Poly(L-glutamic acid)-poly(oxyethylene glycol) systems: Perpetuated cholesteric liquid crystal structures in noncrosslinked and crosslinked solid films

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Abstract
The origin of the peculiar microphase structures of so-called PGA/PEG polyblends and PGA-PEG heterogeneous network polymers cast from dimethylformamide or dioxane-water was studied by means of phase diagrams, infrared spectra, x-ray diffractions, polarizing optical microscopy, and small-angle light scattering. It was demonstrated that in such solvents, poly(ethylene oxide) (PEO) or poly(oxyethylene glycol) (PEG) can fill the interstitial space between the parallel arrays of the α-helices of poly(L-glutamic acid) (PGA) and become an integral constituent of the lyotropic cholesteric liquid crystals. Such structures were found to be perpetuated in the solid films of both the noncrosslinked PGA/PEO and the crosslinked PGA-PEG after the solvent was evaporated. The dynamic mechanical behavior of the solid films was consistently interpreted on the basis of such phase structures.