Research On L-lactide Polymerization In The Presence Of Styrene-acrylate Copolymer

In this paper, the dobby polylactic acid (PLLA-Joncryl) compolymers were prepared,which styrene-acrylate copolymer(Joncryl ADR4370S) was the chain extender, L-LAwas the monomer and Sn(Oct)2was used as the catalyst。And the mechanism of thesynthesis and the chemical structure of the PLLA-Joncryl copolymer were analyzed. Thepolymerization kinetics of L-LA in the presence of Joncryl ADR4370S and theperformances of the branched modified PLA were researched in the paper.Firstly, the synthesis mechanism of the PLLA-Joncryl copolymer was theoreticallyrationalized.And the reaction between L-LA and Joncryl ADR4370S was happened,forming the multi-arm PLLA-Joncryl copolymers, which was confirmed by FT-IR andGPC.Sencondly the L-LA polymerization reaction kinetics under various reactionconditions were studied by GC and GPC in this paper, and the results showed that the thetime linear semi-logarithmic curve was poor and the L-LA polymerization was no longer aliving polymerization after introducing the Joncryl ADR4370S. Also the incresed amoutsof Joncryl ADR4370S, Sn(Oct)2and the incresed reaction temperature were helpful toincrese the polymerization rate.If the polymerization temperature was below120oC orhigher than150oC, the amout of catalyst was higher than1wt%, and the amout ofJoncryl ADR4370S was greater than1wt%, they could all cause the weight distributionfluctuating significantly in the presence of Joncryl ADR4370S, which would cause theproduct elution peak foming the bimodal distribution. The molecular weight of the dobbyhad a increasing trend with increase of the conversion of L-LA, but thecarboxyl-terminated copolymers resulted from Joncryl ADR4370S and high temperaturewould caused the degradation to a certain extent.Then all the propertie changes of PLLA-Joncyrl5copolymers’ final products duringthe reaction process were tracked by GPC, XRD, DMA, TGA, static contact angle testerand universal tensile testing machine.The results showed that the branching coeffient firstdecreased and then increased, the α value of the dobby PLA reached to the max that was0.44. The measurements of DMA showed that their storage modulus increased first andthen decreased with increase of the reaction time, when the reaction time was15min, thestorage modulus arrived the maximum of6350.33MPa. Analysis of XRD showed formation of the crystalline species were α-form., and the crystal spacing decreasing as thereaction proceeded. Since the number of hydroxyl groups increased during the reactionprocess, the thermal stability of the dobby PLAs declined,and their hydrophilic propertiesimproved.The universal tensile machine showed the breaking elongation and tensilestrength increased first and then decreased with increase of the reaction time, when thereaction time was15min, they arrived the maximum of9.12%and56.38MPa.Finally the branching coeffient and thermal stability of the polymers’ under differentreaction conditions were characterized by GPC and TGA.The GPC results showed that thebranching coeffient of the dobby PLA was much greater than pure PLLA’s after theintroduction of Joncryl ADR4370S,when the increase of Joncryl ADR4370S massfraction from0.2wt%to1wt%,the α value of the dobby PLA increased from0.20to0.38,and that meaned the branching coefficent of the dobby PLA fell; With the increase ofstannous tin mass fraction, the α value of the dobby PLA increased from0.22to0.36, andthe branching coefficent of the dobby PLA fell continously; when the polymerizationtemperature increased from120°C to150°C, the α value of the dobby PLA increased from0.14to0.33, and the branching coefficent of the dobby PLA fell.While the TGAmeasurements showed that compared with the pure PLLA the thermal stability of thedobby PLA was significantly decreased after the introduction of Joncryl ADR4370S,when the increase of Joncryl ADR4370S mass fraction from0.2wt%to1wt%, thethermal stability of the dobby PLA incresed and then decreased,and the thermal stability ofthe dobby PLA was the best when Joncryl ADR4370S mass fraction was0.5wt%; Withthe increase of stannous tin mass fraction or the reaction time, the thermal stability of thedobby PLA decresed.