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Magnetic resonance imaging

ABSTRACT:The thermal degradation kinetics of poly(3-hydroxybutyrate) (PHB) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) [poly(HB-HV)] under nitrogen was studied by thermogravimetry (TG). The results show that the thermal degradation temperatures (T o , T p , and T f ) increased with an increasing heating rate (B). Poly(HB-HV) was thermally more stable than PHB because its thermal degradation temperatures, T o (0), T p (0), and T f (0)-determined by extrapolation to B ϭ 0°C/min-increased by 13°C-15°C over those of PHB. The thermal degradation mechanism of PHB and poly(HB-HV) under nitrogen were investigated with TG-FTIR and Py-GC/MS. The results show that the degradation products of PHB are mainly propene, 2-butenoic acid, propenyl-2-butenoate and butyric-2-butenoate; whereas, those of poly(HB-HV) are mainly propene, 2-butenoic acid, 2-pentenoic acid, propenyl-2-butenoate, propenyl-2-pentenoate, butyric-2-butenoate, pentanoic-2-pentenoate, and CO 2 . The degradation is probably initiated from the chain scission of the ester linkage.