Preparation And Characterization Of Block Copolymers Based On Poly(p-dioxanone) And Poly(Lactic Acid)

Poly(p-dioxanone) (PPDO), as an aliphatic polyester, have been widely used in biomedical and pharmaceutical applications such as surgery repair materials and drug delivery systems in recent years due to their excellent biocompatibility and biodegradability. As a promising biodegradable and biocompatible polymer for using in environment-benign material, PPDO has both excellent flexibility and tensile strength. It show promising application not only in medical materials but also in environment-friendly materials. Poly lactic acid (PLA) is another aliphatic polyester with good biocompatibility and biodegradability, it has already been widely used in biodegradable materials such as food package, disposable tableware, textile, mulching film, and electronic device. However, both of the polymers have some unsatisfactory charactors which limit the wild application of the materials, for example, PPDO has very low melt strength and PLA exhibit very poor flexibility.Copolymerization of PPDO and PLA may not only combine the merits of PLA and PPDO in mechanical properties; improve the solubility of PPDO in organic solvents; but also control the crystallinity, crystal morphology, and thermal properties of the copolymer by adjusting the molecular structure. However, the researches on the copolymerization of PPDO and PLA almost use high cost lactide as monomer. The aim of our work is to reduce the cost of PPDO-PLA copolymers by replacing lactide with L-lactic acid. Three different types PPDO-PLA block copolymers with various segment sequence have been prepared, and the structures and properties have also been investigated by several instruments such as NMR, DSC,WAXD,PM and TGA series of P(LA-b-PDO) diblock copolymers with different segment content or different PLA chain length were synthesized via the ring opening polymerization of PDO initiated by PLA macroinitiators in the existence of SnOct2. The structure of copolymers was characterized by ~1H-NMR spectra. The results showed the content of each block was correspond to the feed ratio quite well, and the molecular weight, as well as the molecular structure, of copolymers can be modulated by varying the original molecular weight of PLA propolymers or the PLA/PDO feed ratio. Thermal stabilities, physical properties and biodegradable properties, the crystalline behaviors of P(LA-b-PDO) copolymers have been studied. The results indicated that the content of PLA segment was an dominant factor, which affect the properties of copolymers.PPDO-PLA multiblock copolymers, as well as PLA-PPDO-PLA triblock copoymers, with various molecular structures were also been synthesized by chain extending with HDI. High inherent viscosities chain-extending products can be achieved with optimal feed ratio of prepolymer and chain-extender. ~1H-NMR spectra has been employed to characterize the structure of PPDO-PLA multiblock copolymers. The the machnical test showed that PPDO-PLA triblock and multiblock copolymers have better tensile strength and flexibility than what of P(LA-b-PDO) synthesized previously. The elongation at break of P(LA-b-PDO) was only 2%, however, the values of PPDO/PLA increased evidently, and the maximum was more than 100%.