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Chemistry International
Vol. 24, No. 4
July 2002


Highlights from Pure and Applied Chemistry

Definitions of Basic Terms Relating to Polymer Liquid Crystals (IUPAC Recommendations 2001)

by M. Barón and R. F. T. Stepto
Pure and Applied Chemistry, Vol. 74, No. 3, pp. 493-509 (2002)

This document provides definitions of the basic terms that are used in the field of liquid-crystalline polymers. It is the result of extensive discussions and evaluations by the former Commission of Macromolecular Nomenclature. It was produced with the cooperation and advice of representatives of the International Liquid Crystal Society.

The recommendations concern terminology relating to the structure of liquid-crystalline polymers. In view of the rapid growth of the field, the terms defined have been restricted to those presently in common usage. They have been selected from the recently published comprehensive document "Definitions of Basic Terms Relating to Low-Molar-Mass and Polymer Liquid Crystals" [Pure and Applied Chemistry, 73(5) 845-895 (2001)].

The recommendations are intended to form a readily usable guide for the reader interested in the structural description of polymer liquid crystals. The more comprehensive document (vide supra) should be used for terminology associated with mesophases and the optical textures and physical characteristics of liquid-crystalline materials. The numbering of terms in the document is consistent within itself and cross-references are made to the numbering of terms in the more comprehensive document.

The document contains the following sections: introduction, general definitions, and liquid-crystalline polymers. It also contains a reference list and an alphabetical index of terms that serves as a subject index. The general definitions section gives the definitions of 27 principal terms and some subsidiary terms concerned mainly with the types of mesophase and types of mesogen; one example is reproduced at right. The section dealing specifically with liquid-crystalline polymers defines 12 terms and gives 21 structural examples.

2.7 [2.10] mesogenic group, mesogenic unit, mesogenic moiety

A part of a molecule or macromolecule endowed with sufficient anisotropy in both attractive and repulsive forces to contribute strongly to mesophase or, in particular, LC mesophase formation in low-molar-mass and polymeric substances.

1."Mesogenic "is an adjective that in the present document applies to molecular moieties that are structurally compatible with the formation of LC phases by the molecular system in which they exist.
2. Mesogenic groups occur in both low-molar-mass and polymeric compounds.
3. A majority of mesogenic groups consists of rigid rodor disc-like molecular moieties.


where X and Y are covalent bonds or linking units such as:






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