Residual Strain\nDevelopment in Rapid Frontally\nCuring Polymers

Frontal polymerization (FP) has emerged as a rapid and\nenergy-efficient\nprocess for fabricating thermoset polymers and composites. In this\nprocess, a self-propagating reaction front cures the polymer rapidly\nby the exothermic heat of polymerization reaction instead of an external\nheat source. Design for FP-based manufacturing in commercial applications\nrequires more comprehensive characterization and prediction of material\nevolution and residual deformation throughout the process. Here, we\nreport experimental and numerical studies in response to this need.\nThe experimental study focuses on measuring the temperature and cure-dependent\nproperties of mono/poly dicyclopentadiene to capture the strain evolution\nduring the frontal polymerization process. The experimentally measured\nelastic moduli, Poisson’s ratios, and coefficients of thermal\nexpansion and chemical shrinkage show strong dependence on the degree\nof cure. Based on the experimental output, a coupled thermo–chemo–mechanical\nmodel has been developed to capture the measured residual strains.\nThe chemical shrinkage is closely related to the curing rate, leading\nto strong localization of residual strains in accelerated reaction\nregions, especially where two fronts merge. Preheating of the monomer\n(or gel) at the fronts merging area is suggested as an effective method\nto mitigate residual deformations.