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Lactide Ring-Opening Polymerization Synthesis of Highly Molecular Weight Poly (L-lactide)

Author: XiaoZuo
Tutor: ShenXianDe
School: Harbin Engineering University
Course: Applied Chemistry
Keywords: microwave L-lactide poly(L-lactide) synthesis
CLC: R318.08
Type: Master's thesis
Year: 2009
Downloads: 47
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Abstract


Poly(lactide) (PLA) is a kind of aliphatic polyesters and is a completely degradable environmental friendly material, PLA is a well-known polymer with good biological compatibility, biodegradability and mechanical strength. It has been regarded as one of the best useful biodegradable materials and increasingly used as a biomaterial for temporary therapeutic application, agriculture and packaging. Its raw material is lactic acid obtained from fermentation of starch. The mechanical characteristics of PLA are as excellent as popular plastics in use. In addition, PLA can degrade into carbon dioxide and water in nature after use, thereby can avoid "White Pollution". In recent years, the demand of environmental protection has attracted people’s attention on the study of PLA, this kind of material will have wider application prospect.PLA is usually obtained by direct polycondensation of lactic acid or lactide ring-opening polymerization. The direct polycondensation of lactic acid is commonly known as a process by which high molecular weight PLLA cannot be obtained. Equilibrium between free acids, water and polyesters along with the formation of lactide, was explained to prevent the reaction to get a sufficiently high molecular weight polymer. High molecular weight PLLA has been usually prepared by lactide ring-opening polymerization process. But the traditional production process of PLA has some shortcomings, such as long and complex preparation, high cost. Synthesis of PLLA under microwave irradiation could simplify the process of preparation and reduce the cost.In this paper, PLLA was synthesized by the method of lactide ring-opening polymerization, adopt oil bath and microwave radiation to heat respectively. Stannous octoate was selected as the catalyst. The influences of catalyst concentration, reaction temperature, reaction time, degree of vacuum, and microwave power on the viscosity-average molecular weight of the PLLA were studied in detail. The properties of L-lactide (LLA) and PLLA were characterized by Fourier Transform Infrared Spectrometer (FT-IR),1H-NMR and 13C-NMR, Polarimeter, Polarizing microscope, Differential Scanning Calorimetry (DSC), Thermogravimetric Analysis (TGA), Ubbelohde viscometer, Gel Permeation Chromatogram (GPC).The results showed that, the yield of LLA reached 55%, the melting point of LLA reached 97℃and the optical purity can reach above 99% after three times of recrystallization. The viscosity-average molecular weight of the synthesized PLLA could reach 23.08×104 under the following polymerization conditions: adopt the microwave irradiation for heating, degree of vacuum 500Pa,3g LLA, 0.26wt% catalyst, irradiation temperature 120℃, irradition time 60min and microwave irradiation power 30W.

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