Thermotropic mesomorphism of selected (2-hydroxypropyl)cellulose derivatives

The thermotropic mesomorphism of some cellulose derivatives (CD) based on t he (2-hydroxypropyl)cellulose (HPC) was investigated. Three types of deriva tives: two esters (PPC, HxPC) and cyanoethyl derivative (CEPC) were prepare d. The X-ray diffraction patterns of CDs were compared with the differentia l scanning calorimetry, thermooptical, and mechanical measurements within a broad range of the temperature. Two relaxation processes alpha(a) and alph a(m), observed in the solid state of HPC, are also exhibited by all CDs, ho wever, at lower temperatures. The alpha(m) relaxations, which indicate the transition from frozen anisotropic phase to mobile liquid crystalline (LC)p hase, are shifted towards the lower temperatures with a corresponding incre ase in the d-spacing of the poly(saccharide) main chains of CDs (as seen in the X-ray measurements), The transition temperature to isotropic phase T-n i as well as glass transition temperature T-g (alpha(a)-relaxation) of the investigated CDs depend on the interactions between the lipcophilic side ch ains and the hydrophilic poly(saccharide) main chains of CDs. These interac tions are determined by the length and polarity of the lipophilic side chai ns. The observed changes in the transition temperature to isotropic phase T -ni for CDs is consistent with the assumption that LC-organization of the p oly(saccharide) main chains is stabilized by the lipophilic side-chains sys tem. A significant increase in the length of the lipophilic side chains lea ds to nonlinear conformation, thus reducing the influence of van der Vaals forces, and consequently lowering T-ni. The polymer with high polarity lipo philic side chains (CEPC) exhibits higher T-ni in comparison to the ester d erivative PPC with the same length of the side chains but having lower pola rity. The stabilization effect of the lipophilic side-chains system on the LC-organization of the poly(saccharide) main chains is determined by the dy namic balance between length and polarity of the lipophilic side-chains sys tem. (C) 2000 John Wiley & Sons, Inc.