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

Casein proteins are soluble in 5% aq. ethanolamine, triehtylamine, and triethanolamine, but insoluble in organic solvents. Graft copolymerization of casein (40 g/L) with acrylonitrile (AN) was carried out in 5% w/v aq. triethanolamine at 60°C using potassium persulfate K₂S₂O₈ as an initiator. Percent grafting and grafting efficiency increased with increasing initiator concentrations (up to 1.7 × 10^?2 mole L^?1) and reaction times, but decreasing M]/I] ratios. Fourier transform IR spectra confirmed the formation 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 × 10⁴ dalton and polydispersities between 2.6 and 4.5. The AN‐g‐casein copolymers 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°C, closer to the T_d of the PAN homopolymer (275°C) and significantly higher than that of casein (180°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 dimethylformamide‐like casein. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 2543–2551, 2000