Main-chain Liquid Crystalline Polymer

A. S. Angeloni, D. Caretti, C. Cariini, E. ChieUini, G. Galli, A. Altoare, R. Solaro, and M. Laus, Photochromic liquid-crystalline polymers. Main chain and side chain polymers containing azobenzene mesogens, Liq. Cryst. 4, 513-527 (1989). 

More About Engineering Thermoplastics. Many of the individual resins mentioned in this overview are covered in articles devoted to them. Cross references are provided in Table 1. A list of related articles is as follows Acetal Resins Acrylic Ester Polymers Acrylonitrile and Acrylonitrile Polymers (SAN and ABS) Ethylene-Norbornene Copolymers Liquid Crystalline Polymers, Main-Chain Methacrylic Ester Polymers ... 

Rigid-rod polymers are often liquid crystalline polymers classified as lyotropic, such as the aramid Kevlar (DuPont), or thermotropic liquid crystalline polymers, such as Vectran (Celanese) (see Polyamides, Aromatic Liquid Crystalline Polymers, Main-Chain Liquid Crystalline Thermosets). 

Recently we have developed a new class of thermotropic liquid crystalline (LC) main-chain pol3rmers, i.e., polyethers of mesogenic bis-phenols(16-17.23-26). Since the obtained polymers are not soluble in dipolar aprotic solvents, the only available synthetic avenue for their preparation consists in the phase transfer catalyzed polyetherification. 

The starting point for the preparation of combined liquid crystalline (LC) main-chain/side-chain polymers ( combined LC polymers) was merely a curiosity about what would happen if the structural properties of main-chain and side-chain polymers were combined (see Figure 1) [1]. As a result of these syntheses a variety of new LC polymers were obtained which showed a surprisingly broad range of LC phases. Further interest in combining main-chain and side-chain structures arose from the... 

WITH the easy-processing properties in the liquid crystalline phase, main-chain TLCPs have been widely used as high-strength fiber, fiber reinforcement, in situ reinforcement additive, and injection molded articles, etc, [ 1 -4]. The successful applications are quite dependent on the adhesion at interface of the liquid crystalline polymer and the conventional engineering resin, which is indeed affected by surface tension and/or interfacial tension between the two phases [1-2],... 

The liquid crystallinity in main-chain LC polymers is associated with molecular chains that are uniformly stiffer than those in conventional polymers. This stiffness or rigidity is usually achieved by increasing the aromatic content (e.g., benzene tings) and coimecting the groups so as to increase chain straightness. 

The thermotropic aromatic main chain liquid crystalline polymers are also prepared by the phase transfer catalyzed aromatic nucleophilic polymerization [87]. Polyetherification of bis(4-chloro-3-nitrophenyl) sulfone with mesogenic aromatic diols is shown below ... 

Aromatic polyesters constitute an important class of main-chain liquid-crystalline polymers, but present the inconvenience of their reduced solubility and very high transition temperatures (sometimes not detected before the degradation of the sample). Their processability can be improved in several ways [2,3], e.g., reduction of the rigidity of the mesogen, lengthening of the spacer, or introduction of lateral substituents. 

A block copolymer composed of liquid crystalline polymer (LCP) segments or that composed of segments having an LCP unit in their main chain or side chain was synthesized [67,68]. The latter showed partial compatibility and second-phase separation even when in a melt liquid crystalline state. 

In summary the results of our 2H NMR investigation illustrate the spacer model for liquid crystalline polymers, indicating, however, that the decoupling of the mesogenic groups from the main chain, while effective, is not complete. 

Macromolecules dendritic, 285 hyperbranched, 284-286 Main-chain liquid crystalline polymers, 49 Main-chain polyester LCP mesogenic units, 50... 

Incorporation of flexible siloxane spacers into side chain or main chain liquid crystalline polymers have been shown to drastically reduce the transition temperatures 255,267,271,272,277) anc[ aiso increase the response time of the resultant systems to the applied thermal, optical or electrical fields 350-353>. In addition, siloxanes also provided elastomeric properties and improved the processibility (solution or melt) of the resulting liquid crystalline copolymers. 

Table I demonstrates that most liquid crystalline polymers lacking a spacer are formed from a flexible polyacrylate backbone. In contrast, the methyl substituent in polymethacrylate backbones both reduce main chain mobility and imposes additional steric barriers to mesophase formation. Therefore, successful liquid crystalline formation of polymethacrylates has been achieved only...

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