Preparation And Thermoresponsive Properties Of Polypeptide Bearing Oligo Ethylene Glycol Pendants In Alcoholic Solvents

Thermoresponsive polymers are a class of stimuli-sensitive polymers with many important applications such as smart sensors,tunable optical materials,tissue engineering,and drug/gene delivery.They can undergo solution phase transitions regarding to the changes of temperature.However,most of the theories and applications on thermoresponsive polymers are based on polymer aqueous solutions.The lower critical solution temperature?LCST?-or upper critical solution temperature?UCST?-type phase behavior of polymers in organic media has been less investigated.Synthetic polypeptide is the mimics of nature peptide with biocompatibility and unique secondary structure?e.g.?-helic or ?-sheet?.Thermoresponsive polypeptides can be synthesized by incorportation of thermoresponsive functional groups?such as oligo-ethylene-glycol group?into the side-chain of polypeptide.The development of thermoresponsive polypeptides shall shed light on their structure-property relationsips in various solutions,especially in organic media,which will not only benefit understanding the properties of polymer solution,but also broaden their industrial applications.In this study,we prepared two series of oligo-ethylene-glycol containing poly??-benzyl-L-glutamate?s with different toplogical structures?i.e.,homopolymer and random copolymer?via the ring opening polymerization of N-carboxyanhydrides.1.We prepared a series of poly??-4-olige?ethylene glycol?benzyl-L-glutamate?s?POEG_mBLG;m=2,3?with different molecular weight and narrow molecular weight distribution through esterification,cyclizaton,ring opening polymerization etc.The chemical structures of the intermediates and target products were confirmed by ¹H NMR and FTIR.FTIR analysis revealed that the polymers adopted ?-helical conformation in the solid-state.While they showed poor solubility in water,they exhibited a reversible upper critical solution temperature?UCST?-type phase behavior in methanol,ethanol,1-propanol,1-butanol,and 1-pentanol.Variable-temperature UV-vis analysis revealed that the UCST-type transition temperatures(T_pts)of the resulting polymers were highly dependent on the type of solvent,polymer concentration,side-and main-chain length.2.We prepared a series of poly??-4-olige?ethylene glycol?benzyl-L-glutamate?-random-poly??-benzyl-L-glutamate?s?POEG_mBLG-ran-PBLG;m=2,3?with similar mainchain lengths and different contents of repeating units via the ring opening polymerization of two kinds of N-carboxyanhydride monomers with the triethylamineas an initiator.¹H NMR analysis verified copolypeptides structures and determined the OEG molar content?x?.FTIR analysis further confirmed the molecular structures,indicated ?-helical conformations of copolypeptides in the solid-state,and revealed H-bonding interactions between OEG pendants and alcoholic solvents.The copolypeptides exhibited a reversible upper critical solution temperature?UCST?-type phase behavior in various alcoholic solvents depending on the x values and OEG side-chain lengths?m?.Variable-temperature UV-vis analysis revealed that the UCST-type transition temperatures(T_pts)of the copolypeptides in alcohols decreased as x or m value increased or as polymer concentration decreased.T_pts of copolypeptides with high x values?x?0.50?increased as the number of methylene of the alcoholic solvent increased from 2?i.e.,1-propanol?to 4?i.e.,1-pentanol?.