Polyesters, liquid crystalline thermal properties

The mesophases formed by liquid crystalline (LC) polymers are well known to impart strength, toughness, and thermal stability to plastics and fibers (1-5). While LC polymers have been widely studied, their potential utility as coatings binders seems to have been overlooked. Among the very few reports that may describe LC polymers in coatings are patents claiming that -hydroxybenzoic acid (PHBA), a monomer commonly used in LC polymers, enhances the properties of polyester powder coatings (6-9). 

Griffin, A. C. and Havens, S. J. Mesogenic polymers. III. Thermal properties and synthesis of three homologous series of thermotropic liquid crystalline backbone polyesters. J. Polymer Sci., Polymer Phys. Ed. 19, 951 (1981)... 

Thermotropic polyesters derived from unsubstituted aromatic diols and diacids usually have melting points which approach or exceed the thermal decomposition point. Thus it is reasonable to expect that some modification in molecular structure would be required to render them melt-processable, even though some adverse effects on liquid crystallinity and mechanical properties of the polymers would result. 

Organometallic polyurethanes containing backbone polyether units have been reported.184,185 The incorporation of ferrocenyl segments into the backbone of polyurethanes enhanced thermal stability.186 There have been a number of studies on the incorporation of ferrocenyl units into the backbone of polyesters 101.187-191 A number of polymers of this class exhibited liquid crystalline properties.189-192 The thermal stability and glass transition temperatures of these polymers decreased with an increase in the length of the alkyl chains. 

The first verification of the theoretical predictions of Onsager and of Flory that rod-like molecular chains might exhibit liquid-crystalline properties (see section 1.3.2 and chapter 12) was obtained in the 1960s and fibres from para-aramid polymers were commercialised under the name of Kevlar in 1970. These materials are very stiff and have excellent thermal stability many other materials of this class of rigid main-chain liquid-crystal polymers have been developed. They cannot, however, be processed by the more conventional processing techniques and this led to the development in the 1980s of another group of liquid-crystal polymers, the thermoplastic co-polyesters. 

Thermal Properties and Synthesis of Three Homologous Series of Thermotropic Liquid Crystalline "Backbone" Polyesters, J.Polym.Sci.Polym.Phys.Ed., 19 951 (1981). 

The synthesis and some thermal properties of three series of block copolymers comprising both main-chain and side-chain liquid-crystalline (LC) blocks in the same macromolecular structure are described. The former block is a semiflexible LC polyester (block B), and the latter is an LC polymethacrylate (block A) containing a variously substituted mesogenic unit. The two structurally different blocks were partly phase-separated within the glassy and LC states and underwent distinct phase transitions. Significant deviations of the transition enthalpies relative to those of the corresponding homopolymers suggest the occurrence of a more or less diffuse interphase which may depend on the nature of the mesophase formed. 

Ferrocene was the starting point for organometallic chemistry nearly four decades ago and is still today one of the most studied and versatile organometallic building blocks. Ferrocene has been incorporated in polymeric systems to alter bulk properties of the material. Ferrocene possesses excellent thermal and photochemical stability and can also protect polymeric systems from photodegradation. In addition, the ferrocene building block has been used in conducting polymers and in main chain liquid crystalline polyesters. ... 

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