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preface to fifteenth edition

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POLYMERS, RUBBERS, FATS, OILS, AND WAXES 10.17<br />

A key property is its chemical inertness. Strong oxidizing agents eventually cause some oxidation,<br />

and some solvents cause softening or swelling, but there is no known solvent for polyethylene at<br />

room temperature. The brittleness temperature is 100C for both types. Polyethylene has good<br />

low-temperature <strong>to</strong>ughness, low water absorption, and good flexibility at subzero temperatures.<br />

10.3.17.2 Polypropylene. The polymerization of propylene results in a polymer with the following<br />

structure:<br />

The desired form in homopolymers is the isotactic arrangement (at least 93% is required <strong>to</strong> give<br />

the desired properties). Copolymers have a random arrangement. In block copolymers a secondary<br />

reac<strong>to</strong>r is used where active polymer chains can further polymerize <strong>to</strong> produce segments that use<br />

ethylene monomer.<br />

Polypropylene is translucent and au<strong>to</strong>clavable and has no known solvent at room temperature. It<br />

is slightly more susceptible <strong>to</strong> strong oxidizing agents than polyethylene.<br />

10.3.17.3 Polybutylene. Polybutylene is composed of linear chains having an isotactic arrangement<br />

of ethyl side groups along the chain backbone.<br />

It has a helical conformation in the stable crystalline form.<br />

Polybutylene exhibits high tear, impact, and puncture resistance. It also has low creep, excellent<br />

chemical resistance, and abrasion resistance with coilability.<br />

10.3.17.4 Ionomer. Ionomer is the generic name for polymers based on sodium or zinc salts of<br />

ethylene-methacrylic acid copolymers in which interchain ionic bonding, occurring randomly between<br />

the long-chain polymer molecules, produces solid-state properties.<br />

The abrasion resistance of ionomers is outstanding, and ionomer films exhibit optical clarity. In<br />

composite structures ionomers serve as a heat-seal layer.<br />

10.3.18 Poly(phenylene Sulfide)<br />

Poly(phenylene sulfide) has the following formula:<br />

Therecurring para-substituted benzene rings and sulfur a<strong>to</strong>ms form a symmetrical rigid backbone.<br />

The high degree of crystallization and the thermal stability of the bond between the benzene ring<br />

and sulfur are the two properties responsible for the polymer’s high melting point, thermal stability,<br />

inherent flame retardance, and good chemical resistance. There are no known solvents of<br />

poly(phenylene sulfide) that can function below 205C.

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