ALBERT

Notes: Epoxy resin adhesives are widely used because of their strength, versatility, and ability to bond a variety of substrates. Furfurylamines represent a potential, new class of epoxy curing agents. Furfuryl amine (FA), tetrahydrofurfuryl amine (THFA), and 5,5′-methylenebis-2-furanmethanamine (DFA) were studied as possible epoxy curing agents. The utility of FA and THFA are limited by their volatility at the temperatures needed to effect cure of diglycidyl-ether of bisphenol A (DGEBA) based epoxy resins. DFA is a very effective epoxy curing agent with the ability to cure DGEBA at rates similar to that of standard epoxy curing agents such as liethylenetriamine.

Notes: Factors influencing the binding of tetracationic porphyrin derivatives to DNA have been comprehensively evaluated by equilibrium dialysis, stopped-flow kinetics, etc., for meso-tetrakis (4-N-methylpyridiniumyl)porphyrin TMpyP(4). Technical difficulties have previously precluded a comprehensive study of metalloporphyrins. Since electrostatic interactions with the DNA and metal derivatization of the porphyrins have important consequences, we have investigated in greater detail two isomers of TMpyP(4) {meso-tetra-kis(3-N-methylpyridiniumyl)porphyrin, [TMpyP (3)] and meso-tetrakis (2-N-methylpyridiniumyl)porphyrin [TMpyP(2)]} in which the position of the charged centers has been varied. A comprehensive study of the Cu(II) derivatives, e.g., CuTMpyP(4), was possible since the difficulties encountered previously with Ni (II) compounds were not a problem with Cu(II) porphyrins [J. A. Strickland, L. G. Marzilli, M. K. Gay, and W. D. Wilson (1988) Biochemistry 27, 8870-8878]. At 25°C, the apparent equilibrium constants [Kobs] decreased with increasing [Na+] for all porphyrins. The Kobs values were comparable for TMpyP(4) and TMpyP(3) binding to either polyd(G-C)·polyd(G-C) [poly[d(G-C)2]] or poly[d(A-T)·poly[d(A-T)]][poly[d(A-T)2]]. For the copper (II) porphyrins, the Kobs values were about fivefold greater. The Kobs value for CuTMpyP(2) binding to poly[d(G-C)2] was too small to measure under typical salt conditions; however, Kobs for CuTMpyP(4) or CuTMpyP(3). Application of the condensation theory for polyelectrolytes suggests about three charge interactions when CuTMpyP(4), CuTMpyP(3), and TMpyP(4) bind to poly[d(G-C)2] or poly[d(A-T)2], a result comparable to that reported for TMpyP(4). At 20°C and 0.115 M [Na+], incorporation of copper decreased the rates of dissociation from poly[d(A-T)2] by a 100-fold compared to those reported for TMpyP(4) but had little effect on the rates of dissociation from poly[d(G-C)2]. Also, movement of the H3CN+ group from the fourth to the third position of the pyridinium ring enhanced the rates of dissociation from poly[d(A-T)2] but decreased the rates of dissociation from poly[d(G-C)2]. From polyelectrolyte theory, the [Na+] dependence of the dissociation rates from poly[d(G-C)2] is consistent with intercalative binding, while that for poly[d(A-T)2] is consistent with an outside binding model. For calf thymus [CT]DNA at 20°C, a greater decrease in the AT than in the GC imino 1H-nmr signal was observed upon addition of CuTMpyP(2), suggesting selective outside binding to the AT regions. Flow dichroism experiments with calf thymus DNA revealed a small reduced dichroism [redD] value with CuTMpyP(2), indicative of disordered, outside binding. However, a large redD with CT DNA was found for CuTMpyP(4) and CuTMpyP(3), suggesting ordered intercalative binding. Titrations of closed circular superhelical DNA (CCS DNA) with CuTMpyP(4) and CuTMpyP(3) produced large increases in the solution reduced viscosity (SRV), indicative of unwinding. Twice the concentration of TMpyP(4) was needed for a similar effect, a result suggesting either that CuTMpyP (4) and CuTMpyP(3) intercalate into more sites, or that they produce more unwinding per site. Alternatively, CuTMpyP(4) and CuTMpyP(3) could unwind CCS DNA through a nonintercalative binding mode. Addition of CuTMpyP(4) or CuTMpyP(3) increased the SRV of poly[d(A-T)2], poly[d(G-C)2], and a variety of native linear DNAs varying in percentage GC. However, CuTMpyP(4) decreased the SRV of poly[d (A)]·poly[d(T)]. Whereas the viscosity increases with poly[d(G-C)2] probably result from intercalation, the unusual increase in the SRV of poly[d(A-T)2] could arise from conversion of a small amount of hairpin to the B form or from some other type of cooperative conformational change. Together these results suggest generally more favorable interactions with DNA of the copper porphyrins than the analogous metal-free porphyrins. However, our evidence clearly rules out appreciably greater GC vs AT selectivity for the copper porphyrins. Electrostatic interactions with DNA are similar for the TMpyP(4) and TMpyP(3) species, but are evidently much less favorable for the TMpyP(2) porphyrins. Finally, we find no clear evidence for additional binding modes for copper porphyrins.

