VARIABLES AFFECTING THE METHYLATION REACTIONS OF CELLULOSE

Solubility of methyl cellulose (MC) depends on the degree of substitut ion (DS), the average degree of polymerization (DP), and the distribut ion of methoxyl groups. Of these, the DS appears to be the most import ant. The DS of the MC depends on the conditions of preparation. The co nditions studied in this work revealed that the DS of the MC increased as the concentration of sodium hydroxide increased from 10 to 50%. Th is result is attributed to the increase in the extent of formation of alkali cellulose II as a result of the increase in the alkali concentr ation and hence the increase of the DS of the MC. Decreasing both the ratio of dimethyl sulfate: cellulose and the liquor ratio increased th e DS. High DS was achieved within a period of 2 and 3 h. However, the DS increased as the time increased. The decrease of the DS as the liqu or ratio increased may be attributed to the sol-gel transition due to the interaction of the hydrophobic methoxyl groups within the polymer chains. To reveal the effect of the thermal sol-gel transition, the re action was carried out in nonaqueous medium and the results obtained s howed an increase of the DS with the increase of the solvent ratio unt il a maximum. This result may be contributed to the break-down of the hydrogen bonding in the presence of solvents that transfer the reactio n medium to the sol-form and hence more methylating reaction takes pla ce. The degree of the solvation of the methyl groups into the solvents also plays a role. (C) 1994 John Wiley & Sons, Inc.