| Abstract: | High molecular weight poly-β-hydroxybutyrate (PHB) and poly (β-hydroxybutyrate-co-β-benzyl malate) [P (HB? BM)], were prepared by ring-opening polymerization reactions of racemic β-butyrolactone (BL) and racemic β-benzyl malolactonate (BM) using two types of oligomeric aluminoxane catalysts prepared by the reaction of water with either triethyl-aluminum (EAO) or triisobutylaluminum (IBAO). The stereoregularities, crystallinities, and molecular weights were determined for both the PHB homopolymers and the P (HB? BM) copolymers by nuclear magnetic resonance (NMR), differential scanning calorimetry (DSC), and gel permeation chromatography (GPC). All homopolymers and copolymers obtained could be separated into acetone-soluble and acetone-insoluble fractions. In every case the latter had higher degrees of crystallinity, higher molecular weights and higher degrees of stereoregularity (84–87% isotactic dyads) than the former. Hence all of the polymers obtained from both types of catalysts apparently had stereoblock isotactic structures. Copolymer compositions and monomer dyad sequence distributions were determined by NMR spectroscopy. |
