The Modification Of Poly (p-dioxanone) With Poly (Ethylene Glycol)

As a novel material, Poly (p-dioxanone)(PPDO) has been synthesized in the 1970s, but it has not been widely used now because of its high value and some other defects such as the low biodegradation rate, low crystallization rate, hydrophobicity etc. Therefore, a second polymer is needed to couple with it to expand its application. Poly (ethylene glycol) (PEG), one of the most widely used polymer, exhibiting outstanding chemical and biological properties, which is a supplement for the PPDO, can be used to modify the properties of PPDO.In this paper, PPDO-b-PEG-b-PPDO (PEDO) triblock copolymer was synthesized using stannous octoate (SnOct₂) as a catalyst and PEG as a macroinitiator. Multiblock copolymer was prepared through combination of PEDO with Toluene-2, 4 -diisocyanate (TDI). The effect of condition on the reaction has been studied. A series of PPDO/PEG blends was also obtained by solution blending. They are characterized by IR and H-NMR. Their crystallization, thermal stability, hydrophilicity, biodegradable and mechanic properties were invesigated by DSC, WAXD, PM, TG and so on. The properties of multiblock copolymer and PEDO are also compared.The synthesis of triblock copolyemer indicates that the reaction temperature, reaction time and the ratio of monomer and catalyst have great effect on the yield andinherent viscosities of PEDO.DSC and PM are employed to characterize the crystallization of PEDO. The investigations show that the molecular weight of PEG is a key factor for the crystallization of triblock copolymers. When the molecular weight of PEG is low (800 and 2k), the content of PEG in the PEDO is very small, PEG act as a nucleating agent. As the increasing of the molecular weight (6k and 20k), PEG itself participates in the crystallization, and an independent melting peak of PEG appears at the DSC curves. The photographs of PEDO800 and PEDO6K from PM show that the diameter of PEDO800 is larger than that of PEDO6KThermal stability of PEDO was investigated by TG analysis. The results show that as the increase of the molecular weight of PEG, the thermal stability of PEDO is improved. When the molecular weight of PEG is larger than 800, PEDO begin to decompose in two steps.The comparison of water absorption between PEDO copolymers and PPDO homopolymer indicates that the water absorption of PEDO is higher than that of PPDO. With the increasing of the molecular weight of PEG, the water absorption is also increasing.A series of blends were also synthesized. The investigation shows that the addition of PEG to PPDO could sharply increase the crystallization temperature (Tc) and relative crystallization (Xt%) but can not affect its melting point. The WXRD pattern included all the characteristic peaks, and the position of 2theta is also consistent with both homocopolymers. The nonisothermal crystallization kinetics of blends was analyzed by Ozawa equation. The results showed that the Ozawa equation failed to describe the whole crystallization of the blend. But another equation (Mo) can depict the nonisothermal crystallization perfectly.From the synthesis of multiblock copolymers, we can see that the molecular weights of them are related to the reaction time, reaction temperature and the amount of TDI. The structures of the products have been confirmed by the IR and H-NMR patterns.DSC scanning curves of multiblock copolymers indicate that the molecularweights of PEG have effect on their crystallization, and TG analyses indicate the thermal stability of the copolymers. As the increase of the molecular weight of PEG, the thermal stability of the copolymer improved, too. The mechanical test shows that the molecular weights of PEG have effects not only on the tensile strength, but also on the modulus and the elongation of yield.In-vitro degradation of copolymers films have also been carried out in a buffer solution based on hydrogenated sodium phosphate and di-hydrogenated potassium phosphate with an initial pH of 7.4 at 37°C. The results indicate that with the increasing of the degradation time, the weight-retention and inherent viscosities of copolymers are much smaller than those of PPDO homopolymer. From the exterior changes of the products, we can see the colors of the sample are becoming white, indicating the improvement of the crystallization of samples. Comparing the properties of multiblock copolymers and PEDO copolymers, which contain the same molecular weight of PEG, it indicates that their biodegradable properties in vitro are similar, and their water absorptions are also similar.