Rare Earth Schiff-base Complexes Initiator For Ring-opening Polymerization Of 1, 4-dioxan-2-one

Metal such as Al,Zn,Mg and Ti Schiff-base complexes have been reported to be effective catalyst for the ring-opening polymerization of lactones and show great potential for application. However, little rare earth Schiff-base complexes used as catalysts for the polymerization have been reported. By far, only a few catalysts (such as tin(â…¡) ethylhexanoate) have been used to prepare poly(1,4-dioxan-2-one) (PPDO) with either low reaction rate and low activity or low monomer conversion and low molecular weight. In this thesis, the rare earth lanthanum Schiff-base complexes synthesized from the Schiff-base and anhydrous lanthanum chlorides were used for the homopolymerization of 1,4-dioxan-2-one(PDO) and copolymerization of PDO with e-CL. The process of polymerization and structure of polymer were explored for developing a new approach to synthesize PPDO and providing theoretical foundation for application of biodegradable materials.Lanthanum tris(N-phenylethyl-3,5-di-t-butylsalicylaldiminato)s[La(OPEBS)₃] was an effective initiator for polymerization of PDO, it was found to be more active than Lanthanum tris(2,6-di-methylphenolate)La(ODMP)₃ under conditions tested. So La(OPEBS)₃ was chosen as single initiator for the synthesis of poly(1,4-dioxan-2-one): The results show that temperature influences the monomer conversion slightly, but the molecular weight of PPDO greatly. The higher temperature is, the lower molecular weight is. The monomer conversion (91.5%) with relatively high molecular weight of PPDO(Mv≈5.99×10⁴) can be obtained in mild reaction conditions for 24h. In ¹HNMR spectrum, three characteristic peaks of PPDO were observed:δ=4.45ppm, (-OCH₂COO-,s),δ=4.00ppm(-OCH₂CH₂OCO-, t),δ=4.62ppm (-OCH₂CH₂OCO-,t). The obvious difference between PPDO and PDO was observed in the IR spectrum. The XRD of PPDO showed that the characteristic diffraction peaks (2θ) were at 20-25°The TG-DSC of PPDO (Mv=6.87×10⁴) was detected, thermal degradation of PPDO occurred above 150℃and reached a loss of weight of 100% at 175℃.The copolymerization of PDO withε-CL by lanthanum complexes have been studied. It was proved that the copolymer could be prepared by copolymerization of PDO with e-CL initiated by La(OPEBS)₃, but La(OMDP)₃ and lanthanum Borohydride Complex La(BH₄)₃(THF)₃ nearly no activity. It was found that the feed ratio of monomers influenced the copolymerization greatly. When the feed ratio ofε-CL is more than 0.5, only polymers of PPDO or PCL can be obtained. The copolymer can be prepared when the f_CL is less than 0.5, polymerization temperature is at 50℃, polymerization time is in 24h and the molar ratio of monomer to initiator is 200. The copolymer was extracted by toluene and characterized by ¹H-NMR, both the characteristic peaks of PCL chain and PPDO chain were found in the spectrum:δ=2.32ppmδ=1.64ppm,δ=1.35ppm,δ=4.09ppm of PCL andδ=4.15ppm,δ=3.77ppm,δ=4.33ppm of PPDO.