Controlling Crystallinity in Networks Synthesized from a Semicrystalline Butadiene Derived Oligomer via Thiol-ene Click Chemistry

Abstract

Semicrystalline polymer networks were synthesized from a butadiene-derived cyclobutene oligomer (B4P1) via thiol-ene photopolymerization to investigate how crosslink density and curing temperature jointly control crystallinity and thermomechanical properties. Networks were formulated across four PETMP:B4P1 molar ratios (z = 0.1–0.4), yielding crosslink densities ranging from 1.25 to 5.00 B4P1 units per junction, and cured either at room temperature (25 °C) or above the networks’ melting point (120 °C). Gel fraction analysis confirmed that higher PETMP concentrations produced more complete network formation, while the lowest crosslinker ratio (z = 0.1) exhibited substantial swelling and network defects. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) revealed that increasing crosslink density increases both the glass transition temperature and thermal degradation onset, and that polymerizing the network at 120 °C significantly reduces crystallinity when compared to the room temperature synthesized networks. Dynamic mechanical analysis (DMA) demonstrated that room-temperature networks retain higher rubbery-plateau storage moduli, consistent with trapped crystalline reinforcement, and tan ω profiles suggest a broad crystal-to-rotator phase transition between 50–80 °C. Variable-temperature wide-angle X-ray scattering (VT-WAXS) corroborated the thermal melting behavior observed by DSC. Tensile testing confirmed that room temperature networks exhibit greater stiffness and yield strength, while heated networks display enhanced ductility at higher crosslink densities. Finally, preliminary shape memory experiments demonstrated repeatable thermal programming and recovery, establishing B4P1-based thiol-ene networks as a promising platform for stimuli-responsive smart materials.