Grafting of vinyl polymers with bio-'-6 and s y n t h e t i~~.~ macromolecules has been the subject of interest of several workers. Considerable research has been carried out at the Central Leather Research Institute on the modification of biopolymers and their characterization with respect to collagen? JO gelatin," and casein.12 Though casein has been used for various applications1"lS as is and in modified form and in combination with other polymers, few fundamental studies concerning its modification have been carried out. The present study was undertaken to understand the kinetics and mechanism of modification of casein and the characterization of the graft copolymer. The preliminary results on the modification of casein with poly(buty1 acrylate) are discussed with respect to percent grafting, grafting efficiency (GE), rate of total monomer conversion (R,), rate of graft copolymerization (Rg), and rate of homopolymerization (Rh).
EXPERIMENTAL MaterialsCasein (E. Merck, G.R.) and potassium persulfate (A.R., S.D.'s, India) were used as such without further purification. Butyl acrylate (Rohm and Haas, USA) was purified before use as reported in the 1iterat~re.l~
Grafting ProcedureGrafting reactions were carried out in 100-ml reaction vessels with nitrogen inlet and outlet arrangements. Casein was accurately weighed and placed in a reaction vessel containing 25 ml water thermostatted at 6OOC. After a sufficient time, butyl acrylate was added, followed by the initiator, and the total volume was made up to 50 ml. The reaction was allowed to proceed for the required time interval. After the completion of the reaction, the contents were cooled to 5OC. The products were filtered through weighed sintered crucibles and then Soxhlet extracted.The values of the rate of total monomer conversion and the rate of the homopolymerization were calculated gravimetrically. The rate of graft copolymerization (Rg) and the grafting efficiency (GE)were calculated from the following expressions:
Isolation of GraftsAcid Hydrolysis. The grafted copolymer was hydrolyzed by heating with 6N HCI for 18 hr. The separated poly(buby1 acrylate) was filtered, washed, and dried for viscosity studies.Viscosity. The viscosities of poly(buty1 acrylate) side chains were determined in acetone, and the molecular weight of poly(buty1 acrylate) was calculated from the equation reported in the literature.20Infrared Analysis. Pure casein and graft copolymer were subjected to infrared analysis using a Perkin-Elmer model 337 grating infrared spectrophotometer in the form of potassium bromide pellets (500 mg) containing 2-6 mg powdered .polymers.
RESULTS AND DISCUSSIONTo understand the grafting reaction of poly(buty1 acrylate) onto casein, variations in monomer concentration, initiator concentration, backbone concentration, and temperature were effected.
Small angle neutron scattering experiments were made on an ionomer synthesized from perdeuterostyrene and an ion pair comonomer. A Debye plot based on data from the sample with lower ion concentration gave a correlation length of 5.3A. Clustering is not significant in this sample. With a higher concentration of ionic groups a peak in the scattering curve is interpreted as due to clusters about 20A in diameter. These studies along with X‐ray scattering and electron microscopy also indicate the presence of larger ion rich domains.
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