SalenAl(OiPr)催化CO2与氧化环己烯共聚及影响因素研究

以SalenAl(OiPr)为催化剂,分别加入各种路易斯碱作为共催化剂催化二氧化碳与氧化环己烯共聚,发现共聚催化效率与共催化剂的供电子能力有关.分别研究催化剂浓度、共催化剂的用量、反应时间、反应温度、CO2压力等各种因素对该共聚反应的影响,发现SalenAl(OiPr)浓度为2 g/L时,以等摩尔量的二甲氨基吡啶(DMAP)作为共催化剂,在4 MPa的CO2和80℃下反应32 h,可得到碳酸酯键含量>99%的共聚产物,其催化效率高达495 g/g,13C-NMR检测表明共聚物为无规立构聚合物,GPC测得分子量Mn为55900,分子量分布比较窄(PDI=1.32).DSC得到共聚物的玻璃化转变温度为136℃,热重分析(TGA)可以看出共聚物在350℃可完全分解,具有优良的热分解性.

Studies of the Copolymerization of Carbon Dioxide and Cyclohexene Oxide with Salen Al(OiPr) Catalyst and Effects of Reaction Consitions

SalenAl(O~iPr) complex,prepared by reaction of SalenH_2(N,N′-bis(salicylidene)-1,2-phenylene-diamine) and isopropoxide aluminum,has been shown to be an effective catalyst for the coupling of carbon dioxide and cyclohexene oxide to afford poly(cyclohexenylene carbonate)(PCHC) with small quantities of byproduct.The addition of various cocatalysts,including 4-dimethyl(amino) pyridine(DMAP),N-methyl imidazole(N-MeIm),1,8-diazabicyclo(5.4.0)undec-7-ene(DBU) and tetra-n-butylammonium chloride(Bu_4NCl) can greatly enhance the catalytic efficiency,and more donating DMAP can offer the best copolymerization result.The relative DMAP loading also plays an important role in polymer formation.Experiments indicated that 1 equiv of DMAP was the optimum cocatalyst loading.At higher cocatalyst loading,there is a little increase in polyether linkages as well as a dramatic decrease in the molecular weight of the coplymer.Effects of reaction condition such as catalyst concentration,reaction time,temperature,CO_2 pressure on copoymerization were probed in detail.Through varying catalyst concentration,it was found that both lower and higher catalyst concentration led to lower catalytic efficiency and lower M_w,and maximum catalytic efficiency was observed in the presence of catalyst concentration around 2 g/L.The catalyst concentration seemed not to influence the carbonate content in the copolymer significantly.Almost in all cases highly alternative copolymers were obtained.As far as reaction time is concerned,the catalytic efficiency and molecular weight are enhanced with increasing time at the beginning,it reaches a maximum around 32 h,and then drops slowly.Carbonate content as low as 96.5% was observed at the very beginning,afterward the copolymerization quickly tended to proceed alternatively.Both the catalytic efficiency in copolymerization and molecular weight of PCHC raised with increasing reaction temperature from 40℃ to 80°C.At temperatures above 80℃,the polymer yield and molecular weight went down with further increasing temperature due to serious degradation of the obtained polymer.Increasing CO_2 pressure,while was less than 4 MPa,enhanced the catalytic efficiency.Higher pressure favored the formation of alternative copolymer as expected,but rather high CO_2 pressure was harmful to copolymerization.In conclusion,the best results were obtained from the reaction at 80℃ for 32 h,with 2.0 g/L SalenAl(O~iPr) and CO_2 pressure of 4 MPa using 1.0 equiv of 4-dimethylaminopyridine(DMAP) as cocatalysts.The highest turnover number(TON) is 495 g of polymer/g of catalyst.The produced copolymer is completely alternated polymer(percent of carbonate> 99%),and had a M_n value of 55900 with a polydispersity index of 1.32 as determined by gel permeation chromatography.On()~(13)C-NMR spectroscopy,chemical shifts observerd at 153.7,153.2,and 153.0 indicate the production of largely atactic polymer.The thermal properties of the copolymer were obtained by means of differential scanning calorimetry(DSC) and thermogravimetric analysis(TGA) in N_2 and at a heating rate of 10 K/min.DSC showed that the high alternating PCHC copolymer exhibited higher glass transition temperature(136℃) than their corresponding values reported in the literature,and TGA results indicated that the high alternating PCHC copolymer began its decomposition at 280℃ and then decomposed completely upon 350℃.The high alternating PCHC has excellent thermal decompose properties,and can be applied as MEMS sacrificial material.