Conformational Analysis of Model Poly(ether urethane) Chains in the Unperturbed State and under External Forces

Abstract

Conformational features of model poly(ether urethane) (PEU) single chains are investigated in the unperturbed state and under external force. Model PEUs consisting of symmetrical, aromatic, 1,4-phenylene diisocyanate (PDI) hard segments and poly(tetramethylene oxide) (PTMO) soft segments with varying lengths are considered. Rotational potential maps are calculated quantum mechanically using the AM1 parametrization with Gaussian98. Configurations of the chains are generated by the Monte Carlo technique, using the rotational isomeric state formalism and successive matrix multiplication scheme. Unperturbed dimensions, the change in dimensions when a force acts along the end-to-end vector, the stiffness, and toughness of the chain and orientability of segments under external force are characterized and compared with properties of polyethylene. The characteristic ratio of a long PEU chain is 5.0, and the Kuhn length for a single block is 9.2 A, both of which are smaller than the corresponding polyethylene values. The model chains are significantly more ductile and tougher than polyethylene. The orientability of the backbones exhibits a strong even-odd effect, with strongly orientable bonds neighbored by weakly orienting ones. The degree of rigidity of the phenyl group does not propagate far along the chain. The projection of the bond vectors on the phenyl axis decay rapidly with increasing distance of the bond along the chain.