxation strength with that expected on the basis of full participation of amorphous dipoles indicates that only a small fraction (∼10% in oxidized linear polymers) of them are involved in the relaxation. Thus it would seem that a glass-rubber transition interpretation is not indicated but rather a localized chain motion. It is suggested that the γ process, including its intensity, width, and activation parameters, can be interpreted in terms of an (unspecified) localized conformational (bond rotation) motion that is perturbed by differing local packing environments. The thermal expansion lessens the effects of variations in packing and leads to narrowing with increasing temperature. The conformational motion itself leads to increase in thermal expansion and hence a transition in the latter property. Some previously proposed localized amorphous phase conformational motions appear to be suitable candidates for the bond rotation motion. A weak relaxation peak found at temperatures below the γ and at 10 kHz may possibly be the dielectric analog of the δ cryogenic peak found previously mechanically at lower frequencies.

Notes: Dynamic mechanical properties of m,n-ionenes, the structure of which are shown in Figure 1, were examined by torsional braid analysis. Three relaxations designated as α,β and γ were found. The α relaxation, ascribed to the primary relaxation due to an amorphous phase, was observed at 70-130°C, the temperature increasing with an increase of the ion concentration along the polymer chains. The β relaxation at around 0°C was related to the ionic portions of the polymers. The γ relaxation at around-120°C was a so-called local mode relaxation. The γ relaxation peak was split into two peaks in the very slowly cooled 12,10-ionene sample and the formation of an inhomogeneous structure in the amorphous phase is proposed.

Notes: Two dielectric relaxations have been studied on poly(2-vinyl-N-ethylcarbazole) (P2VK) and poly(3-vinyl-N-ethylcarbazole)(P3VK), poly(2-vinylanthracene) (P2VA) and poly(α-methyl-2-vinylanthracene) (PMe2VA). The relaxations in P2VK and P3VK occur in the temperature regions 220°C and -150°C. Evidence for a third relaxation in both polymers at ca. 120°C has been found; and, for this reason, the relaxations studied (220°C and -150°C) are labeled α and β, respectively, and have been attributed to Tg and carbazole rotational libration about the bond connecting the carbazole moiety to the polymer backbone. Additionally β (ca. 20°C) and γ(ca. -150°C) relaxations in P2VA and MeP2VA have been observed and assigned, respectively, to wagging motion and rotational libration of the pendant anthracene moiety.

Notes: Very few analyses exist for determining the adhesion f thin brittle films in the micron range on low modulus polymeric substrates. A theoretical model and experimental means are developed to determine the adhesion for this situation using the concept of fracture mechanics and Griffith's energy criterion. An expression for the adhesion is derived in terms of the external loading, material constants, and thicknesses of the films.The model is compared with measurements of brittle films vacuum deposited onto polymeric substrates. Excellent agreement is obtained and interfacial energies are calculated. Since the moduli of thin films are very difficult to determine accurately, the effect of a variation in measurements of this material parameter on the adhesion is calculated. The effect of varying preparative conditions is also discussed.

Notes: Results are presented of neutron incoherent scattering experiments on isotropic linear polyethylene samples of high (80%) and low (48%) crystallinity in the temperature range between -180°C and +85°C for values of the scattering vector between 0.29 Å-1 and 1.81 Å-1 obtained with a high resolution backscattering spectrometer (Δħω = 0.25 - 1.0 μeV) and between 0.57 Å-1 and 2.4 Å-1 with a time-of-flight spectrometer (Δħω = 420 μeV). From a comparison of the results on these samples one concludes that relaxation takes place predominantly in the noncrystalline regions. This motion cannot be adequately accounted for by any of the existing models for the γ-process. Therefore, a more liquidlike motion is suggested. Diffusion of shorter chain segments has also been ruled out since it is too slow to be observed. A simplified model of protonic jumps between equidistant sites located on the periphery of a circle of radius 2.5 Å reproduces the experimental results well. For the average time between successive CH2-group reorientations one obtains τ1 = τ0 exp(EactRT) with τ0 = (2.0 ± 1.5) × 10-13 sec and Eact = (4.5 ± 1.0) kcal/mole. The values join up well with those for the γ-process observed by NMR. It has been concluded that 60-90% of the protons in the noncrystalline regions participate in this motion.

