Systematic Exploration of Molecular Architecture Effects on Polymer Network Crystallinity

Semi–crystalline polymers comprise a large fraction of commodity materials. While significant efforts have been made to elucidate the fundamental physics of crystallization of these materials, much less work has focused on how the introduction of crosslinks and emergent network architecture augment crystallization kinetics and thermodynamics. Here, we use thiol-ene chemistry to prepare spatially homogeneous networks to systematically investigate the effect of network strand length and crosslink distribution on the extent of crystallinity. Employing a combination of differential scanning calorimetry (DSC) and x–ray scattering, we find that characteristic enthalpies of melting and long–range order increase with molecular size of strands and decrease with crosslinking density. Further, we investigate the effects of polymerization conditions on controlling the rate and extent of crystallization in these materials via the interplay between polymerization and crystallization kinetics. Our findings indicate that a judicious choice of network composition allows for independent control of both the thermal transition onset and associated melting endotherm. Finally, we correlate these data with the mechanical properties of these materials, such as stiffness and toughness. The insights from this work are expected to have implications for the design of materials for thermal energy storage as well as a wide variety of commodity materials.