Preparation And Properties Of Biodegradable Polylactide And Its Copolymers

Polylactide is a kind of biocompatible and biodegradable polymers, which has been attracting widely attention in biological medicine field, but the high cystallinity and hydrophobicity of polylactide greatly constrains its applications such as tissue engineering scaffolds. One of the possible and promising approaches to overcome this problem is to introduce hydrophilic units into the aliphatic polyester to control the hydrophilicity, cystallinity and biodegradability. In this paper, xylitol and itaconic anhydride were used to react with lactide. The reasons for selection of these two monomers are as follows:(1) Xylitol is a polyol, its5hydroxy widely improving the hydrophilicity of poly (lactic acid xylitol) ester material. Xylitol is non-toxic and has been accepted by the U.S. Food and Drug Administration (FAD).(2) Itaconic acid is an unsaturated dibasic organic acid and an important functional monomer for the production of polymer materials. And itaconic anhydride is the derivative of itaconic acid. Reaction between itaconic anhydride and lactide, not only introducing a double bond, but also can improve the hydrophobicity and degradation of polylactide. In this paper, polylactide, poly (lactic acid xylitol) ester and Poly(lactic acid itaconic anhydride) ester were synthesized by molecule design in order to synthesized polylactide and its branch and multi-functional copolymers. Main contents and results are as follows:1. The monomer L-lactide was prepared by polycondenasation and decomposing rection. This results showed that high-purity lactide obtained, and melting point of LLA is98.5℃, yield of LLA reached40%.2. Poly-L-lactide (PLLA) was prepared from L-lactide (LLA) under the normal pressure through the ring-opening polymerization. The structure of LLA and PLLA were characterized by FT-IR and1H-NMR. Effects of polymerization time on the molecular weight of PLLA were investigated. The properties of PLLA films were characterized by TGA, XRD, tensile testing machine and weight loss. The controled release properties of PLLA films were evaluated by a permeation study of an exemplary drug theophylline. The results showed that the Mn of PLLA which was polymerized within20hours under the normal pressure reached8.14×104. Tg and Tm of PLLA was60.3℃and169.9℃, respectively. And the film has good thermal stability and mechanical properties. The degradation rate of PLLA films had decreased with the increasing of the molecular weight of PLLA. The diffusion of theophylline in the film of PLLA follows approximately a Case Ⅱ mechanism (near zero-order release mechanism).3. Star-shaped PLLAX copolymers were prepared in reduced pressure by the ring-opening of LLA in the presence of xylitol and tin (Ⅱ) octoate as initator. The structure of PLLAX were characterized by1H-NMR. Effects of molar content of xylitol on the molecular weight of PLLAX were investigated. The properties of PLLAX were characterized by TGA, XRD, DSC and weight loss. Hydrogen nuclear magnetic resonance spectrum(1H-NMR) showed that the synthetic copolymers were the expected products. DSC spectra showed that the melting point(Tm) and glass transition temperature(Tg) gradually decreased with the increasing of xylitol component. TGA analysis indicated that the thermal stability gradually decreased with the increasing content of xylitol. The result of degradation tests in the phosphate buffer solution indicated that the rate of degradation of copolyesters had significantly increased with the increasing content of xylitol.4. Itaconic anhydride was prepared from itaconic acid with acetyl chloride as dehydrating agent in normal pressure under100℃. The structure of itaconic anhydride was characterized by1H-NMR and13C-NMR. The result showed that the synthetic product was itaconic anhydride.5. Double bond of PITLA copolymers were prepared in reduced pressure by the ring-opening of LLA in the presence of itaconic anhydride and tin (Ⅱ) octoate as initator. The structure of PITLA were characterized by1H-NMR. Effects of molar content of itaconic anhydride on the molecular weight of PITLA were investigated. The properties of PITLA were characterized by TGA, XRD, DSC and weight loss. Hydrogen nuclear magnetic resonance spectrum(1H-NMR) showed that the synthetic copolymers were the expected products. DSC spectra showed that the melting point(Tm) and glass transition temperature(Tg) gradually decreased with the increasing of itaconic anhydride component. TGA analysis indicated that the thermal stability gradually decreased with the increasing content of itaconic anhydride. The result of degradation tests in the phosphate buffer solution indicated that the rate of degradation of copolyesters had significantly increased with the increasing content of itaconic anhydride.