Can tetraphenylethane (TPE) “iniferter” groups be introduced into polymer chains by coupling TPE diol with diisocyanates?

Abstract

Several different articles have appeared in recent years concerning the application of tetraphenylethane (TPE) groups, which are able to dissociate to free radicals under mild heating, for the initiation of radical polymerization of vinyl monomers. It has been claimed that the TPE group is introduced into the polymer chain by the reaction of 1,1,2,2-tetraphenyl-1,2-ethanediol (TPED) with diisocyanate, optionally with the application of the additional oligodiol. This approach is based on the presumed reaction of the isocyanate group with a tertiary hydroxyl group that is supposed to form urethane linkages. In the present study, we checked whether such a reaction can indeed occur under the applied conditions. A kinetic study of the reaction of poly(tetrahydrofuran) diol plus TPED or polylactide diol plus TPED with diisocyanate (aromatic or aliphatic) was performed in two different solvents, and conversion of isocyanate groups was followed by FT IR spectroscopy. Independently, the kinetics of the reaction of TPED alone with diisocyanates were investigated. The products of the reactions were analyzed by the 1H NMR method for the expected consumption of tertiary –OH groups and urethane bond formation. Theoretical calculations for the reactivity of tertiary –OH groups in TPED with isocyanate groups are presented as additional proof that this reaction should not proceed under the conditions applied in earlier papers. A new approach to the introduction of TPE units into polymer structures is suggested.