Convective Preheating Enhances Front Propagation in DCPD Frontal Polymerization

TL;DR

This study demonstrates that convective preheating significantly accelerates front propagation in DCPD frontal polymerization, with buoyancy-driven convection enhancing heat transfer at low viscosities, and a transition to conduction at higher viscosities.

Contribution

It reveals how trigger direction and monomer viscosity influence front velocity, highlighting the role of buoyancy-driven convection in FP dynamics and offering strategies to control polymerization speed.

Findings

Bottom-triggered fronts are ~50% faster at low viscosities.

Convection dominates heat transfer at low viscosities, enhancing front speed.

A transition from convection to conduction occurs as viscosity increases.

Abstract

Frontal polymerization (FP) enables rapid curing of thermosets via a self-sustaining thermal wave, but its propagation mechanism can shift dramatically depending on processing conditions. In this study, we investigate the effect of trigger direction and monomer viscosity - controlled via hold time - on the front velocity in frontal ring-opening metathesis polymerization (FROMP) of dicyclopentadiene (DCPD). Our experiments reveal that at low viscosities, bottom-triggered FP fronts propagate significantly faster, ~50% faster front speed compared to top-triggered ones, driven by buoyancy-enhanced convection that preheats the unreacted monomer ahead of the front, that can have important implications for manufacturing applications. However, with increasing hold time, the monomer viscosity rises steeply, suppressing convection and causing the front velocity for top and bottom triggering to converge. This behavior reflects a convection-to-conduction (thermal-diffusion) transition in heat transport during FP. Complementary simulations incorporating buoyancy-driven advection reproduce the observed trends and highlight the importance of fluid flow in front dynamics. These results provide new insight into the coupled thermo-fluid-chemical mechanisms in FP offer strategies to tailor front behavior through viscosity and initiation geometry.