Concentration-Dependent Dynamic Evolution in Hyperbranched Polymerization under Semidilute Conditions: From Cooperative Diffusion to Constrained Relaxation

Abstract

Hyperbranched polymerization in semidilute solution involves complex coupling between chain overlap, collective dynamics, and topological evolution. Using in situ static and dynamic light scattering, we studied the step-growth polymerization of linear AB2 polystyrene macromonomers above the overlap concentration. The results reveal no detectable variation in the apparent static correlation length within the resolution of the technique. This suggests that polymer growth may primarily occur within pre-existing intermolecular correlation environments, without forming new long-range structures on the length scales probed. Throughout the reaction, the dominant dynamic mode remains cooperative diffusion, but a slow relaxation mode progressively emerges, whose contribution strongly depends on the initial overlap concentration and chain length. This slow mode reflects local long-lived dynamic correlations rather than a global dynamical transition. After redissolution, the intrinsic dynamics of the final hyperbranched structures become apparent: products formed at low overlap retain diffusion-dominated- behavior, whereas those formed at high overlap exhibit confined relaxation with finite spatial scales. These results establish a concentration-dependent- framework linking solution thermodynamics, collective dynamics, and topological development in hyperbranched polymer formation under semidilute conditions.