Polymers, liquid crystalline polyester type

The above definitions have been suggested by Karger-Kocsis and Fakirov [13] and they will be followed strictly in the current text. This means that the commercially available and widely cited [17-20] as SPC type of materials based on the homopolymer polypropylene (PP) (as reinforcement) and the random copolymer of PP [usually with polyethylene (PE)] (as a matrix) do not belong to SPCs because the two components are chemically different, i.e., such composites belong to the category of polymer-polymer composites. The same holds for thermoplastic polyester copolymers reinforced with poly(ethylene terephthalate) (PET) or with liquid crystalline polyester. Details about these PPCs can be foimd in the review by Matabolaet al. [17] as well as in a very recent review of Karger-Kocsis and Barany [20]. 

Thermotropic liquid crystalline polymers, like polyesters containing mesogenic units on the main chain, may not be described by the wormlike chain model (cf. Sect. 1.2). The present article does not consider this type of polymers. 

Iimura, K., Koide, N., Ohta, R. and Takeda, M. Synthesis of thermotropic liquid crystalline polymers, 1, azoxy and azo-type polyesters. Makromol. Chemie 182, 2563 (1981)... 

It was, however, observed that such systems under appropriate conditions of concentration, solvent, molecular weight, temperature, etc. form a liquid crystalline solution. Perhaps a little digression is in order here to say a few words about liquid crystals. A liquid crystal has a structure intermediate between a three-dimensionally ordered crystal and a disordered isotropic liquid. There are two main classes of liquid crystals lyotropic and thermotropic. Lyotropic liquid crystals are obtained from low viscosity polymer solutions in a critical concentration range while thermotropic liquid crystals are obtained from polymer melts where a low viscosity phase forms over a certain temperature range. Aromatic polyamides and aramid type fibers are lyotropic liquid crystal polymers. These polymers have a melting point that is high and close to their decomposition temperature. One must therefore spin these from a solution in an appropriate solvent such as sulfuric acid. Aromatic polyesters, on the other hand, are thermotropic liquid crystal polymers. These can be injection molded, extruded or melt spun. 

Ringsdorf s research group have prepared novel types of rigid-rod polyesters and polyamides 56 with a disc-like mesogen in tte mainchain [75]. Most polymers with six lateral substituents appear to be thermotropic liquid crystals. Polyamides with Z = H and having four substituents on the diamine component are not liquid crystalline. The two substituents on the diacid component seem to contribute to decrease further the intermolecular hydrogen bonding. 

LlOl Luperox 101 (2,5-di-(t-butylperoxy)-2,5-dimethylhexane) L130 Luperox 130 (2,5-dimethyl-2,5-di-(t-butylperoxy) hexyne-3) LCP Liquid crystalline polymer(s) (polyester-type unless noted)... 

A lot of molecular structures give rise to thermotropic liquid crystallinity, but only the aromatic ester type polymers and copolymers are successfully prepared as structural materials. Aromatic polyesters can be classified into three types based on their molecular composition and thermomechanical property [74]. 

The commercial polymers used in the study are characterized in Table 1. The polypropylenes PP1-PP5 were homopolymers exhibiting different melt viscosities (see Fig. 1) supplied by Neste Chemicals. Liquid-crystalline polymer 1 (LCPl) (Vectra A950 by Hoechst Celanese) is a totally aromatic polyester-type thermotropic main-chain LCP copolymer based on p-hydroxybenzoic acid (HBA) and 6-hydroxy-2-naphthoic acid (HNA). Liquid-crystalline polymer 2 (LCP2) (Rodrun LC-3000 by Unitika Ltd) is a more flexible thermotropic main-chain LCP copolyester consisting of 60%... 

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