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Macromolecular mesomorphism

For the purpose of discussing mesophase formation in polymers it is conveiuent to partition the polymers into two categories and introduce abbreviations that refer to these categories. Polymerized liquid crystals, here abbreviated PLCs, are derived from known, low molecular weight monomer liquid crystals (MLCs) that contain polymerizable functionality (e.g. vinyl units). We designate liquid-crystalline polymers (LCPs) to be semiflexible, linear polymers that are structurally related to conventional engineering thermoplastics, i.e. polymers derived from poly(ester)s, poly(amide)s, poly(imide)s, etc. We will examine the attributes of polymerized liquid crystals first, stressing the similarities between their properties and those of MLCs. [Pg.353]

Inserting a spacer chain into the backbone of a MCPLC yields a regular alternating copolymer . .. core-spacer-core-spacer This MCPLC topology exhibits [Pg.355]

Another example of the role of covalent connectivity of cores is suggested by the fact that the temperature range of mesophase stability for a particular mesogen can be increased by incorporating it into a polymer. There are even instances in which a particular core that does not exhibit mesomorphism as a monomer will become mesomorphic when it is polymerized [64]. Presumably in such situations the spatial restrictions imposed on such nonmesogenic cores when they are covalently linked together in the polymer allow them to achieve the required relative orientations for mesomorphism over some temperature range. [Pg.356]

Polymerization of MLCs introduces covalent connectivity between meso-gens and thereby introduces orientational and translational restrictions into the [Pg.356]

Viscoelasticity is perhaps the most ubiquitous characteristic of high molecular weight polymers at temperatures above Tg. Here we consider the implications of coupling rubber elasticity and mesomorphism via synthesizing covalent networks from conventional elastomers (siloxanes, isoprenes, etc.) and typical MLC mesogenic cores such networks are thermotropic PLCs. At low levels of crosslink densities in the PLC network, there is no appreciable change in the transition temperatures (Tg, Td, etc.) from those of the uncross-linked PLC (and its ancestral MLC) [68]. Below Td, rather modest mechanical deformations (extension ratio A 1.5) may convert an initial random and disclination-ridden texture into a [Pg.358]


The macromolecular nature provides an interesting feature of LC polymeric cholesterics, namely the possibility of obtaining monochromic films. Thus for polymeric liquid crystals the helix pitch is practically not altered with temperature below Tg, when a cholesteric phase is frozen in a glassy matrix (Fig. 23a). This implies that fast cooling of polymeric films from a mesomorphic state (shown with arrows) fixes their optical properties, which makes it possible to use them at ordinary temperatures as selective monochromic reflectors. On the other hand, such polymeric films display the extraordinary polarizing properties of cholesterics, i.e. the different absorption... [Pg.224]

The study by low-angle X-ray diffraction of AB and ABA block copolymers of styrene and isoprene has allowed Gallot et al.1S9-166) to demonstrate that the existence of mesomorphic structures is a quite general property of block copolymers this property is related to the incompatibility of the macromolecular chains11 and the presence in the molecule of a crystallizable (e.g. poly(ethylene oxide)) block is not the condition that governs the formation of mesomorphic structures. [Pg.126]

Molecular theories of mesomorphic polymers may serve to give a better insight into the mechanisms involved in the formation of ordered phases in macromolecular liquids. The importance of parameters such as chain length, chain flexibility... can be explored and the results used in synthesis of new systems with well-defined characteristics. Studies of the influence of solvents on the mesomorphic phase transition and the possibility of ordering by external fields (electric, magnetic, flow) are problems of technological in-ter>est in the spinning of fibers and in the formation of new polymer blends. [Pg.109]

The chain flexibility can be a function of temperature or solvent concentration and possible conformational changes in mesomorphic polymers have been both predicted by theoretical calculations and observed in experiment. The elastic chain model takes intrachain interactions into account in a very simple way but neglects fine details of macromolecular structure. We present some results within this model for liquid crystalline behaviour and finally... [Pg.109]

Generally speaking, the morphological features of the solid state of LCPs are derived from the forms of macromolecular organization exhibited by mesomorphic... [Pg.374]


See other pages where Macromolecular mesomorphism is mentioned: [Pg.353]    [Pg.353]    [Pg.355]    [Pg.357]    [Pg.359]    [Pg.361]    [Pg.363]    [Pg.353]    [Pg.353]    [Pg.355]    [Pg.357]    [Pg.359]    [Pg.361]    [Pg.363]    [Pg.142]    [Pg.126]    [Pg.308]    [Pg.238]    [Pg.56]    [Pg.269]    [Pg.67]    [Pg.13]    [Pg.144]    [Pg.138]    [Pg.164]    [Pg.316]    [Pg.317]    [Pg.318]    [Pg.315]    [Pg.27]    [Pg.32]   


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