SYNTHETIC POLY[(R,S)-BETA-HYDROXYALKANOATES] WITH BUTYL AND HEXYL SIDE-CHAINS

Synthetic poly[(R,S)-beta-hydroxyheptanoate] (PHH) and poly[(R,S)-beta -hydroxynonanoate] (PHN) were prepared from the ring-opening polymeriz ation of (+/-)-beta-heptanolactone and (+/-)-beta-nonanolactone, respe ctively, using an in situ trimethylaluminum/water catalyst. Molecular weights of about 550 000 and 750 000 for PHH and PHN, respectively, we re determined by GPC. Both PHH and PHN are predominantely isotactic '' as synthesized''; i.e., the isotacticity diad indices are between 80 a nd 82%. Amorphous and crystalline regions could be distinguished in th e solid-state C-13 NMR spectra for both polymers which indicated lower motional freedom for the backbone carbons compared to those in the si de chain. Melting points of approximately 60-degrees-C and glass trans ition temperatures between -30 and -45-degrees-C are close to those of bacterial analogues. The unit cell dimensions of PHH are a = 5.26 ang strom, b = 31.25 angstrom, and c = 4.55 angstrom, based on an orthorho mbic unit cell and a P2(1)2(1)2(1) space group. Compared to poly(beta- hydroxybutyrate), the compressed fiber repeat with maintainance of the 2(1) helix is attributed to the intramolecular interactions of the ex tended alkane side chains.