Custom then is the great guide of human life.
—David Hume,Concerning Human Understanding
A systematic IUPAC nomenclature exists for polymers just as it does for organic and inorganic chemicals. This polymer nomenclature is rarely used, however, because a trivial naming system is deeply entrenched through the force of usage.
A similar situation prevails with all chemical species that are commercially important commodities. Thus, large-scale users of the compound 1-40
1-40 CH3 C CH2CH3
O
will know it as MEK (methyl ethyl ketone) rather than 2-butanone. The com- mon polymer nomenclature prevails in the scientific as well as the technological literature. (It is not used inChemical Abstractsand reference should be made to Volume 76 [1972] of that journal for the indexing of polymers.)
Reference [4] gives details of the systematic IUPAC nomenclature. The remainder of this section is devoted to a review of the common naming system, a knowledge of which is needed in order to read current literature.
Although the common naming system applies to most important polymers, the system does break down in some cases. When inconsistencies occur resort is made to generally accepted conventions for assignment of names to particular polymers. The nomenclature is thus arbitrary in the final analysis. It usually works quite smoothly because there are probably no more than a few dozen poly- mers that are of continuing interest to the average worker in the field, and the bur- den of memorization is thus not excessive. The number of polymeric species that require frequent naming will eventually become too large for convenience in the present system, and a more formal nomenclature will probably be adopted in time.
Although there are no codified rules for the common nomenclature, the following practice is quite general.
Polymers are usually named according to their source, and the generic term is
“polymonomer” whether or not the monomer is real. Thus we have polystyrene (1-1) and poly(vinyl alcohol) (1-7). Similarly, polyethylene is written as 1-3 although the representation (CH2)2nand the corresponding name “polymethylene”
could have been chosen equally well to reflect the nature of the repeating unit.
The monomer name is usually placed in parentheses following the prefix
“poly” whenever it includes a substituted parent name like poly(1-butene) (1-41) or a multiword name like poly(vinyl chloride) (1-4):
27 1.10 Polymer Nomenclature
1-41 CH2
CH2 CH3 C H
A particular common name is used even if the polymer could be synthesized from an unusual monomer. Thus, structure 1-42 is conventionally called poly (ethylene oxide), since it is derived from this particular monomer.
1-42
CH2 CH2 x O
The same name would ordinarily be used even if the polymer were synthesized from ethylene glycol (HOCH2CH2OH), ethylene chlorohydrin (ClCH2CH2OH), or bischloromethyl ether (ClCH2OCH2Cl). Similarly, structure 1-13 is called polycaprolactam because it is made industrially from the lactam by reaction (1-5), in preference to polymerization of the parent amino acid, H2N(CH2)5COOH.
It is useful to digress at this point to review some common names for frequently used vinyl monomers. These are summarized inFig. 1.4. Alternative names will be apparent, but these are not used by convention. (Thus, acrylonitrile could logically be called vinyl cyanide, but this would be an unhappy choice from a marketing point of view.) The polymer name in each case is poly “monomer.”
A few polymers have names based on the repeating unit without reference to the parent monomer. The primary examples are silicones, which possess the repeating unit:
1-43 Si R
R' O
The most common silicone fluids are based on poly(dimethyl siloxane) with the repeating unit structure:
1-44
Si i
CH3
CH3 O
CH2 COOH Acrylic acid
C H
CH2 C
O NH2
Acrylamide C H
Acrylonitrile CH2 C CN
H
Vinyl bromide CH2 C Br
H
Tetrafluoroethylene CF2 CF2
Vinylidene bromide CH2 CBr2
CH2 COOH
Methacrylic acid C CH3
CH2 COOCH3
Methyl methacrylate C
CH3
Hydroxethyl methacrylate CH2 C COOCH2CH2
CH3
N − Vinyl pyrrolidone C O CH2
H2C
HC CH2 CH2
N
Butadiene CH2 C CH2
H
CH2
Chloroprene CH2 C C
Cl H
CH2
Isoprene CH2 C C
H CH2 CH3
N − Vinyl carbazole HC CH2 N
OH
FIGURE 1.4
Some common vinyl monomers.
29 1.10 Polymer Nomenclature
The nomenclature of copolymers includes the names of the monomers sepa- rated by the interfix co-. Thus, 1-25 would be poly(vinylchloride-co-vinyl ace- tate). The first monomer name is that of the major component, if there is one.
This system applies strictly only to copolymers in which the monomers are arranged more or less randomly. If the comonomers are known to alternate, as in 1-26, the name would be poly(styrene-alt-maleic anhydride). Interfixes may be omitted when the name is frequently used, as in styrene-acrylonitrile copolymers (Section 1.5.3).
