On the use of PET‐LCP copolymers as compatibilizers for PET/LCP blends

Abstract

Copolyesters of poly[ethylene terephthalate) (PET) with a liquid crystalline polymer (LCP), SBH 1:1:2, have been synthesized by the polycondensation, carried out in the melt at temperatures up to 300 degrees C of sebacic acid (S), 4,4'-dihydroxybiphenyl (B), and 4-hydroxybenzoic acid (H) in the presence of PET. The PET-SBH copolyesters have been characterized by differential scanning calorimetry, scanning electron microscopy, X-ray diffraction, etc., and the relationships between properties and preparation conditions are discussed. The copolyesters show a biphasic nature, which is more evident for the products synthesized with a thermal profile comprising relatively lower temperatures (220-230 degrees C) in the initial stages of the polycondensation. Another procedure, whereby the addition of PET to the monomer charge was made at a later stage of the reaction, has also been devised to prepare copolyesters with enhanced blockiness. The compatibilizing effect of the PET-SBH copolymers toward PET/SBH blends has been investigated. PET/SBH blends (75/25, w/w) have been prepared in a Brabender mixer at 270 degrees C and 30 rpm, with and without the addition of appropriate amounts (2.5, 5, and 10%, w/w) of 50-50 PET-SBH copolyesters. Different blending techniques have been used according to whether the three components were fed into the mixer at the same time, or one of them was added at a later stage. The effect of the type and the amount of added copolyester has been studied through morphological, thermal, and mechanical characterizations. The results show that the addition of small amounts similar to 5 wt% of copolyesters leads to improved dispersion and adhesion of the minor SBH phase. Moreover, while the tensile modulus of the blends is practically unaffected by the addition of the copolymer, a substantial increase of both tensile strength and elongation to break is found for a concentration of added copolyester of similar to 5 wt%. Slightly better results were apparently obtained by the use of a block copolyester

Polymer‐dispersed liquid‐crystal polymers (PDLCPs). Morphology of the LCP droplets

“…Thus, the droplets were in the LC state at the end of the synthesis, and appear as monodomains when the cryofractured material is viewed with the electron microscope (Rg. 6). Because the two phases of COP-2 have closer chemical composition and, hence, fairly good interfacial adhesion, the U P droplets are severely involved in the fracture thus allowing a direct observation of the structure of the nematic domains.…”

Highly Aromatic Liquid Crystalline Copolyesters Synthesized by Transesterification of Poly(ethylene terephthalate) with Acetoxybenzoic Acid, Diacetoxybenzene and Terephthalic Acid

“…This approach proved unsuccessful, however, when we tried to synthesize p(ETHSB) copolyesters by the transesterification of p(ET) with a mixture of H, sebacic acid (S), and 4,49-diacetoxybiphenyl (B). [24] In fact, the presence of S did increase considerably the tendency of the reaction mixture to separate into an aromatic-rich nematic phase and an isotropic phase rich of E and S units, with the result that a true "synthetic blend" composed of a low melting isotropic matrix with high melting LCP inclusions was finally obtained. [24] On the contrary, Li et al, [25,26] who investigated the synthesis of p(ETHX) copolyesters with H partially substituted with small amounts of aromatic comonomers X, with the main scope of enhancing the polymerization rate, were apparently able to obtain products with improved randomness, especially when X was vanillic (i. e., 4-hydroxy-3-methoxybenzoic) acid.…”

Effect of PP-g-LCP compatibilizer on the structure and crystallization of blends of isotactic polypropylene (PP) with a semiflexible liquid crystalline polymer (LCP)

“…We had the same approach to the compatibilization of blends of PE1"-16) or poly(ethy1ene terephthalate) 598 T. Miteva, L. Minkova (PET)17) and a semirigid LCP. It was found that the addition of small amounts of ad hoc synthesized PE-g-LCP or PET-LCP copolymers, gave rise to an improvement of the interfacial adhesionl6, 17) and to a significant improvement of the tensile ~t r e n g t h '~) and the elongation to breaki6.I7) of these blends.…”