showing a rubbery plateau at temperatures above Tg (Figure ). Tensile test (Figure ) showed that the para-phthalamide polymer behaved like a typical glassy but brittle network polymer, with a tensile strength of 50 MPa, Young's modulus of 1.4 GPa, and elongation-at-break of 6%, in agreement with what Hakkarainen et al. reported in a similar system. Similar to aromatic polyamide thermoplastics, paraphthalamide (Kevlar®) offers a higher strength than meta-phthalamide (Nomex®) but at the expense of brittleness. The ortho-phthalamide polymer showed decent toughness with a tensile strength of 42 MPa, Young's modulus of 1.2 GPa, and elongation-at-break of 28%. It is worth noting that ortho-phthalamide can form intramolecular H-bonding, which may result in a slightly softer material (Figure ). To our surprise, the meta-phthalamide polymer showed high ductility, with a tensile strength of 49 MPa, Young's modulus of 1.5 GPa, and elongation-at-break of 161%. Strain-hardening was observed at a strain beyond 150%. All numerical polymer properties can be found in Table . We were motivated to further understand the unique toughness found in the meta system in the following work. The effect of hydrogen bonding on material tensile toughness. The enhanced H-bonding in amides resulted in enhanced toughness in comparison to urethanes. To study the role of H-bonding in these thiol-ene networks, we designed two control systems comprising a meta-substituted diallyl urethane monomer and a metasubstituted diallyl ester monomer. The urethane and ester polymers were also prepared by thiol-ene photopolymerization with EBMP-TEMPIC thiol monomers. Diallyl urea monomers were also synthesized for comparison; however, extremely high melting points proved difficult to overcome when melting resin to form polymers. The ester network was a rubbery material showing a low Tg of 8 °C due to the absence of Hbonding; the urethane network was glassy, though with a lower Tg (48 °C) than that of the amide network (Figure ). Both urethane and ester networks are fully crosslinked, showing a rubbery plateau at temperatures above Tg (Figure ). The urethane polymer, although glassy, exhibited lower toughness than the amide polymer. The urethane polymer showed a Young's modulus of 1.1 GPa, a tensile strength of 39 MPa, and an elongation-at-break of 144% (Figure ). It is worth noting that comparable elongation-atbreak values were observed among the three systems, but the strength varied significantly. The variances in H-bonding were verified by FTIR (Figure ), with the carbonyl group in the amide being more electronwithdrawing, making the proton more available for H-bonding. We believe the H-bonding constitutes a secondary supramolecular network that contributes to enhancing of Tg and toughness. (C) Engineering stress-strain curves obtained by tensile test conducted at ambient conditions (23 °C). All three network polymers showed a similarelongation-at-break, but the polyamide network outperformed in toughness. (D) FTIR spectrum focusing on N-H stretch. The polyurethane network showed a blue shift, while the polyester showed the absence of hydrogen bonding (the full FTIR spectrum can be seen in Figure ).