Soft materials can sustain large,
elastic, and reversible deformations,
finding widespread use as elastomers and hydrogels. These materials
constitute 3-D polymer networks and are typically synthesized by cross-linking
polymer chains or copolymerizing monomer and cross-linker. Seminal
investigations have enabled control over the network architecture
by cross-linking chains of poly(dimethylsiloxane), poly(1,4-butadiene),
or tetra-poly(ethylene glycol); however, as soft materials become
attractive for robotics, electronics, and prosthetics, codesigning
the network architecture, mechanical, and functional properties has
become pressing. We investigate the relationship among reaction pathway,
network architecture, and mechanical properties in poly(ethyl glycidyl
ether) networks synthesized by epoxide ring-opening polymerization
with two organoaluminum catalysts. The key result is that uncontrolled
polymerizations yield loosely cross-linked, entangled, soft, and extensible
networks, whereas more controlled polymerizations, instead, lead to
highly cross-linked, stiff, and brittle networks. Such catalytic control
over network architecture and mechanical properties could enable design
of novel soft, tough, and functional materials.