Poly(alpha-isobutyl-beta-D,L-aspartate)s: Polymerization effects on configuration and crystal structure of the stereocopolymers

Different polymerization methods were used for the preparation of poly(alpha-isobutyl-beta-D,L-aspartate)s containing variable ratios of D- to L-aspartic units and the microstructure of the resulting stereocopolymers was examined by NMR spectroscopy. Anionic ring-opening polymerization in solution of enantiomeric mixtures of alpha-isobutyl-beta-D- and L-aspartalactams was found to proceed stereoselectively rendering block copolymers composed of right- and left-handed helical sequences. Configurationally statistical copolymers were obtained instead when the enantiomeric lactam mixtures were polymerized in the bulk. Random stereocopolymers could be prepared also by polycondensation in solution of mixtures of pentachlorophenyl alpha-isobutyl-beta-D and -L-aspartates. The conformation in solution and the crystal structure of the resulting copolymers were investigated in connection with their stereo-chemical configuration and these features compared with those displayed by optically pure poly(alpha-isobutyl-beta-L-aspartate). (C) 1996 John Wiley & Sons, Inc.