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  • 1
    ISSN: 1022-1352
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: N-Carboxy-(N∊-benzyloxycarbonyl)-L-lysine anhydride (Z-L-lysine NCA) was polymerized in dimethylformamide with triethylamine, diethylamine or hexylamine as initiator, at varying molar ratios of NCA to initiator (M/I ratio). After removal of the protecting Z-group the resulting poly-L-lysine was characterized with 1H NMR and MALDI TOF MS. Both diethylamine- and hexylamine-initiated polymerization yielded poly-L-lysine in which the initiators were incorporated at the carboxylic end of the polymer. This indicates that the NCA polymerization occurred exclusively via nucleophilic attack of the initiator on the monomer. On the other, hand, when triethylamine was used as the initiator, poly-L-lysine was obtained in which no triethylamine-derived end group could be detected by MS. These polymer chains are most likely end-capped with an N-acyl-2,5-dioxopiperazine group at the carboxylic end of the polymer. Incorporation of diethylamine and hexylamine allowed determination of the degree of polymerization (DP) of the obtained polymers by 1H NMR. The DP depended linearly on the M/I ratio, for both diethylamine and hexylamine, with higher DPs for the diethylamine-initiated poly-L-lysine at equal M/I ratio.
    Additional Material: 6 Ill.
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  • 2
    Electronic Resource
    Electronic Resource
    Chichester [u.a.] : Wiley-Blackwell
    Surface and Interface Analysis 16 (1990), S. 216-217 
    ISSN: 0142-2421
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
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  • 3
    ISSN: 0323-7648
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The kinetics of the emulsion polymerization of butyl acrylate at 20°C in Smith-Ewart interval III were investigated using a redox initiator system peroxodisulfate-bisulfite-copper. The aim of this work was to obtain more basic knowledge about the kinetic behavior of the butyl acrylate system. Monomer conversion into polymer was based on gravimetrically calibrated online densitometry. The experimentally obtained conversion versus time curves for these seeded reactions were fitted by a linear regression procedure (slope and intercept) as well as by a nonlinear regression procedure based upon zero-one kinetics. The conclussion is that the emulsion polymerization of butyl acrylate may reflect zero-one kinetics up to a particle size of approximately 130 nm. The rate coefficients for entry and exit can be obtained fairly accurately with the slope and intercept procedure and with the nonlinear regression method if the propagation rate coefficient is accurately known. However, this is not the case. Therefore the development of universal procedures for obtaining the propagation rate coefficients is essential, since this parameter is of paramount importance in all further model calculations concerning emulsion polymerization.
    Additional Material: 5 Ill.
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  • 4
    ISSN: 0025-116X
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Additional Material: 3 Ill.
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  • 5
    ISSN: 0887-624X
    Keywords: emulsion copolymerization ; terpolymerization ; composition drift ; chemical composition distribution ; gradient polymer elution chromatography ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In Part I of this series the reactivity ratios of the comonomer pair methyl acrylate-methyl methacrylate were determined with low-conversion bulk polymerizations. It was shown that the binary reactivity ratios of the systems styrene-methyl acrylate, styrene-methyl methacrylate, and methyl acrylate-methyl methacrylate describe composition drift in low-coversion bulk terpolymerizations with these monomers reasonably well. A computer model was developed to simulate the composition drift in emulsion co- and terpolymerizations. The composition drift in two batch emulsion copolymerization systems (styrene-methyl acrylate and methyl acrylate-methyl methacrylate) and one emulsion terpolymerization system (styrene-methyl acrylate-methyl methacrylate) was investigated both experimentally and with the model. Experimental results were compared with model calculations. The copolymer chemical composition distributions (CCD) were determined with gradient polymer elution chromatography (GPEC®). This technique was also used for the first time to obtain information about the extent of composition drift in emulsion terpolymerizations. Cumulative terpolymer compositions were determined with 3H-NMR as a function of conversion and with this information the three-dimensional CCD was obtained. The composition drift was analyzed with respect to free radical copolymerization kinetics (reactivity ratios) and monomer partitioning. It was shown that in most emulsion copolymerizations the composition drift is mainly determined by the reactivity of the monomers and to a lesser extent by monomer partitioning, except in systems where there is a large difference in water solubility. The model predictions for cumulative terpolymer composition as a function of conversion and the three-dimensional terpolymer CCD showed excellent agreement with the experiments. The GPEC® elution chromatogram of the terpolymer was found to be in accordance with the predicted CCD and the experimentally determined CCD. © 1996 John Wiley & Sons, Inc.