Notes: Samples of poly(vinylidene fluoride) were crystallized either (a) isothermally at a series of temperatures, or (b) in the presence of varying amounts of diluent (dimethylphthalate or dimethylacetamide). The α-polymorph was the only crystalline form present in these samples. Melting points of the first series (a) were determined by DSC and of the second (b) by dilatometry. The same equilibrium melting point for the α-polymorph (178°C) was obtained from analysis of the two sets of data. A value of 1425 cal mole-1 (5.96 kJ mole-1) for the heat of fusion of this polymorph was obtained from analysis of the polymer-diluent melting data. The heat of fusion and the entropy of fusion calculated therefrom correlated well with corresponding values for other fluoroethylene polymers. Thus, the equilibrium melting point and the heat of fusion could be predicted for a fluoropolymer for which data have not yet been reported-poly(trifluoroethylene). The melting point predicted, 222°C, agreed remarkably well with that determined here for an experimental sample, thereby lending support to the empirical correlations. The heat of fusion of poly(trifluoroethylene) is, therefore, expected to be approximately 1300 cal mole-1.

Notes: An initial series of energy calculations is aimed at predicting the epitactic behavior of S2N2 as deposited from the vapor phase upon NaCl-type alkali halide substrates and preferred orientation of molecular chains in the (SN)x polymerized phase. Although the preferred orientation of a single S2N2 molecule is identical for NaCl and NaF, the energetics of dimer formation on the surface greatly favor use of the latter substrate as a heterogeneous nucleation catalyst. Enhancement of dimer formation on NaF is due to a near match between S2N2-S2N2 equilibrium distance and substrate unit-cell spacing. Furthermore, the (SN)x chain-orientation tendency also appears to be a function of alkali halide type. On NaCl, the chain axis lies along the 〈110〉 surface direction above cationic rows, the plane of interatomic bonds being perpendicular to the surface. For NaF the axial direction is 〈100〉 with alignment between rows of alternating charge, with the molecular plane in this case parallel to the substrate surface. From the calculations it appears that primary Coulombic forces are not a significant factor in dictating the epitactic properties of monomer or polymer.

Notes: Highly porous interpolymer ion-exchange membranes of poly(styrene sulfonic acid) and poly(vinylidene fluoride) have been investigated under pressure filtration with KCI, Na2SO4, erythrosin, and bovine serum albumin as solutes in the feed solution. The rejection of the ionic solutes is governed by a Donnan exclusion of electrolyte from the membrane phase. A model for the transport behavior is proposed that includes both diffusive and convective salt transport. The calculated rejections agree adequately with the observed data.

Notes: Dynamic mechanical properties of cellophane, amylose, and dextran have been obtained over the temperature range 100-520°K and frequency range 10-2 to 10+2 Hz on specimens containing various amounts of water. Four mechanical transitions have been characterized. At about 180°K, there is a γ transition that has been assigned to rotation of methylol groups; no comparable transition was found to exist in dextran. At about 240°K, there is a β transition that has been assigned to rotation of methylol-water complexes, but the β transition in dextran appears to be due to some other kind of motion. In cellophane at about 450°K there is an α2 transition which appears to have contributions from motion of chain segments in disordered regions. The α1 transition for cellophane occurs at temperatures too high to measure and may be due to segmental motions in chains within crystalline regions. Dextran and amylose were found to have at these same temperatures α loss processes that probably correspond to glass-rubber transitions in amorphous material. The changes in these mechanical loss mechanisms due to moisture uptake suggest that sorbed water associates with glucose repeat units in ways ranging from those which stiffen molecular structure to those which allow greater freedom for other types of motion to occur.

