High molecular weight polyethers polyurethanes from

Thermoplastic polyurethane elastomers are produced from prepolymers by polycondensation (12,13). A relatively high molecular-weight polyester or polyether with terminal hydroxy groups (a polyglycol) first reacts with an excess of a diisocyanate. 

Volume resistivities are listed in Table 5.2. They range from as low as 2 ohm.cm for epoxy resins to as high as 16-18 ohm.cm for high-density polyethylene, polyether ether ketone, polystyrene, polymethylpentene, polyethylene terephthalate, polyarylates, polyphenylene oxide, polyamide imide, polyimides, polyurethane, polytetrafluoro-ethylene, perfluoroalkoxy ethylene, fluorinated ethylene-propylene copolymer, ultra-high-molecular-weight polyethylene, polysulfones, and polyethersulfones. 

Hydroxy-terminated polyethers have now assumed a dominant role in the commercial production of polyurethanes. The most widely used polyethers are derivatives of propylene oxide and these polymers are described in Section 8.4.3.1. Linear, glycol-initiated propylene oxide polymers and propylene oxide-ethylene oxide block copolymers find some use in the preparation of elastomers. Polyether triols of relatively high molecular weight (about 3000) are extensively used for the production of flexible foams whilst polyols of low molecular weight (about 500) are used for rigid foams and surface coatings. Poly(oxytetramethylene) glycols prepared from tetrahydrofuran (Section 8.4.6) are used for the preparation of elastomers and spandex fibres. 

The soft prepolymer segment from Reaction 14 is in turn condensed with a low molecular weight chain extender (HO-R2OH) and excess diisocyanate (Reaction 15) to give the block polymer (A-B) which possesses soft polyether segments and hard crystalline (high MP) polyurethane segments ... 

The principal of formation of this type of polyurethane elastomer medium, based on a cationic urethane latex, is where an isocyanate-terminated prepolymer derived from either a polyester or polyether diol and toluene diisocyanate is first chain-extended with an alkyl diethanolamine to yield a relatively low molecular weight urethane capable of further chain-extending reactions. Emulsification occurs when the partially extended urethane is added with high-speed mixing to 3% aqueous acetic acid. Curing of the latex takes place either by reaction of water with the terminal isocyanate groups or by reaction with water-soluble diamines. 

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