LIVING ORGANOTITANIUM(IV)-CATALYZED POLYMERIZATIONS OF ISOCYANATES

An organotitanium(IV) compound, TiCl3OCH2CF3, 1, was found to polymeri ze n-hexyl isocyanate to high yields and without the formation of cycl ic trimer. CpTiCl(2)L (L = -OCH2CF3, -N(CH3)(2), -CH3), 2-4, respectiv ely, likewise polymerized n-hexyl isocyanate but also polymerized isoc yanates in the presence of donor solvents and isocyanates possessing d onor functional groups, activated olefins, and strained olefins. The a ctivity 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 isoc yanate 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-hex yl isocyanate using catalysts 1-4 varied linearly as a function of the monomer-to-initiator ratio and the percent conversion of the polymeri zation. Polymerizations using 2 can be endcapped quantitatively, and w ell-defined block copolymers can be synthesized using catalysts 1-4. T he kinetics for polymerizations using catalysts 1 and 2 are first-orde r 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 us ing 3 was observed using IR spectroscopy, and the frequency of the IR stretch (1548 cm(-1)) was consistent with an eta(2)-amidate endgroup s tructure. 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 bifunctiona l activation mechanism.