Propylene-liquid-crystalline polymer

Polymeric nanocomposites are a class of relatively new materials with ample potential applications. Products with commercial applications appeared during the last decade [1], and much industrial and academic interest has been created. Reports on the manufacture of nanocomposites include those made with polyamides [2-5], polyolefins [6-9], polystyrene (PS) and PS copolymers [10, 11], ethylene vinyl alcohol [12-15], acrylics [16-18], polyesters [19, 20], polycarbonate [21, 22], liquid crystalline polymers [8, 23-25], fluoropolymers [26-28], thermoset resins [29-31], polyurethanes [32-37], ethylene-propylene oxide [38], vinyl carbazole [39, 40], polydiacethylene [41], and polyimides (Pis) [42], among others. 

If one assumes the total production is a single 5 denier per filament (dpf) ( 20 pm in diameter) filament, the total length would be about 0.01 light years ( 10 " m) or the equivalent of about one million trips to the moon. While other polyesters are commercially produced in fiber form—poly(ethylene naphthalate) (PEN) poly(butylene terephthalate) (PBT) poly(propylene terephthalate) (PPT) and poly(lactic acid) (PLA) thermotropic polyester (liquid crystalline polymer (LCP)—these are of insignificant volume compared to PET. Hence this chapter focuses primarily on PET. 

Melt compounding is most commonly utilized for the preparation of PO/silica nanocomposites. POs and their blends, such as PP [326-337], PE [338-343], ethylene-propylene copolymer [344-354], ethylene-octene copolymer [347], thermoplastic POs [348-350], PP/ EPDM [351,352], and PP/liquid-crystalline polymer (LCP) [353-357] blends, have been used as the matrices in the preparation of PO/silica nanosystems and nanomaterials by twin-screw extrusion and injection molding or lab-scale single-screw extrusion and compression molding. 

Acrylonitrile Butadiene Styrene Acrylonitrile Styrene Acrylate Cyclic Olefin Copolymer Polyethylene Chlorotrifluoroethylene Polyethylene Tetrafluoroethylene Ethylene Vinyl Acetate Fluorinated Ethylene Propylene High Density Polyethylene High Performance Polyamide Liquid Crystalline Polymer Low Density Polyethylene Linear Low Density Polyethylene Medium Density Polyethylene Polyamide (Nylon)... 

Chakraborty S, Sahoo N G, Jana G K and Das C K (2004) Self-reinforcing elastomer composites based on ethylene-propylene-diene monomer rubber and liquid-crystalline polymer, J Appl Polym Sa 93 711-718. 

Figure 5.2.4 shows a network surface structure of a VA/AA-based emulsion with 6.6 wt% soiids. The repeat unit in the network structure is between 5 and 10 jtm. The formation of the network or bicontinuous surfactant structure is well established in relatively high molecular weight ethylene oxide/propylene oxide segmented block copolymer nonionic surfactants, and it has been ascribed to the formation of liquid crystalline macromolecular assemblies. Upon dilution, the emulsion showed 5-10 ttm spherical domains that could form aggregates up to about 60p.m in size (Fig. 4.4.5). In Fig. 5.2.5, bubble surfaces are shown with the network surfactant structure, even in the diluted emulsion. Apparently, the surfactant macromolecules tend to concentrate on bubble surfaces and form a more viscous and probably elastic polymer surface layer. 

Synthesis. The early PP plants used a slurry process adopted from polyethylene technology. An inert liquid hydrocarbon diluent, such as hexane, was stirred in an autoclave at temperatures and pressures sufficient to keep 10-20 percent of the propylene monomer concentrated in the liquid phase. The traditional catalyst system was the crystalline, violet form ofTiCl3 and A1C1(C2H5)2. Isotactic polymer particles that were formed remained in suspension and were removed as a 20-40 percent solid slurry while the atactic portion remained as a solution in the liquid hydrocarbon. The catalyst was deactivated and solubilized by adding HC1 and alcohol. The iPP was removed by centrifuging, filtration, or aqueous extraction, and the atactic portion was recovered by evaporation of the solvent. The first plants were inefficient because of low catalyst productivity and low crystalline yields. With some modifications to the catalyst system, basically the same process is in use today. 

Polymers with extremely high molecular weights result from the polymerization of ethylene oxide initiated by the carbonates of the alkaline earth metals, e.g., strontium carbonate, which must, however, be very pure. Poly(ethylene oxides) having molecular weights up to about 600 are viscous liquids above that they are wax-like or solid, crystalline products that are readily soluble not only in water but also in organic solvents such as benzene or chloroform. Polymers of propylene oxide and generally substituted ethylene oxides can be produced in both atactic amorphous and isotactic crystalline forms. Optically active poly(propylene oxide)s can be obtained from propylene oxide. 

Slurry-phase processes may involve either an inert diluent such as iso-butane or heptane, or condensed monomer such as propylene. In either case the catalyst particles are suspended and well mixed in the liquid medium. Monomer concentrations are high and the liquid provides good removal of the heat produced by the polymerization of the polymer particles. The two main reactors for slurry-phase olefin polymerization are the loop reactor and continuous-stirred tank. Slurry-phase processes are very attractive for high crystalline homopolymer products such as polypropylene and polyethylene. 

Propylene oxide has an asymmetric carbon atom. The normal commercial epoxide is a racemic mixture of the d- and 1-isomers. Osgan and Price did extensive work with both the 1-propylene oxide and the d,l-propylene oxide in both potassium hydroxide and ferric chloride/propylene oxide-initiated polymerizations. Their results are summarized in Table 5 (48). C. C. Price and coworkers first demonstrated that polymerization of pure 1-propylene oxide with an anhydrous potassium hydroxide (solid KOH) initiator led to a crystalline, rather than the usual amorphous, liquid, polymer. After extensive study by a number of researchers (69), this polymerization was shown to proceed by a stepwise anionic mechanism. The uses found for polymers of propylene oxide largely have been those requiring the amorphous polymer in elastomeric applications. Stereospecificity, however, has proved to be a key tool in understanding the polymerization mechanisms. 

Synthesis The early polypropylene plants used a slurry process adopted from polyethylene technology. An inert liquid hydrocarbon diluent, such as hexane, was stirred in an autoclave at temperatures and pressures sufficient to keep 10 to 20 percent of the propylene monomer concentrated in the liquid phase. The traditional catalyst system was the crystalline, violet form of TiCla and AlCl (C2Hs)2- Isotactic polymer particles... 

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