Polymers are among some of the most useful and valuable products of the chemical industry. In general, polymer products are classified as plastics and resin products or as rubber products. A plastic material is defined as a solid, high-molecular-weight, polymerized organic substance and typically involves liquid-phase manufacturing or processing of the material [2]. Plastic and resin products include chemicals such as polyolefins (polyethylene/polypropylene), polyesters (PET, PBT), polyamides (nylons), and formaldehyde-based resins. Rubber products are, similarly, polymers having a high molecular weight, but in contrast to plastic and resin products, they exhibit elastic behavior and often are called elastomers [1]. Rubber products include synthetic rubber, latex, nitrile, silicone, and other rubbers.
The polymer product sector is inevitably linked to the basic organic chemicals and the petrochemicals. Most of the polymers are formed either through addition reactions (involving addition of the monomer molecule to the polymer chain) or condensation reactions (involving reaction groups belonging to two different monomer units). Most of the polyolefins, such as polyethylene, polypropylene, and PVC, are formed through the addition polymerization reactions. Such polymers typically soften and melt without decomposition upon heating and can be resolidified into new forms without losing their polymer characteristics. These polymers are called thermoplastics [1]. Phenolic resins, such as phenol-formaldehyde resins, and polyesters, such as PET, are formed by condensation reactions. These polymers are characterized by strong chemical bond crosslinking of units. They typically decompose upon heating and, unlike thermoplastics, cannot be reconstituted upon cooling. Figure 2.4 shows some of the important polymer products. The figure offers only a brief glimpse into the world of polymers and does not include several other products of equal significance.
Figure 2.4 Classification and examples of polymer products. ABS, acrylonitrile-butadiene-styrene; LDPE, low-density polyethylene; HDPE, high-density polyethylene; PBT, polybutylene terephthalate; PET, polyethylene terephthalate; PVC, polyvinyl chloride; SBR, styrene butadiene rubber.
The polymer sector of the chemical industry includes the manufacture not only of the polymer (polyester, for example) but also of fibers and filaments based on these polymers. Polymers are highly versatile chemicals with remarkable properties that allow them to be shaped into thin films, flexible nets, rigid furniture, cloth, and countless other products that make them so ubiquitous in modern society.
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