Structural Morphology and Dynamical Confinement in PIB/β-alanine Graft Copolymer Nanocomposites

Polymer chains when grafted to nanoparticles at high grafting densities are stretched more near the nanoparticle interface. Such strong stretching can lead to chain confinement close to the nanoparticle/polymer interface. Further from this interface, stretching decreases. This phenomena were studied in three different Polyisobutylene (PIB) graft copolymer rubbers. The grafts on the PIB backbones contain β-alanine trimers which self-assemble into crystalline nanodomain. By tailoring the chemistry of the grafts, the nanodomain length in one rubber was shortened by about 10 times, relative to the others.  The effects of molecular design on domain self-assembly were quantified using small angle neutron scattering (SANS).  The effects on chain dynamics close to the domain interfaces in swollen rubber was probed using neutron spin echo (NSE). SANS showed that these systems adopted a core shell morphology with varying extents of the region over which chain stretching occurs. NSE results showed that in the system designed to have the most highly stretched chains, confinement effects were seen over the widest range of length scales. The strongest dynamical confinement in the swollen state was observed at lengths of the order of the mean distance between nanodomains.