Network Structure in Acrylate Systems: Effect of Junction Topology on Cross-Link Density and Macroscopic Gel Properties

A range of poly(ethylene glycol) (PEG)-based polyacrylate networks with two different topological properties were synthesized by photoinitiated free-radical polymerization and analyzed by mechanical, chromatographic, and NMR methods. Comparison between networks with ziplike and pointlike junctions pinpointed the critical role of network topology in generating the so-called “short chain abnormality” in polymer dynamics. In particular, double quantum (DQ) NMR analysis of the ziplike networks identified strong topological constraints on isotropic movement of network chains directly resulting in increased effective functionality of the system. The failure of classical rubber elasticity theory in treating networks with ziplike cross-links is found to arise primarily from non-Gaussian behavior of these network chains caused by the topological constraints.