The goal of the Commission, which our Committee fully supports and is committed to promote, is to improve communication in the polymer scientific community worldwide by providing standardized descriptions of the materials and processes of polymer science and technology. For the international readers of Polymer Preprints, it may of interest to note that three complete translations of the "Purple Book" have been published: Japanese,(2b) Polish,(2c) and Spanish.(2d)

GRAPHIC REPRESENTATIONS OF MACROMOLECULES

There is no argument that chemical formulas, chemical structures, chemical drawings, or graphic representations of chemical compounds are the international language of chemistry, bypassing the various intricacies and idiosyncrasies of corresponding names in different alphabets and languages, which in addition employ numerous trivial and semi-systematic names for compounds and substituent groups.

By the way, a presumably old adage, "a picture is worth a thousand words", often attributed to Confucius, has been recently reported as having its origin of its present form in an American advertisement of 1921.(4)

The principal author of the IUPAC recommendation, Dr. Rolf E. Bareiss, chose a motto a citation from the German astronomer, Johannes Kepler (1571-1630): "Ubi material ibi geometria" ("Where there is matter, there is geometry").

In comparison with chemical formulas of low-molecular-weight compounds, chemical formulas of polymers must additionally reflect the multiplicity of constitutional repeating units in a macromolecule and the various possibibilities for connecting the constitutional units in a macromolecule.

Most likely, the most inconsistent representation encountered in the literature is related to copolymers, when no clear differentiation is made between:

(i) a two-block copolymer consisting, for instance, of a block containing p monomeric units A and a block containing q monomeric units B:

and

(ii) a random copolymer:

where the mass fraction or mass percentage ratio of the two comonomeric units is known, e.g., 75:25 mass %, but not their sequence.

Here is an example from the literature that may illustrate a potential misunderstanding:

At a first glance, it would appear that this is a 2-block copolymer consisting of "ethylenecarbonyl" and "propylenecarbonyl" blocks, but the accompanying text makes it clear that in the total macromolecule propylene is substituted randomly for ethylene and that a better representation would be:

indicating that both repeating units exist in the copolymer, but their exact sequence is not known.

It might be useful to state first a few key rules before proceeding to several specific examples:

1. The representation of constitutional units and monomeric units shall be in accordance with usage in organic and inorganic chemistry.
2. While dashes representing chemical bonds may be omitted within the formula, unless necessary for clarity, at the ends of the constitutional repeating units and monomeric units, dashes must be attached.
3. Enclosing marks (parentheses or square brackets) together with subscript letters denote multiplicity of the enclosed constitutional units.
4. The subscript letters n, p, g, r, etc. denote multiplicities of polymeric sequences, whereas the subscript letters a, b, c, etc. denote multiplicities of oligomeric sequences.
5. Specifications about mass fractions, mole fractions, molar masses, degree of polymerization, etc., may be expressed in numerical values in parentheses after the formula of the macromolecule.

Examples

1. Regular homopolymer or copolymer:

Notes:
a. The order of citation of constitutional repeating units within the formula is arbitrary and need not reflect the order of citation dictated by structure-based nomenclature.(5)
b. The chemical bonds connecting the constitutional repeating units are represented by dashes drawn across the enclosing marks.
c. The formulas of end groups are attached to the bonds at the ends of the constitutional units, but placed outside the enclosing marks.

2. Irregular homopolymer or copolymer:

an irregular polymer derived from vinyl chloride, the units of which are joined both head-to-tail and head-to-head

an irregular polymer derived from the condensation of ethylene glycol with terephthalic acid and isophthalic acid

Notes:
a. The oblique stroke drawn between the constitutional units indicates the irregular or unknown sequential arrangement of these units.
b. The dashes at each end of the formula are drawn fully inside the the enclosing marks, because they do not necessarily denote terminal chemical bonds of the macromolecule.

3. Block copolymer:

polystyrene-block-polybutadiene-block-polystyrene (known sequence of regular blocks)

4. Graft copolymer:

REFERENCES

1.IUPAC. "Graphic Representations (Chemical Formulae) of Macromolecules". Pure Appl. Chem. 1994, 66, 2469-2482.
2.a. IUPAC "Compendium of Macromolecular Nomenclature" (The Purple Book). Blackwell Scientific Publications, Oxford, 1991; available in the U.S from CRC Press, Boca Raton, Florida.
b. "Kobunshi Meimeho". Committee of Macromolecular Nomenclature, Society of Polymer Science, Japan. McGraw-Hill, Tokyo, 1993.
c. "Kompendium Nomenklatury Makromolekularnej". Komisja Nomenklatury, Polskie Towarzystwo Chemiczne. Warszawa, 1995.
d. "Compendio de Nomenclatura Macromolecular". Consejo Superior de Investigaciones CientÌficas, Real Sociedad EspaÒola de QuÌmica. Madrid, 1993.
3.Polym. Prepr. 1992, 33(1), 6-11.
4.Mieder, W. "Proverbs Are Never Out of Season". Oxford University Press, New York, 1993.
5.IUPAC. "Nomenclature of Regular Single-Strand Organic Polymers". Pure Appl. Chem. 1976, 48, 373-385. Reprinted as Chapter 5 in Ref. 2.


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* Chemical Abstracts Service, P.O. Box 3012, Columbus, OH 43210.