Notes: It is shown that the distribution of normal stress around a craze, found by Knight using a Fourier transform method may not be uniquely determined, and that in fact the stress field cannot be computed unless the rheological properties of the craze tip material are known.

Notes: The piezoelectric effect due to shear in oriented films of DNA is strongly dependent on the relative humidity at which the films are equilibrated. Below about 60% relative humidity, the sign of the piezoelectric modulus is negative and its magnitude passes through a maximum with increasing temperature. This type of polarization appears to be due to the stress-induced orientation of dipoles in sugar-phosphate main chain. Above 75% relative humidity, water molecules are adsorbed by the bases and stabilize the ordered structure of double strand helices. In this crystalline state, the sign of the piezoelectric modulus is positive and its magnitude decreases markedly at about-75°C. This type of polarization appears to be due to the stress-induced orientation of dipoles in bases attached to the main chain. From comparisons between piezoelectric, elastic, and dielectric measurements, it is concluded that the piezoelectric relaxation observed at-75°C and 75% relative humidity is mainly due to the dielectric relaxation of the bases in the double helix.

Notes: A study has been carried out of the differences in mechanical properties of oriented fibers of poly(ethylene terephthalate) (2GT), poly(trimethylene terephthalate) (3GT), and poly(tetramethylene terephthalate) (4GT). The properties studied include the tensile stress-strain behavior, the recovery from strain, shrinkage at 100°C and the glass-transition temperatures. The stress-strain curves of the three materials differ markedly. 2GT shows a monotonic increase in stress with increasing strain up to failure, which occurs at ∼20% strain, and the oriented fibers possess a comparatively high initial modulus. 3GT shows a much lower initial modulus and there is an inflection in the stress-strain curve at about 5% strain. The stress-strain curve of 4GT shows a number of distinct features. Although the initial modulus of 4GT is similar to that of 3GT, the stress-strain curve shows a pronounced plateau in the region between 4% and 12% strain. At higher strains the stresses rise rapidly before failure. These features of the stress-strain curves in the three polymers can be related to previous studies where the x-ray diffraction spectrum and the Raman spectrum have been examined for fibers under stress. The ranking of both the recovery and shrinkage behavior of these materials is in the order 3GT 〉 4GT 〉 2GT. These results can also be understood in terms of the results of the previous structural studies, and it is concluded that the molecular conformations in both the crystalline and noncrystalline regions play a key role in determining the mechanical behavior.

Notes: The effect of concentration of the crosslinking agent (ethylene dimethacrylate) and diluent (water) during the crosslinking copolymerization on the shape and position of retardation spectra in the dry state has been investigated for poly(2-hydroxyethyl methacrylate) networks. With increasing water content during network formation, the maxima of the retardation spectra, Lm, increase and the position of the spectra is shifted toward shorter retardation times, τ. The results are in quantitative agreement with the modified Rouse-Mooney (R-M) molecular theory and suggest the influence of deformation due to the diluent during network formation on the viscoelastic behavior. With increasing content of the crosslinking agent, the retardation spectra are shifted toward longer times. At a constant reference temperature T0 = 115°C the retardation time, τm, at the maxima of the spectra increases with increasing content of effective chains in the network, νe. However, after a correction for the effect of the monomeric frictional coefficient, ξM0, τm/ξM0 decreases with increasing ve at a rate which agrees quantitatively with the R-M theory. The slope of the retardation spectra in the main transition region and the value of their maxima decrease with increasing ve; a comparison of these dependences with theory leads to the most probable distribution of submolecules in the chains. The contribution of long retardation times to the equilibrium compliance, Je, of the systems under investigation was estimated; it was shown that the application of the Thirion-Chasset extrapolation method for the determination of Je of loose networks requires a certain type of dependence of the retardation or relaxation spectra on τ.

