Polyester thermotropic

In 1975, the synthesis of the first main-chain thermotropic polymers, three polyesters of 4,4 -dihydroxy-a,a -dimethylbenzalazine with 6, 8, and 10 methylene groups in the aHphatic chain, was reported (2). Shortly thereafter, at the Tennessee Eastman Co. thermotropic polyesters were synthesized by the acidolysis of poly(ethylene terephthalate) by/ -acetoxybenzoic acid (3). Copolymer compositions that contained 40—70 mol % of the oxybenzoyl unit formed anisotropic, turbid melts which were easily oriented. 

Polybibenzoates are a kind of thermotropic polyesters obtained by polycondensation of 4,4 -biphenyldicar-boxylic acid (p,p -bibenzoic acid) with a diol. These polyesters contain the biphenyl group, which is one of the simplest mesogens. They are synthesized by melt transesterification of the dimethyl or diethyl ester of p,p -bibenzoic acid and the corresponding diol, using a titanium compound as catalyst, according to the following scheme ... 

Figure 16 Loss tangent (tanS) at 3 Hz, as a function of temperature for a series of main chain thermotropic polyesters having oxyethylene spacers.

This method is attractive, since polymers with good thermal stability are obtained, especially with aryl or halogeno substituents.165 174 Moreover, a number of substituted polyester LCPs exhibit solubility in common organic solvents, thus facilitating their structural characterization. However, the cost of starting monomers has hampered the commercial development of thermotropic polyesters based on substituted monomers. 

Liquid crystalline polymers (LCPs), 49 melt rheology of, 52 Liquid crystalline (LC) state, 48-49 Liquid crystalline thermotropic polyesters, 20... 

In order to make polymers behave as liquid crystals it is necessary to introduce some structural rigidity. A typical polymer which has the required rigidity is poly(phenylenetetraphthalamide) (10.7). This material belongs to a class of polymer known as the aramids. Other liquid crystalline polymers are the thermotropic polyesters derived from /7-hydroxybenzoic acid, p, p -biphenol and terephthalic acid (10.8). 

Thermotropic liquid crystals, 15 86-98 bent-core, 15 98 discotic phases of, 15 96 frustrated phases of, 15 94-96 metallomesogens, 15 97 nematic liquid crystals, 15 86-92 smectic liquid crystals, 15 92-94 Thermotropic mesophases, 20 79 Thermotropic polycarbonates, 19 804 Thermotropic polyesters, liquid-crystalline, 20 34... 

Warner, S. B, and Jaffe, M. Quiescent crystallization in thermotropic polyesters. J. Crystal Growth 48, 184 (1980)... 

Jo, B. W. and Lenz, R. W. Liquid crystalline polymers, 7, thermotropic polyesters with main chain phenyl- 1,4-phenylene, 4,4 -biphenylene, and 1,1 -binaphthyl-4,4 -ylene units. Makromol. Chem. Rapid Commun. 3, 23 (1982)... 

Most recently Horie et al. [134,135] have used x-ray and fluorescence methods to investigate the microstructure of the 4,4 -dialkoxy-containing thermotropic polyester, 68. This polyester is crystalline and enters a smectic H (SH)... 

As known [7,8], the thermal expansion coefficient is reduced in the direction of the molecular orientation obtained by stretching of a thermoplastic polymer during or directly after its processing. In special cases thermotropic polyesters are applied to facilitate the process of molecular orientation [9]. However, in all these cases solidification must proceed either by cooling down from the melt or by evaporation of the solvent. These relatively slow processes are not suited for on-line optical fiber coating. 

Figure 11.13 Viscosity (a) and first normal stress difference (b) versus shear rate for OQO(phenylsulf-onyl)10—thermotropic polyester...

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. 

Although studies concerning main chain liquid crystalline polymers were originated by Onsager (la) and Ishihara (lb) in the late 1940 s, extensive work in this field did not really begin until the early 1970 s. Jackson and Kuhfuss (2) reported the first thermotropic polyester by modifying polyethylene terephthalate with various amounts of p-hydroxybenzoic acid (HBA). They found that the copolyester with HBA content of at least 35 mole % have opaque melts. Subsequent studies in the area of aromatic polyesters by various authors resulted in a large number of patents and publication. (3.) These polymers were all derived from unsubstituted and... 

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 preparations of thermotropic polyester-amides from comparable monomers as those of thermotropic polyesters were a logical extension of a series of studies in thermotropic polyesters and lyotropic polyamides. (4.) However the inclusion of carbonates had rarely been explored.(5) Because of the flexibility of carbonate compared to substituted aromatic rings, it should be an even more effective approach in lowering the melting temperatures of the unmodified all aromatic polyesters into the easily processable range. 

The solid-state heat-treatments of thermotropic polyester fibers to obtain fibers with high tenacity were reported before. (6.) However, the nature of this process was not clear when we commenced this study. 

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. 

The solid-state heat-treatments of thermotropic polyester-carbonates in fine pieces were conducted in a Blue M high temperature inert gas oven (Model AGC170EMTI). These samples were treated at different temperatures, for different period of time. The treated samples were characterized further by DSC and viscosity measurements. The treated samples were used in fiber-spining and plastic processing studies.17.81... 

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 I. Thermotropic Polyester-carbonates Derived From BHQ/MHQ/DPT/DPC...

Thermotropic polyester-carbonates containing only HQ and RO have melting points near thermal decomposition. However when MHQ and BHQ were included in the composi-tions, the melting temperatures were depressed somewhat close to 300°C as shown in Table II. 

Table II. Thermotropic Polyester-carbonates Derived from HQ/RO/BHQ/MHQ and DPT/DPC (molar ratio 50/50)...

The Effect of Solid-State Heat-Treatment on Molecular weight and Crystallinity. Solid-state heat-treatment had been done before on thermotropic polyester fiber to obtain advancement in tenacity (6) and on polyester-carbonate samples to get advancement in molecular weight.(H) It was understood that post polymerization and thermal annealing occurred on thermotropic polymers at solid state, as the term post-polymerization has been used interchangeably for solid-state heat-treatment. 

The objectives of carrying out solid-state heat-treatments of thermotropic polyester-carbonates were twofold. One, to study the heat-treatment phenomena. Two, to prepare samples of higher molecular weight for processing studies into high performance fibers and plastics if heat-treatment did cause advances in molecular weight. 

Because high molecular weight thermotropic polyester-carbonate products can be obtained by this process, the difficulty in obtaining high molecular weight materials directly from melt-polymerization is circumvented. 

Correlation of Transition Temperatures with Molecular Weight. Table V shows the Tin s and Tg s of thermotropic polyester-carbonates of higher molecular weight after heat-treatments. In all three series, the Tm advanced as the molecular weight increased, but it reached a asymptotic figure. The Tg s stayed relatively constant. The Tm vs reduced viscosity were plotted in Figure 1. 

Thermotropic Polvester-carbonates as Fibers and Self-reinforced Plastics. The major objective of our study in thermotropic polyester-carbonates was to evaluate... 

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