Engineered plastics comonomer

Cyclic ether and acetal polymerizations are also important commercially. Polymerization of tetrahydrofuran is used to produce polyether diol, and polyoxymethylene, an excellent engineering plastic, is obtained by the ring-opening polymerization of trioxane with a small amount of cycHc ether or acetal comonomer to prevent depolymerization (see Acetal resins Polyethers, tetrahydrofuran). 

Empirical Ci9H2oBr404 Properties Solid sol. in oxygenated and chlorinated soivs. insol. in water and aromatic soivs. m.w. 631.98 dens. 1.8 kg/l m.p. 116 C Toxicology LD50 (oral, rat) > 5000 mg/kg, (dermal, rabbit) > 2000 mg/kg Uses Comonomer for fire-retarded unsat. polyester resins and engineering plastics ... 

An example of the latter is Dow s development of syndiotactic polystyrene, which has the properties of an engineering plastic. Also important is the incorporation of comonomers in a highly uniform manner. Again, Dow has produced an 80% ethylene/20% octane elastomer (89). Metallocene polymers have mainly been used in higher priced specialty applications (). 

Figure 6.6 Structure of a single-site catalyst described by Goodall. Catalyst is capable of copolymerizing ethylene with polar comonomers without cocatalysts (BL Goodall, NT Allen, DM Conner, TC Kirk, LH McIntosh III and H Shen, International Conference on Polyolefins, Society of Plastics Engineers, Houston, TX, February 25-28, 2007).

Uses Disinfectant solvent for wire enamels pharmaceuticals insecticides fungicides herbicides plasticizers mbber chemicals paints additives to lubricants and gasoline mfg. of polyphenylene oxide wetting agents dyestuff synthetic resin comonomer for alkali-resist, phenolic resins froth flotation agent engine cleaner ingred. 

For most engineering polymers a high Tg (above 100 C) is required, whereas elastomers (synthetic rubbers) need low Tg (usually below — 50 C). It is also possible to reduce Tg by external plasticification (addition of plasticizers which generate a solid solution with organic liquids of very low transition temperatures) or by polymerization with other comonomers which leads to lower transitions. 

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