Notes: The sorption isotherm and the polymer mass-fixed diffusion coefficients, D, for toluene in butyl rubber have been measured by the incremental sorption method to concentrations of 130%, corresponding to a solvent volume fraction of 0.578. The increase in D with concentration is strongly exponential to a concentration of 30% and then begins to level out. Since the nature of the dimensional change occurring in vapor sorption was not known, the values of D were converted to solvent self-diffusion coefficients, D1, assuming both swelling in the thickness direction (1D) and isotropically (3D). The free volume (FV) theory of Fujita was fitted to the resulting D1 with the zero concentration diffusion coefficient and the self-diffusion coefficient of toluene as limiting values leaving only a single arbitrary parameter. In this form the FV theory was able to describe the trend of the experimental D1 for the 1D and 3D cases equally well. Values of D were back-calculated from the FV relations for the 1D and 3D cases for comparison with the experimental results and with the diffusion coefficient determined by immersion in toluene. These comparisons favor the assumption that swelling is isotropic. It appears that the simple free volume relation is capable of providing a satisfactory representation of the experimental data with only a single fitting parameter, although there are moderate quantitative discrepancies. © 1994 John Wiley & Sons, Inc.

Notes: Two different phenol-formaldehyde (PF) resole resins are serving as models in a study aimed at establishing the effects of moisture, temperature, pressure, and time on resin cure and bonding during the pressing of wood flakeboard. This phase of the program had two goals: first, to characterize the two resins in terms of their structure and chemistry during synthesis, aging, and cure - using viscosity measurement, gel permeation chromatography (GPC), nuclear magnetic resonance (NMR), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), and dynamic mechanical analysis (DMA); second, to make a preliminary evaluation of the utility of DSC, FTIR, and DMA for measuring the degree of resin cure. The two resins differed significantly in relative amounts of hydroxymethyl groups and methylene linkages (NMR), in molecular weight and its distribution (GPC), and in reaction rate (as measured by viscosity, DSC, FTIR, or DMA). The degree of cure developed during constant heating rate DSC scans was calculated for a series of maximum DSC temperatures from both the loss in hydroxymethyl groups (FTIR) and the decrease in available exothermic heat (DSC). Agreement between the two methods was quite good, considering the inherent difficulties in quantifying infrared data. For comparison, the degree of cure developed during constant heating rate DMA scans was calculated for a series of maximum DMA temperatures from both the increase in storage modulus (DMA) and the decrease in exothermic heat (DSC after rewetting). Samples that apparently achieved complete cure in the DMA still exhibited significant residual cure potential in the DSC. We attribute the lower apparent cure in the DMA to loss of moisture from samples during the DMA scan, with consequent loss in plasticization and molecular mobility.

Notes: A spectral assay has been developed that permits reliable determination of polymer gelling times. Water-soluble, isocyanate-containing polyether prepolymers initiate chain extension on contact with water and after some period of time form a semisolid hydrogel matrix. Techniques based on visual observations used to determine the end point for this process generally produce erratic results. By following scattered transmittance of visible light by an aqueous solution of prepolymer during the gelation process, it is possible to obtain a more objective determination of the gelation time. It was empirically demonstrated that the minimum of the first derivative of the scattered transmittance versus time spectrum correlated with the observed gel time over a wide time scale. © 1993 John Wiley & Sons, Inc.

