Biodegradable Graft Copolymers And Blends From Poly (1,4-dioxan-2-one) And Poly (Vinyl Alcohol)

Poly(1,4-dioxan-2-one) or poly (p-dioxanone), PPDO, is a well-known aliphatic polyester having good physical properties and bio-compatibility, and has been used to make monofilament sutures with good tenacity and knotting. But the high cost is the key factor limiting PPDO's wide application. In order to lower its cost and expand its application, low-cost polymers such as poly(vinyl alcohol) (PVA) can be blended or grafted with PPDO. Thus, a new biodegradable polymer will be made. And PPDO is viewed as a candidate not only for medical use, but also for universal uses such as films, molded products, laminates, foams, non-woven materials, adhesives, and coatings. Poly(vinyl alcohol)-g-poly(1,4-dioxan-2-one) (PGP) was synthesized by using the ring-opening graft polymerization of PDO monomer onto PVA backbone with stannous octoate (SnOct2) as catalyst. The detailed analysis on the microstructure of the resulting PGP was characterized by FT-IR, one-and two-dimensional NMR spectroscopy. The thermal properties, crystallization behaviors, and kinetics of thermal degradation of PGP were investigated by differential scanning calorimetry (DSC), thermogravimetry analysis (TGA). It was found that the thermal decomposition of the graft copolymer had two stages: the first stage was discovered at 220-234℃, which was considered as the decomposition of PPDO side chains; and the second stage was discovered at 285℃, which was the main decomposition of PVA. And the thermal stability of PGP was increased with the increasing of molecular weight of PGP. Due to its particular molecular architecture, in which the short PPDO chains IIIwere grafted onto linear PVA, which destroyed to a certain extend the regularity of the molecular structure, the crystallization rate of the copolymer was so slow that the crystallization peak could hardly be observed during the cooling scanning even if the scanning rate was decreased to 2.5°C/min, although the Tm could be observed during the first heating scanning. And the study of the kinetics of thermal degradation about PGP indicated that the values of E showed no obvious distinction no matter at N2 or air. And the kinetics mechanism of thermal degradation at N2 or air was F3 and F2, respectively. The thermal stability of the PPDO/PVA blend was also investigated. The addition of the PVA increased the thermal stability of PPDO, which could be seen by the increasing of initialization decomposition temperature and maximum decomposition temperature. DSC measurement showed that the addition of PVA increased the crystalline temperature and crystalline degree of the blend. This means the presence of PVA can act as nucleating agents for PPDO component,which hence the nucleus numbers on unit volume. When the content of PVA increased to 20wt%, the crystalline temperature of blend system (80/20) increased to 65.8℃,and the crystalline degree increased to 60.7%. The further elevation of PVA component (e.g. 30% PVA component) could not improve them, and destroyed the self-nucleation of PPDO. Moreover, the Tg and Tm of the PPDO component for all the PPDO/PVA blends were almost constant with the composition variation. Furthermore, WAXD measurements demonstrated that PPDO and PVA crystallized separately to form isolated PPDO and PVA crystalline phases that were free of interpolymer interaction existing in the crystalline phase of these blends. Nonisothermal crystallization analysis showed that, for both PPDO composition in blends and neat PPDO, the crystallization rate increased linearly with the increase of the cooling rate. This might due to that the addition of PVA has improved the nucleating effect of the blend, which increased the crystalline rate of PPDO. The kinetic results of Ozawa method showed that it successfully described the nonisothermal crystallization process of the PPDO component in blends and PPDOhomopolymer. The calculated n value was 2.74, and 2.73 for the blend system and neat PPDO, respectively. The mechanical properties of blend were decreased when starch was added, but this situation could be alleviated when PGP was added. From the SEM photographs we could see clearly that PPDO formed a continuous phase and PVA formed a separated phase. The in vitro degradation experiments of PPDO and PGP films showed that the degradation rate of PGP was much faster than that of the neat PPDO. And the degradation rate of PGP increased with the increase (increasing)of the lengths and numbers of PPDO chains.