When the repeating unit of linear polymers contains other atoms as well as carbon, the polymer can frequently be named from the linking group between hydrocarbon portions. Thus, polymer 1-45
1-45 R OCR'
O
is evidently a polyester,
1-46 H RNCR'
O
is a polyamide,
1-47 R O CNR'
O H
is a polyurethane,
1-48 H RNCNR'
O H
is a polyurea, and
1-49 O RS R'
O
is a polysulfone. These polymers are generally made by reacting two monomers with the elimination of a smaller molecule [reactions (1-1) and (1-7), for exam- ple]. They are thus called condensation polymers (see alsoSection 7.1).
Condensation polymers are named by analogy with the lower-molecular- weight esters, amides, and so on. Thus, since the names of all esters end with the suffix -ateattached to that of the parent acid (e.g., 1-50)
1-50 COCH3CH3 CH3
O
is ethyl acetate, polymer 1-5 is named poly(ethylene terephthalate). The parent acid here is terephthalic acid, which is the para isomer. (The ortho diacid is phthalic acid and the meta isomer is isophthalic acid.) The alcohol residue must be a glycol if the polymer is to be linear, and so it is not necessary to use the word glycol in the polymer name. The word ethylene implies the glycol. Note that the trade name is usually used for the monomers. Thus, structure 1-51 would be named poly(tetramethylene terephthalate) or poly(butylene terephthalate) rather than poly(1,4-butane terephthalate).
1-51 CH2 CH2 O
CH2 C
n O C
O O CH2
Polyamides are also known as nylons. They may be named as polyamides.
Thus 1-6 is poly(hexamethylene adipamide). This name indicates that the poly- meric structure could be made by condensing hexamethylene diamine, H2N (CH2)6NH2, and adipic acid, HOOC(CH2)4COOH. The dibasic acids are named according to their trivial names: oxalic (HOOC—COOH), HOOC(CH2)COOH malonic, HOOC(CH2)2COOH succinic, glutaric, adipic, and so on. (The mne- monic is OMSGAPSAS: oh my, such good apple pie, sweet as sugar. We leave it to the reader to fill in the trivial names after adipic, if and when they are needed.) There is also an alternative numbering system for synthetic polyamides.
Polymers that could be made from amino acids are called nylon-x, where xis the number of carbon atoms in the repeating unit. Thus, polycaprolactam (1-13) is nylon-6, while the polymer from ω-aminoundecanoic acid is nylon-11. Nylons from diamines and dibasic acids are designated by two numbers, in which the first represents the number of carbons in the diamine chain and the second the number of carbons in the dibasic acid. Structure 1-6 is thus nylon-6,6. Nylon-6,6 and nylon-6 differ in repeating unit length and symmetry and their physical properties are not identical.
31 1.10 Polymer Nomenclature
Polymers such as polyamides (1-13), polyesters (1-5), and so on are not named as copolymers since the chemical structure of the joining linkage in each case shows that the parent monomers must alternate and copolymer nomenclature would therefore be redundant.
There are a few common polymers also in which the accepted name conveys relatively little information about the repeating unit structure. This list includes polycarbonate (1-52)
1-52
C O C
O
x
O CH3
CH3
and poly(phenylene oxide) (1-14). ABS polymers (Section 1.5.3) are an important class of thermoplastics which consists of blends and/or graft copolymers. A sim- ple repeating unit and name cannot usually be written for such species.
Graft copolymers like 1-27 are named as poly(A-g-B) with the backbone poly- mer mentioned before the branch polymer. Examples are poly(ethylene-g-styrene) or starch-g-polystyrene. In block copolymer nomenclature b is used in place ofg and the polymers are named from an end of the species. Thus, the triblock macro- molecule 1-53
1-53
H H
H CH3 H
H H H
CH2
x y z
C C C C C CH2 C
is called poly(styrene-b-isoprene-b-styrene). When such materials are articles of com- merce they are usually designated by the monomer initials, and this structure would be named SIS block copolymer. Reference[5]may be consulted for further details of copolymer nomenclature. Reference[6]lists locations of International Union of Pure and Applied Chemistry recommendations on macromolecular nomenclature.
Note that the common nomenclature generally uses trivial names for mono- mers as well as the corresponding polymer (1-1 and 1-2 are examples).
This brief review has emphasized the exceptions more than the regularities of the conventional polymer nomenclature. The reader will find that this jargon is not as formidable as it may appear to be on first encounter. A very little practice is all that is usually needed to recognize repeating units, parent monomer struc- tures, and the common names.