Macromolecules, Vol.37, No.6, 2144-2150, 2004
Concentrated solutions of partly deuterated triblock polybutadiene. Segmental analysis of NMR properties
The comparison of proton transverse relaxation properties observed on polybutadiene (PB, M = 1.07 x 10(5) or 2.08 x 10(5)) with those observed on a triblock copolymer with deuterated end blocks (PB-DHD, M = 0.98 x 10(5)), was used to investigate two different segmental behaviors detected along any protonated chain. All relaxation curves recorded from PB or PB-DHD as a function of temperature or polymer concentration c in deuterated cyclohexane were found to exhibit two components: a fast decay and a long tail clearly governed by two distinct partial motional averages of proton-proton couplings called Delta(I) and Delta(II), respectively. Delta(1), independent of molecular weight, obeyed the empirical dependence on polymer concentration: Delta(1) = 1740c(1 - 0.29c) rad(.)s(-1) while Delta(II) approximate to Delta(1)/4.5 (0.51 less than or equal to c less than or equal to 1.0 w/w). On one hand, the nonlinear 1/c dependence of the effective segmental length represented by 1/Delta(1) could not be directly correlated to the c-1 dependence usually assigned to the mean segmental spacing between entanglements. On the other hand, the long tail amplitude A,, observed from PB obeyed the empirical equation MA(II) = [5886 + 8800(1/c - 1)] corresponding to a number of monomeric units involved in the definition of All equal to 109 in the pure polymer and independent of molecular weight; a long tail was still observed on pure PB-DHD although the total number of deuterated units (185) in end blocks was higher than 109: the product MA(II), varied as [2816 + 5456(1/c - 1)] and showed that deuterated end blocks eliminated the relaxation of only 62/c units per chain. The relaxation tail observed from fully protonated PB was assigned both to monomeric units attached to so-called end segments formed from 2 x 27/c units and to neighboring units in dynamic interaction with end segments.