Notes: Nonisothermal differential scanning calorimetry data for neat polypropylene and polypropylene with variously treated cellulose fillers has been used to solve for the Avrami exponent, n. Results show neat polypropylene to have an Avrami exponent value very close to the theoretically excepted value of 4.0. The addition of untreated cellulose fibers to polypropylene, which has been shown to produce a transcrystalline region, results in an exponent value of 2.7-2.9 for the initiation stage, followed by a value of 3.9 for the bulk stage. Treatment of the cellulose with alkyl ketene dimer, alkenyl succinic anhydride, or stearic acid results in intermediate exponent values from 2.7 to 3.9. These results verify the effectiveness of surface treatments in reducing the natural nucleating ability of cellulose. Sample mixing and filler content were also shown to play a role in the crystallization process. © 1994 John Wiley & Sons, Inc.

Notes: Composition depth profiles of the outer 50 Å of plasma-fluorinated poly(ethylene terephthalate) fibers were obtained by angle-dependent X-ray photoelectron spectroscopy (XPS). The effect of sample geometry on XPS sampling depth and the depth distribution function (DDF) was determined theoretically for cylindrical and hemispherical surfaces. The theoretical DDFs are nonexponential. For cylindrical surfaces, the effect is small, a 22% increase in surface sensitivity. The average XPS sampling depth for smooth, properly oriented fibers is shown to vary, as it does for a planar surface, as the sine of the nominal takeoff angle. The DDF appropriate for cylindrical surfaces was incorporated into a computer program for inversion of angle-dependent XPS data to obtain composition depth profiles of the fibers. Plasma-fluorinated PET fibers were used to demonstrate the use of angle-dependent XPS on fibers. XPS results indicate that most fluorination occurs within the top few “monolayers,” attack is preferentially at the phenyl ring, both —CHF— and — CF2 — moieties are formed, and fluorination causes partial loss of aromaticity. © 1994 John Wiley & Sons, Inc.

Notes: Well defined, narrow molecular weight distribution polydimethylsiloxane (PDMS) oligomers containing single, terminal, reactive end groups were synthesised by the anionic polymerisation of hexamethylcyclotrisiloxane (D3). A variety of functionalities were obtained by termination with an appropriate silyl chloride end blocker, e.g. styryl, allyl, silyl chloride, silane, hexenyl etc. Certain monomeric end blockers were also synthesised where necessary. The resulting oligomers were subjected to detailed characterisation using 1H NMR, gel permeation chromatography (GPC), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and IR spectroscopy.

Notes: The objective of this study was to improve the durability and stability of urea-formaldehyde-bonded wood products by decreasing the internal stress developed during resin cure and by improving the ability of the cured resin to withstand cyclic stresses. This paper presents initial results from modifying a urea-formaldehyde resin by incorporating di- and trifunctional amines. The amines were incorporated by adding them as amines during resin synthesis, by adding urea-capped amines during resin synthesis, and by using amine hydrochlorides as acidic curing agents. Addition of amines during resin synthesis produced uncurable resins. However, modification with urea-capped amines or curing with amine hydrochlorides provided cure rates comparable to that of unmodified resin cured with ammonium chloride. These modifications also reduced the tendency of the resin to crack and fracture and substantially improved the resistance of bonded joints to cyclic stress imposed by cyclic wet-dry exposures. Resins cured with amine hydrochlorides had lower formaldehyde liberation than those cured with ammonium chloride. Thus, incorporation of flexible di- and triamines offers promise for improving the durability and stability of urea-formaldehyde-bonded wood products.

Notes: The sol-gel transition mechanism of a thermoreversible hydrogel composed of a copolymer comprising poly(N-isopropylacrylamide) and poly(ethylene glycol) (PNIPAAm-PEG) was studied by NMR. The 1H- and 13C-NMR spectra measured on a PNIPAAm-PEG solution in 99.9% D2O showed a remarkable line width broadening of the PNIPAAm block of more than that of the PEG block, during thermally induced hydrogel formation. This result suggested that the mobility of the PNIPAAm block is more restricted than that of the PEG block during gelation. A crosslinked polymer network formation was ascertained by a sudden reduction in the spin-lattice relaxation time (T1) of the residual HDO proton during gelation. The temperature dependency of the T1 values for the PNIPAAm and PEG blocks revealed that the microscopic condition of the PNIPAAm block in water was drastically changed during gelation, while that of the PEG block was unchanged. The experimental results from NMR supported the following gelation mechanism; that an aggregation of PNIPAAm blocks in the separate copolymers caused by hydrophobic interaction forms crosslinking points to give an infinite three-dimensional network structure. The hydrated PEG chains in the copolymers provide the network with a swelling property in water, and prevent the aggregation from causing a macroscopic phase separation.