Naphthalene thermotropic

Xue Y, Kara M, Yoon HN (1998) Ionic naphthalene thermotropic copolyesters divalent salts and tensile mechanical properties. Macromolecules 31 7806-7813... 

Fig. 5.72 A polarized light micrograph of a sectioned nematic naphthalene thermotropic polymer (NTP) reveals a schlieren texture.

Main Chain LC Polymers. New thermotropic copolyesters with either random or ordered mesogenic sequences have been reported with a wide range of mesophase behaviors. Recent developments in this field have included the use of naphthalene, stilbene and related structures in addition to the traditional phenylene groups to produce the required rigid main chain, and these are described in chapters by Jin, Jackson and Morris, and Skovby et al. Efforts have been undertaken to control transition temperatures and solubility through the use of either substituents or changes in the monomer sequence distribution. Successful application of these efforts have led to the commercialization of several thermotropic aromatic copolyesters (23.24). 

Hydroquinone(HQ) or a naphthalenediol in the above reactions can be replaced with other diols such as biphenols and bisphenols. In the same manner, other dicarboxylic acid such as cyclohexane dicarboxylic acid, isophthalic acid, naphthalene dicarboxylic acids can be used in place of terephthalic acid. Of course, these substitutes should not destroy the linearity of the polymer chains if one is to obtain thermotropic compositions. 6-Hydroxy-2-naphthoic acid is a substitute for 4-hydroxybenzoic acid in Reactions 18 and 19. 

The next step of the investigation deals with the study of the behaviour of still larger molecules, namely mono and dimethyl naphthalenes. It was observed that the smaller naphthalenes could diffuse into the tube, while the larger naphthalenes is unable to enter the mouth of the tube. 2,6-dimethyl naphthalene (DMN) is a valuable intermediate for the preparation of monomer to produce thermotropic liquid crystalline polymers, altho-... 

Since 1991 Kricheldorf has published many other articles on liquid crystal polyesterimides. These include two series of thermotropic copoly(esterimides) derived from N-(3 -hydroxyphenyl)trimellitimide and 4-hydroxybenzoic acid or 6-hydroxy-2-naphthoic acid, in which the critical compositions for obtaining mesophases were discovered by varying monomer levels [34]. A series of homopoly(esterimide)s were synthesised from N-(4-carboxyphenyl)trimelliti-mide and various diacetylated linked diphenols. When the diphenol contained an ether or carbonyl linking group, mobile nematic phases were observed. Various naphthalene diols were also employed instead of the diphenol, but only the 2,7-dihydroxy naphthalene produced a nematic phase [35]. 

A new class of diamine spacer was synthesised from a,co-diaminoalkanes and 4-nitrophthalic anhydride the resulting a, -bis(4-aminophthalimido)alkanes were polycondensed with one of the following acid chlorides terephthaloylchlo-ride, 2-phenylthioterephthaloylchloride, naphthalene-2,6-dicarboxylic acid or 4,4 -biphenyldicarboxylic acid chloride [40]. Thermotropic behaviour was con-... 

Table 4.4 Processing parameters and mechanical properties for injection molded thermotropic copolyester of 60 mol% p-acetoxybenzoic acid, 20 mol% terephthalic acid and 20 mol% naphthalene. (Reprinted with permission from [21], copyright 1983 Society of Plastics Engineers, Inc.)...

As illustrated in Figures 4(b) and 4(c), the thermotropic main-chain LC polymers can be obtained from polymers that contain only rigid-rod units or a combination of rigid-rod and flexible units. The main stmctural elements of such linear polymers are composed of benzene or naphthalene rings, or different heterocyclic fragments collmearly linked to one another by such groups as... 

DuPont workers have described (7) a wide variety of tractabilizing molecules and the thermotropic polyesters derived therefrom. Their research has focused for the most part on ring substituted monomers such as chloro, methyl or phenyl substituted hydroquinone and swivel" or linked ring molecules, examples of which are 3,4 or 4,4 functionally (hydroxy or carboxy) disubstituted diphenyl ether, sulfide or ketone monomers. Use of the parallel offset or crankshaft" geometry provided by 2,6 functionally disubstituted naphthalene monomers has been the major thrust of the Celanese Corporation development of easily processed, high performance wholly aromatic thermotropic polyesters. 

Specifically, Celanese has defined families of thermotropic polyesters derived from 2,6-naphthalene dicarboxylic acid (NOA), 2,6-dihydroxynaph-thalene (DHN) or 6-hydroxy-2-naphthoic acid (HNA). Indeed, the Vectra LCP engineering resins of Celanese Corporation are based on these monomers. 

Composition/Tm Relationships of Naphthalene Derived Thermotropic Polyesters... 

Thermotropic aromatic copolyester fibers are produced by melt spinning since the combination of an aromatic backbone and flexible segments results in an LCP which can be melt processed. Copolyesters, such as p-hydroxybenzoic add (PHBA) modified poly(ethylene terephthalate) (PET), 60/40 PHBA/PET (X7G) polymers, have been produced by the Tennessee Eastman Company [425-427]. Other melt processable nematic thermotropic LCPs (TLCP), based on combinations of 2,6-naphthalene dicarboxylic add (NDA), 2,6-dihydroxynaphthalene (DHN) and 6-hydroxy-2-naphthoic acid (HNA), and referred to as Vectra LCP resins, have been conunercialized (trademark by Hoechst Celanese Corporation [406]). 

The aromatic semiflexible polyesters can be formed by varying the dicarboxylic multi phenyl acid structure (naphthalene and diphenol) and non-linear aromatic diol (3,4 -dihydroxybenzophenone). 3,4 -dihydroxybenzophenone can be synthesized from 4-methoxy bromobenzene and m-methoxybenzonitrile via multistep reaction, which can be condensed with respective diacid chloride in o-dichlorobenzene at reflux temperature [43]. It is well known that dimethyl siloxane spacer can make a flexible/semiflexible LC polymer. Thermotropic flexible liquid-crystalline main chain polyesters... 

Among melt-spun fibers, those based on thermotropic liquid-crystalline melts have the highest strength and rigidity reported to date, and appear comparable to polyamides spun from lyotropic liquid-crystalline solutions. This was a very active field of research in the 1970s and later, and many comonomers have been reported. Obviously, these compositions must contain three components at a minimum, but many have four or five components. Some frequently used constituents, in addition to those mentioned above, are 2,6-naphthalene-dicarboxylic acid, hydro-quinone, 4,4 -biphenol, isophthalic acid, and 4,4 -dihydroxy-diphenyl ether. 

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