CONFORMATIONAL ANALYSIS OF REGIO-SELECTIVELY SUBSTITUTED CELLULOSE ESTERS

Abstract

The conformation of two regio-selectively substituted cellulose esters, cellulose propionate diacetate (CPDA, 2, 3-di-O-acetyl-6-O-propionyl cellulose) and cellulose acetate dipropionate (CADP, 6-0-acetyl-2, 3-di-O-propionyl cellulose), has been investigated through X-ray and electron diffraction methods. CPDA crystallizes forming an orthorhombic unit cell with dimensions a=1.358nm, b=2.221nm and c (fiber axis)=1.044nm. The unit cell of CPDA has three sets of twofold screw axes parallel to the three orthogonal crystallographic axes, and the space group of CPDA is most likely P2₁2₁2₁. On the other hand, CADP crystallizes as a monoclinic unit cell with dimensions a=1.108nm, b=1.536nm, c (fiber axis)=1.500nm and γ=90°. CADP has a threefold screw symmetry along the molecular axis as does cellulose tripropionate (CTP). The space group is P2₁ with b as the unique axis.