This paper reviews the literature of polymer blends containing low and high molar mass liquid crystals. Low molar mass liquid crystals have been used as plasticizers for thermoplastic polymers and in applications such as electro-optics, optical recording media, and membranes. High molar mass liquid crystalline polymers have been primarily used in polymer blends as processing aids and as an incipient reinforcing phase for “self-reinforced” materials. This review discusses the phase behavior, rheology, and mechanical properties of these blends.

Polymer Blends Containing Liquid Crystals: A Review

Liquid crystal polymers

The field of mesophases is subdivided into six different phases: liquid crystals, plastic crystals, condis crystals and the corresponding LC, PC, and CD glasses. Liquid and plastic crystals are the traditional phases with positional and orientational disorder, respectively. Condis crystals are conformationally disordered. On hand of tables of thermodynamic transition parameters of small and large molecules it is shown that the orientational order in liquid crystals is only a few per cent of the total possible, while the positional order in plastic crystals is virtually complete. Condis crystals have a wide variety of different degrees of conformational disorder. The glass transitions of all mesophases are similar in type. Macromolecules in the liquid crystalline state produce high orientation on deformation. Plastic crystals consist always of small molecules. Condis crystals may under proper conditions anneal to extended chain crystals.

Thermotropic mesophases and mesophase transitions of linear, flexible macromolecules

A thermotropic liquid crystalline polymer (LCP), when added to polystyrene (PS), can function as both a processing aid and a reinforcing filler. Thermal, rheological, and mechanical properties of the pure components and blends containing up to 10 percent LCP are reported. The LCP used is immiscible with PS, and when an extensional component of flow is present during processing, the LCP forms an elongated fibrous phase oriented in the flow direction. This oriented phase lubricates the melt, substantially lowering the viscosity. When the processed blend is cooled, the dispersed fibrous LCP phase is preserved in the solidified material. The LCP microfibers behave like short reinforcing fibers to improve the mechanical properties of the blend; for example, at an LCP concentration of 4.5 percent, the modulus is increased about 40 percent vs. pure PS.

Novel reinforced polymers based on blends of polystyrene and a thermotropic liquid crystalline polymer

The article covers synthesis, structure and properties of thermotropic liquid-crystalline (LC) polymers with mesogenic side groups Approaches towards the synthesis of such systems and the conditions for their realization in the LC state are presented, as well as the data revealing the relationship between the molecular structure of an LC polymer and the type of mesophase formed Specific features of thermotropic LC polymers and copolymers of nematic, smectic and cholesteric types are considered

https://link.springer.com/content/pdf/10.1007%2F3-540-12994-4_4.pdf

Thermotropic liquid-crystalline polymers with mesogenic side groups

Details of the thermal behavior, including transition temperatures, transition heats and transition entropies, are reported for three series of nematic liquid-crystalline “backbone” polyesters having the general structure 






All polysters described above were examined by differential scanning calorimetry and were found to have reproducible thermal behavior once the polymer had been annealed by heating to the isotropic phase and then subsequently cooled. Enantiotropic nematic phases were found for all 30 polysters studied. Many polymers showed multiple endotherms on melting to the nematic phase. Plots of solid–nematic and nematic–isotropic transition temperatures versus number of carbon atoms in the diacid segment (x) for each (y) reveal an even–odd alternation reminiscent of trends in homologous series of small-molecule liquid crystals. Enthalpies for the solid nematic and nematic isotropic transitions do not show such a precise alternation.

Mesogenic polymers. III. Thermal properties and synthesis of three homologous series of thermotropic liquid crystalline ``backbone'' polyesters

A new series of thermotropic liquid crystalline polymers has been synthesized. These materials have incorporated a mesomorphic moiety, 4-alkoxyphenyl 4′-alkoxybenzoate, into the polymer backbone. T...

Polymeric Liquid Crystals Structurally Related to 4-Alkoxyphenyl 4′-Alkoxybenzoates

Effect of molecular structure on mesomorphism. 7. Enhancement of smectic-isotropic transition temperatures in binary mixtures of a new liquid crystal series: the 4-nitrophenyl 4'-n-alkoxybenzoates

Phase studies of polymer/small‐molecule liquid‐crystalline mixtures by differential scanning calorimetry

Most binary mesophase systems exhibit mesophase-isotropic transition temperatures which are linearly dependent on composition. There are however exceptions. Demus (1) reported non-linear behavior for some mixtures when one component was a chloro mesogen. Dave (2) found similar behavior with chloro and nitro liquid crystals and postulated a structural rationale based on dipolar characteristics of the constituent molecules. Schroeder and Schroeder (3) reported in 1968 that non-mesomorphic nitro-terminated anils enhanced (4) the smectic phase of di-n-hexyloxyazoxybenzene. These authors suggested a loose dimeric association of the nitro anils as part of a molecular explanation for this enhanced smectic phase.

Stephen J. Havens

Papers

Mesogenic polymers. III. Thermal properties and synthesis of three homologous series of thermotropic liquid crystalline ``backbone'' polyesters

Polymeric Liquid Crystals Structurally Related to 4-Alkoxyphenyl 4′-Alkoxybenzoates

Effect of molecular structure on mesomorphism. 7. Enhancement of smectic-isotropic transition temperatures in binary mixtures of a new liquid crystal series: the 4-nitrophenyl 4'-n-alkoxybenzoates

Phase studies of polymer/small‐molecule liquid‐crystalline mixtures by differential scanning calorimetry

Effect of Molecular Structure on Mesomorphism. 6. Non-Linear Thermal Behavior in Some Binary Liquid Crystal Systems