Rare Earth Catalysts Adipic Acid Anhydride Ring-opening Polymerization

Polyanhydride, as a new biodegradable polymer, for its potentialities in design of artificial organs and drug delivery systems has attracted ever-increasing attention recent years. Ring opening polymerization (ROP) provides a direct access to the related polyanhydrides and is most likely the best way of avoiding all disadvantages of the traditional polycondensation method. To study the homopolymerization of anhydride and the copolymerization of anhydride with aliphatic cyclic esters and carbornates is significant for the development of the new biodegradable polymers. However, almost all the catalysts reported for the ROP of adipic anhydride (AA) are alkyloxide metal or alkyl metal. To the best of our knowledge, the ROP of AA catalyzed by rare earth aryloxide has not been reported so far. In this paper, lanthanum tris(2,6-di-tert-butyl-4-methylphenolate) was firstly applied to catalyze the ROP of AA and the copolymerization of AA with CL or DTC. The polymer structures are identified by GPC, 1H NMR, DSC, MS and PLM.Lanthanum tris(2,6-di~tert-butyl-4-methylphenolate) was firstly used to catalyze the ROP of AA, exhibiting high catalytic activity. Poly(adipic anhydride) (PAA, Mn = 1,500) was obtained with a conversion of 86.0% within 1 hr in methylene chloride at 20 ℃. Three melting peaks were found in the DSC curve of the polymer at 51.4, 64.5 and 108.9 ℃, respectively.Block copolymers of AA with CL or DTC were prepared by La(OAr)3 for the first time, respectively, and the copolymer structures are identified by GPC, 1H NMR and DSC.poly(DTC-b-AA) with Mn = 12.3 x 104, Mw/Mn = 1.64, DTC/AA = 34.1/65.9 was prepared by block copolymerization of DTC with AA in methylene chloride at 25 ℃ by using La(OAr)3 as catalyst. Three melting peaks were found in the DSC curve of the copolymer at 56, 65 and 103 ℃. The copolymerization mechanism was proved to be a "coordination anionic mechanism". DTC monomer coordinated to rare earth metal on the carbonyl group, and opened ring via acyl-oxygen bond cleavage to form a "living" chain with the end group- La-OCH2C(CH3)2, then the AA monomer insert into the La-0 bond to form the PAA block. However, the end group of PAA-La-OOCCH2CH2CH2CH2 shows no catalytic activity to the ROP of DTC.poly(CL-b-AA) with Mn = 5.2xl04. Mw/Mn = 1.13, CL/AA = 1 was prepared by block copolymerization of CL with AA in methylene chloride at 25 ℃ by using La(OAr)3 as catalyst. Three melting peaks were found in the DSC curve of the copolymer at 55.3, 71.3 and 119.7℃. The copolymerization mechanism was proved to be a "coordination anionic mechanism". CL monomer coordinated to rare earth metal on the carbonyl group, and opened ring via acyl-oxygen bond cleavage to form a "living" chain with the end group- La-OCH2CH2CH2 CH2CH2, then the AA monomer insert into the La-0 bond to form the PAA block. However, the end group of PAA-La-OOCCH2CH2CH2CH2 shows no catalytic activity to the ROP of CL.