Thermal and redox dual responsive poly(L-glutamate) with oligo(ethylene glycol) side-chains

A series of poly( L -glutamate)s grafted with oligo(ethylene glycol) (OEG) side-chains through the thioether linkages (PALG n - g -EG x , x = 2, 3 and 4) were prepared by ring-opening polymerization (ROP) of γ-allyl- L -glutamate N -carboxyanhydride (ALG-NCA) and thiol-ene photoaddition. The chemical structures and physical properties were characterized by 1 H-NMR, Fourier transform infrared (FTIR), circular dichroism (CD), etc . The PALG n -g-EG x samples with x = 3 and 4 displayed lower critical solution temperature (LCST) in water due to the presence of OEG units. The clouding point (CP) of polypeptides can be finely tuned by changing the side chain structures, molecular weights and sample concentrations. In addition, the thioether linkages in the side chains offer additional redox-responsive properties. The influence of both OEG units and thioether linkages on the LCST behavior was systematically investigated. This work provides an efficient way to prepare multi-stimuli responsive materials with highly tunable properties.