Common Classes of Polymers

Polymers are often distinguished by the structure of the linkages that are produced. Table 3.1 in the text provides seven common classes of polymers that can be produced by step growth polymerization. We will consider each of these in depth, and identify the functional groups that are needed in the monomers to produce the desired polymers. Be conscious of whether the reactions are polycondensation or polyaddition reactions (refer back to Lesson 1 - What is a Polymer).

Polyesters

Polyesters can be produced from the reaction between carboxylic acids or acid halide groups with alcohols (Figure 2.5). Notice that when a carboxylic acid is used, water is a product; when an acid halide is used, acid is a product.

Molecular diagram of Polyesters
Figure 2.5 Polyesters
Source: Lauren Zarzar

A very common polyester is polyethylene terephthalate, or PET (Figure 2.6). If you see recycling symbol #1 on your container, it's PET! PET is the most common thermoplastic polymer and is frequently used in synthetic fibers. Even though there are many different polyesters, PET is so common - 18% of world polymer production - that it is often just identified by the general name, "polyester". So if you look on your clothing label and find that it says "polyester", now you know that it's PET. The inclusion of aromatic groups in the backbone lends the polymer more mechanical and thermal stability. University of Liverpool - Chem Tube 3D.

Molecular diagram of Polyethylene terephthalate (PET)
Figure 2.6 Polyethylene terephthalate (PET)
Source: Lauren Zarzar

Polyamides

Polyamides are produced from the reaction between carboxylic acids or acid halides with amine groups that creates amide bonds (Figure 2.7).

Molecular diagram of Polyamides
Figure 2.7 Polyamides
Source: Lauren Zarzar

Nylon is a great example of a polyamide. Nylon 6,6 is shown in Figure 2.8; the "6,6" part comes from the fact that each monomer has 6 carbons; there are many other kinds of nylon as well, depending on the specific monomers used. Nylons have extensive hydrogen bonding between polymer chains which generates a relatively high degree of order (and crystallinity) contributing significantly to nylon's strength and rigidity. This ordering also makes nylon great for fibers. Nylon 6,6 can be easily made from interfacial polymerization, because the adipic acid (or sebacoyl chloride) is water soluble and the hexamethylenediamine is oil soluble. (VIDEO/www.youtube.com/watch?v=VtCBarLbHRM)

Molecular diagram of Nylon 6,6
Figure 2.8 Nylon 6,6
Source: Lauren Zarzar

Other important examples of polyamides are polypeptides or proteins. Proteins are polypeptides, produced from the polymerization of amino acid monomers. The generic structure of an amino acid is shown in Figure 2.9. Do you see how the polymerization of an amino acid would create an ARB type polymer?

Molecular diagram of Polypeptides or proteins
Figure 2.9 Polypeptides or proteins
Source: Wikipedia - Amino acid ball.

Polyethers

Polyethers are formed from reactions between diols in an RA2 type polymerization.

Molecular diagram of Polyethers
Figure 2.10 Polyethers
Source: Lauren Zarzar

Polyurethanes

Polyurethanes are formed from the reaction between diisocyanates with diols (Figure 2.11).

Molecular diagram of Polyurethanes
Figure 2.11 Polyurethanes
Source: Lauren Zarzar

Polyurea

Polyurea is formed from the reaction between diisocyanates with diamines (Figure 2.12)

Molecular diagram of Polyurea
Figure 2.12 Polyurea
Source: Lauren Zarzar