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25.20: Polymerization - Condensation Polymers

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  • Animal gut and silk were used for all guitar strings for centuries until modern technology and changes in musical taste brought about significant changes. There are two major types of guitar strings in use today. Steel strings (first developed around 1900) are found on acoustic and electric guitars. They have a bright, crisp sound that lends itself well to diverse music as jazz, rock and roll, and bluegrass. Nylon strings are a more recent development. During World War II, the silk and animal products needed to manufacture steel guitar strings were not available. Nylon quickly proved to be a more than adequate substitute. Now nylon strings are found on all classical guitars. Their sound is somewhat softer than the steel strings and the tone quality suits that genre of music better.

    Polymerization - Condensation Polymers

    condensation polymer is a polymer formed by condensation reactions. Monomers of condensation polymers must contain two functional groups so that each monomer can link up with two other monomers. One type of condensation polymer is called a polyamide. An amide is characterized by the functional group shown below wherein the carbon of a carbonyl group is bonded to the nitrogen of an amine.

    Structure of an amide

    Figure 25.20.1: Amide.

    One pair of monomers that can form a polyamide is adipic acid and hexanediamine. Adipic acid is a carboxylic acid with two carboxyl groups on either end of the molecule. Hexanediamine has amino groups on either end of a six-carbon chain. When these molecules react with each other, a molecule of water is eliminated, classifying it as a condensation reaction (see figure below).

    Example of a condensation reaction to form a polyamide

    Figure 25.20.2: Nylon synthesis.

    The polymer that results from the repetition of the condensation reaction is a polyamide called nylon-66. Nylon-66 was first invented in 1935 and has been used in all sorts of products. It and other polyamides are commonly found in fibers and clothing, cooking utensils, fishing line, and carpeting, among many other applications.

    Nylon-66 is a commonly used polymer

    Figure 25.20.3: Nylon spatula.

    Polyester is another common type of condensation polymer. Recall that esters are formed from the reaction of an alcohol with a carboxylic acid. When both the acid and alcohol have two functional groups, the ester is capable of being polymerized. One such polyester is called polyethylene terephthalate (PET) and is formed from the reaction of ethylene glycol with terephthalic acid. The structure of PET is shown below.

    Polyethylene terephthalate (PET) is a polyester

    PET is used in tires, photographic film, food packaging, and clothing. Polyester fabric is used in permanent-press clothing. Its resistance to wrinkling comes from the cross-linking of the polymer strands.

    Contributors

    • CK-12 Foundation by Sharon Bewick, Richard Parsons, Therese Forsythe, Shonna Robinson, and Jean Dupon.