Part Ⅰ Introduction to Polymers
Chapter 1 Introduction
1.1 Introduction
Polymers are large molecules made up of simple repeating units.The name is derived from the Greek， poly means “many” and mer means “part”. Macromolecule is a term synonymous with polymer. Polymers are synthesized from simple molecules called monomers（single part）. A few representative monomers， together with the repeating units of the corresponding polymer， are given in the following reactions：
Ethylene 
Tetrafluorethylene 
Styrene 
Methyl methacrylate 
1，3-Butadiene 
Ethylene oxide 
Ethylene glycol 
4-Hydroxymethyl benzoic acid 
It should be noted that with the first six of the above eight examples the repeating units contain the same atoms as the corresponding monomers， whereas with the last two the repeating units contain fewer atoms because a by-product is formed in the polymerization process. The former types are commonly referred to as addition polymers， and the latter as condensation polymers. However， this terminology， while deeply ingrained in the language of polymer chemistry， can lead to confusion， as is shown by the fact that the structures of the sixth and seventh examples are identical. Is 
OCH2CH2
an addition polymer or a condensation polymer？ This ambiguity in defining polymer types will be considered latter. The first four examples involve ordinary addition to a double bond， while the fifth is an example of 1，4-addition of conjugated diene. Polymerization of the ethylene oxide involves a ring-opening reaction of a strained three-membered ring. Ethylene glycol gives the same product， a polyether， by dehydration， and 4-hydroxymethyl benzoic acid undergoes ordinary esterification to form ester. It should be noted that the fundamental difference between polymerization reaction of latter type and simple organic reactions is that di-or polyfunctional compounds are necessary for polymer formation， whereas monofunctional compounds can only form simple compounds. Thus， ethyl alcohol and benzoic acid react to form ethyl benzoate， whereas ethylene glycol and terephthalic acid give polyester.