    Additional Material: 11 Ill.
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  • 6
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Chemical shifts of base and H1′ protons of the single-stranded hexamers d(ATTACC) and d(GGTAAT), of the 1 : 1 mixtures of these complementary hexamers, and of the self-complementary dodecamer d(ATTACCGGTAAT) were measured at various temperatures in aqueous solution. Four different sample concentrations were used in the case of the dodecamer and of the mixture of the complementary hexamers; the individual hexamers were measured at two different DNA concentrations. Absorbance temperature profiles at five different NaCl concentrations were measured for the dodecamer in order to quantify the effect of the ionic strength on the duplex formation.Under suitable conditions of nucleotide concentration, temperature, and ionic strength, the dodecamer adopts either a B-DNA duplex or a hairpin-loop structure. Chemical shift vs temperature profiles, constructed for all samples, were used to obtain thermodynamic parameters either for the various stacking interactions in the single strands or for the duplex or the hairpin-loop formation. In the analysis of the duplex formation of the hexamers, a two-state approach appeared too simple, because systematic deviations were revealed. Therefore, a new three-state model (DUPSTAK) was developed. In order to investigate the magnitude of error arising from the use of the two-state approach in cases where the DUPSTAK model appears more appropriate, a series of test calculations was made. The magnitude of error in the enthalpy and in the entropy of duplex melting is found to depend linearly upon the actual melting temperature and not upon the individual ΔHOd and ΔSOd values.Thermodynamic analysis of the chemical shift vs temperature profiles in D2O solution (no added salt) yields an average Tmd value of 341 K (1M DNA) and ΔHOd of -121 kJ · mol-1 for the dimer/random-coil transition of the hexamer duplex d(ATTACC) · d(GGTAAT). For the duplex ⇄ random-coil transition of the 12-mer d(ATTACCGGTAAT) an average Tmd value of 336 K (1M DNA) and ΔHOd of -372 kJ · mol-1 are found. The hairpin/random-coil transition of d(ATTACCGGTAAT) is characterized by a rather large ΔHOh value, -130 kJ · mol-1, and an average Tmh value of 304 K.
    Additional Material: 9 Ill.
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  • 7
    ISSN: 0006-3525
    Keywords: DNA structures ; nucleic acids ; structure elucidation ; nmr spectroscopy ; molecular modeling ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: TheDNA sequences 5′-d(CGC-AC-GCG)-3′ (HPAC), 5′-d(CGC-AA-GCG)-3′ (HPAA), 5′-d(CGC-TC-GCG)-3′ (HPTC), and 5′-d(CGC-CT-GCG)-3′ (HPCT), were studied by means of nmr spectroscopy. At low DNA concentration and no added salt all four molecules adopt a minihairpin structure, containing three Watson-Crick base pairs and a two-residue loop. The structure of the HPAC hairpin is based on quantitative distance restraints, derived by a full relaxation matrix approach (iterative relaxation matrix approach), together with torsion angles obtained from coupling constant analysis. The loop folding is of the H1-family type, characterized by continuous 3′-5′ stacking of the loop bases on the duplex stem. The structure of the HPAA hairpin is similar to that of HPAC, but is more flexible and has a lower thermodynamic stability (Tm 326 K vs 320 K). According to “weakly” distance-constrained simulations in water on the HPAC minihairpin, the typical H1-family loop folding remains intact during the simulation. However, residue-based R factors of simulated nuclear Overhauser effect spectroscopy spectra, free molecular dynamics simulations in vacuo, and unusual chemical shift profiles indicate partial destacking of the loop bases at temperatures below the overall melting midpoint. The dynamic nature of the loop bases gives insight into the geometrical tolerances of stacking between bases in H1-family minihairpin loops. The HPTC and HPCT minihairpins, both containing a pyrimidine base at the first position in the loop, adopt a H2-family type folding, in which the first loop base is loosely bound in the minor groove and the second loop base is stacked upon the helix stem. The thermal stability for these two hairpins corresponds to 327-329 K, but depends on local base sequence. Preference for