Condensation polymerization of N‐dithiocarbonyl alkoxycarbonyl‐amino acids. Part 4. Effect of optical isomer on condensation polymerization of N‐dithiocarbonyl ethoxycarbonyl‐alanine

<jats:title>Abstract</jats:title><jats:p>Condensation polymerization of N‐dithiocarbonyl ethoxycarbonyl‐<jats:sc>L</jats:sc>‐alanine (DTE‐<jats:sc>L</jats:sc>‐alanine) was carried out in various solvents and the effect of an optical isomer was examined. The rate of polymerization of the <jats:sc>L</jats:sc>‐ as well as the racemic monomer increased with increasing monomer concentration, polarity of solvent, and polymerization temperature. However, the molecular weight of the polymer was independent of the polarity of solvent. High polymers were obtained in 1.4‐dioxane, ethylene glycol diacetate, and <jats:italic>n</jats:italic>‐butyl acetate. Poly‐alanine having a high molecular weight (η<jats:sub>sp</jats:sub>/c > 1.5) in dichloroacetic acid at 30°C was prepared under profitable conditions.</jats:p><jats:p>The rate of polymerization of the <jats:sc>L</jats:sc>‐monomer and the molecular weight of the polymer obtained were much larger than that of the <jats:sc>DL</jats:sc>‐monomer. Addition of a small amount of <jats:sc>DL</jats:sc>‐monomer to the <jats:sc>L</jats:sc>‐monomer remarkably decreased both the rate of polymerization and the molecular weight of the polymer. In the polymerization of DTE‐<jats:sc>L</jats:sc>‐alanine without catalyst no racemization was observed. <jats:sc>L</jats:sc>‐Monomer was preferentially incorporated into the growing polymer produced from <jats:sc>L</jats:sc>‐monomer, <jats:italic>i.e.</jats:italic> asymmetric selection was observed as was the case with N‐carboxy‐alanine anhydride.</jats:p>