Preparation of 6-O-(4-alkoxytrityl)celluloses and their properties

Abstract

Cellulose was reacted with a series of 4-alkoxytrityl chlorides (C_nTCl, n: number of carbon atoms in a saturated alkyl chain) under homogeneous reaction conditions in LiCl–N,N-dimethyl acetoamide to give a series of 6-O-(4-alkoxytrityl)celluloses (C_nTC) with a high degree of substitution (DS), from 0.94 to 0.99, and with high regioselectivity at the 6-O position. Solubility of the C_nTC in nonpolar solvents depended on the alkyl chain length: as the alkyl chain lengthens, cellulose derivatives become more hydrophobic and are readily soluble in nonpolar solvents, but not in polar solvents. Acetates of the C₄–C₁₈TC (C₄–C₁₈TCAc) showed anisotropic structures over melting temperatures (T_m) examined under a polarized optical microscope (POM). Over isotropization temperatures (T_i), flow birefringence were detected for C₁₂–C₁₈TCAc.The T_m and T_i decreased linearly with an increasing number of carbon atoms in the alkyl substituent. Wide-angle X-ray scattering (WAXS) studies of C_nTC indicated that the fully extended side chains were perpendicular to the polymer backbone and interdigitated. These C_nTC with the improved solubility may be used as starting materials for further derivatization focused on the secondary hydroxyl groups at the C-2 and C-3 positions.