Preparation And UCST-type Phase Behaviours Of Polypeptide Bearing Pyridinium Salt Pendants In Alcohol Or Water

Polymers with ionic liquid(PILs)moieties(e.g.imidazolium and pyridinium)are a class of polyelectrolytes,which exhibit attractive physical properties including conductivity and low glass transition temperatures.These PILs have demonstrated significant potential applications in various fields such as in energy,catalysis,and biomedical science.Recently,PILs with thermoresponsive properties have gained increasing attention owing to their distinct charged groups and polymer–solvent interactions from traditional thermoresponsive polymers bearing non-ionic or weakly charged pendants.In the present study,we report a series of poly(?-4-methylbenzyl-L-glutamate)pyridinium tetrafluoroborate conjugates,whichwere synthesized by the combination of nucleophilic substitution and ion-exchange reaction.1.We synthesized a series of poly(?-4-methylbenzyl-L-glutamate)pyridinium tetrafluoroborate conjugates containing various pyridinium moieties(i.e.pyridinium,2-methylpyridinium,3-methylpyridinium,and 4-methylpyridinium)were prepared by nucleophilic substitution between poly(?-4-chloromethylbenzyl-L-glutamate)and pyridine or methylpyridines with different substituent positions,followed by ion-exchange reaction in the presence of NaBF4.1H NMR spectroscopy and Fourier transform infrared spectroscopy analyses confirmed the molecular structures.1H NMR analysis additionally revealed that they showed high grafting efficiency in the range of 93–97%.Variable-temperature UV-visible spectroscopy was used to characterize the solution phase behaviours and UCST-type phase transition temperature(Tpt)values,which were in the range of 24.9–37.2 ? in methanol(3mg/mL)and 40.9–55.7 ? in water(10mg/mL).Tpt decreased significantly with decreasing polymer concentrations.2.We synthesized a series of water-soluble random copolypeptides bearing pyridinium tetrafluoroborate(PyBF4)and oligo-ethylene glycol(OEG)pendants(PPLG-PyBF4-r-OEG).They were prepared bysequential postpolymerizations including nucleophilic substitution of poly(?-3-chloropropyl-L-glutamate)with sodium azide to partially convert chloro groups into azido groups,copper-mediated [2 +3] alkyne-azide 1,3-dipolar cycloaddition to conjugate OEG pendants,another nucleophilic substitution to conjugate pyridinium chloride,and ion-exchange reaction.FTIR and CD analysis revealed that PPLG-PyBF4-r-OEG samples with suitable molar content of PyBF4(x ? 0.4)were water-soluble and adopted ?-helical conformation in both the solid-state and aqueous solution.