Thiol-lsocyanate-acrylate ternary networks by selective thiol-click chemistry

摘要

Thiol-isocyanate-acrylate ternary networks were formed by the combination of thiol-isocyanate coupling, thiol-acrylate Michael addition, and acrylate homopolymerization. This hybrid polymerization reaction sequence was preferentially controlled by using phosphine catalyst systems in combination with photolysis. The reaction kinetics of the phosphlne/acrylate thiolisocyanate coupling reactions were systematically investigated by evaluating model, small molecule reactions. The thiol-isocyanate reaction was completed within 1 min while the thiol-acrylate Michael addition reaction required ～10 min. Both thiol-isocyanate coupling and thiol-acrylate Michael addition reactions involving two-step anionic processes were found to be both quantitative and efficient. However, the thiol-isocyanate coupling reaction was much more rapid than the thiol-acrylate Michael addition, promoting initial selectivity of the thiol-isocyanate reaction in a medium containing thiol, isocyanate, and acrylate functional groups. Films were prepared from thiol-isocyanate-acrylate ternary mixtures using 2-acryloyloxyethylisocyanate and di-, tri-, and tetra-functional thiols. The sequential thiol-isocyanate, thiolacrylate, and acrylate homopolymerization reactions were monitored by Infrared spectroscopy during film formation, whereas thermal and mechanical properties of the films were evaluated as a function of the chemical composition following polymerization. The results Indicate that the network structures and material properties are tunable over a wide range of properties (T_g - 14-100 °0C, FWHM ～ 8-46 °C), while maintaining nearly quantitative reactions, simply by controlling the component compositions.