A thermotropic cholesteric polymer, (acetoxypropyl)cellulose (APC) is synthesized by reacting (hydroxypropyl)cellulose and acetic anhydride. The molar etherification and esterification values, determined by chromic acid oxidation and saponification are 3.1 (+OR-) 0.3 and 1.9 (+OR-) 0.1, respectively. Fractions ranging in molar mass from 2.2 x 10('4) to 6.5 x 10('5) g mol('-1), and of the same chemical composition, are obtained by addition of n-heptane to a dilute alcoholic solution. / The phase separation behaviour of APC in dibutyl phthalate (DBP) is adequately explained by the modified lattice theories for freely-jointed chains, even when orientational interactions are neglected. The volume fraction of APC needed for anisotropic phase separation is 0.52 (+OR-) 0.02 in DBP at 25(DEGREES)C, while the isotropic phase is stable below a polymer volume fraction of 0.69 (+OR-) 0.04. Between these concentrations, the ordered phase coexists with a more dilute isotropic phase. The concentration of both phases increases with that of the solution. The molar mass of APC in the mesophase exceeds that in the isotropic phase. The critical concentration determined by optical microscopy and differential scanning calorimetry increases markedly with temperature from 25(DEGREES) to 150(DEGREES)C. This increase is attributed to a decrease in the stiffness of the chain; the axial ratio of the Kuhn segment decreases from 10.8 (+OR-) 0.8 to 5.6 (+OR-) 0.4 over the same temperature range. The axial ratio of the Kuhn segment is calculated from the limiting viscosity numbers of the APC fractions in dimethyl phthalate. / Variations in cholesteric pitch of APC with temperature and with diluent concentration are determined from the spectrophotometrically measured changes in the wavelength of light reflected by thin layers of the mesophase. The pitch increases with both DBP content and temperature for all the samples. As predicted by Kimura (1982), the temperature dependence of the pitch decreases with increasing DBP concentration. Quantitative agreement with Kimura's theory requires the use of physically reasonable dimensions for the optically active APC chain. / Analysis of the refractometric data indicate that shearing of the cholesteric mesophase transforms it into a nematic-like arrangement. The birefringence of the undiluted nematic APC is 0.013 at 26(DEGREES)C, from which a nematic layer order parameter of 0.73 (+OR-) 0.3 is calculated. The order parameter appears to be concentration independent.

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