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LANGE'S HANDBOOK OF CHEMISTRY

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10.4.12 Polysulfide Rubbers<br />

Polysulfide rubbers are prepared as follows:<br />

POLYMERS, RUBBERS, FATS, OILS, AND WAXES 10.61<br />

Cl9R9Cl Na9S9S9S9S9Na : HS[9R9S9S9S9S9] nR9SH<br />

where R can be<br />

9CH 2CH 29, 9CH 2CH 29O9CH 2CH 29,<br />

or 9CH 2CH 29O9CH 29O9CH 2CH 29.<br />

Polysulfide rubbers possess excellent resistance to weathering and oils and have very good electrical<br />

properties.<br />

10.4.13 Poly(vinyl Chloride) (PVC)<br />

Poly(vinyl chloride) as previously discussed in Sec. 10.3, Formulas and Key Properties ofPlastic<br />

Materials, has the following structures:<br />

PVC polymer plus special plasticizers are used to produce flexible tubing which has good chemical<br />

resistance.<br />

10.4.14 Silicone Rubbers<br />

Silicone rubbers are prepared as follows:<br />

Other groups may replace the methyl groups.<br />

Silicone rubbers have excellent ozone and weathering resistance, good electrical properties, and<br />

good adhesion to metal.<br />

10.4.15 Styrene-Butadiene Rubber (GRS, SBR, Buna S)<br />

Styrene-butadiene rubber is prepared from the free-radical copolymerization of one part by weight<br />

ofstyrene and three parts by weight of1,3-butadiene. The butadiene is incorporated by both 1,4addition<br />

(80%) and 1,2-addition (20%). The configuration around the double bond ofthe 1,4-adduct<br />

is about 80% trans. The product is a random copolymer with these general features:

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