The IUPAC Commission has now published an extension to these recommendations, "Nomenclature of Regular Double-Strand (Ladder and Spiro) Organic Polymers".(3) Double-strand polymers were extensively reviewed in the late 1960's and this is when the first attempt was made to formalize their nomenclature.(4,5) More recently, William J. Bailey, just before his untimely death, wrote a revised chapter on "Ladder and Spiro Polymers" for the second edition of the Encyclopedia of Polymer Science and Engineering.(6) Double-strand polymers continue to be reported in the literature, as evidenced by recent reviews.(7,8)

REGULAR DOUBLE-STRAND ORGANIC POLYMERS

In a double-strand polymer, the macromolecules consist of an uninterrupted sequence of rings with adjacent rings having one atom in common (a spiro polymer) or two or more atoms in common (a ladder polymer).

As for a single-strand polymer, a single preferred constitutional repeating unit (CRU) must be selected in order to obtain a unique name. Since the polymer has a sequence of rings, in order to identify a preferred CRU, the rings must be broken by observing the following criteria in decreasing order of priority.

(i) Minimize the number of free valences in the CRU.

(ii) Maximize the number of most preferred hetero atoms in the ring system.

(iii) Retain the most preferred ring system.

The CRU can be, depending on the complexity of the double-strand polymer, (1) a tetravalent acyclic group, (2) a tetravalent ring system-containing group, or (3) a combination of a cyclic group with one or two bivalent acyclic groups.

1.	2.	3.

Prior to naming, the CRU has to be oriented as illustrated above:

(1) the acyclic CRU in such a way that the lowest free valence locant is at the lower left;

(2) the ring-containing CRU in such a way that the lowest free valence locant is at the lower left and the next locants in the ascending order proceed in a clockwise direction;

(3) the ring- and acyclic group-containing CRU in a such a way that the ring system is on the left side and the acyclic subunits on the right of the ring system.

The polymer is named with the prefix "poly" followed by the name of the preferred CRU enclosed in parentheses or brackets.

For a polymer consisting of adjacent six-membered saturated carbon rings

the name based on the preferred CRU is

poly(butane-1,4:3,2-tetrayl)

Two additional examples of more complex double-strand polymers contrast the structure-based names (1) with the source-based names (2).

a. A ladder polymer known by its generic name and acronym as benzimidazobenzophenanthroline (BBL):(9)

(1) poly[(7-oxo-7H,10H-benz[de]imidazo[4',5':5,6]benzimidazo[2,1-a]isoquinoline-3,4:10,11-tetrayl)-10-carbonyl]

(2) ladder-poly[(1,4,5,8-naphthalenetetracarboxylic acid)-alt-(1,2,4,5-tetraaminobenzene)]

b. A spiro polymer generically described as a poly(spiroketal):(10)

(1) poly(2,4,8,10-tetraoxaspiro[5.5]undecane-3,3:9,9-tetrayl-9,9-diethylene)

(2) spiro-poly(1,4-cyclohexanedione-co-pentaerythritol)

The structure-based names provide complete information on the polymer repeating unit, whereas the source-based names do not. Unlike for most simple homopolymers and copolymers for which a structural repeating unit can easily be deduced from starting monomers, source-based names for double-strand polymers indicate the starting monomers but not much more. Double-strand polymers are often formed through multi-step reactions and the ring formation varies.

Both of these examples illustrate the rules of maximizing the number of hetero atoms in the ring system and of not breaking the aromatic ring if there is a choice.

Once the ring system has been selected according to the rules, its name and numbering scheme (locants) can easily be ascertained by consulting Chemical Abstract Service's Ring Systems Handbook. Its new 1993 edition has recently been published.(11)


REFERENCES

1.Polym. Prepr. 1992, 33(1), 6-11.
2.Polym. Prepr. 1991, 32(1), 655-656; 1992, 33(2), 6-7; 1993, 34(1), 6-9; 34(2), 6-9.
3.IUPAC Commission on Macromolecular Nomenclature. Pure Appl. Chem. 1993, 65(7), 1561-1580.
4.Livingston, H. K.; Fox, R. B. Polym. Prepr. 1968, 9(2), 1344-1349; J. Chem. Doc. 1969, 9(4), 232-234.
5.ACS Polymer Nomenclature Committee. Macromolecules 1968, 1, 193-198.
6.Bailey, W. J. Encyclopedia of Polymer Science and Engineering. 2nd ed. Wiley-Interscience, New York, 1990. Index Vol., pp. 158-245.
7.L–ffler, M.; Schl¸ter, A.-D. GIT Fachz. Lab. 1992, 36(11), 1101-1107.
8.Wang, C.-S. Trends Polym. Sci. 1993, 1(7), 199-205.
9.Van Deusen, R. L. J. Polym. Sci., Part B: Polym. Lett. 1966, 4(3), 211-214.
10.Bailey, W. J.; Volpe, A. A. Polym. Prepr. 1967, 8(1), 292-302.
11.Chemical Abstracts Service. Ring Systems Handbook. 1993 ed. Columbus, Ohio, 1993.


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*Mailing address: Chemical Abstracts Service, P.O. Box 3012, Columbus Ohio 43210.