Hydrogen Bonding Enhances the Crystallinity of Polymer Networks Synthesized by Rapid and Solventless Photopolymerization

The effect of interchain interactions such as hydrogen bonding on crystallinity is well understood in linear polymers but not in network polymers. To this end, we synthesized aliphatic polyester networks and polyamide networks, both by thiol-ene free-radical photopolymerizations. These polymer networks were directly synthesized from low-viscosity neat liquid resins comprising an aliphatic dithiol, an ester or amide containing dialkene, and a trifunctional cross-linker. Interchain hydrogen bonding from the amide groups enhanced backbone rigidity, raising glass transition temperatures by 35-40 °C compared to the polyester systems. In the crystalline domain, hydrogen bonding raised the equilibrium melting temperature by 60 °C but reduced the melting enthalpy. Further, hydrogen bonding did not alter the threshold of chain length between cross-links for crystallization (>2500 g/mol). We believe these network polyamides present a robust platform for synthesizing high-performance 3D printing polymers and shape-programmable materials.