Semicrystalline chain-growth photopolymer networks synthesized by orthogonal neat polymerization reactions

A sequential and orthogonal polymerization reaction strategy was developed to synthesize semicrystalline polymer networks. Acrylate-terminated oligomers were first prepared by thiol-Michael oligomerization between difunctional aliphatic acrylate and thiol monomers, giving oligomers with molecular weight ranges of 3.1-12.4 kDa. These crystalline oligomers were then photopolymerized in their molten state at 70 °C. The longer oligomers yielded semicrystalline networks, confirmed by thermal, mechanical, optical, and X-ray diffraction characterizations, whereas shorter-chain analogs were weakly crystalline or amorphous. Mechanical testing suggested strain-induced crystallization behavior, in which samples crystallized under tension reached 680% elongation-at-break and 15 MPa ultimate tensile strength.