Controlling topology and mechanical properties of polymer networks through kinetics of gelation

Soft materials are widespread in adhesives, elastomers, and hydrogels, but the molecular design of their mechanical properties remains challenging due to their network-like disordered structure. Recent investigations have quantitatively related the presence of topological defects to the elastic modulus and fracture energy, but a missing link still exists on how those defects are formed during gelation.

We gelled model poly(ethyl glycidyl ether) networks with two organoaluminum-based catalysts, and investigated the relationship between rate of gelation, network architecture, and mechanical properties. The key result is that slow gelation, as measured by the rate of polymerization, yields highly crosslinked, stiff, and brittle networks; whereas fast gelation, instead, results in loosely crosslinked, soft, and extensible ones. Controlling the mechanical properties through the rate of gelation serves to understand defect formation, and molecularly design soft materials.