As poly(p-dioxanone) (PPDO) with a high molecular weight (viscosity-average molecular weight (Mm)> 100,000 g/mol) is not easy to be obtained in a short time, a new approach has been developed to produce high molecular weight poly(pdioxanone) (HPPDO-T) by chain-extending reaction of hydroxyl-terminated PPDO (HPPDO) prepolymers using toluene-2,4-diisocyanate (TDI) as chain extender. Here HPPDO prepolymers were synthesized via ring-opening polymerization of p-dioxanone (PDO) monomer initiated by 1,4-butanediol (BD) with Stannous octoate (SnOct2) as catalyst. The resulting polymers, having a highest Mm of 250,000g/mol, were characterized by 1H NMR, TG, DSC and WXRD. HPPDO prepolymers can react with TDI more effectively than the PPDO prepolymers initiated by mono-functional initiators, and the molecular weights of resulting chain-extended products increase several decade times in an hour comparing to the prepolymers. The chain extended products HPPDO-T have better thermal stability, and higher glass transition temperatures and lower crystallization rates than PPDO homopolymer.

This paper reviews recent developments related to biodegradable polymer nanocomposites. The preparation, characterization, properties, and applications of nanocomposites based on biodegradable polymers are introduced systemically. The related biodegradable polymers include aliphatic polyesters such as polylactide (PLA), poly (ε-caprolactone) (PCL), poly(p-dioxanone) (PPDO), poly(butylenes succinate) (PBS), poly (hydroxyalkanoate)s such as poly(β-hydroxybutyrate) (PHB), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), and natural renewable polymers such as starch, cellulose, chitin, chitosan, lignin, and proteins. The nanoparticles that have been also utilized to fabricate the nanocomposites include inorganic, organic, and metal　particles such as clays, nanotubes, magnetites, Au and Ag, hydroxyapatite, cellulose, chitin whiskers and lignin.

Poly (p-dioxanone) (PPDO) samples with different molecular weights have been synthesized by the ring-opening polymerization of p-dioxanone. The thermogravimetric analysis of PPDO shows that the increase of molecular weights can improve the thermal stability of PPDO. The rheological property of PPDO with different molecular weights has been investigated using a Capillary Rheometer. The results show that PPDO exhibits a shear-thinning behavior; the apparent viscosity of melt increases with the molecular weight of PPDO and is very sensitive to temperature, decreasing sharply with the rise of temperature. In vitro degradation of PPDO films has also been carried out and excellent degradability has been found. The mechanical test shows that the tensile strength and modulus of PPDO increase with molecular weights.

The kinetics of the thermal degradation and thermal oxidative degradation of poly (p-dioxanone) (PPDO) were investigated by thermogravimetric analysis. Kissinger method, Friedman method, Flynn-Wall-Ozawa method and Coats-Redfern method have been used to determine the activation energies of PPDO degradation. The results showed that the thermal stability of PPDO in pure nitrogen is higher than that in air atmosphere. The analyses of the solid-state processes mechanism of PPDO by Coats-Redfern method and Criado et al. method showed: the thermal degradation process of PPDO goes to a mechanism involving random nucleation with one nucleus on the individual particle (F1 mechanism); otherwise, the thermal oxidative degradation process of PPDO is corresponding to a nucleation and growth mechanism (A2 mechanism).