10.20 |
SECTION 10 |
10.3.22Sulfones
Below are the fomulas for three polysulfones.
The isopropylidene linkage imparts chemical resistance, the ether linkage imparts temperature resistance, and the sulfone linkage imparts impact strength. The brittleness temperature of polysul-
fones is 100 C. Polysulfones are clear, strong, nontoxic, and virtually unbreakable. They do not hydrolyze during autoclaving and are resistant to acids, bases, aqueous solutions, aliphatic hydrocarbons, and alcohols.
10.3.23Thermoplastic Elastomers
10.3.23.1 |
Polyolefins. |
In these thermoplastic elastomers the hard component is a crystalline poly- |
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olefin, such as polyethylene or polypropylene, and the soft portion is composed of ethylene-propyl- |
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ene rubber. Attractive forces between the rubber and resin phases serve as labile cross-links. Some |
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contain a chemically cross-linked rubber phase that imparts a higher degree of elasticity. |
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10.3.23.2 |
Styrene-Butadiene-Styrene Block Copolymers. |
Styrene blocks associate into domains |
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that form hard regions. The midblock, which is normally butadiene, ethylene-butene, or isoprene blocks, forms the soft domains. Polystyrene domains serve as cross-links.
10.3.23.3Polyurethanes. The hard portion of polyurethane consists of a chain extender and polyisocyanate. The soft component is composed of polyol segments.
10.3.23.4Polyesters. The hard portion consists of copolyester, and the soft portion is composed
of polyol segments.
10.3.24 Vinyl |
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10.3.24.1 Poly(vinyl Chloride) (PVC). |
Polymerization of vinyl chloride results in the formation |
of a polymer with the following formula: |
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When blended with phthalate ester plasticizers, PVC becomes soft and pliable.
Its key properties are good resistance to oils and a very low permeability to most gases.