70 u00b0 c and held at that temperature for three hours the mixture was then cooled to room temperature and neutralized by using a 37 by weight hydrochloric acid the product was filtered and washed several times by using a 75 ethanol solution the solid was then dried in an overnight at 50 u00b0 c a 2 l steel reactor was charged with 100 parts acid thinned dent corn starch 1 5 parts sodium hydroxide 3 parts sodium chloride and 500 parts of water the reactor was sealed and then flushed several times with nitrogen the mixture was vigorously stirred at room temperature for 20 minutes the reactor was then charged with 3 parts propylene oxide and the resulting mixture was then heated at 50 u00b0 c for 4 hours following the desired amount of time the mixture was cooled to 30 u00b0 c and stirred at that temperature for 19 hours the slurry was then neutralized with 37 by weight hydrochloric acid the white solid was washed with water followed by an additional wash of an aqueous solution of methanol the solid was then filtered and dried at 50 u00b0 c for 12 hours the hydroxypropyl substitution content was determined according to the method of astm d 3876 96 2001 the hydroxypropyl starch was dried in an oven to remove residual moisture and then treated with an aqueous solution of hydroiodic acid liberating ispropyl iodide the isopropyl iodide was extracted in situ with an organic solvent and quantitated by gas chromatography using an internal standard technique table 2 shows the.