Calixarene-Core Multifunctional Initiators for the Ruthenium-Mediated Living Radical Polymerization of Methacrylates

Abstract

Tetra-, hexa-, and octafunctional initiators constructed with calix[ n ]arene cores ( n = 4, 6, and 8) and dichloroacetate units led to living radical polymerization of methyl methacrylate (MMA) to give star polymers with four, six, and eight arm chains of controlled lengths, respectively, when coupled with RuCl 2 (PPh 3 ) 3 and Al(O i Pr) 3 in toluene at 80 °C. The produced polymers had controlled molecular weights and narrow molecular weight distributions ( M̄ w / M̄ n = 1.1−1.2). Hydrolysis of the ester linkage between the core and the arm chains gave linear polymers whose number-average molecular weights are almost 1 / 4, 1 / 6, and 1 / 8 of those for tetra-, hexa-, and octaarmed star polymers, respectively, consistent with the arm numbers expected from the initiator functionality. Octaarmed star polymers consisting of block copolymers of MMA and n -butyl methacrylate as arm chains were also synthesized by the sequential block copolymerizations initiated with the calix[8]arene-based initiator in conjunction with RuCl 2 (PPh 3 ) 3 and Al(O i Pr) 3 .