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preface to fifteenth edition

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10.20 SECTION 10<br />

10.3.22 Sulfones<br />

Below are the fomulas for three polysulfones.<br />

The isopropylidene linkage imparts chemical resistance, the ether linkage imparts temperature<br />

resistance, and the sulfone linkage imparts impact strength. The brittleness temperature of polysulfones<br />

is 100C. Polysulfones are clear, strong, non<strong>to</strong>xic, and virtually unbreakable. They do not<br />

hydrolyze during au<strong>to</strong>claving and are resistant <strong>to</strong> acids, bases, aqueous solutions, aliphatic hydrocarbons,<br />

and alcohols.<br />

10.3.23 Thermoplastic Elas<strong>to</strong>mers<br />

10.3.23.1 Polyolefins. In these thermoplastic elas<strong>to</strong>mers the hard component is a crystalline polyolefin,<br />

such as polyethylene or polypropylene, and the soft portion is composed of ethylene-propylene<br />

rubber. Attractive forces between the rubber and resin phases serve as labile cross-links. Some<br />

contain a chemically cross-linked rubber phase that imparts a higher degree of elasticity.<br />

10.3.23.2 Styrene-Butadiene-Styrene Block Copolymers. Styrene blocks associate in<strong>to</strong> domains<br />

that form hard regions. The midblock, which is normally butadiene, ethylene-butene, or isoprene<br />

blocks, forms the soft domains. Polystyrene domains serve as cross-links.<br />

10.3.23.3 Polyurethanes. The hard portion of polyurethane consists of a chain extender and<br />

polyisocyanate. The soft component is composed of polyol segments.<br />

10.3.23.4 Polyesters. The hard portion consists of copolyester, and the soft portion is composed<br />

of polyol segments.<br />

10.3.24 Vinyl<br />

10.3.24.1 Poly(vinyl Chloride) (PVC). Polymerization of vinyl chloride results in the formation<br />

of a polymer with the following formula:<br />

When blended with phthalate ester plasticizers, PVC becomes soft and pliable.<br />

Its key properties are good resistance <strong>to</strong> oils and a very low permeability <strong>to</strong> most gases.

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