二氧化碳-环氧乙烷-氧化环己烯三元共聚物的制备与性能

采用稀土三元催化剂实现了二氧化碳、氧化环己烯与环氧乙烷的三元共聚,当环氧乙烷和氧化环己烯等摩尔投料时催化活性达到690 g/(mol Zn h),所得三元共聚物的数均分子量达到7.9×104,远程异核多量子相关核磁谱证明所得共聚物主要是无规三元共聚物,其中环氧乙烷-二氧化碳结构单元与氧化环己烯-二氧化碳结构单元相连的全交替结构占26.9%.二氧化碳-氧化环己烯共聚物的脆性导致其熔体加工十分困难,引入环氧乙烷为第三单体进行三元共聚,实现了二氧化碳-氧化环己烯共聚物的增韧,解决了其熔体加工难题,而且改变环氧单体比率能够调节三元共聚物的耐温性能和力学性能,当环氧乙烷与氧化环己烯等摩尔投料时,所得三元共聚物在20℃下的杨氏模量达到(900±17)MPa,拉伸强度为(38±2)MPa,断裂伸长率为(26.3±9.2)%.

SYNTHESIS AND PROPERTIES OF CARBON DIOXIDE-ETHYLENE OXIDE-CYCLOHEXENE OXIDE TERPOLYMERS

Poly(cyclohexene carbonate)(PCHC) is one of the few biodegradable polymers maintaining dimension stability over 100℃ due to its high T_g of 115℃,but PCHC is quite difficult for melt processing because of its brittleness.In this work,backbone modification route was proposed by intercalating soft ethylene carbonate segments among the hard cyclohexene carbonate segments,where the terpolymerization of carbon dioxide(CO_2),ethylene oxide(EO) and cyclohexene oxide(CHO) was carried out under ternary rare earth metal coordination catalyst prepared from Y(CCl_3COO)_3,glycerin,and ZnEt_2.The terpolymerization was carried out at 70℃ in a 2000 mL autoclave for 10 h.The obtained terpolymers were subjected to 1H-NMR,13C-NMR experiments for structure analysis,Gel permeation chromatograhy(GPC) was used to determine the number average molecular weight and its polydispersity,and dynamic mechanical analysis(DMA) was used for thermo-mechanical studies,the mechanical performance was done with a ZWick/Z010 multi-function mechanical testing instrument.The catalytic activity was between 425 g/(mol Zn h) and 691 g/(mol Zn h),depending on the molar ratio of CHO to EO,and the number average molecular weight ranged between 7.2×104 and 7.9×104,with polydispersity index changing from 3.17 to 3.57.The optimal catalytic activity reached 691 g/(mol Zn h) when equal molar ratio of EO and CHO was added,and the obtained terpolymer showed a number average molecular weight of 7.9×104 with polydispersity index of below 3.5.The absorption peaks in 1H-NMR spectra of poly(ethylene carbonate),poly(cyclohexene carbonate) and related terpolymer were assigned.For the terpolymer obtained from equal molar ratio of EO to CHO,heteronuclear multiple-bond correlation(HMBC) experiments showed that alternating linkages between ethylene carbonate and cyclohexene carbonate were only 26.9% in the terpolymer,and random structure consisting of ethylene carbonate(EC) units and cyclohexene carbonate(CHC) units was predominant.For the terpolymer obtained from equal molar ratio of EO to CHO,the dynamic mechanical analysis(DMA) spectra showed three peaks,one peak at-80℃ was attributed to a second transition in the terpolymer,the another two peaks appeared at 20℃ and 80～100℃ were assigned to the glass transitions of the polymer related to ethylene carbonate segments and cyclohexene carbonate segments,respectively,the existence of two glass transitions at different temperatures indicated that the existence of soft and hard segments in the backbone.Introducing EO as the third comonomer was effective to solve the brittleness of PCHC making it melt processable,moreover,the thermal and mechanical properties of the terpolymer can be adjusted by changing the molar ratio of EO and CHO in comonomers.For the terpolymer obtained from equal molar ratio of EO to CHO,the Young's modulus at 25℃ was 995.7 MPa,and its tensile strength was 27.1 MPa with elongation at break of 42.3%.When the temperature was raised to 50℃,the Young's modulus maintained 868.7 MPa,and its tensile strength was 15.2 MPa with elongation at break of 57.6%.As a reference,poly(propylene carbonate) lost mechanical strength at 50℃,the Young's modulus at 40℃ was found to be 56.8 MPa,and its tensile strength was 2.1 MPa with elongation at break of 1814.9%.Therefore,by means of terpolymerization of CO_2,EO and CHO,a melt processable biodegradable polymer with improved dimension stability at higher temperatures was prepared.