Cp₂TiCl-Catalyzed SET Reduction of Aldehydes:  A New Initiating Protocol for Living Radical Polymerization

The Cp 2 TiCl-catalyzed SET reduction of aliphatic, α,β-conjugated, and aromatic aldehydes generates reactive α-titanoxy radicals which add readily to styrene and initiate a radical polymerization. The linear dependence of molecular weight on conversion in conjunction with the relatively narrow molecular weight distributions and linear kinetics support the living character of the process which is mediated by the reversible termination of the growing chains with Cp 2 TiCl . Investigations of the reaction variables reveal a living polymerization in all cases, but with progressively narrower molecular weight distributions ( M w / M n ∼ 1.2) and larger initiator efficiencies (0.7−0.9) with increasing the Cp 2 TiCl 2 /aldehyde, aldehyde/styrene, and Zn/Cp 2 TiCl 2 ratios at 70−90 °C for a wide variety of aldehyde structures. Aldehydes are thus introduced as a new class of initiators for living radical polymerizations and may also provide novel avenues for the synthesis of block and graft copolymers.