Living organotitanium(IV)-catalyzed polymerizations of isocyanates

An organotitanium(IV) compound, TiCl3OCH2CF3, 1, was found to polymerize n-hexyl isocyanate to high yields and without the formation of cyclic trimer. CpTiCl(2)L (L = -OCH2CF3, -N(CH3)(2), -CH3), 2-4, respectively, likewise polymerized n-hexyl isocyanate but also polymerized isocyanates in the presence of donor solvents and isocyanates possessing donor functional groups, activated olefins, and strained olefins. The activity of the organotitanium(IV) catalysts decreased with increasing steric bulk about the metal center and increasing electron donation to the metal center from the ligands. The polymerization of n-hexyl isocyanate using organotitanium(IV) compounds is living. The PDIs of PHIC synthesized using catalysts 1-4 were found to range from 1.05 to 1.2. The molecular weight of the polymer formed in polymerizations of n-hexyl isocyanate using catalysts 1-4 varied linearly as a function of the monomer-to-initiator ratio and the percent conversion of the polymerization. Polymerizations using 2 can be endcapped quantitatively, and well-defined block copolymers can be synthesized using catalysts 1-4. The kinetics for polymerizations using catalysts 1 and 2 are first-order in both monomer and catalyst (k(1) = 8.5 x 10(-4) mol L(-1) s(-1), k(-1) = 3.8 x 10(-4) s(-1)). The active endgroup of a polymerization using 3 was observed using IR spectroscopy, and the frequency of the IR stretch (1548 cm(-1)) was consistent with an eta(2)-amidate endgroup structure. Finally, the kinetic data for the polymerization of n-hexyl isocyanate and the known chemistry of CpTiCl(2)L compounds were found to be consistent with a propagation step that occurs via a bifunctional activation mechanism.