CHEMOENZYMATIC SYNTHESIS AND STUDY OF POLY(ALPHA-METHYL-BETA-PROPIOLACTONE) STEREOCOPOLYMERS

A chemoenzymatic route from racemic alpha-methyl-beta-propiolactone (M PL) to optically active (R)-poly(alpha-methyl-beta-propiolactone), (R) -PMPL, was demonstrated which involved lipase catalyzed resolution of MPL enantiomers in organic media and subsequent chemical polymerizatio n. From a comparative study of different enzymes and organic media, ca talysis by the lipase PS-30 from Pseudomonas fluorescens suspended in diethyl ether was found to be most suitable for MPL enantioselective a lcoholysis reactions. MPL having up to 93% (R) content was thus obtain ed, mixed in various proportions with racemic MPL, and polymerized usi ng CH3COOK/dibenzo-18-crown-6. From a plot of specific rotation vs % e nantiopurity, it was estimated that the [alpha]D-25 for 100% (R)-PMPL is -38.4 degrees (c 0.8 g/dL, CHCl3). C-13 NMR LR analysis (62.9 MHz) provided information on triad sequence distributions from observation of methine carbons, while the methyl and carbonyl carbons were sensiti ve to diad sequences. The polymerization of 50% (R)-MPL followed Berno ulli random chain propagation statistics. In contrast, polymerizations of 74% and 93% (R)-MPL deviated from the Bernoulli model. Further ana lysis showed that these latter polymerizations fit the enantiomorphic- site model. Thus, isoregulating characteristics of the CH3COOK/dibenzo -18-crown-6 catalyst for enantioenriched MPL polymerizations were demo nstrated. By increasing the % (R)-content in the monomer feed to 93%, a product was obtained which, by DSC, had T-m and Delta H-f values of 131 degrees C and 22.0 cal/g, respectively. Furthermore, WAXS analysis carried out on a melt-annealed 90% (R)-PMPL sample showed that the po lymer was highly crystalline (approximately 73%). FTIR analysis was us ed to identify vibrational bands at 997, 1010, 1059, 1185, 1249, and 1 334 cm(-1) which were crystalline-sensitive, while the band at 1465 cm (-1) was crystalline-insensitive.