OPTICAL-PROPERTIES OF CHOLESTERIC (2-HYDROXYLPROPYL) CELLULOSE (HPC) ESTERS

Acetoxypropylcellulose (APC) and propionic, n-butyric, isobutyric, val eric, isovaleric, hexanionic, and heptanionic acid esters of hydroxypr opylcellulose (HPC) (respectively PPC, BPC, iBPC, VPC, iVPC, HexPc, an d HepPc) were prepared and characterized by differential scanning calo rimetry, chromatography, polarizing microscopy, chemical methods, and spectroscopy. All these esters form thermotropic cholesteric liquid cr ystalline phases. The glass (T(g)) and clearing (T(c)) transition temp eratures were determined. The stability interval of the mesophases app ears to be greater in the case of longer-linear side chains. The mesop hases of APC, PPC, iBPC, VPC, and iVPC exhibit reflection bands in the visible region, at wavelengths that depend on temperature, moisture c ontent, size and number of substituents, and degree of polymerization (DPBAR). The pitch of the cholesteric helical structure increases with side chain length and with increasing temperature. At room temperatur e, a fingerprint-like pattern can be observed for HepPc. No reversal i n the sense of the pitch with temperature variations was observed. The pitch of BPC increases with moisture content and with decreasing valu es of the degree of esterification (DEBAR) and DPBAR. A theory for cho lesteric mesophases composed of helical rod-like species and a model o f elastic bend chain have been compared to the experimentally observed changes in the pitch with temperature and with the length of the side chain substituents (for iBPC, iVPC, BPC, PPC, and APC) and DEBAR and DPBAR (for BPC). (C) 1994 John Wiley & Sons, Inc.