Study On The Polymer Structure Control And Properties Based On Poly(Lactide)

Poly(lactide)(PLA)is a biodegradable polymer material with excellent performance.It has been widely used in disposable tableware,daily necessities and biomedicine.However,PLLA-based materials still have some defects compared with traditional polymer materials,which limits their further application.The chemical modification of polylactide is a commonly used means to obtain PLLA-based materials with different properties.In this paper,a series of multi-arm and block PLLA materials initiated by different arms with soft or rigid cores and polyamide 6(PA6)were successfully synthesized.The influence of branched structure and polyamide block on thermal and crystallization properties was also studied.Considering that it's difficult to obtain high molecular weight polymers using rigid core as initiator,we have successfully synthesized a series of PLLA samples varing molecular weights(6k?54k)by combining bulk polymerization and solution polymerization.It was found that the larger the steric hindrance caused by the number and position of hydroxyl groups on the benzene ring,the more difficult ring-opening polymerization of PLLA.The GPC results indicate that the synthesized PLLA sample has a narrow molecular weight distribution and a linear increase in molecular weight as the ratio of monomer to initiator increases.In addition,the structure of PLLA samples was characterized by 1H NMR.The results showed that all hydroxyl groups on the benzene ring can initiate the ring opening of lactide,and the multi-arm structure can be well controlled by the number of benzene ring hydroxyl groups.According to DSC and POM results,the crystallization and thermal properties of rigid multi-arm PLLA were systematically studied by DSC and POM.The effects and regularityof rigid,flexible core,substitution position,number of different arms and molecular weight on the crystallization and thermal properties of the samples were analyzed.The DSC results show that the melting point of the same molecular weight PLLA is B-1-PLLA>B(1,4)-2-PLLA?B(1.3)-2-PLLA>B(1,2)-PLLA>B-3-PLLA,crystallization rate is B-1-PLLA>S-2-PLLA>B(1,4-2-PLLA>B(1,3)-2-PLLA>B(1,2)-PLLA,ie.both the number of arms and the substitution position on the benzene ring(steric effect)affect the melting point and crystallization rate of the polymer.The results of DSC and POM indicate that the rigidity of the central core limits the movement and regular alignment of the molten PLLA chain during crystallization,so the crystallization rate and the thickness of the lamellae are both reduced.However,as the molecular weight increases,the influence of the central nucleus gradually decreases,so the melting point and crystallization rate of the high molecular weight PLLA are barely affected by the central nucleus.A series of PA6-b-PLLA block copolymers were successfully synthesized for the first time using Bronsted acidic ionic liquid(1-butylsulfonicate-3-methylimidazolium bisulfate)and PA6-NH2 as catalyst and initiator respectively.The reaction is carried out at 140? under solvent-free condition,is energy-saving and environmentally friendly,and has strong industrial applicability.The structural analysis of the block copolymer showed that the ester-acyl exchange reaction did not occur during the reaction,Meanwhile PA6 and PLLA were directly linked by chemical bonds,and the regular diblock polyesteramide was successfully prepared.