Enantioselective polymerization of (R,S)‐α‐methylbenzyl methacrylate initiated with products resulting from grignard reagents and axially dissymmetric [1,1′‐binaphthyl]‐2,2′‐diamine

Abstract

AbstractEnantioselective polymerization of (R,S)‐α‐methylbenzyl methacrylate [(R,S)‐3] was investigated in tolurene at −30°C with a variety of chiral anionic catalysts, prepared in situ by reaction of axially dissymmetric [1,1′‐binaphthyl]‐2,2′‐diamine (1) and Grignard reagents (RMgX, R = alkyl). The enantioselectivity was found to be dependent upon the halogen ions of RMgX, but scarcely upon the alkyl groups. The catalyst systems involving (R)‐1 polymerize more or less preferentially (S)‐3 over (R)‐3. The selectivity is also discussed with respect to the mole ratio of RMgX to 1. The system cyclohexylmagnesium bromide (cHexMgBr)/(R)‐1, in a mole ratio of 1,5:1,0, shows high selectivity, and the optical purity of the initially formed polymer was found to reach 83%. The change in the optical purities of polymer and unreacted monomer can be represented satisfactorily by the integrated composition equation for an “ideal” copolymerization of (R)‐and (S)‐monomers, and the enantioselectivity ratio, r, was estimated to be 10,6. The polymers produced are almost completely isotactic, and contain a binaphthyl moiety as initiator fragment.