The effect of acrylate functionality on frontal polymerization velocity and temperature

Frontal polymerization is a method of converting monomer(s) to polymer via a localized reaction zone that propagates from the coupling of thermal diffusion with the Arrhenius kinetics of an exothermic reaction. Several factors affect front velocity and temperature with the role of monomer functionality being of particular interest in this study. Polymerizing a di and triacrylate of equal molecular weight per acrylate revealed that as the proportion of triacrylate was increased the velocity and temperature increased. This is attributed to increased crosslinking and autoacceleration. Comparing several different acrylate monomers, both neat and diluted with dimethyl sulfoxide (DMSO) so as to maintain constant acrylate group concentration, shows that velocity increases with increased functionality from mono to difunctional monomers. This trend breaks when applied to tri- and tetraacrylates, with fronts containing trifunctional monomer being the fastest. Acrylates containing hydroxyl functionality, as in the case of pentaerythritol-based triacrylates, are slower than acrylates without. This is attributed to a chain-transfer event and was tested using octanol and a hydroxyl-free acrylate. It has also been shown that small amounts of water cause a lowering of front velocity due to energy lost via vaporization, which lowers the front temperature. (c) 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 982-988