Synthesis And Property Of Vinyl-modified Star Polylactic Acids

At present,the polymer materials are widely used in some fields including automotive,medical equipment,food packaging,construction,aerospace and military,which has become an indispensable important materials in our life.However,most of the waste polymer materials can not be effectively degraded in the natural environment.The incineration will produce harmful gases,resulting in secondary pollution while the landfill will take up a lot of land,resulting in soil degradation.Therefore,the research and development on degradable polymer materials is currently the focus of research.Polylactic acid(PLA),as a kind of polyester material with good biodegradability,biocompatibility and excellent mechanical properties,can be used in the preparation of biomedical products such as fracture fixation and tissue engineering scaffolds.However,the poor brittleness and impact strength of PLA greatly limits its application in the field of biomedicine.Thus,the modification of PLA is of great theory and practical significance at present.In this paper,the star polylactic acids with different molecular weights were synthesized by lactide and glycerol as the raw materials and then modified by acryloyl chloride to make the vinyl-modified star polylactic acids.The content of this thesis is listed as follows:Synthesis and characterization of vinyl-modified star polylactic acids.Firstly,three-arm star polylactic acids with different molecular weights were synthesized by ring-opening polymerization using lactide and glycerol as the raw materials under the catalysis of stannous octarolactone.Secondly,vinyl-modified star polylactic acids were prepared by the modification of star polylactic acids using acryloyl chloride.And then these two kinds of polylactic acids were characterized by nuclear magnetic resonance(~1H NMR),infrared spectroscopy(IR),gel permeation chromatography(GPC),etc.Finally,the UV-curing reaction of vinyl-modified star polylactic acids was carried out and their cross-linking structures were measured by IR.All experiment data evidenced the form of these products.Properties of vinyl-modified star polylactic acids.The thermal stability,crystallization behavior,melting behavior,microstructure,water absorption and mechanical properties of three-arm star polylactic acids,vinyl-modified star polylactic acids and photo-curable vinyl-modified star polylactic acids were studied herein.The thermogravimetric analysis(TGA)analysis showed that vinyl-modified star polylactic acids possessed higher thermal stability than star polylactic acids because of the double bonds,meanwhile,their cross-linking network had three different levels of heat loss peaks after the cross-linking reaction.The differential scanning calorimetry(DSC)analysis indicated that the intergranular interaction force and the glass transition temperature of vinyl-modified star polylactic acids were reduced due to the effect of double bonds.The mechanical property analysis demonstrated that three-arm star polylactic acids appeared hard and brittle,however,vinyl-modified star polylactic acids became as the flexible materials due to the impact of hydroxyl groups and strong inter-chain force.Moreover,the tensile strength and elongation at break of the cross-linking structures of vinyl-modified star polylactic acids were improved after UV-curing.