Stereoselective polymerization of rac-lactide using a monoethylaluminum Schiff base complex.
A monoethylaluminum Schiff base complex (2) with formula LAlEt (L = N,N'-(2,2-dimethylpropylene)bis(3,5-di-tert-butylsalicylideneimine) was synthesized and employed for the stereoselective ring-opening polymerization of rac-lactide (rac-LA). The complex 2 was characterized by nuclear magnetic resonance, crystal structure, and elemental analysis. It contains a five-coordinate aluminum atom with distorted trigonal bipyramidal geometry in the solid state. In the presence of 2-propanol, 2 showed high stereoselectivity for the polymerization of rac-LA. The polymerization yielded crystalline poly(rac-LA) with a high melting temperature (193-201 degrees C). NMR, differential scanning calorimetry, and wide-angle X-ray diffraction indicated that the poly(rac-LA) was highly isotactic, and a stereocomplex was formed between poly-l- and poly-d-lactide block sequences. By the analysis of electrospray-ionization mass spectrometry and (1)H NMR, the polymer was demonstrated to be endcapped in both terminals with an isopropyl ester and a hydroxy group, respectively. The polymerization was of first order in rac-LA concentration. The relationship between the rac-LA conversion and molecular weights of the polymer was linear so that the polymerization could be well controlled.
Tang
Zhaohui
Z
State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, People's Republic of China.
Chen
Xuesi
X
Pang
Xuan
X
Yang
Yongkun
Y
Zhang
Xuefei
X
Jing
Xiabin
X
D017607:Aluminum Compounds / Q000737:chemistry*; D002152:Calorimetry, Differential Scanning; D009682:Magnetic Resonance Spectroscopy; D011091:Polyesters / Q000737:chemistry*; D012545:Schiff Bases / Q000737:chemistry*; D013237:Stereoisomerism; D014961:X-Ray Diffraction
D017607:Aluminum Compounds; D011091:Polyesters; D012545:Schiff Bases; C033616:poly(lactide)