| Amphiphilic copolymers contain both hydrophilic and oleophilic chemical structures in their molecular chain segments, which provides their unique self-assembly behaviors in solutions and makes them especially suitable to be used as pharmaceutical carriers in micelles, microspheres, drug loaded membranes and other new-type drug delivery system. At present, block copolymers containing PCL and PEG chains are mainly prepared by active ionic polymerization using traditional chemical catalysts, some toxic organometallic compounds. As in biomedical materials, even a tiny quantity of catalyst remains can cause serious toxicity problems. Therefore, it is of vital importance to find some highly efficient and non-toxic catalysts. One of a possible ways to solve this problem is to use enzyme preparations instead of chemical catalysts.In this work, amphiphilic triblock biodegradable PCL-b-PEG-b-PCL and diblock copolymers MPEG-b-PCL prepared by the ring-opening polymerization ofε-caprolactone (ε-CL) in organic medium toluene, at 70℃, employing lipase Novozym 435 as catalyst with double-hydroxyl capped poly (ethylene glycol) (PEG, Mn=1 000, 2 000, 4 000, 6 000) or monomethoxy polyethylene glycol (MPEG, Mn=2 000, 5 000) as macromolecular initiator, respectively. The prepared copolymers were characterized by GPC, FTIR, 1H NMR, 13C NMR, DSC and WAXD. The results show that the production possessed the expected triblock or diblock structure containing both poly (ε-caprolactone) and poly (ethylene oxide) chains. Neither PCL-b-PEG-b-PCL or MPEG-b-PCL the molecular weight can be well controlled by adjusting the feeding molar ratio ofε-CL to EO ([ε-CL]/[EO]) and the molecular weight of the macromolecular initiators to PEG or MPEG. When [ε-CL]/[EO] holding with 2, the molecular weight of PEG got from 2 000 to 6 000, the molecular weight of the triblock copolymers PCL-b-PEG-b-PCL got from 11 900 to 19 000. But keeping the molecular weight of PEG with 2 000, [ε-CL]/[EO] with 2 and 4, the molecular weight of PCL-b-PEG-b-PCL were 11 900 and 19 000. When triblock copolymers PCL-b-PEG-b-PCL with the molecular weight of PEG got from 2 000 to 6 000, the crystallization and melting peaks and crystalline diffraction peaks which belong to PCL block, which indicated that PCL crystalized first and PEG was restricted. When [ε-CL]/[EO] holding with 2, the molecular weight of MPEG with 2 000 or 5 000, the molecular weight of MPEG-b-PCL were 10 000 and 11,000. But keeping the molecular weight of MPEG with 2 000, [ε-CL]/[EO] with 2 and 4, the molecular weight MPEG-b-PCL were 10 000 and 19 900. Diblock copolymers MPEG-b-PCL with the molecular weight of MPEG at 5 000, when MPEG was longer than PCL, the crystallization and melting peaks and crystalline diffraction peaks belong to MPEG and PCL, respectively. But PCL longer, the crystallization and melting peaks and crystalline diffraction peaks which belong to PCL block.On the basis, we prepared the diblock copolymer MPEG2000-PCL1 nano-micelles by the methods of self-emulsification diffusion method, nano meter precipitation method and dialysis method, according to micellar particle size and distribution, make sure dialysis method was the most suitable. Moreover, the different compositions of block copolymers were prepared by dialysis method. Empolying particle size analyzer to measurement micellars particle size and distribution, and TEM to study micellars morphological characteristics. The critical association concentrations (CACs) were determined by fluorescence technique using pyrene as probe, and the critical flocculation point (CFPTs) were determined by ultraviolet-visible pectrophotometer. The results showed that, nano-micelles possessed a core-shell structure, regularly spherical in shape. The nano-micelles made from triblock copolymers and diblock copolymers particle size were between 80~160 nm and 45~90 nm, respectively. The CAC were all less then 1.62×10-3 g/L, with lower mass fraction of PEG or MPEG to 10.5%, the CAC decreased to 1.12×10-3 g/L. With higher mass fraction of PEG or MPEG, the CFPTs of block copolymers were increased, improved the nano-micelles stability.
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