Influence of Attractive Functional Groups on the Segmental Dynamics and Glass Transition in Associating Polymers

A recently developed microscopic statistical mechanical theory for how strong short-range attractions between sticky groups copolymerized in the backbone of associating polymer liquids perturb the segmental dynamics and glass transition temperature (T-g) is quantitatively compared with a large body of experimental data on end-functionalized telechelic melts of variable polymer backbone chemistry, association strengths, and chain lengths. For strong associations and PDMS-based telechelic melts, a universal growth in T-g is predicted and experimentally observed as a function of sticker fraction or telechelic chain length which does not depend on sticker chemistry. The predictions of a stronger than exponential growth of the alpha relaxation time, but perturbative or negligible changes in dynamic fragility, with increasing sticker fraction are also in good accord with the experimental observations. The theory is extended to the case of weaker sticker associations where the "transient cross-linked" network picture based on a large time scale separation between the nonsticker alpha relaxation time and the sticker bonding lifetime does not hold. The new physics is theoretically accounted for by introducing larger length scale dynamic sticker fluctuations consistent with weaker physical bonding. A smaller growth in T-g with sticker fraction is predicted which depends in a continuous manner on the degree of dynamical loosening of sticker bonding. The theoretical results are consistent with our experimental data for PPG-based telechelic melts. Overall, the theory provides guidelines for the design of polymers with dynamic bonds with controlled enhancements of T-g and segmental alpha time.