Acrylonitrile graft copolymerization of casein proteins for enhanced solubility and thermal properties

Casein proteins are soluble in 5% aq. ethanolamine, triethylamine, and trie thanolamine, but insoluble in organic solvents. Graft copolymerization of c asein (40 g/L) with acrylonitrile (AN) was carried out in 5% w/v aq. trieth anolamine at 60 degrees C using potassium persulfate K2S2O8 as an initiator . Percent grafting and grafting efficiency increased with increasing initia tor concentrations (up to 1.7 x 10(-2) mole L-1) and reaction times, but de creasing [M]/[I] ratios. Fourier transform IR spectra confirmed the formati on of the acrylonitrile-grafted-casein (AN-g-casein) copolymers. Under the reaction conditions studied, the grafted PAN side chains were characterized by gel permeation chromatography to have M-n between 1.58 and 5.88 x 10(4) dalton and polydispersities between 2.6 and 4.5. The AN-g-casein copolymer s behaved more like a PAN homopolymer in terms of their thermal properties and solubilities. The decomposition temperatures of AN-g-casein copolymers were between 255 and 273 degrees C, closer to the T-d of the PAN homopolyme r (275 degrees C) and significantly higher than that of casein (180 degrees C). The AN-g-casein copolymers are soluble in 50% aq. NaSCN and ZnCl2, but are insoluble in 32:28:40 wt % CaCl2/CH3CH2OH/H2O like PAN and dimethylfor mamide-like casein. (C) 2000 John Wiley & Sons, Inc.