Sub-Rouse Dynamics in Poly(isobutylene) as a Function of Molar Mass

We report on the molar mass dependence of the segmental, sub-Rouse, and terminal relaxation processes of poly(isobutylene). For this purpose, seven samples were synthesized with molar masses in the range from 2.8 to 172 kg.mol(-1) and investigated by temperature-modulated differential scanning calorimetry, dielectric spectroscopy, and rheology. Rheology provided access to the terminal times that were found to scale as tau(term) similar to M-3.2. On the other hand, the sub-Rouse dielectric process shows a very weak molar mass dependence (tau(sub - Rouse)/tau(SM) similar to M-0.1), that is, distinctly different from the Rouse and terminal dynamics. We infer that the sub-Rouse mode has a lengthscale intermediate to the statistical segment length (similar to 1.25 nm) and the length of an entanglement strand (similar to 2.3 nm).

Automated summary

The study investigated the impact of molar mass on the segmental, sub-Rouse, and terminal relaxation processes of poly(isobutylene). It was found that the terminal times scaled with molar mass as tau(term) similar to M-3.2, while the sub-Rouse dielectric process showed a weak molar mass dependence (tau(sub - Rouse)/tau(SM) similar to M-0.1). The sub-Rouse mode was inferred to have a lengthscale intermediate to the statistical segment length and the length of an entanglement strand.