Synthesis And Properties Of Novel PLA/PBAu Multiblock Copolymers

The PLA and PBAu have been successfully synthesized with adipic acid,1,4-butylene glycol,urea and lactic as the main raw materials.The molecular weight of PLA and PBAu both are about 6000 g/mol.A new PLA/PBAu block copolymer is prepared with PLA and PBAu as prepolymers,and hexamethylene diisocyanate(HDI)as chain extender.In order to determine the best chain extension process,the influences of the amount of chain extender,chain extension temperature and the amount of catalyst on the molecular weight of PLA/PBAu block copolymer are studied.According to the best polymerization conditiona,a series of PLA/PBAu block copolymers,with different feed compositions that mass ratio of PLA to PBAu are 100:0,70:30,50:50,30:70,0:100,respectively,have been synthesized.After that,the influence of the introduction of PBAu segment on the thermal properties,isothermal crystallization kinetic and nonthermal crystallization kinetic of PLA-based polymers are investigated.The PLA/PBAu block copolymer films are prepared by calendered film method.Then,the mechanical properties,transmittance,oxygen permeability and degradation properties of different films are studied.The best reaction condition is adding 0.2 wt % of the catalyst and 6 wt % of the chain extender,and the chain extension temperature is 162 oC.By differential scanning calorimetry(DSC)and thermo gravimetric analysis(TG),it can be found that the addition PBAu flexible segments enhances the interaction of PLA/PBAu block copolymers,and increases the thermal decomposition temperature from 309 oC to 415 oC.The introduction of PBAu segment improves the thermal properties and crystallinity of block copolymers.The polarizing microscope(POM)and DSC show that the spherulite size of PLA and PLA/PBAu copolymer increases linearly with time in all crystallization temperature ranges,and the spherulite growth rate is the fastest at 110 oC.Avrami equation is used to analyze the isothermal crystallization kinetics of PLA and PLA/PBAu copolymer.By fitting curve analysis,the Avrami exponent is close to 3,which suggests that the changing trend of PLA and PLA/PBAu copolymer crystal growth is from two-to three-dimensional.In the course of nonisothermal crystallization analysis,the Ozawa,Jeziorny and Mo equations are chosen to simulate this process.After a serious of data calculate,the Mo equation can more precisely describe the nonisothermal crystallization process.The effect of PBAu on PLA is analyzed comprehensively,suggesting that the PBAu only changes the growth rate of PLA,and it doesn’t modify the crystal structure of PLA.Obviously,the introduction of PBAu segment can increase the elongation at break of PLA/PBAu copolymer films.Adjusting the content of PBAu,the film with good mechanical properties can be prepared.The oxygen permeation rate,the transmittance and degradation performance of the films are relative to the crystallinity.The oxygen permeation rate,the transmittance and degradation performance are lower when the crystallinity is higher.