Design,synthesis And Properties Study For Model Compounds Of Syndiotactic Polycarbonates

Carbon dioxide is the main greenhouse gas.The convert of carbon dioxide into compounds with economic value has always been a research hotspot.The alternating copolymerization of carbon dioxide and epoxides to prepare aliphatic polycarbonates with biodegradability is an important reaction.In recent decades,significant study progress has been made in catalyst activity,product selectivity,polymerization mechanism and the polymer stereoregularity.Among them,the stereochemical microstructure of polymer is closely related to its biodegradability and mechanical properties.Therefore,the stereoregularity of polymeric microstructure is a challenge goal in the field of stereoselective catalytic polymerization.In 2013,a chiral catalyst system based on enantiopure dinuclear Co（III）complexes with a biphenyl linker was reported by our group.This catalyst system exhibited excellent activity and stereoselectivity in the asymmetric alternating copolymerization of carbon dioxide with meso-epoxides（including cis-2-butene oxide and cyclohexene oxide）under mild conditions.By analyzing the ¹³C NMR spectra of highly isotactic polycarbonates,the carbonyl carbon information of the isotactic sequence can be assigned.However,since there are few reports about the catalyst system for achieving perfect syndiotactic polycarbonates,it is one of the more methods to speculate the attribution of syndiotactic sequence by synthesizing syndiotactic model compounds.In this paper,（R,R）/（S,S）-2,3-butanediols and（R,R）/（S,S）-1,2-cyclohexanediols were used as raw materials to synthesize four kinds of syndiotactic model compounds of poly（2,3-butene carbonate）and poly（cyclohexene carbonate）,respectively.By comparing the signals in ¹³C NMR spectra,we concluded that the signals at 154.09 ppm,75.07 ppm and 15.51 ppm of the copolymer are attributed to syndiotactic sequene for the carbonyl,methine and methyl resonances of poly（2,3-butene carbonate）,respectively,while that of 153.17 ppm,76.18 ppm,28.72-28.69 ppm and 22.28-22.23 ppm are assigned to syndiotactic sequene for the carbonyl,methine and two kinds of methylenes resonances of poly（cyclohexene carbonate）,respectively.In addition,the crystallinity of syndiotactic model compounds of poly（2,3-butene carbonate）and poly（cyclohexene carbonate）was investigated through wide-angle X-ray diffraction（WAXD）experiments.The results showed the crystalline form of syndiotactic model compounds is different from isotactic polycarbonates.