The effect of acrylate functionality on frontal polymerization velocity and temperature

© 2019 Wiley Periodicals, Inc. 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. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 982–988

Thermal transport and chemical effects of fillers on free‐radical

© 2020 Wiley Periodicals LLC Frontal polymerization (FP) is a process in which a front propagates in a localized reaction zone, converting monomer into polymer through the coupling of thermal diffusion with the Arrhenius kinetics of an exothermic reaction. Fillers are added to control the rheological properties of the formulation and to enhance the mechanical properties of the product. However, the thermal and chemical effects of these fillers on the front propagation have not been thoroughly explored. Herein we report the thermal and chemical effects of fillers on free-radical frontal polymerization. It was found that fillers with high thermal diffusivities, such as milled carbon fiber and boron nitride increased the front velocity. Despite their high thermal diffusivities, fillers such as aluminum and alumina decreased the front velocity. This is likely due to the radical-scavenging ability of aluminum oxide, which was explored with clay minerals. It was found that the presence of water within clay fillers can also decrease the front velocity. To probe the chemical effects, acid-activated clay minerals were utilized. The results demonstrate that some fillers can increase front velocity through their high thermal diffusivities while others decrease it by acting as radical scavengers

Cure-on-demand wood adhesive based on the frontal polymerization of acrylates

© 2016 Wiley Periodicals, Inc. We demonstrated for the first time a cure-on-demand wood adhesive using thermal frontal polymerization with Southern Pine wood. Monomer structure, initiator loading, and filler loading all had an impact on the strength of the adhesive and the cure-on-demand ability. More flexible, ethoxylated monomers produced stronger adhesives; though, the ethoxylate groups reduce the ability of the system to be polymerized frontally. Addition of a highly reactive comonomer (acrylic acid) to increase molecular weight between crosslinks along with the ethoxylated triacrylate increased the propensity for frontal polymerization and made a tougher polymer. Increasing initiator loading could help ensure front propagation, but a maximum initiator loading was reached where the gaseous byproducts of the peroxide initiator made the network highly porous and thus lacking strength. Fillers such as kaolin and sawdust helped overcome decreases in strength at high initiator loadings. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 44064