VERSATILE ORGANOMETALLIC INITIATORS FOR THE LIVING POLYMERIZATION OF ISOCYANATES

Shashoua and Sweeney first demonstrated that isocyanates could by poly merized via an anionic mechanism to form high molecular weight materia ls. We have sought to eliminate the problems associated with the anion ic procedure by developing transition metal complexes which are capabl e of catalyzing the living polymerization of isocyanates. Recently, we reported the living polymerization of alkyl isocyanates using TiCl3OC H2CF3, I. Using I, polyisocyanates with controlled molecular weights a nd narrow polydispersities can be obtained at room temperature. eta(5) -CpTiCl(2)N(CH3)(2) (Cp = cyclopentadienyl), III, is also an excellent catalyst for the polymerization of isocyanates, and in terms of ease of handling and purification and tolerance toward monomer functionalit y, superior to I. In order to prepare triblock copolymers containing a morphous segments sandwiched between two isocyanate segments, we have prepared bimetallic initiators comprised of titanium alkoxides connect ed by flexible linkers. These linkers may be a small molecule (1,4-dih ydroxycyclohexane, V) or a polymer (polydimethylsiloxane, PDMS, VI). C omplexes V and VI can be used to initiate the living polymerization of isocyanates to yield polymers possessing central cyclohexyl bends ('' broken worms'') or PDMS segments (triblock copolymers), respectively. Finally, cyclopolymerizations of 1,2-diisocyanates using these organom etallic initiators are reported.