双(烷氧-亚胺芳氧)基钛(IV)配合物催化D,L-丙交酯开环聚合、动力学及机理

ROP of D,L-Lactide Catalyzed by Bis(alkoxy-imine-phenoxy) Titanium(IV) Complex: Kinetic and Mechanism

合成了双(烷氧-亚胺芳氧)基钛(IV)配合物,通过IR,1H NMR和元素分析对其进行表征,X射线单晶衍射测定了其晶体结构.单晶结构分析表明,该晶体属于三斜晶系,空间群为P1,a=14.294(9)?,b=16.206(10)?,c=18.458(12)?,V=3911(4)?3,Dc=1.098 g?cm-3,μ=0.262 mm-1,F(000)=1589,Z=2,R1=0.081,wR2=0.240.实验结果表明该配合物在130℃以上能引发D,L-丙交酯单体开环聚合,可得数均分子量(Mn)为8.8×104 g/mol的聚(D,L-乳酸)(PDLLA).动力学研究表明该聚合反应对D,L-丙交酯单体浓度和催化剂浓度分别呈2级和1级,表观活化能和频率因子分别为76.63 kJ/mol和2.91×1011.通过苄基封端聚合物1H NMR谱的研究,表明钛配合物引发D,L-丙交酯开环聚合是基于以Ti—O键为活性中心引发D,L-丙交酯单体酰氧键断裂开环聚合的"配位-插入"机理.

A bis（alkoxy-imine-phenoxy） titanium（IV） complex was synthesized and characterized by IR,1H NMR,elemental analysis and single crystal X-ray diffraction method.The crystal of titanium（IV） complex belongs to triclinic system with space group,P,a=14.294（9）,b=16.206（10）,c=18.458（12）,V=3911（4） 3,Dc=1.098 gocm-3,μ=0.262 mm-1,F（000）=1589,Z=2,R1=0.081,wR2=0.240.The ring-opening polymerization（ROP） of D,L-lactide catalyzed by the titanium（IV） complex could take place over 130 ℃ and the maximum number-averaged molecular weight（Mn） of poly（D,L-lactic acid）（PDLLA） was 8.8×10^4 g/mol.Kinetics experiments indicate that the polymerization shows second-order kinetics in D,L-lactide monomer concentration and first-order kinetics in catalyst concentration.The apparent activation energy（Ea） and frequency factor（A） amount to 76.63 kJ/mol and 2.91×1011,respectively.1H NMR spec-troscopy of polymer terminated by benzyl group suggests that the polymerization proceeds via a conven-tional coordination-insertion mechanism and Ti-O active centers initiate the cleavage of acyl-oxygen bond of D,L-lactide monomer.