Notes: The morphology and growth of the disordered hexagonal phase which crystallizes in films of cis-polyisoprene at pressures in excess of 3 kbar is discussed. A two-stage growth process is proposed consisting of nucleation and crystallization followed by a pressure-enhanced thickening process. The phase is metastable and is replaced by normal spherulitic growth at long times. It transforms into lamellar sheafs with higher than usual lamellar thicknesses when pressure is lowered at constant temperature.

Notes: Stained and unstained sections of nylon 6 fibers are examined by means of transmission electron microscopy. Data are presented regarding dimensions and shape of macrofibrils, microfibrils, amorphous, and crystalline domains of the microfibril and the spacing between the microfibrils. The new results support the conclusions of a previous SAXS and diffusion study carried out with the same fibers.

Notes: Thermally stimulated and isothermal depolarization currents of three low-density polyethylenes are investigated in the temperature range 80-320°K. The thermally stimulated current spectra can be analyzed in terms of a continuous relaxation time spectrum. This spectrum can be resolved into three Gaussian distributions of activation energies centered near 140°K (γ-relaxation), 205°K, and 245°K (β-relaxation) in agreement with electrical and mechanical loss factor measurements. The experimental observation are explained in terms of reorienting dipoles, coupling the molecular motion to the electrical field.

Notes: The Fröhlich model of discrete reorienting dipoles has been extended to include a continuous spectrum of relaxation times and applied to the measurement of thermally stimulated and isothermal depolarization currents of low-density polyethylenes. The experiments can only be interpreted if the detailed history of polarization and depolarization prior to the actual current measurements are taken into consideration. With certain simplification the spectrum of activation energies can be directly derived from the complete thermally stimulated current profile.

Notes: The shrinkage of commercial oriented poly(ethylene terephthalate) filaments was studied within the framework of the kinetic theory of rubberlike elasticity. Previous workers had found that the shrinkage and optical behavior of amorphous polymers could be satisfactorily explained in terms of this theory. Such an analysis is now applied to semicrystalline samples of moderate and high draw ratios (from 2× to 6×).It was found in this work that the thermal shrinkage force behavior as well as the optical anisotropy as a function of stretch can be explained in terms of the theory of rubberlike elasticity, if the following reasonable assumption is made: the average number of statistical segments per network chain in the noncrosslinked sample increases as a function of the draw ratio. A possible mechanism for such behavior is the relaxation of some of the chain entaglements due to the strain imposed externally on the fiber.

Notes: Brillouin scattering has been studied from amorphous bisphenol-A polycarbonate in the temperature interval 60-240°C. Both longitudinal and transverse Brillouin peaks are observed over the entire range. The behavior of both types of Brillouin splittings, Δωl and Δωt, in the region of the glass-rubber relaxation is typical of an amorphous polymer. Equilibrium values of Δωl and Δωt were obtained 20°C below the glass-transition temperature Tg determined at cooling rates of 20°C/hr. Comparison of the present results with previous ultrasonic data reveals a considerable dispersion in the longitudinal phonon velocity below Tg. The origin of the large transverse Brillouin intensities is related to the structure of polycarbonate.

Notes: The acoustic emission from a crazing polyvinyltoluene in a tensile and bending experiment is described. Acoustic emission appears as a series of bursts which most likely correspond to the initiation and growth of crazes. The emission intensity is characterised by acoustic activity (pulse rate) measured by the ring-down technique. The average activity increases with strain. During repeated loading the acoustic activity shows a measurable intensity and significant rise only beyond the maximum strain of the former runs. This is equivalent to Kaiser's effect in metals. Acoustic emission during the creep experiment occurs in three characteristic periods. They are characterized as the relaxation, fatigue, and breakdown periods. Visual observations indicate that the relaxation period corresponds to the initiation, and the fatigue period to the growth of crazes. In the breakdown period a macroscopic crack develops and the sample fails.

