低分子量结晶性丙交酯/乙交酯与己内酯/乙交酯共聚物热转变温度的组成与分子量依赖性

以1,4-丁二醇为引发剂、辛酸亚锡为催化剂,通过L-丙交酯(LLA)、乙交酯(GA)、ε-己内酯(CL)的开环共聚,制得了低分子量的端羟基结晶性LLA/GA共聚物(PLLGA)和CL/GA共聚物(PCG),分别以FTIR1、H-NMR、GPC、DSC对其微结构和热转变温度进行了表征,重点考察了其热转变温度的组成、分子量依赖性.结果表明,利用辛酸亚锡/二元醇引发开环聚合,通过改变单体配比和单体/引发剂配比,可方便地调控共聚物的组成和分子量;通过改变共聚物的组成和分子量,可在较宽的范围内调节共聚物的热转变温度,并得到了玻璃化温度和熔点与组成、分子量之间定量的经验关系式.

Composition and Molecule Weight Dependences of Thermal Transition Temperatures o f Dihydroxy-Telechelic Poly(LLA-co-GA) and Poly(CL-co-GA) Crystalline Polymers

Hydroxy-telechelic aliphatic(co)polyesters are important building blocks of biodegradable multiblock copolymers which can be used as biodegradable elastomers and biodegradable shape memory polymers(BSMPs).For BSMPs,the transition or switch temperature at which the shape memory effect takes place is determined by the thermal trasition temperature of the reversible phase or soft segments,and the shape memory properties and mechanical properties are maily affected by the condensed state of the fixed phase or hard segments.Therefore,the thermal transition temperatures of hydroxy-telechelic aliphatic(co)polyesters are critical parameters for successful design of BSMPs.This article aims to report the relationship among the thermal transition temperature of two important hydroxy-telechelic aliphatic copolyesters,poly(L-lactide-co-glycolide)(PLLGA) and poly(ε-caprolactone-co-glycolide)(PCG),and their molecular weight and copolymer composition.Hydroxy-telechelic PLLGA and PCG are synthesized via ring-opening copolymerization of L-lactide and glycolide(LLA/GA) and ε-caprolactone and glycolide(CL/GA) using 1,4-butanediol as initiator and stannous octoate as catalyst at 140℃.After dissolving in chloroform,precipitated from methanol and drying under vacuum at 75℃ for 48 h,purified PLLGA and PCG were obtained and characterized by FTIR,~1H-NMR,GPC and DSC.The polymerization took place in a living/controlled manner,and the molecular weight was adjusted by the monomer/initiator ratio in the range of 2000～14000.The polydispersity index ranged from 1.1 to 1.3.The GA content in the copolymers is of 0～0.22 for PLLGA and 0～0.32 for PCG and can be adjusted by the GA content in monomer feed(_(GA),0～0.2).The contents of GA in copolymers are higher than _(GA) because of higher reactivity ratio of GA than LLA and CL.For convenience,_(GA) was used to denote the copolymer composition.The FTIR and~1H-NMR spectra indicate that the copolymers are hydroxy-telechelic.The DSC results indicate that the copolymers with above mentioned copolymer composition and molecular weight are all semi-crystalline polymers.The melt temperatures(T_m) of both PLLGA and PCG were determined from the second scan.The T_m ranged from 37℃ to 58℃ for PCG and from 80℃ to 162℃ for PLLA.They increased with increasing the molecular weight but decreased with increasing the copolymer composition.The glass transition temperature(T_g) of PLLGA was obtained from the second scan and ranged from 35℃ to 54℃.It also increased with increasing the molecular weight but decreased with increasing the copolymer composition.By ploting T_g and T_ms with the reciprocal of number average molecular weight(M_n),linear relationships,T_g=T_g(∞)-K/M_n and T_m=T_m(∞)-K′/M_n,are observed.For T_m,the interceptions T_m(∞) are linearly decreased with increasing _(GA),but the slope K′ is independent of _(GA).Therefore,experiential linear equations T_m=T_m(H)-A_(GA)-K′/M_n have been established to describe their relationship,in which T_m(H) is the melt temperature of PLLA and PCL homopolymers.For PLLGA,the values of T_m(H),A and K′ are 166.9,129.5 and 1.48×10~5,respectively.For PCG,they are 60.4,82.0 and 2.92×10~4,respectively.From these results,one can design and synthesize hydroxy-telechelic PLLGA and PCG copolymers and corresponding shape memory multiblock copolymers with desired transition temperatures.