The influence of flexible side chains on the dimensions of flexible polymers

Abstract

Molecular dynamics simulations of single chains in vacuo have been used to investigate the role of flexible branches on the dimensions and in particular the backbone rigidity of flexible polymers. A series of isotactic poly-α-olefin chains was chosen as a model system to study because of their simplicity of structure. Θ-conditions were simulated for each branched chain by careful adjustment of the Van der Waals parameters, and properties such as end-to-end length, radius of gyration and persistence length were measured. As expected the backbone rigidity of the polymers was found to be determined by a balance between the coiling of the backbone induced by a gauche state at the branch point and the size of the side chain. Trends in persistence length with branch content compared favourably to the previous Rotational Isomeric State and experimental measurements of the characteristic ratio. The stiffening of the backbone under good solvent conditions was also investigated and it was found that the persistence length could be systematically increased by increasing the size of the side group, with the shape of the side group also making a small difference to the sampled backbone conformations.