Thermotropic polyesters properties

A number of thermotropic polyester-carbonates were prepared through melt-polymerization of substituted hydroquinones and diphenyl tere-phthalate and diphenyl carbonate to have high molecular weight, with reduced viscosity in the range of 2-3. The molecular weights of the polymers can be advanced further by solid state heat-treatment, with the rate of postpolymerization depending on temperature and Concentration of catalyst. Samples of some compositions can be spun into high performance fibers and processed into self-reinforced plastics. The properties of thermotropic polyester-carbonates and polyesters were compared as fibers and plastics. 

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. 

The objectives of this paper are to disclose the less explored thermotropic polyester-carbonates and to demonstrate the nature of heat-treatment of the thermotropic polymers using polyester-carbonates as examples. In addition, the properties of thermotropic polyesters and polyester-carbonates as fibers and plastics are compared. 

Polymer Composition-Property Relationship. Tables I summarized the representative thermotropic polyester-carbonate samples prepared from BHQ/MHQ/DPT/DPC. The first series (entry 1-3) of compositions under investigation was those containing BHQ. Higher DPT/DPC ratio gave polymer with higher melting temperature. 

Table VI. Comparative Properties of Thermotropic Polyester and Polyester-carbonates...

Extrusion of thermotropic polyesters through a slit die leads to the formation of a film, as for conventional thermotropic polymers, and the film is highly oriented in the extrusion direction. The films are usually rather weak in the transverse direction, so the production of films with similar mechanical properties parallel and perpendicular to the extrusion direction requires rather special techniques. Thicker sections, such as rods and tubes, can also be extruded. 

The conformational properties of polymer molecules with mesogenic groups in the main chain were studied in the series of alkylene-aromatic thermotropic polyesters in which the length of flexible methylene parts was varied polydeca-, penta- and tetramethylene-tere-phthaloyl-di-para oxybenzoate (P-IOMTB, P-5MTB, P-4MTB). 

The primary motivation for industrial participation in the development of liquid crystalline polymers was the search for high performance tensile properties, i.e., fiber tensile strength and modulus. As it later turned out, the wholly aromatic, thermotropic polyesters were found to offer a great many more useful properties than just their now well-known tensile capabilities. 

The industrial challenge ahead will be to define and develop applications which take advantage of the unique properties of aromatic thermotropic polyesters. Already, commercial demand is growing in the fiber optic, chemical process, electrical/electronic, automotive and houseware markets, and new areas of potential application continue to emerge. 

There are several commercial thermotropic polyesters that exhibit outstanding high-temperature capabilities. These include (14,15) an increasing number of fibers and high temperature plastics. Similar to the lyotropic liquid crystalline polymers, the thermotropics exhibit unusually low viscosities because of orientation and lack of entanglement. Of course, the orientation serves to improve their mechanical properties. The chemical structure can be varied significantly. 

Thermotropic polyesters can be shaped by mouldings and film forming by thermoplastic deformation. Filaments and fibres having extraordinary mechanical properties can be produced by spinning from the melt if the polyesters do not decompose under melt condition. 

Mostly thermotropic polyesters show a nematic phase with a typical appearance that is called a marbled texture, a Schlieren texture, a threaded texture, or, a nematic droplets depending on the thickness and temperature of the polyester. Only in a few cases, they exhibit low-order smectic phases [100], which are identified through the observations of fan-shaped and broken fan textures in their LC phases. No report of higher-order smectic phases has been observed in this class of pol)nners. It is worth mentioning that nematic texture can simply be frozen into a glassy state in the case where there is no interference from the crystallization process. An intriguing property of an LC polyester is its biphase structure over... 

One of the initial motivations for developing thermotropic LCPs was the search for high-tensile-performance fibres with properties similar to those exhibited by DuPont s Kevlar , a lyotropic LCP [3]. As polymer developments continued, the wholly aromatic, thermotropic polyesters were found to offer useful properties in addition to excellent tensile capabilities, especially as engineering thermoplastics [4]. 

The design of the die also plays a certain role. It is expedient to use dies with a ratio of the channel I gth to the diameter of no less than S to increase the stability of formatitm and the mechanical properties of the fibos [65]. Fibers from thermotropic polyesters are formed on ordinary spinning equipm t for forming from a melt for die draw ratios of up to 5000% and speeds of 50-4500 m/min. 

Tables 4 and 5 show the general structures and mesomorphic characteristics of the homo- and co-polycondensate liquid crystal systems, respectively. Chiral thermotropic polyesters have been studied mainly by Blumstein and Krigbaum, almost simultaneously with, or immediately following, the first report by Strzelecki and co-workers.The latter report described also the preparation and properties of a cholesteryl end-capped polyester based on achiral components 4 -hydroxyphenyl 4-hydroxy benzoate and pimelic acid (Table 5).

Properties" of Thermotropic Polyesters Based on Mono(4-carboxyphenyl) Terephthalate (HT) or Bis(4-carboxyphenyl)... 

In the late 1980s, new fully aromatic polyester fibers were iatroduced for use ia composites and stmctural materials (18,19). In general, these materials are thermotropic Hquid crystal polymers that are melt-processible to give fibers with tensile properties and temperature resistance considerably higher than conventional polyester textile fibers. Vectran (Hoechst-Celanese and Kuraray) is a thermotropic Hquid crystal aromatic copolyester fiber composed of -hydroxyben2oic acid [99-96-7] and 6-hydroxy-2-naphthoic acid. Other fully aromatic polyester fiber composites have been iatroduced under various tradenames (19). 

Properties. As prepared, the polymer is not soluble in any known solvents below 200°C and has limited solubiUty in selected aromatics, halogenated aromatics, and heterocycHc Hquids above this temperature. The properties of Ryton staple fibers are in the range of most textile fibers and not in the range of the high tenacity or high modulus fibers such as the aramids. The density of the fiber is 1.37 g/cm which is about the same as polyester. However, its melting temperature of 285°C is intermediate between most common melt spun fibers (230—260°C) and Vectran thermotropic fiber (330°C). PPS fibers have a 7 of 83°C and a crystallinity of about 60%. 

Naphthalenedicarboxylic Acid. This dicarboxyhc acid, a potential monomer in the production of polyester fibers and plastics with superior properties (105), and of thermotropic Hquid crystal polymers (106), is manufactured by the oxidation of 2,6-dialkylnaphthalenes (107,108). 

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