ABSTRACT
In formulas representing polymers, the end groups are often ignored because they may not have a major effect on the properties of the polymer. For example, the polymer based on vinyl chloride is represented in the following way:
CH2=CHCl
vinyl chloride poly(vinyl chloride)
( CH2 CHCl )x
Also, the fact that several monomers are dispersed at random in a chain may not be explicit to allow us to abbreviate the structure, as in the random copolymer of styrene and butadiene:
—( CH2-CH )—–( CH2-CH=CH-CH2)—xy
Styrene-butadiene rubber copolymer
In nylon 6,6, the repeating unit is made up of a diamine and a diacid:
Nylon 6,6 (a polyamide based on hexamethylenediamine and adipic acid)
In some cases two monomers may be combined to form a dimer, three to form a trimer, and so on. The number of repeating monomer units is referred to as the degree of polymerization, indicated by x or y in the formulas shown (see also Section 4.4). When more than one monomer is present in the polymer, as in styrenebutadiene rubber (SBR), the overall degree of polymerization may be ambiguous. For low-molecular-weight polymers, the term oligomer (oligo being a prefix of Greek origin meaning “few”) is often used. Typically, oligomers might encompass degrees of polymerization of 2-20. The analogous term oligosaccharide usually includes molecules with 2-6 sugar units (see Figure 15.3).
