Growth mechanism of crystals of glycine‐<scp>L</scp>‐alanine copolymer in the course of polymerization

Abstract

Abstract In order to examine the growth mechanism of copolymer crystals formed during polymerization, the heterogeneous copolymerization of glycine N ‐carboxy anhydride (NCA) and L ‐alanine NCA has been studied in acetonitrile. In the polymerization systems with higher contents of glycine, the crystal growth occurs through formation of the cross‐β type structure as proposed previously for poly( S ‐methyl‐ L ‐cysteine), giving rise to chain‐folded crystals and rather high conversions. The high conversion is accounted for by the widening of the cross‐section of the β‐chains in the backbone crystal, due to the introduction of L ‐alanine residues into the polyglycine chain. Copolymerization at higher contents of L ‐alanine leads to conversions over 90% and extended chain crystals, due to the formation of α‐helices on the ribbon‐like crystals composed of the β‐structure just as in the case of L ‐alanine NCA homopolymerization, indicating the occlusion of the glycine residues into the helices.