Chapter Eleven – Polymerization

Publisher Summary This chapter covers details about polymerization, which is a reaction in which chain-like macromolecules are formed by combining small molecules (monomers). One natural polymer is cellulose (the most abundant organic compound on earth), a molecule made of many simple glucose units (monomers) joined together through a glycoside linkage. Proteins, the material of life, are polypeptides made of ά amino acids attached by an amide The polymer industry dates back to the 19th century, when natural polymers, such as cotton, were modified by chemical treatment to produce artificial silk (rayon). The first synthetic polymeric material was made using a condensation reaction between formaldehyde and phenol. Currently, these polymers serve as important thermosetting plastics (phenol formaldehyde resins). Many modern commercial products (plastics, fibers, rubber) are derived from polymers. The huge polymer market directly results from extensive work in synthetic organic compounds and catalysts. Ziegler's discovery of a coordination catalyst in the titanium family paved the road for synthesizing many stereo regular polymers with improved properties. The physical properties of polymers are described including the density, melt flow index, crystalline, and average molecular weight. Mechanical properties of a polymer, such as modulus (the ratio of stress to strain), elasticity, and breaking strength, essentially follow from the physical properties. Synthetic polymers may be classified into addition or condensation polymers according to the type of reaction. A second classification depends on the monomer type and the linkage present in the repeating unit into polyolefins, polyesters, polyamides, etc. Other classifications depend on the polymerization technique or on the polymer's end use. The latter classifies polymers into three broad categories: plastics, elastomers, and synthetic fibers.