Notes: The solubility, permeability, and diffusion time lag for carbon dioxide in polycarbonate are reported at 35°C for pressures ranging from 1 atm to 23 atm. The solubility data are very well described by the dual sorption mechanism model, Henry's law plus Langmuir adsorption, proposed for glassy polymers. Both the permeability and time lag decrease with increased CO2 pressure. These observations are not consistent with the proposal that CO2 sorbed by the Langmuir contribution is totally immobilized; however, all of the results are entirely consistent with an extension of this proposal which considers partial immobilization. The data have been quantitatively analyzed in terms of this partial immobilization model, and the results suggest for polycarbonate at 35°C that the CC2 sorbed by the Langmuir portion of the isotherm behaves as if it has only about 10% of the mobility of the gas sorbed by the Henry's law part of the isotherm. The results have also been interpreted in terms of a concentration-dependent diffusion coefficient which is shown to be mathematically equivalent to the partial immobilization model. The latter model was also formulated in thermodynamic terms, whereby fugacity was used rather than pressure, and diffusion coefficients were defined in terms of chemical potential gradients rather than concentration, but the consequences of these changes proved to be minor and no better. The significance of these observations and their interpretation is discussed.

Notes: The tensile strength of poly(methyl methacrylate) (PMMA), polycarbonate (PC), polychlorotrifluoroethylene, and polysulfone was measured in liquid nitrogen over the strain rate range of 2 × 10-4 to 660 min-1. These polymers deformed by crazing which was induced by the liquid nitrogen. The stress versus log strain rate curve was sigmoidal in that its slope increased and then decreased with strain rate. Above a critical strain rate of about 200 min-1, which varied somewhat with the polymer, crazing was not observed with the optical microscope; the behavior became brittle, and the tensile strength became constant. The nonlinear behavior of stress versus log strain rate at low strain rates was associated with a decrease in activation volume with increasing strain rate whereas the nonlinear behavior at high strain rates was associated with an increase in density and decrease in length of the crazes with strain rate. The strain rate effect was the basis for calculating the diffusion coefficient of nitrogen into the polymers at 77°K.The shear deformation mode of PC was measured under compression and under tension. The compressive strength versus log strain rate was linear throughout the entire range giving a compression shear activation volume of 360 Å3. The shear tensile strength of PC varied only slightly with strain rate when compared to the compressive strength. The brittle fracture stress of PMMA, in the absence of crazing, in compression and in tension, did not vary with strain rate.

Notes: The effect of casting solvent on the material properties of poly(γ-methyl-D-glutamate), PMDG, was investigated. The specific solvents used were chloroform, trifluoroacetic acid, dichloroacetic acid, methylene chloride, hexafluoroisopropanol, and tetrachloroethane. The different nature of these solvents controlled the degree of α, β, or random coil contents of the final film. The effect of the morphology on material properties induced by the respective solvents was investigated by dynamic mechanical measurements of the dry films, stress strain behavior of both wet and dry films as well as by wide-angle x-ray diffraction, small-angle light scattering, and optical microscopy. Infrared spectroscopy was used to help determine α or β content. It was found that the casting solvent has considerable influence on material behavior and morphology. These differences are reflected in both the dynamical mechanical (small strain) and stress-strain (large strain) measurements as well as the x-ray scattering and optical microscopy. It was noted by light scattering that all films gave rise to anisotropic rod scattering with the exception of the β film cast from trifluoroacetic acid. This latter film appeared to be optically isotropic.

Notes: The expansion coefficient of a flexible polyelectrolyte molecule is evaluated as a function of the concentration of simple salt added to the solution. It is shown that the coefficient has a term which is inversely proportional to the square root of the concentration of added salt.

Notes: There is much controversy in the literature concerning the nature of the thermal transitions observed for segmented polyurethanes. In this study calorimetric and NMR data on a polyurethane reveal ordered structures similar to that previously observed. However, based on a recently observed semi-ordered polymeric phase and the observation of a time-dependent calorimetric effect not observed previously, the data are interpreted in terms of a high-temperature short-range order and a low-temperature long-range order. The former appears to form faster and annealing of both ordered phases increases their thermal stability.

