Asymmetric‐selective polymerization of (R,S)‐α‐methylbenzyl acrylate initiated with Grignard reagent/(‐‐)‐sparteine and its modified systems

Abstract

Asymmetric-selective (or stereoelective) polymerization of racemic a-methylbenzyl acrylate (2a) was studied with Grignard reagent/( -)-sparteine and its modified catalyst system in toluene. All catalyst systems polymerized preferentially the @)-monomer over the (S)-monomer. The Grignard reagent/( -)-sparteine system showed very low activity and gave the polymer only in a few per cent yield at -78 "C. The addition of secondary amines such as piperidine and diethylamine to the catalyst system improved not only the activity but also the selectivity. The optical purity of the polymer initially formed with the cyclohexylmagnesium bromide/ (-)-sparteine/diethylamine system at -78 "C was 84%, and at about 80% polymer yield almost optically pure monomer was recovered. Asymmetric selectivity decreased with an increase of temperature. The dyad tacticity of the polymer was determined by 'H NMR spectroscopy. There was no clear correlation between the selectivity and tacticity. The role of the amines in the catalyst systems was investigated by 'H NMR spectroscopy.

(−)‐Sparteine: The compound that most significantly influenced my research

“…18,19 The tacticity of the polymer was not high, and the reasons for these results are not clear even today.…”