Accelerated degradation of biodegradable poly(ester)s by acidic catalysts.

摘要

Poly(ϵ-caprolactone) (PCL), a biodegradable polyester, has found limited use because of its extended degradation time of more than two years. PCL accelerated degradation by sulfonates and sulfates in acidic media was studied as a means to reduce PCL's degradation time. Degradation was significantly enhanced in these media, with up to four-fold higher rates for aromatic sulfonic acids and seven-fold higher rates for aliphatic sulfonic acids compared to HCl. Rates of weight loss correlated well with sulfonate or sulfate chain lengths, suggesting a partitioning dependence for catalytic activity. Energy dispersive X-ray microanalysis (EDX) spectra of PCL samples demonstrated increasing sulfur content with time and with increasing sulfate-catalyst chain length.; PCL's physical properties were characterized during acid-catalyzed degradation. Gel permeation chromatograms (GPC) of degraded samples broadened with time and became multi-modal under several conditions. PCL's molecular weight (MW) decreased with time and its rate of reduction was dependent on acid-catalyst chain length. The crystallinity of degraded samples increased with time, suggesting preferential hydrolysis of amorphous regions. Two morphologies, crystalline spherulites and lamellar structures, were observed in partially degraded samples. Acid-catalyzed degradation of PCL cylinders exhibited an outer degradation zone, which increased with time, suggesting non-homogeneous degradation.; The effects of sodium dodecyl sulfate on hydrolytic degradation of poly(hydroxybutyrate-co-hydroxyvalerate) (PHBHV, 80:20) in acidic conditions were investigated. PHBHV samples degraded in acidic media containing dodecyl sulfate lost weight at an accelerated rate, giving approximately 10% weight loss within 5 months, compared to HCl solutions without catalyst where no weight loss was seen in this time period. GPC demonstrated an overall reduction in molecular weight with time and production of multi-modal chromatograms, indicating non-homogeneous degradation. Morphological characterization of PHBHV samples exhibited cracks and fissures, which increased in number and depth over time. Micrographs of polymer pellet cross-sections showed a time-dependent degradation zone, providing further evidence for non-homogeneous degradation.; A mechanism for the acid-catalyzed hydrolysis of PCL and PHBHV is proposed that involves partitioning of the protonated sulfonic/sulfuric acid catalyst into the solid polymer phase, followed by protonation of the ester moiety and subsequent hydrolysis/solvolysis of these ester linkages.