Tris (2,4,6 - Trimethylbenzene Oxy) Rare Earth Complexes, Single-component Catalytic Cyclic Ester Polymerization And Controlled Synthesis Of Amphiphilic Block Copolymer Micelles

Biodegradable materials are attracting more and more attentions due to the environmental problems and clinic demands. Exploring new catalysts with high efficiency and low toxicity is crucial to the research of biodegradable materials. In this dissertation, single component tris(2,4,6-trimethylphenolate)s rare earth complexes (Ln(OTMP)₃) have been developed to initiate the homo-polymerizations and copolymerizations of E-caprolactone(CL), DL-lactide(DLLA), L-lactide(LLA). Ln(OTMP)₃ are highly efficient catalysts for these monomers. The characteristics, kinetics and mechanism of these polymerizations initiated by Ln(0TMP)3 have been thoroughly investigated and the resultant polymers have been characterized by GPC, NMR, DSC etc measurements.Controllable polymerization can prepare polymers with predictable molecular weights or structures. It is a very effective method in polymer design and synthesis, which is widely used in the preparations of amphiphilic block or graft copolymers. The amphiphilic tri- or di-copolymers of P(DTC-b-EG-b-DTC) and P(EG-b-DTC) have been synthesized by PEG with large molecular weight in the presence of lanthanide tris(2,6-di-tert-butyl-4-methylphenolate)(Ln(OTMP)₃). These copolymers have been characterized by NMR, GPC and DSC measurements. These amphiphilic block copolymers were self-assembled into micelles. These micelles have been measured by fluorescence spectrophotometer(FLS), dynamic light scattering(DLS), transmission electron microscopy(TEM). Finally, the micelles encapsulated indomethacin have been prepared and the drug loading content and entrapment efficiency have been determined.tris(2,4,6-trimethylphenolate)s rare earth complexes (Ln(0TMP)₃) were applied to the polymerization of CL. The rare earth elements and solvents affect the catalytic activities, and the tris(2,4,6-trimethylphenolate)s lanthanum complex(La(OTMP)₃) shows the highest activity in toluene. It could prepare PCL with molecular weight of 7.5 ×10⁴ and polydispersity of 1.6. Kinetics study indicates that the polymerization is of first order with respect to monomer and to catalyst concentration, and the overallactivation energy amounts to 58.7kJ/mol. *H NMR spectrum analyses of PCL demonstrates that the polymerization of CL proceeds through acyl-oxygen bond cleavage.The polymerizations of DLLA with Ln(OTMP)3 were investigated. Ln(OTMP)3 were proved to be highly efficient catalysts for the DLLA polymerization. La(0TMP)3 could prepare PDLLA with conversion of 98%, molecular weight of 5.83 X104 and polydispersity of 1.55 and it could maintain its high activity when the [DLLA] varied from 1 to 4M or M/I fluctuated in the range of 600¹500. Kinetics study indicates that the polymerization is of first order with respect to monomer and catalyst concentration respectively and the overall activation energy amounts to 62.9kJ/mol. The DSC curve and XH NMR spectrum suggested the amorphous structure of the PDLLA and La(0TMP)3 showed no selectivity towards the D- or L-lactide polymerization. The NMR spectrum analysis of PDLLA demonstrates that the polymerization of DLLA proceeds through acyl-oxygen bond cleavage.Ring opening polymerizations of LLA have been carried out with Ln(0TMP)3. La(OTMP)3 could produce PLLA with molecular weight of 5.93 X 104 and polydispersity of 1.54 and it could hold its high activity when the [LLA] varied from 1.5 to 4M or M/I fluctuated in the range of 600¹200 at 80°C. The rotatory power values indicated that PLLA prepared from La(0TMP)3 having 100% optical purity, Furthermore, the DSC and NMR measurements proved this results again. The PLLA showed spherulitic morphology with polarizing microscope. End group analysis suggested that LLA inserted into the growing chains with the acyl-oxygen bond scission.Block copolymerizations of CL and LA have been successfully conducted with single component La(OTMP)3. The copolymerization of LA with CL can only be achieved when CL is first polymerized followed by LA. La(OTMP)3 could prepare P(CL-b-LLA) with molecular weight of 5.84 X104 and the polydispersity of 1.82. It could also produce P(CL-b-DLLA) with molecular weight of 6.75 X104 and the polydispersity of 1.85. The GPC, NMR, DSC etc measurements all indicated that La(OTMP)3 prepared pure di-block copolymer.The amphiphilic tri- or di-copolymers of P(DTC-6-EG-6-DTC) and P(EG-6-DTC) have been synthesized by PEG with large molecular weight in the presence of lanthanide tris(2,6-di-ter?-butyl-4-methylphenolate)(Ln(OTMP)3). The catalytic system could prepare block copolymers with predictable molecular weights. NMR spectrum confirmed the block structure of these copolymers. GPC curves showed that the molecular weight of the copolymer increased with the rise of [DTC]/[PEG] values. These amphiphilic block copolymers were self-assembled into micelles. The critical micelle concentration(CMC) was determined by FLS using pyrene as probe. These values of CMC are all below 10mg/L, and decreased with the longer of the PDTC segment. DLS measurements showed the diameters of micelles formed from di-block are below 50nm and tri-block below 80nm, and all increased with the bigger micelle core of PDTC segments. TEM pictures showed the micelles possessed spherical morphology with narrow polydispersity. The micelles formed from these di- or tri- copolymers used as the carrier of indomethacin which greatly enhanced the solubility of indomethacin in water. The entrapment efficiency of micelles of tri-blocks could reach to90%, which are higher than that of di-blocks. P(DTC-b-EG-fc-DTC) and P(EG-fc-DTC) micelles might have potential use as carriers of hydrophobic drugs.