ABSTRACT
This reaction has been modified slightly by P. J. Flory, considering the mechanisms of the polymerization reactions. He has reclassified the polymerization reactions in the form of step reactions and chain
+ (1.3) In the first of these, the reaction kinetics reveals a gradual formation of product with high relative molar mass as the reaction proceeds. On the other hand, the chain reactions occur with rapid buildup of a few high-relative-molar-mass molecules, whereas the rest of the monomer remains unreacted. This means that the large molecules with high relative molar mass are formed at the beginning of the polymerization reaction, and also the monomer molecules exist during reaction. Step reactions can produce macromolecules, having simple no-branched linear structures and also having an intensive crosslinked network. The final structure of the polymer depends on the number of functional groups of the parent monomer, whereas the highly crosslinked network can emerge if a sufficient degree of the branching exists. By contrast, the chain reactions can produce only linear or low-branched polymers. By taking into account the thermoset and thermoplastic classification, it can be said that the chain reactions form thermoplastics, while the step reactions may give either thermoplastics or thermosets. Also there are many classifications based on different perspectives. Some of these classifications are given next. 1.1.2.1 Based on originPolymers can be obtained from natural sources and as synthetics. Natural polymers can be originated from proteins and carbohydrates. The typical polymer examples based on proteins and carbohydrates are silk, collagen, keratin, cellulose, starch, and glycogen. Synthetic polymers, which are prepared in the laboratory, are referred to as synthetic polymers or man-made polymers. Some examples of synthetic polymers are polyethylene, polystyrene, Teflon, PVC, synthetic rubber, nylon, Bakelite, Orlon, polyester, and Terylene (Charles and Carraher, 2003).
