Rigid Random Coils: Rotationally Confined Chain Molecules

Abstract

Considered are chain molecules characterized by rotational potentials with a set of low energy states separated by large energy barriers. The expectation is that such chain molecules should exhibit unique properties. Polynorbornene and laterally substituted polynorbornenes are characteristic examples. Simulations based on ab initio methods, semiempirical quantum mechanical methods, and force field methods are employed in order to derive information on the chain conformation and dynamics of the polynorbornenes. The finding is that they display a random rigid coil with a characteristic ratio of the order of 10, that they are not able to collapse even in poor solvents, and that isolated chains are rigid up to temperatures well above room temperature. Details of the rotational potential can be controlled by a proper selection of lateral substituents.