Curing kinetics study for designing of novel electronic adhesives

The current trend in the electronics industry is to use rapid cure adhesives in order to save processing time and energy. It is essential to understand the effects of chemical structure on the curing kinetics in order to formulate adhesives for fast cure applications. In this study, the curing kinetics of free radical curable monomers has been systematically investigated both by differential scanning calorimetry (DSC) and molecular modeling. Model compounds have been categorized based on their electronic characteristics for this study. The factors in this study include functionality groups, backbone structures, stoichiometry ratio and diluent systems. The experimental results show that a strong electron donor is difficult to cure and should co-cure with an electron acceptor. However, electron accepters can achieve sufficiently fast cure without co-cure agents. A pair of electron donor and acceptor reagents with 1:1 mole ratio give superior fast cure. A system containing a fast cure electron acceptor and a slow cure electron acceptor shows superior fast cure and is independent of stoichiometry. Molecular modeling results are consistent with these experimental observations and provide in-depth understanding of the relation between the electronic characteristics of the monomers and their curing rate. In general, the more negative HOMO energy and LUMO energy, less negative partial atomic charge, and lower the bond order, the faster the curing rate.