Cholesterol-containing polymers

This was qualitatively shown in investigations of conformational behaviour and intramolecular mobility (IMM) of cholesterol-containing polymers in dilute solutions as of a function of solvent quality 134-136,185-l88) and temperature. Polarization luminescence provides one of the most fruitful methods for the evaluation of IMM l75,176). The method permits to get direct information about rotational mobility of the macromolecule as a whole, as well as about the mobility of the main chains and side branches. This is achieved via the attachment to macromolecules of so called luminescent markers (LM) — anthracylacyloxymethane groups in the case reported. Below are shown the chain fragments with LM which give information on the mobility of main chains (LM-1) and of side groups (LM-2) ... 

Table 17. Values of relaxation times xw) xraal and xsid<. for cholesterol containing polymers PChMA-n and PChMO-n in different solvents at 25 °C 135-136.iss-is )...

Table 17 presents relaxation time values characterizing the intramolecular mobility of various fragments of cholesterol-containing polymers with LM in various solvents9. As is seen, the values of relaxation times measured for the same polymer in various solvents differ significantly, which reflects the specificity of conformational state and intramolecular organization. 

The variation of the temperature interval of structure formation is also accounted for by the effect of side chain mobility on mesophase nucleation. The solutions of cholesterol-containing polymers with longer spacer groups have to be cooled further for mesophase nuclei to be formed. For instance, in a series of PChMO-n polymers the interval of structure formation is for PChMO-14 — 308-313 K, for PChMO-lO — 323-333 K and for PChMO-5 the internal structure is formed at even higher temperatures 187). 

The study of the relaxation of dipole polarization, as well as of the dipole moments of cholesterol-containing polymers and copolymers128 "134,191 193) presents a sensitive confirmation for the existence of intramolecular structuration of mesogenic groups. This is indicated for instance, by the high values of relaxation times (Tjj p) and activation energy (EJ p) of dipole polarization, as well as by the large values of correlation parameter g, which is a relative measure of the internal rotational retardation in macromolecules (Table 18). 

V.P.Shibaev, N.A.Plate, and Ya.S.Freidzon, Thermotropic liquid crystalline polymers. Cholesterol containing polymers and copolymers, J.Polym.Sci., Polym.Chem.Ed. 17 1655 (1979). 

V.P.Shibaev, Ya.S.Freidzon, and N.A.Plate, Liquid crystal cholesterol-containing polymers, Dokl.Akad.Nauk SSSR 227 1412 (1976). 

N.A. Plate, Condition of Formation of Liquid Crystalline State in Cholesterol Containing Polymers , ill Advances in Liquid Crystal Research and Applications, L. Bata, Ed., Pergamon Press, Oxford, Akade-mai Kiada, Budapest, 899 (1980). 

Another example demonstrates the effect of formation of a network of hydrogen bonds between linkages on the phase transition temperatures and molecular mobility of cholesterol-containing polymers ... 

As the results reported above show, all of the cholesterol-containing polymers form smectic mesophases and the cholesteric mesophase is only observed in polymers 2.2, 2.3, and 2.4 (see Table 7.4) in a narrow temperature range. 

Fig. 7.10. Diagrams of the packing of the side groups of macromolecules of cholesterol-containing polymers in the 5 phase (a-c) and arrangement of the layers in the 5 phase (d) and the cholesteric phase (e) a) parallel bilayer packing b) antiparallel monolayer packing c) inteimediate packing with partial overlap of the side groups.

The chain structure of the macromolecules of LC polymers results in the appearance of a major new type of structures an intramolecular mesophase, i.e., a mesophase formed on the level of one macromolecule. This is especially clearly manifested in cholesterol-containing polymers [35-37] ... 

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