Thermotropic main-chain LCPs

Materials with totally new property combinations may be achieved by blending two or more polymers together. Through blending of thermotropic main-chain LCPs with engineering thermoplastics, the highly ordered fibrous structure and good properties of LCPs can be transferred to the more flexible matrix polymer. LCPs are blended with thermoplastics mainly in order to reinforce the matrix polymer or to improve its dimensional stability, but LCP addition may modify several... 

LC polyesters belong to the class of thermotropic main-chain LCPs, which also comprises polymers such as polycarbonates, polyethers, polyphenylenes, polyester-imides, polymers containing azo- or azo V-oxide linking groups, some cellulose derivatives, and polypeptides such as po 1 y (y - be n zy 1 -1. - g 1 u tamate). Both from the academic and industrial points of view, polyesters are by far the most important representatives of this class of polymers. 

RESEARCH FOCUS OF THERMOTROPIC MAIN-CHAIN LCPs... 

SINCE the discovery of liquid crystalline phenomenon for low molecular weight liquid crystals (LMWLCs) more than 100 years ago, anisotropic ordering behaviors of liquid crystals (LCs) have been of considerable interest to academe [1-8], In the 1950s, Hory postulated the lattice model for various problems in LC systems and theoretically predicted the liquid crystallinity for certain polymers [1-3], As predicted by the Hory theory, DuPont scientists synthesized lyotropic LCPs made of rigid wholly aromatic polyamide. Later, Amoco, Eastman-Kodak, and Celanese commercialized a series of thermotropic main-chain LCPs [2]. Thermotropic LCPs have a unique combination of properties from both liquid crystalline and conventional thermoplastic states, such as melt processibility, high mechanical properties, low moisture take-up, and excellent thermal and chemical resistance. Aromatic main-chain LCPs are the most important class of thermotropic LCPs developed for structural applications [2,4-7]. Because they have wide applications in high value-added electronics and composites, both academia and industry have carried out comprehensive research and development. 

Thermotropic main-chain LCPs have unique combination of properties from both LC and conventional thermoplastic states these include melt processibil-ity, high mechanical properties, low moisture take-up, and excellent thermal and chemical resistance. With the successful development of these LCPs and recognition of their imique properties, comprehensive research and development have been carried out by both academia and industry (3,5,9,11,14,16-26). Among various R D directions, the synthesis of new LCPs (3,14,16,17,19-22,24,26), their rheology behavior (27-31), morphology, compatibility and processing of LCPs and blends (32-34) have received most attention. 

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%... 

Rheological Behavior of Thermotropic Main-Chain LCPs... 

Growth of Shear Stress and First Normal Stress Difference During Transient Shear Startup of Thermotropic Main-Chain LCPs... 

Evolution of Dynamic Moduli of Thermotropic Main-Chain LCPs Upon Cessation of Shear Flow... 

Low-molecular-weight liquid-crystalline compounds have been known for about 100 years. However, main chain liquid crystal polymers (MCLCPs) have attained prominence only in the last 15 years. In 1956 Flory predicted lyotropic behaviour and this theoretical prediction was well demonstrated in the synthetic polymer area with the discovery by Kwolek of the aramids, e.g. poly(/ -phenyleneterephthamide). This led to interest in thermotropic main chain LCPs and, although aromatic polyesters which are thermotropic were described during this period in patents issued to and Carborundum Co., their liquid-crystalline... 

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