Notes: An analytical solution of the Poisson-Boltzmann equation is presented for the cell model of a polyelectrolyte solution with two species of monovalent counterions of different size. On this basis the osmotic coefficient is calculated as a function of the mole fraction of counterions and their radii. It is shown that the degree of binding of the smaller ion species increases as its mole fraction decreases.

Notes: The Vibrational analysis of polyethylene terephthalate, polyethylene-d4 terephthalate, and polyethylene terephthalate-d4 has been carried out using a valence force field calculated from the infrared and Raman spectra of a series of low molecular weight aromatic esters. The Raman spectra for polyethylene-d4 terephthalate and polyethylene terephthalate-d4 are presented and band assignments for these compounds and polyethylene terephthalate are discussed.

Notes: Dynamic viscoelastic measurements, E′ and E″, were carried out on solution-crystallized and melt-crystallized samples of fractionated isotactic polypropylene over the temperature range of -100°C to 150°C. The molecular weight ranged from 1.26 × 104 to 1.77 × 105. The effects of swelling and annealing on the α and β peaks were more pronounced for the lower molecular weight fraction than for the higher one. It was found that both the untreated solution-crystallized and quenched melt-crystallized samples contain a fair amounts of a constrained amorphous phase in which the molecular motions were so depressed that the corresponding peak could be observed as the low-temperature component of the α peak. These constraints on the molecular motions are considered to originate from the spatial restrictions imposed by the presence of the surrounding crystallities.

Notes: Deformation structures resembling kink bands have previously been reported in a number of oriented semicrystalline polymers which have undergone various modes of deformation. In the present work, such structures have been observed and studied in solid-state extruded polyethylene which has been processed to give a biaxial, “single crystal” texture. Deformation of this material by bending followed by unbending has been observed to lead to shear during the bending stage and to void formation during the unbending stage. The kink bands which form during this treatment exhibit a single morphology regardless of the axis of bending so long as the direction of compression during bending is parallel to the original extrusion direction. Besides intracrystalline slip, which is known to contribute at least in part to the process of kink band formation, mechanisms involving interlamellar slip and interfibrillar slip are also considered. These mechanisms are considered in terms of three distinct experimental observations: the relationship between the kink boundary and the x-ray long period, the process of void formation during unbending, and the single characteristic morphology of the kink bands.

Notes: Solvent coating is an important commercial technique utilized in fabricating thin films. In certain cases, undesirable strains may be built into the composite as the solvent is removed. The stress field in a two-layer sample and its distribution along the interface have been analyzed. By considering the shrinkage of the solvent cast film equivalent to applying an axial compressive load, interfacial expressions were derived which are valid for solvent drying of solution cast films. Experimental procedures and measurements are presented for the solvent casting of thin brittle films onto flexible polymeric substrates. Interfacial strains are determined and their dependence on accurate material property measurements is evaluated. The relation between the bulk and interfacial strain is illustrated.

Notes: The equilibrium compliance of three low molecular weight polystyrene melts has been determined over the range 15-70°K above Tg from dynamic viscoelastic measurements using alternating shear. Results are favorably compared with the previous results of Plazek and O'Rourke obtained from creep measurements, but agreement with predictions based on the Rouse theory is obtained only in the case of the highest molecular weight sample.

Notes: Dielectric relaxation measurements at very low frequency were carried out on polycarbonate. Two prominent peaks were resolved from the broad β-relaxation peak with activation energies of 0.28 and 0.52 eV, respectively. Thermally stimulated discharge current was also studied and compared to the results obtained from the dielectric relaxation measurements.

Notes: Dynamic mechanical and thermally stimulated depolarization current data have been obtained on polyethylene, γ-irradiated in the molten state, as a function of irradiation dose. The β peak which appears in mechanical experiments has been attributed to motions of the chain backbone. The branches, like the crosslinks coming from γ-irradiation, are fixed tie points for the chains.

