PREPARATION AND THERMAL-PROPERTIES OF HIG HLY SUBSTITUTED BENZYL STARCH

Starch reacts in alkaline medium with benzyl chloride yielding benzyl starch with various degrees of substitution. The resulting derivatives were characterized and the influence of the reaction conditions on th e degree of substitution and the yield were determined. In aqueous-alk aline medium? benzyl starch with a maximum degree of substitution of 0 .9 was obtained. Under water-free conditions higher degrees of substit ution are possible. The highest substitution (2.9-3.0) is found by rea ction of starch dissolved in dimethylsulfoxide with sodium hydroxide a nd benzyl chloride. Somewhat lower degrees of substitution (2.7-2.8) c an be obtained in homogeneous medium with sodium hydride and benzyl ch loride in dimethylsulfoxide. In dependence on the benzyl chloride conc entration, also derivatives with lower degrees of substitution can be prepared. The glass transition temperatures of benzyl derivatives of s tarch with degrees of substitution above 2.5 are at about 45-55 degree s C; with decreasing degree of substitution an increase of the glass t ransition temperature up to about 70 degrees C is observed. The meltin g range of benzyl starch was found between 150 to 180 degrees C; at th ese temperatures some decomposition starts.