the type of folding depends on a single substitution from a pyrimidine (H2 family) to a purine (H1 family) at the first position of the miniloop and is explained by differences in base stacking energies, steric size, and the number of possible candidates for hydrogen bonds in the minor groove. In view of newly collected data, previous models of the H1-family and H2-family hairpins had to be revised and are now compatible with the reported HPTC and HPAC structures. The structural difference between the refined structure of HPAC and HPTC show that a conversion between H1-family and H2-family hairpins is geometrically possible by a simple pivot point rotation of 270° along two torsion angles, thereby swiveling the first loop base from a stacked position in a H1-family folding toward a position in the minor groove in a H2-family folding. The second loop residue subsequently shifts to the position of the first base in a concerted fashion. © 1998 John Wiley & Sons, Inc. Biopoly 46: 375-393, 1998
    Additional Material: 7 Ill.
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  • 8
    Electronic Resource
    Electronic Resource
    Hoboken, NJ : Wiley-Blackwell
    Journal of Biomedical Materials Research 32 (1996), S. 307-320 
    ISSN: 0021-9304
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Medicine , Technology
    Notes: The in vivo biocompatibility and biodegradation of crosslinked (co)polyethers with and without tertiary hydrogen atoms in the main chain and differing in hydrophilicity were studied by means of subcutaneous implantation in rats. After 4 days, 1 month, and 3 months postimplantation, the tissue reactions and interactions were evaluated by light microscopy (LM) and transmission electron microscopy (TEM). Poly(tetrahydrofuran) (poly(THF)), poly(propylene oxide) (poly(POx)), and poly(tetrahydrofuran-co-oxetane) (poly-(THF-co-OX)) were tested as relatively hydrophobic polyethers, and poly(ethylene oxide) (PEO) and a poly(THF)/PEO blend were used as more hydrophilic materials. In general, all polyethers showed good biocompatibility with respect to tissue reactions and interactions, with low neutrophil and macrophage infiltration, a quiet giant cell reaction, and formation of a thin fibrous capsule. For the relatively hydrophobic polyethers studied, the biostability increased in the order poly(POx) 〈 poly(THF-co-OX) 〈 poly(THF), probably indicating that the absence of tertiary hydrogen atoms has a positive effect on the biostability. Concerning the more hydrophilic materials, crosslinked PEO showed the highest rate of degradation, probably due to the mechanical weakness of the hydrogel in combination with the highest presence of giant cells as a result of the high porosity. A frayed surface morphology was observed after implantation of the crosslinked poly(THF)/PEO blend, which might be due to preferential degradation of PEO domains. © 1996 John Wiley & Sons, Inc.
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  • 9
    ISSN: 0142-2421
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: The use of imaging and static secondary ion mass spectrometry is demonstrated for the chemical characterization of the top monomolecular layers of chemically modified and patterned silicon wafers. Surfaces with areas of different chemical compositions and reactivities (e.g. hydrophobic/hydrophilic) were created by chemical modification with a light-sensitive organosilane, followed by UV irradiation or by chemical modification with 3-aminopropyltriethoxysilane, followed by local removal of the silane through oxidation with UV ozone. The latter surfaces were also selectively metallized on the aminosilylated areas as an example of the applications possible for these patterned surfaces.The chemical surface composition and structure of the organosilylated and selectively metallized silicon wafers are adequately characterized with static SIMS. The patterns created on the wafers are observed with good contrast in the SIMS images of the molecular ionic fragments and elemental ions characteristic for the particular surface compositions. The results can be used to improve the chemical modification reactions.
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  • 10
    ISSN: 0935-9648
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Additional Material: 4 Ill.
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