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

Diblock copolymers of ethylene oxide (E) and 1,2-butylene oxide (B), E₃₀B_n, with a constant E-block length of 30 units and various B-block lengths (n=3-30), were investigated, in parallel with a series of homopoly(oxybutylene)s of similar B-block lengths, using broadband dielectric relaxation spectroscopy (10^-2 10⁹ Hz). The normal mode relaxation process due to reorientation of the end-to-end vector, as well as the main (segmental) process caused by local chain motions, exhibited by the B-blocks in the copolymers and respectively by the homopoly(oxybutylene), were studied in comparison with each other. The Rouse model has been found to describe satisfactorily the molecular mobility of B_n blocks in the copolymers, whereas deviations from that model have been observed for the homopolymers. The results show that the B-blocks in the copolymers, constrained between lamellar crystals created by E-blocks, exhibit slower large scale motions