Preparation And Thermoresponsive Properties Of Poly(_L-glutamate) Bearing Oligo Ethylene Glycol Pendants

Thermoresponsive polymers are a class of polymers which can undergo solution phase transitions regarding to the changes of temperature. It has been widely studied due to their application in biomedical materials such as temperature-sensitive nanopaticles, hydrogels etc. However, the derivatives of polyacrylate and poly(N-isopropylacryamide)(e.g. PNIPAM) are non-biodegradable leading to limitation in biomedical materials application. Synthetic polypeptide is the mimics of nature peptide with biocompatibility and unique secondary structure(e.g. α-helic or β-sheet). Therefore, it will enrich the types and properties of thermoresponsive polypeptide by introducing temperature sensitive functional groups(such as oligo-ethylene-glycol group) into the side-chain of polypeptide, leading to the development of polypeptide on the field of biomedical materials.In this thesis, we synthesized two series of oligo-ethylene-glycol containing poly(L-glutamate)s with different toplogical structures(i.e., homopolymer and random copolymer) via the combination of the ring opening polymerization of N-carboxyanhydrides and 1,3-dipolar cycloadditions and studid their thermoreponsive properties.1. We prepared a series of poly(γ-propyl-L-glutamate)-graft-(oligo ethylene glycol)s with different degrees of polymerization through esterification, cyclizaton, ring opening polymerization, etherification, 1,3-dipolar cycloaddition etc. The chemical structures of the intermediates and target products were confirmed by 1H NMR and FTIR. The conformations of polypeptides were characterized by CD and FTIR, and the results reviewd that polypeptides adopt α-helical conformations both in water and solid state. Thermoresponsive properties of poly(γ-propyl-L-glutamate-graft-oligo ethylene glycol)s were characterized by DLS. Increasing the main-chain length and concentration of the polypeptides can decrease the cloudy point, however, increasing the side-chain length can significantly increase the cloudy point.2. We prepared a series of poly(γ-3-chloropropanyl-L-glutamate)-random-poly(γ-benzyl-L-glutamate)s with similar molecular weights and different proportion of repeating units via the ring opening polymerization of two kinds of N-carboxyanhydride monomers with the n-butylamine as an initiator. We prepared poly(γ-propyl-L-glutamate)-graft-(oligo-ethylene-glycol)3-random-poly(γ-benzyl-L-gl utamate)s(PPLG-g-OEG3-ran-PBLGs) with LCST-type thermoresponsive properties through the reaction between PCPLG-ran-PBLGs and sodium azide and 1,3-dipolar cycloaddition. The chemical structures of the intermediates and target products were verified by 1H NMR and FTIR. CD and FTIR results showed co-polypeptides adopt α-helical conformation both in water and solid states. The reversible thermoresponsive behavior of co-polypeptides was revealed by UV-vis, Cloudy point can be increased by increasing the content of hydrophilic group or decreasing the content of hydrophobic group. Meanwhile, there is a good linear relationship between the content of hydrophilic group and cloudy point.