Jin-Hae Chang

Blends of PBT with rigid thermotropic LCP having flexible side groups: Comparison of their tensile properties with semirigid main‐chain TLCP blends

Two new thermotropic liquid crystalline polymers (LCPs) were synthesized. One is a di-mesogenic LCP having a flexible hexamethylene spacer in the main chain, the other is a rigid-type main-chain LCP having alkoxy side groups on the terephthaloyl moiety of the polymer. Blends of LCP with poly(butylene) terephthalate were melt-spun at different LCP contents and different draw ratios to produce a monofilament. Maximum enhancement in the ultimate tensile strength was observed for the blends containing 5% LCP at any draw ratio, and decreased with further increase in LCP content. The initial modulus monotonically increased with increasing LCP content. The tensile properties of the rigid-type LCP blends were higher than those of the flexible main-chain LCP blends.

Synthesis and properties of copolyesters having an ordered comonomer sequence : copolyesters prepared from naphthylene bis (4-hydroxybenzoate)s and α,ω-bis(4-carboxyphenoxy)alkanes

Abstract A series of sequentially ordered copolyesters were prepared from isomeric naphthylene bis(4-hydroxybenzoate)s (NBHBs) and α,ω-bis(4-carboxyphenoxy)alkanes (BCPAs) with varying length of α,ω-alkylene units. All of the copolyesters were composed of naphthalenediol (NAPH), BCPA and p -hydroxybenzoic acid (POB) (1:1:2 molar ratio). The polymer chains were made up of POBNAPHPOBBCPA segments. The naphthalene units were derived from 1,5-, 1,6-, 2,6- and 2,7-naphthalenediols. The BCPAs employed were 1,4-butane, 1,5-pentane and 1,10-decane derivatives. The melting points and crystallizability of these copolyesters were found to be much higher than those of the corresponding random copolyesters having the same overall compositions. All of the polymers, with the exception of the polyester derived from 2,7-naphthalenediol and 1,5-pentane spacers, formed nematic phases in melts. The ordered sequence copolyesters were found to undergo a rapid sequence randomization at temperatures higher than their melting points. A model compound of a copolyester, 2,7-naphthylene bis[4-(4-n-butoxybenzoyloxy)-benzoate], was also synthesized and its thermal behaviour and liquid crystal properties were studied.

Dependence of properties of liquid crystalline aromatic copolyesters on monomer sequence-copolyesters derived from terephthalic acid, 2,7-naphthalenediol and p-hydroxybenzoic acid

SummaryAn aromatic copolyester with the ordered sequence of terephthalic acid (TA)-p-hydroxybenzoic acid (HB)-2,7-naphthalenediol (ND)-p-hydroxybenzoic acid (HB) was prepared and its properties were compared with those of the corresponding random copolyester having the same overall monomer composition. Thermal and crystallizing properties of the two polymers are quite different. The former exhibits significantly higher glass transition and melting temperatures than the latter. The formers degree of crystallinity also is much higher than the latters. Both polymers are thermotropic and form nematic melts.

Phase-Transfer Polycondensation of Bisphenolate Anions and 1,6-Dibromohexane

Phase-transfer catalysis, also often referred to as “ion pair partition” is a novel synthetic technique which has been the subject of much interest in recent years not only in the field of organic synthesis but also in polymer chemistry. The term “phase-transfer catalysis” was first introduced in 1971 by Stark1,2 who studied kinetics in detail and the mechanism of reactions which are catalyzed by small amounts of onium salts such as quaternary ammonium or phosphonium compounds. Brandstrom3–5 and Makosza6–8 also made major initial contributions in the understanding of such reactions and the application thereof in various synthetic reactions. A generally accepted phase-transfer reaction scheme is shown in Fig. 1 for the reaction of RX + Y-→ RY + X-. Catalytic onium ion (Q+) transfers the nucleophile Y- into the organic phase in the form of ion pair Q+Y-, which then reacts with RX in organic phase producing the products RY and X-. X-’s are removed by Q+ from organic phase into aqueous phase as they are formed.

Synthesis and Characterization of Siloxane Contained Liquid Crystalline Polymers with Two Symmetric Mesogens

Abstract New thermotropic siloxane contained liquid crystalline polymers with two symmetric mesogens were prepared by hydrosilation with Rh(PPh3)3Cl catalyst. It was found that Rh(PPh3)3Cl catalyst was effective for low molecular weight polymerization. The resulting polymers exhibited good solubility in organic solvents such as tetrahydrofuran(THF), chloroform, and so on. The structures of the monomer and polymers were confirmed by IR, 1H and 13C NMR spectra. The number average molecular weight(Mn) values of the polymers were in the range of 2000∼6000. Thermal properties of the monomers and the polymers were analyzed by differential scanning calorimetry(DSC), and polarized optical microscopy. Monomers did not show liquid crystalline phase but the polymers exhibited nematic phases.