Synthesis And Properties Of Amphiphilic Block Copolymers Based On Cholesterol And Poly (Ethylene Glycol)

Due to the unique amphipathicity and microphase separation of molecular structure, amphiphilic block copolymers have strong self-assembling ability to form molecular orderly body, which make it become the hot topic of polymer research. Thus preparing the amphiphilic block copolymers with controlled molecular weight and distribution and designed structure is the critical condition to some related research.At present,the majority of block copolymers are diblock and triblock,the molecules with special structure are rare; PEG is widely used in polymer modification, but the polymers with the PEG backbone are little.Besides,ordinary hydrophobic chain are always block chain, using cholesterol as the hydrophobic end which has massive steroidal structure.In this paper, we use two different ideas to synthesis novel amphiphilic block copolymers based on cholesterol and poly(ehtylene glycol), then the relationship between the polymer structure and properties was studied. (1)Using cholesterol as the starting point, succinic anhydride was used to modify the secondary hydroxyl group to produce monocholesterylsuccinate, and then the NHS activation were carried on. The structure of synthesized products were in accord with the expectation, but the reaction condition with EDA need further dicussion. (2)First, acryloyl chloride and methoxy poly(ethylene glycol) were used to synthesis the mPEG macromonomer. Then,0.5G and 1.0G ethanolamine dendrimers were prepared by the traditional "divergent method". At the last, the Michael addition reaction was achieved by the amino group and double bond. The structure of target product was characterized by IR and NMR. The results indicated that because of the length and flexibility of PEG chain, which cause great steric hindrance and reactive sites were buried, so the reaction was not ideal. The bigger the molecular weight is, the more difficult the Michael addition reaction is. (3)Linear single and double end-capped cholesterol-poly(ethylene glycol) amphiphilic polymer were synthesized by carbonyl chlorides method and DCC/DMAP method, IR and NMR confirmed the existence of expected products.Cholesterol is hydrophobic, rigid and liquid crystalline state, and poly(ethylene glycol) has long chain structure which is flexible and amorphous, the change of cholesterol and poly(ethylene glycol) certainly lead a series of variation of self-assembly behaviors for copolymers in bulk and selective solvent. For Ch-mPEGn series, with n increases, absorption peaks and exothermic peaks of the corresponding temperature (melting temperature and crystallizing temperature) in turn increased, the peak area also increased. When the molecules have the same poly (ethylene glycol) chain length, the crystallization temperature permutation order are as follows: Ch-mPEG-Ch