POLYSTEREOISOMERS WITH 2 STEREOGENIC CENTERS OF MALIC-ACID 2-METHYLBUTYL ESTER CONFIGURATIONAL STRUCTURE/PROPERTIES RELATIONSHIP

Poly(beta-malic acid alkyl esters) with two stereogenic centers have been synthesized by anionic ring-opening polymerization of racemic and optically active 4-[(2-methylbutyl)oxycarbonyl]-2-oxetano and characterized. The two asymmetric centers have been introduced in the monomer by using malic acid or aspartic acid enantiomers as chiral synthons and 2-methyl-1-butyl alcohol enantiomers as lateral ester groups. By combining the different enantiomers during the beta-substituted beta-lactone synthesis route, it has been possible to prepare five stereoisomers which have conducted to five different stereocopolymers. The configurational structure of racemic and optically active poly(2-methylbutyl beta-malates) has been determined by C-13 NMR analysis, and differentiation between polydiastereoisomers has been possible by using this spectroscopy method. Several main-chain and side-chain carbon atoms were stereosensitive to the presence of the two asymmetric centers per repeat unit, and the optical purities of main-chain and side-chain stereogenic centers have been deduced from C-13 NMR spectra. Thermal properties of the different polystereoisomers have been correlated with the configuration of the two chiral sites in the macromolecular chain. It has been shown that crystallinity was dependent on the configurational structure of the main chain and very poorly sensitive to the enantiomeric composition of the ester pendant group.