Thiol-Isocyanate-Acrylate Ternary Networks by Selective Thiol-Click Chemistry

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 phosphine/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 similar to 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, thiol-acrylate, 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) similar to 14-100 degrees C, FWHM similar to 8-46 degrees C), while maintaining nearly quantitative reactions, simply by controlling the component compositions. (C) 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3255-3264, 2010