SYNTHESIS AND CHARACTERIZATION OF pH SENSITIVE AMPIPHILLIC NEW COPOLYMER OF METHYL METHACRYLATE GRAFTED ON MODIFIED STARCH: INFLUENCES OF REACTION VARIABLES ON GRAFTING PARAMETERS

摘要

Objectives: The present study was performed to investigate the effect of graft copolymerization on modified maize starch for providing a pH sensitive matrix system along with the moisture, chemical and thermal resistance. Methods: Starch was acetylated with acetic anhydride using 0.5N NaOH as a catalyst and methyl methacrylate (MMA) was grafted onto acetylated starch (Ast) by using ceric ion induced free radical polymerization. Different reaction parameters such as initiator concentration, monomer concentration, reaction time and temperature were optimized to get maximum graft yield (45.93%) and graft efficiency (94.64%). Physicochemical properties were characterized by FTIR, 1H NMR, [13]C NMR, SEM, X-RD and TG-DTA analysis. Results: Structures of acetylated starch and graft copolymer was confirmed by IR and NMR spectroscopic analysis. Particle shape and morphology were studied by SEM which shows that graft copolymerization leads to enhancement of roughness of carbohydrate surface. Moreover, graft copolymer has been found to be more moisture and chemical resistant. TG-DTA studies revealed that the decomposition temperature of grafted starch was higher than that of native starch and acetylated starch. A suitable mechanism to explain initiation, propagation and termination of graft copolymerization has also been proposed. Conclusions: Graft copolymer showed higher acid, base and thermal resistance, lower crystallinity and increased moisture resistance as compared to the acetylated and native starch. Swelling behavior at pH 1.2-10 revealed that graft copolymer provided a pH sensitive matrix system and may be useful to overcome the harsh environment of the stomach