Quasielastic neutron scattering study of microscopic dynamics in polybutadiene reinforced with an unsaturated carboxylate.

We studied the dynamics of zinc diacrylate (ZDA) reinforced polybutadiene rubber (BR) (ZDA/BR) using the quasielastic neutron scattering technique to determine the effect of concentration of ZDA on polymer dynamics. First, we evaluated the temperature dependence of mean square displacements (〈u2〉) for ZDA/BR with different ZDA volume fractions. 〈u2〉 increased with temperature below 170 K, and we observed no significant ZDA volume fraction dependence. However, it increased more steeply above 170 K, and the value of 〈u2〉 was smaller for the samples with increasing ZDA fraction. To elucidate the origin of the decrease in 〈u2〉 with increasing ZDA content, dynamic scattering laws (S(Q,ω)) were analyzed. An increase in the elastic component, an increase in the mean relaxation time, and a broadening of distribution of relaxation time were observed with the increasing volume fraction of ZDA. In addition, the ZDA volume fraction dependence of the elastic component roughly corresponded to that of elastic modulus, indicating that the elastic component is related to its mechanical strength. Referring to the previously reported static structure of the present ZDA/BR system, a model for the heterogeneous BR dynamics was proposed. This model assumes the coexistence of immobile, mobile, and interfacial constrained mobile regions. It was found to be appropriate for the explanation of the observed dynamics. We proposed that a network-like structure of the BR having a high crosslinking density around ZDA aggregates is mainly responsible for the high elastic modulus of ZDA/BR.