Comparative dielectric studies of segmental and normal mode dynamics of poly(oxybutylene) and poly(oxyethylene)-poly(oxybutylene) diblock copolymers

Diblock copolymers of ethylene oxide and 1,2-butylene oxide, E30Bn, with co nstant E-block length of 30 units and various B-block lengths (n = 3-30) we re investigated, in parallel with a series of homopoly(oxybutylene)s of sim ilar to B-block lengths, using broad-band dielectric relaxation spectroscop y (10(-2)-10(9) Hz). The normal mode relaxation process due to reorientatio n of the end-to-end vector and the main (segmental) process caused by local chain motions, exhibited by the B-blocks in the copolymers and by the homo poly(oxybutylene), were studied in comparison to each other. The dynamics o f the free chains in the liquid homopolymers is described more appropriatel y by the Rouse model, whereas the B-blocks in the crystallized copolymers e xhibit significantly different dynamics. The results show that the B-blocks in the copolymers, constrained between lamellar crystals created by E-bloc ks, are more oriented and expanded, as compared to the chain conformation o f the homopolymers. Comparative study of normal mode and main relaxations r eveals, only for the homopolymers, a correlation length xi for the main pro cess on the order of 1-2 nm at temperatures close to the glass transition t emperature, T-g.