Synthesis of Aluminum-Schiff Base Catalyst and Their Stereoselective Polymerization of Lactides†

doi:10.7503/cjcu20130958

Abstract

Abstract:

A series of asymmetric Schiff-base ligands and their aluminum Al(Ⅲ) complexes that contained different steric substituent were designed and synthesized. The structures of ligands and their complexes were characterized. One crystal of Schiff-base aluminum complex was obtained. X-Ray diffraction analyses showed that the central aluminum atoms of the complex adopt twisted four pyramid geometry. They were chiral but racemic complexes with two enantiomers in solid state. Their catalytic properties in the solution polymerization of racemic lactides(rac-LA) in the presence of 2-propanol were investigated in detail. All of the complexes had poor stereoselectivity for ring-opening polymerization(ROP) of rac-LA(P_m about 0.55), the polymerization rate of asymmetric complex was much faster than symmetric complex in ROP of rac-LA. The results evaluate that the substituent of ligands has great influence on the catalytic properties of the complex.

Key words: Lactide, Biodegradable, Stereoselective polymerization, Schiff-base

CLC Number:

O631

TrendMD:

QU Zhi, LI Xiang, PANG Xuan, DUAN Ranlong, GAO Bo, CHEN Xuesi. Synthesis of Aluminum-Schiff Base Catalyst and Their Stereoselective Polymerization of Lactides^†[J]. Chem. J. Chinese Universities, 2014, 35(3): 626.

Figures/Tables 6

Scheme 1 Syntheses of ligands and complexes

Fig.1 Perspective view of complex 2a with thermal ellipsoids drawn at 30% probability level Hydrogens are omitted for clarity.

Table 1 Polymerization data of rac-LA using complexes 1a—3aa

Complex	T/℃	t/h	[M]₀/[Cat]	Conv.^b(%)	10^-3M_n(GPC)^c	PDI^c	$P m d$
1a	70	60	50	95	6.8	1.16	0.53
1a	90	24	50	94	7.5	1.21	0.50
1a	110	14	50	93	8.6	1.35	0.46
2a	70	60	50	88	6.6	1.17	0.52
2a	90	24	50	87	7.9	1.23	0.49
2a	110	14	50	89	8.0	1.33	0.46
3a	70	60	50	96	6.5	1.19	0.52
3a	90	24	50	90	7.5	1.20	0.51
3a	110	14	50	95	8.5	1.30	0.45

Table 1 Polymerization data of rac-LA using complexes 1a—3aa

Complex	T/℃	t/h	[M]₀/[Cat]	Conv.^b(%)	10^-3M_n(GPC)^c	PDI^c	$P m d$
1a	70	60	50	95	6.8	1.16	0.53
1a	90	24	50	94	7.5	1.21	0.50
1a	110	14	50	93	8.6	1.35	0.46
2a	70	60	50	88	6.6	1.17	0.52
2a	90	24	50	87	7.9	1.23	0.49
2a	110	14	50	89	8.0	1.33	0.46
3a	70	60	50	96	6.5	1.19	0.52
3a	90	24	50	90	7.5	1.20	0.51
3a	110	14	50	95	8.5	1.30	0.45

Fig.2 1H NMR spectrum of PLA oligomer

Fig.3 Methine region of homonuclear decoupled 1H NMR spectrum of poly(rac-LA) using complex 2a

Fig.4 Kinetics curve of complex 2a with n(M0)/n(Al)/n(2-propanol)=50:1:1

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