I. THEORETICAL STUDY OF THE THERMOELASTIC AND ELASTIC PROPERTIES OF ELASTIN MODEL COMPOUNDS. II. MODELS FOR THE TRAPPING OF CYCLIC POLY(DIMETHYLSILOXANE) (PDMS) CHAINS IN PDMS NETWORKS AND IMPLICATIONS OF BACKBONE INVERSION ON THE CONFIGURATIONAL CHARACTE

The temperature coefficient of the unperturbed chain dimensions (,0) was investigated for polypeptides composed exclusively of one of three highly conserved repeat sequences present in the bioelasto- mer elastin. Conformational energy maps of the relevant amino acids were generated and a standard matrix method used. Various levels of intramolecular hydrogen bonding were studied, ranging from none to the inclusion of a longer-range hydrogen bond implicated in stabilizing a (beta)-bend conformation considered of importance due to a Pro-Gly pair present in each of the three repeat peptides. The calculated values of dln(,0)/dT compared favorably with experimental results for native elastin in the literature.; Theoretical stress-strain curves for the elastin model chains were evaluated using Monte-Carlo techniques to evaluate the distri- bution functions of the end-to end distance vector r, from which the modulus as a function of elongation was determined. With minor exception, the results for degree of polymerization DP = 5 and DP = 10 chains showed little deviation from gaussian behavior for elongation ratios up to 2.; Two theoretical methods were developed to model the trapping of poly(dimethylsiloxane) (PDMS) rings present at the time of network formation by end-linking of PDMS chains. Monte Carlo methods were used to generate representative samples of cyclics of DP = 20, 40, 75, 120, and 200; with criteria developed to determine whether a particular ring would be topologically trapped by one or more network chains. One model yielded excellent agreement within experimental and theoretical error over the entire DP range.; Also investigated for PDMS was the effect of a low energy barrier to inversion at the backbone oxygen atoms on the temperature coefficients of three configuration-dependent properties. A quartic potential energy function was used. The results indicated that this neglected contribution to these properties could be significant in the case of a low barrier.; The NMR spectrum of the (alpha)-methyl protons in poly((alpha)-methyl- styrene) (PAMS) was studied theoretically. The averaged chemical shifts were determined using calculated conformational probabilities in the ten pentad stereochemical environments and the chemical shift of the central methyl protons in each conformation induced by the four phenyl groups. Several methods of treating the methyl pro- tons were used, including exact rotational averaging. Theoretical values in agreement with experiment were found upon minor modification of the chain statistics.