Notes: Polyethylenes were prepared by γ-ray-induced polymerization in ethyl and n-butyl alcohols, tert-butyl alcohol containing 5 vol-% of water, 2,2,5-trimethylhexane, 2,2,4-trimethylpentane, and cyclohexane in the temperature range 25-90°C. The morphology of the polymers as-polymerized and studied by electron microscopy depends on three factors through the degree of undercooling: the affinity of the solvent, polymerization temperature, and the polymer molecular weight. Large lamellar crystals are formed even in the alcohols when at least two of them are chosen properly.

Notes: A non-Gaussian theory of the stress-induced crystallization of polymeric networks is presented. It is predicted that for uniaxial extension of crosslinked polyethylene, a perfectly oriented, extended-chain crystal is formed initially, changing to one-fold crystal oriented perpendicular to the stretch direction at low extension and to a two-fold crystal having nearly perfect orientation at high extension. The stress is predicted to decay initially and then to rise as the network chains switch from an extended- to a folded-chain morphology, the rise being delayed and finally suppressed by additional crosslinking. The final, equilibrium birefringence is calculated and found to be negative at low extension and positive at high extension. The initial rate of crystallization is calculated using irreversible thermodynamics and is found to increase with extension and decrease with increasing crosslinking and temperature. All of the theoretical predictions are in qualitative agreement with experiment.

Notes: The piezoelectric d- and e-constants, together with the elastic constant and the dielectric constant, were measured for oriented poly(γ-benzyl-glutamate) (PBG) films with various elongation ratios as a function of frequency and temperature, using an apparatus developed by us. The results are discussed in terms of a general theory of piezoelectricity for inhomogeneous systems, in particular for a disperse two-phase system. The piezoelectricity of PBG film is proved to originate from the piezoelectric and optically active symmetry of PBG crystallities and their orientation distribution by three findings: (1) the d14 component of the piezoelectric matrix, which is the only component for a uniaxially or uniplanarly oriented system, is observed; (2) d14 〉 0 for PBDG and d14 〈 0 for PBLG; (3) d14 is proportional to the degree of orientation Fc of PBG crystallites, as determined by x-ray diffraction. By extrapolating to perfect orientation, d14 is determined to be 5 × 10-8 cgs esu, if the side chains of PBG are rigid. The piezoelectric relaxation of PBG due to thermal motion of the side chains has a dual character: it is relaxational at lower frequencies and retardational at higher frequencies. On the assumption that the α-helical main chains surrounded by the bulky side chains are responsible for the origin of the piezoelectricity, such relaxation phenomena are interpreted in terms of the relaxation of the local elastic field in the main chains. An equivalent model having the same frequency characteristics is proposed to include the higher order structure of the PBG film.

Notes: Defect structures in (SN)x crystals obtained by solid-state polymerization are so numerous and varied that they are likely to conceal inherent property aspects of the defect-free polymer. In addition to frequent macroscopic twinning, three different kinds of defect sites are observed. These sites are related to the disruption of molecular orientational order about the chain axis direction and the sequencing of chain types in the periodic phase. The origin of these defects is explained by the nonuniqueness of solid-state polymerization and recrystallization processes, which transform the initial dimer phase to the final polymer phase. The orientational relationship between the dimer and polymer phase is predicted from the observed twinning mode and the structural relationship between these phases. The change from dimer phase (at zero and at intermediate conversions involving solid solution formation) to polymer phase can be described by a shear transformation on the (001) dimer plane. This observation suggests an analogy with known martensitic reactions and a method for improving the perfection of (SN)x.

