卟啉铝催化下二氧化碳与氧化环己烯共聚反应研究

COPOLYMERIZATION OF CYCLOHEXENE OXIDE AND CARBON DIOXIDE CATALYZED BY ALUMINUM PORPHYRIN

利用四苯基卟啉氯化铝(TPPAlCl)与双三苯基膦氯化铵(PPNCl)组成的二元催化剂催化二氧化碳与氧化环己烯共聚合,80℃下反应9 h,二氧化碳-氧化环己烯共聚物(PCHC)的收率为97.2%,分子量分布窄(Mw/Mn=1.12),但数均分子量仅为6.8×103.研究发现溶剂的浓度和极性变化对聚合过程中的链转移反应影响不大,而降低单体浓度,链转移反应明显减少,由此推断聚合过程中存在明显的向单体的链转移反应.进而采用基质辅助激光解析电离飞行时间质谱(MALDI-TOF/MS)对聚合物结构进行分析,提出了聚合反应过程中的链增长和链转移反应机理,即:在TPPAlCl/PPNCl二元催化剂催化二氧化碳与氧化环己烯共聚合反应中,除了引发剂引发单体聚合外,通过链转移又产生了其它新的活性中心,导致所生成的聚合物的数目远多于引发剂数目,而且络合铝离子在各聚合物链端的交换反应速率远大于链增长的速率,从而得到具有极窄分子量分布的聚碳酸酯.上述交换反应的可逆性是各分子链休止、增长交替进行的关键.

Chloro（5,10,15,20-tetraphenyl-porphyrinato）-aluminum（TPPAlCl） in combination with bis（triphenylphosphine） iminium chloride（PPNCl） was used as binary catalyst for the copolymerization of cyclohexene oxide and CO2.After 9 h reaction at 80℃,poly（1,2-cyclohexylene carbonate）（PCHC） with narrow molecular weight distribution（Mw/Mn =1.12）was obtained and the yield was as high as 97.2%.However,the number average molecular weight was only 6.8 ×103.It＇s found that the concentration and polarity of solvents have little effect on the chain transfer reaction,whereas a decrease in monomer concentration leads to a remarkable reduction in the chain transfer reactions,indicating that there exists obvious chain transfer to monomers.Furthermore,the structure of PCHC was analyzed by matrix-assisted laser desorption ionization time-of-flight mass spectrometry（MALDI-TOF/MS） technique,upon which the mechanism of chain growth and chain transfer reaction in the polymerization process was proposed：during the copolymerization of cyclohexene oxide and CO2 catalyzed by TPPAlCl/PPNCl system,besides the added initiator,newly active centers were generated by chain transfer,thereby the number of the polymer molecules exceeded the number of the added aluminium porphyrin molecules.Furthermore,the narrow molecular weight distribution of the obtained polymer indicates that the rate of chain exchange is much faster than that of chain propagation.The reversibility of the rapid exchange reaction is the key of alternation of chain termination and chain propagation.