Synthesis and properties of TLCPs with 2,6‐naphthalene‐based mesogen, polymethylene spacer, and nonlinear 4,4′‐thiodiphenyl links

Abstract

A series of new thermotropic main-chain liquid crystalline copolyesters were prepared by polycondensation of 2,6-naphthalenedicarbonyl chloride, 4,4Ј-thiodiphenol, and ␣,-alkanediols (n ϭ 4 -10) in diphenyl ether at 200°C. Thermal transition behaviors of these copolyesters were investigated by differential scanning calorimetry. Moreover, their thermal stabilities and mesomorphic textures were studied by thermogravimetric analysis and polarizing optical microscopy, respectively. Corresponding model compounds with terminal mesogenic units and central polymethylene spacers were also synthesized for comparison. Both copolymers and model compounds exhibit odd-even dependency of melting temperatures, transition enthalpy (⌬H m ), and entropy (⌬S m ) on the number of methylene units in the spacer. However, the odd-even effects in model compounds are much more distinctive. Nematic mesophases are the only texture observed in melts, except the model compounds with longer methylene units (n ϭ 8, 10), in which smectic mesophases can be observed. The T m values of the copolyesters (TDP/HD ϭ 1/1) are between 233 and 259°C, depending on spacer length. The initial decomposition temperatures of the copolyesters are above 419°C under N 2 atmosphere.

Odd−Even Effects in Charge Transport across Self-Assembled Monolayers

“…While the values of μ log generally decrease with increasing chain length, the reversal of the inequalities between SC 11 and SC 12 and between SC 17 and SC 18 is a clear deviation from the trend observed in the separate odd and even datasets and, thus, constitutes one piece of evidence for an odd-even effect.…”

Synthesis and properties of liquid crystalline polymers with low Tm and broad mesophase temperature ranges

“…In order to reach more practical conditions for industrial processing, several approaches have been utilized to reduce the transition temperatures of LCPs. These include frustrated chain packing [10], flexible spacers [11], and nonlinear links [12]. The insertion of flexible segments or spacers to separate the mesogenic units along the polymer backbone is aimed to reduce the transition temperature and to preserve the chemical periodicity of the molecules of LCPs.…”

Aromatic liquid crystalline copolyesters with low Tm and high Tg: Synthesis, characterization, and properties

“…According to the Gibbs free energy equation T m = Δ H /Δ S , when the chemical reaction is at equilibrium state, the methods whatever can decrease Δ H or increase Δ S can be adopted to decrease the melting temperature. Based on this principle, several effective ways have been developed by researchers via incorporating asymmetrically substituted monomer, kinked or nonlinear comonomer, flexible spacers to synthesize desirable TLCP. Most of these ways were investigated extensively except by utilizing a kinked monomer.…”