Subchain Dynamics in Disordered Diblock Copolymer: Poly(isoprene-block-butadiene)

Abstract

We investigated the dielectric normal mode relaxation on diblock copolymers poly(isoprene-block-butadiene) (I-B) with several polyisoprene (PI)/polybutadiene (PB) compositions. Through the dielectric measurements on I-B, we can obtain information about the dynamics of the PI subchain since the PI block is labeled with type-A dipole but PB is not. At the same time, we carried out viscoelastic measurements on the same I-B samples to obtain information of the whole chain motion, especially the longest relaxation times and the plateau moduli. From these viscoelastic and dielectric data, we can directly compare the relaxation spectra of subchains with those predicted by the tube model. From such comparison, we have found that the end part of the chain relaxes faster than the theoretical prediction suggesting extra relaxation mechanisms other than reptation in the dynamics of chain ends.