Application of NMR to the study of molecular motion in SBS copolymers

NMR T1 and T2 data are presented for two styrene-butadiene-styrene block copolymers along with results for homopolymers of polystyrene and polybutadiene. The relaxation processes in both polymers are discussed. The results indicate that the glass transition temperature for polystyrene is lower in the SBS copolymer than for the homopolymer, in agreement with earlier findings. It is concluded that the vigorous motions in the polybutadiene phase of the copolymer instigate motion in the polystyrene phase prematurely. The data further indicate that motion in polybutadiene is more hindered in SBS than in the pure polymer as a result of the cross-linking effect of the polystyrene domains; however, there is little effect on Tg for polybutadiene. Finally, the T1 results indicate that spin diffusion is operative between the two phases in the SBS block copolymer. The principal features of this effect are satisfactorily explained in terms of a simple model which neglects the geometry of the interface between the two phases.