Notes: Thermal behaviors of extended-chain crystals of polyethylene formed during various crystallization processes and conditions under about 5000kg/cm2 were studied by high-pressure dilatometry and differential scanning calorimetry. The experiments indicate that by isothermal crystallization at small undercoolings for prolonged periods, the products show two endothermic peaks in the melting region of the usual extended-chain crystals. This means of the presence of a bimodal lamellar thickness distribution in the extended-chain crystals. A phase diagram has been made for pressures up to 5000 kg/cm2. The experimental results confirm the existence of two kinds of extended-chain crystals, i.e., ordinary extended-chain and highly extended-chain crystals, as suggested previously by the authors.

Notes: Application of the van der Poel equation (as recently corrected and simplified by Smith) to modulus-composition data on polymer composites is discussed. The van der Poel equation is in good agreement with experimental results on systems for which the ratio of filler to matrix modulus is either much less than or, if the filler particles are large enough, much greater than unity. For these systems, it is shown that the van der Poel equation is essentially equivalent to an empirically modified form of the Kerner equation. Discrepancies between the van der Poel equation and experimental modulus values for the remaining systems are analyzed in terms of an effective volume fraction veff. A functional form for veff found to be in agreement with experimental results on several systems is: veff = vf + k′(vf/d)2/3 where vf is filler volume fraction, d is filler particle size, and k′ is an empirical parameter. For the systems studied, k′ ranges between 0.28 and 1 μm2/3.

Notes: The effects of cyclic loading on several physical properties of some polymers have been investigated. The results indicate that internal damping, shear modulus, heat capacity, and density of poly(methyl methacrylate) and alkali-polymerized polyamide 6 in the glassy state undergo changes during cyclic loading well before the appearance of crazes. It is suggested that cyclic loading induces a nonuniform volume contraction in the structure of the material.

Notes: Potential energy calculations were performed on the isolated chain of Kapton H (KH) in order to obtain information on the most probable conformations. A model with a C—O—C angle of 130° and with the segments joining the ether oxygens forming a planar zigzag chain satisfactorily fits the x-ray experimental data. Although the equatorial reflections are very few and diffuse, it seems likely that the space group is P21 and the unit cell parameters are a = 4.66 Å, b = 32.9 Å, c = 5.96 Å, β = 100°. The observed density is in agreement with two monomers in the unit cell. An intrachain vector distribution map was computed by rotating (angle θ) the pyromellitic acid dimide (DIPA) unit about the N—C bond in the KH monomer. This map was compared with a one-dimensional Patterson synthesis calculated along b, the fiber axis, to establish the value of θ. Van der Waals' energy calculations were subsequently accomplished in the crystal as a function of θ and of the rotation around the helical axis of the KH chains. The results allowed us to choose a reasonable macromolecular conformation and packing in the crystal. KH is mainly ordered along the fiber axis but shows little order in the packing of adjacent helixes. The macromolecules are held together by Van der Waals' and, probably, by charge-transfer forces.

Notes: The catastrophic failure of a polymeric material is preceded by a number of complex, partially understood events occurring on the molecular level. These events range from the flow of ordered regions to the cleavage of primary bonds in the chain. In recent years, stress-induced bond cleavage in polymers has received increased attention, many authors nothing the presence of free radicals and/or volatile products released upon fracture; a free-radical decomposition mechanism involving up to 103 molecules per chain rupture also has been postulated. A special tensile stress-strain and shear apparatus was developed and located inside the ion-source housing of a time-of-flight mass spectrometer to characterize the volatile products released during mechanical degradation of polystyrene. Volatile compounds evolved during stress and fracture of polystyrene were monitored either continuously or by z-axis modulated oscilloscopic display. The polystyrene was purified by two methods: vacuum outgassing and fractional reprecipitation. Large amounts of styrene evolved from both the as-received and outgassed samples; however, essentially none was observed from the reprecipitated samples. Previous reports on monomer evolution during mechanical stress of polystyrene may be the result of residual monomer and not mechanical degradation products. The product of the surface density of primary radicals and the chain length for unzipping is less than 3 × 1010 radicals/mm2 indicating a maximum radical concentration of approximately 1010 radicals/mm2.