Nonisothermal and isothermal cold crystallization behaviors of poly(p-dioxanone) (PPDO) were investigated by differential scanning calorimetry (DSC). There were two crystallization exothermsa major exotherm between 25 °C and 50 °C and a minor one almost unchanged at 77 °C with various heating ratesin the heating scans of PPDO during nonisothermal cold crystallization. Temperature-modulated differential scanning calorimetry (TMDSC) revealed the major crystallization exotherm in the low-temperature range to be the real cold crystallization peak, and the minor one in the high-temperature range to be the melt-recrystallization peak of crystals with lower thermal stability. Several methods, including the Avrami, Tobin, and Ozawa equations, were employed to analyze the nonisothermal cold crystallization kinetics of PPDO. The efficiencies of the Avrami and Tobin methods were compared, and the results suggest that the Avrami equation is more suitable for describing nonisothermal cold crystallization kinetics of PPDO. The activation energy for nonisothermal cold crystallization of PPDO was calculated to be 35.27 kJ/mol, using the Kissinger method. In addition, the Avrami equation was also used to describe the isothermal cold crystallization kinetics of PPDO.

Ring-opening polymerization of 1,4-dioxan-2-one in bulk was initiated by three titanium alkoxides, titanium dichlorodiisopropoxide (TiCl 2 (OiPr) 2 ), titanium chlorotriisopropoxide (TiCl(OiPr) 3 ), and titanium tetraisopropoxide (Ti(OiPr) 4 ). The results indicate that the polymerization rate increased with number of OiPr groups in the initiator. High conversion of monomer (90%) and high molecular weight (11.9 Â 10 4 g/mol) of resulting polymer can be achieved in only 5 min at 60 C with Ti(OiPr) 4 as an initiator. Analysis on nuclear magnetic resonance (NMR) spectra suggests the initiating sites for TiCl 2 (OiPr) 2 , TiCl(OiPr) 3 , and Ti(OiPr) 4 to be 1.9, 2.6, and 3.8, respectively. Coordinationinsertion mechanism for the polymerization via cleavage of the acyl-oxygen bonds of the monomer was proved by NMR investigation. Kinetic studies indicate that polymerization initiated by Ti(OiPr) 4 followed a first-order kinetics, with an apparent activation energy of 33.7 kJ/mol. It is noteworthy that this value is significantly lower than earlier reported values with other catalysts, namely La(OiPr) 3 (50.5 kJ/mol) and Sn(Oct) 2 (71.8 kJ/mol), which makes it an attractive catalyst for reactive extrusion polymerization. V C 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: [5885][5886][5887][5888][5889][5890] 2010