21.2: Characteristics and Nomenclature of Homopolymers
Polymers that are made up of identical monomer units are called homopolymers. Only one repeating unit is involved in the construction of the homopolymer structure. For example, as depicted in Figure 1, polypropylene is a homopolymer constituted of propylene monomers. Here, the only repeating unit in the polymer chain is propylene.
Figure 1: Propylene homopolymerization to polypropylene.
The chemical name of a homopolymer is generated by using the name of its monomer with a prefix ‘poly’. For example, the homopolymer synthesized from propylene is known as polypropylene. At times, the monomer name is enclosed with a parenthesis distinct from the prefix poly, such as when multiple components or substituents are present in the monomer. Figure 2 illustrates one such example with the homopolymer obtained from tetrafluoroethylene. Another popular example is poly(vinyl chloride).
Figure 2: Tetrafluoroethylene homopolymerization to poly(tetrafluoroethylene).
The other components of the structure like the notations of unsaturation, stereochemistry around the unsaturation, and the position of functional groups in the monomer are often placed in front of the prefix poly in the polymer’s nomenclature. This is illustrated in Figure 3, which shows the polymerization of chloroprene (2-chloro-1,3-butadiene) to poly(chloroprene), or neoprene (synthetic rubber).
Figure 3: Polymerization of chloroprene (2-chloro-1,3-butadiene) to trans-1,4-poly(chloroprene) (sometimes trans-2-chloro-1,3-polybutadiene).
Formal scientific usage may employ a fully structure-based convention wherein the entire structural repeating unit is enclosed in parentheses or brackets after ‘poly’, as in poly(2-chlorobuta-1,3-diene) or poly[(Z)-1-chlorobut-2-ene-1,4-diyl].
However, most often, polymers are known by their trade name rather than the chemical name. This is evidenced in the case of the lesser-known chemical names of well-known polymers based on compositions like poly(tetrafluoroethylene) and poly(paraphenylene terephthalamide).
