Poly -liquid-crystalline blends

PEEK showed extreme thermal stability, but when blended with a liquid crystalline poly(hydroxybenzoic/naphthoic acid) copolymer, LCP, there is a measurable reduction in this property [Mehta and Isayev, 1991]. 

One of the basic problems confronting molecular composites is the difficulty of finding miscible combinations of rigid rod polymers with flexible chain polymers. Poly(p-phenylene benzobisthiazole)/poly(-2,5(6)-benzimidazole block copolymers have been reported by Tsai et al. [1985] and are noted to exhibit better processability and mechanical properties than the simple blends of the block copolymer constituents. Chang and Lee [1993] prepared poly(p-benzamide)/Pl block copolymers and reported on the liquid crystalline behavior. Such approaches would appear to have future implications. As an example PA e.g., PA-66) block copolymers with rigid rod polyamides could be prepared and used in blends with PA-66 to yield the desired molecular composite. 

P. C. Yung and H. C. Linstid, 111. Blends of liquid crystalline polymers and poly(arylene sulfide)s having reduced viscosities. US Patent 5418 281, assigned to Hoechst Celanese Corporation (Somerville, NJ), May 23, 1995. 

W. Grasser, H.-W. Schmidt, and R. Giesa. Fibers spun from poly(ethyl-ene terephthalate) blended with a thermotropic liquid crystalline copolyester with non-coplanar biphenylene units. Polymer, 42(21) 8517-8527, October 2001. 

Gopakumar et al. [10] reported the in situ compatibilization of poly(phenylene sulfide) (PPS)/wholly aromatic thermotropic liquid crystalline polymer (TLCP) Vectra A950 blends by reactive extrusion. The authors prepared the in situ compatibilized PPS/TLCP blends in a twin-screw extruder by reactive blending of PPS and TLCP in the presence of dicarboxyl-terminated poly(phenylene sulfide) (DCTPPS). Block copolymer was formed during reactive blending, by transesterification reaction between carboxyl... 

Gopakumar, T. G., Ronrathnam, S., Lele, A., Rajan, C. R., and Fradet, A. 1999. In situ compatibilisation of poly(phenylene sulphide)/wholly aromatic thermotropic liquid crystalline polymer blends by reactive extrusion Morphology, thermal and mechanical properties. Polymer 357-364. 

PRELIMINARY THERMAL AND STRUCTURAL STUDIES OF BLENDS BASED ON A THERMOTROPIC LIQUID CRYSTALLINE COPOLYESTER AND POLY(ETHYLENE) TEREPHTHALATE... 

In this and the following two sections we consider the data for a PLC and for different blends of that PLC with isotactic polypropylene (PP). The PLC used in this study was liquid crystalline copolyester PET/0.6PHB, where PET = poly (ethylene terephthalate), PHB = p-hydroxybenzoic acid and 0.6 is the mole fraction of PHB in the copolymer, manufactured by Unitika Ltd, Kyoto, Japan. The content of the PLC in the blends with PP was varied from 0 to 20 wt%. The samples were prepared by injection molding. PP, resin VB65 llB, was supplied by Neste OY, Finland. 

Differential scanning calorimetry was used to study the non-isothermal crystallization behavior of blends of poly(phenylene sulfide) (PPS) with the thermotropic liquid-crystalline copoly(ester amide) Vectra-B950 (VB) [126], The PPS crystallization temperature and the crystallization rate coefficient increased significantly when 2-50% VB was added. The Ozawa equation was shown to be valid for neat PPS as well as for the blends. The values of the Avrami exponents matched well against those determined previously using isothermal analysis, and they are independent of the concentration of VB. 

Y. Mi, S. Zheng, C.-M. Chan, and Q. Guo, Blends of phenolphthalein poly(ether ether ketone) and a thermotropic liquid crystalline copolyester. Journal erf Applied Polymer Science, 69,1923... 

Skin/core morphologies are common in blends of LCP s and thermoplastic polymers and they play a significant role in defining the properties of both extruded and injection molded samples. Usually, LCP s in the skin have a higher degree of orientation than in the core when the blends are extruded or injection molded (Husman et al. 1980 Hedmark et al. 1989 Lee 1988). Baird et al. (Baird and Mehta 1989 Baird and Sukhadia 1993) observed a skin/core morphology in blends of PA 66 with HBA/HNA and 40 PET/60 PHB and 20 PET/80 HBA copolyesters. More LCP fibers were present in the skin than in the core for both systems. Isayev and Swaninathan (1994) also reported shell-core structure in the fracture surfaces of injection molded blends of HNA/HBA liquid crystalline copolyesters and poly (etherimide). 

Flow curves illustrating this point are shown in figg.lO, 11 for the blends of polycarbonate (PC) and a liquid-crystalline copolyesther, poly(ethylene therephthalate-co-p-oxybenzoate) (PET/PHB60), at 240 and 260°C. 

Blends of Poly(amide imides) and Liquid-Crystalline Polymers... 

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