Investigation of Thermo-chemo-mechanically Coupled Phenomena in Frontal Polymerization

Frontal polymerization is a proven energy-saving and rapid method of synthesizing polymers with good mechanical properties. With a small energy input, a reaction front propagates rapidly through the sample, transforming monomer (liquid or soft gel) into polymer (stiff solid), and is self-sustained by heat released from the polymerization reaction itself. A thermo-chemical coupled model has been proposed to describe the frontal polymerization process, and recent experiments have shown that such coupling could lead to an unstable propagating front. However, the influence of mechanical forces has been absent in previous analyses of frontal polymerization, which could be significant considering local volume change caused by thermal expansion and chemical shrinkage as the front propagates. In this thesis, we will explore the mechanical behavior and potential thermal-chemo-mechanically coupled effects that may emerge during frontal polymerization of soft gels. We will show that non-uniform residual stress distribution could be generated due to differences in thermal and chemical properties on both sides of the propagating front. Our experiments further confirm that the emergence of stress could in turn influence the propagation of front, and our model describes such coupling effects to predict the dynamics of a propagating front in agreement with experimental observation. Our findings suggest that the mechanical effects need to be taken into consideration for industrial applications of frontal polymerization at large scales. ; S.M.