Polyoxirannes et polythiirannes comportant un centre chiral dans la chaîne latérale, 3. Polymérisation de (2RS,3S)‐ et (2R,3S)‐épithio‐1,2 méthyl‐3 pentanes

Different mixtures of (2R,3S)‐ and (2S,3S)‐1,2‐epithio‐3‐methylpentanes (1) were polymerized using anionic (sodium), stereoselective (ZnEt2/H2O, cadmium tartrate) and stereoelective (ZnEt2/R(−)‐3,3‐dimethyl‐1,2‐butanediol (R(−)DMBD)) initiator systems. In all cases a preferential consumption of the (2R,3S)‐diastereoisomer was observed. The reactivity ratios of the two diastereoisomers (2R,3S) and (2S,3S) in the copolymerization, initiated with sodium, were determined: r1 = 1,40 ± 0,08 and r2 = 0,54 ± 0,05. A low but significant diastereoisomeric enrichment was observed in stereoselective polymerization. It results from different consumption rates for the two diastereoisomers on enantiomorphic sites of the initiator. The election obtained with a stereoelective system is much higher. It is, however, not very different from that observed with isopropylthiiranne, which does not bear an additional chiral center in the alkyl substituant.