Longitudinal PLCs

Because of the importance of longitudinal PLCs -class "alpha" according to (2(5) - in the development of high-modulus materials, a polyester easy to obtain and to modify was chosen as the rigid-rod type PLC component the Jackson and Kuhfuss (15) copolyester based on poly(ethylene terephthalate) (PET) and p-hydroxy-benzoate (PHB). The polyester can be prepared and... 

A simple application of the self-assembly of complementary bifunctional small molecules to form extended-chain structures, or longitudinal PLCs, is given in references 6-8. Griffin and coworkers report that hydrogen bond-driven association between bispyridyl-terminated and bisbenzoic acid-terminated species can lead to liquid crystalline materials with polymeric characteristics. Typical compounds employed are shown in Figure 3.2. None of the starting components are liquid crystalline. 

Figure 3.2 Bifunctional molecular components for longitudinal PLCs assembled with hydrogen bonds.

Figure 3.3 Representation of the self-assembly of longitudinal PLCs through single hydrogen bonds, using the complementary components of Figure 3.2.

Among the several hundreds of PLCs reported in papers and patents, thermotropic longitudinal PLCs [1] comprise a very important category. Longitudinal PLCs, formerly called main-chain PLCs, are those whose backbones consist of rod-like mesogens connected parallel to the backbone. Most thermotropic longitudinal PLCs are aromatic LC... 

Morphology of thermotropic longitudinal PLCs Skin layer... 

The morphology and properties of injection molded thermotropic longitudinal PLC products are similar to those of extrudates, i.e., macroscopic skin/core structure, microscopic hierarchically layered and... 

Blundell [28] first demonstrated that the main features of crystallization for thermotropic longitudinal PLCs are (1) small crystallites ( 5 nm for quenched samples and about 10 nm across for annealed ones) (2) limited crystallinity (about 20% in wide angle X-ray diffraction (WAXD)) (3) low surface energy of the crystallites (4) little change of molecular conformation before and after melting and (5) low fusion entropy and enthalpy (sometimes no detectable endotherm on DSC thermograms). A model of small crystal size for extended chain polymers was proposed by Blundell [28]. 

Polymorphism is also common for thermotropic longitudinal PLCs. Two types of crystal lattice exhibit in these PLCs orthorhombic and... 

The characteristics of the crystallization behaviors of thermotropic longitudinal PLCs can be summarized as (1) small and imperfect lamellae about lO-lOOnm in size (2) limited crystallinity (3) an increase of lamellar thickness, improvement of lateral correlation and transformation of the lattice resulting from annealing and (4) formation of high-melting crystals in the partially molten state. 

Blends of rigid longitudinal PLCs HNA/xPHB copolyesters... 

PLCs have been shown to nucleate systems which are hard to crystallize by any other means. Polyethersulfone (PES) is a high temperature thermoplastic which, even when cast from solution, is unable to crystallize [84], as opposed to, for example, PC. However, when solution blended with 30 wt% wholly aromatic longitudinal PLC (structure not reported), spherulites of the PES can be formed and it is suggested that the combined effect of solvent molecules to lubricate the motion of the crystallizing PES molecules and a nucleant (PLC) is required, either condition on its own not being sufficient. Similar attempts to crystallize the blend from the melt failed. 

---