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Chapter

Cover Making the Transition to University Chemistry

Polymers  

This chapter focuses on the polymer, which is the resulting very large molecule following the reactions of monomers. Polymers, then, are classified as either addition polymers or condensation polymers. As well as polymers, the addition polymerization of alkenes involves the formation of a large molecule by combining a large number of alkene monomers. The chapter also identifies ethene as the monomer of polyethene. Condensation polymers are generated through the reaction of varying factors such as polyesters, polyamides, dicarboxylic acid, diamines and diols. Chain polymerization can help form polyethene, while step polymerization aid in generating condensation polymers like polyurethanes, polyesters and polyamides.

Chapter

Cover Polymers

Three-dimensional networks  

This chapter focuses on three-dimensional networks, which are the toughest and most rigid materials, since the polymer chains are linked together in all directions to give effectively a single giant molecule. Three-dimensional networks do not melt, although segments may go through phase changes with temperature. They are insoluble, although lightly cross-linked ones can be solvent-swollen. They are therefore prepared in two stages, the first giving a processable intermediate that becomes the intractable final product in the second one. These principles are demonstrated for several systems, including Bakelite (phenol-formaldehyde polymers) and fibre glass (linear unsaturated polyesters), and also the vulcanization of rubber. Polymers which set hard after heating, usually because of a thermal cross-linking reaction, are called thermosets. The chapter then looks at electron beam cross-linking and physical cross-linking.