nomenclature instances, the illogic of an obviously ridiculous sourcehased name was overcome and a name hased on the polymer structure was used; an example is the preference for nolvmethvlene over "nolv(diazomethane) ." .. Thus, I;olymer nomenclature today siffers under a varietv of "svstems" of limited utilitv. In addition to polymer names based on an actual source, the most frequently encountered nomenclatures lead to
.~ A
ROBERT B. FOX Naval Research Laboratory
Washington, D. C. 20375
Naming Organic Polymers I. Problems with Present-Day Nomenclature The language of chemistry, like any language, is in a continual state of evolution. Sometimes the developmental course of a language is outstripped by the development of the fields utilizing the language. This has happened in some areas of polymer science, and it is particularly the case with the language used to describe the substances with which polymer science deals. At the time (1892) of the Geneva Convention dealing with the nomenclature of organic chemistry, almost nothing was known of the chemical structure of organic polymers. As these materials increased in commercial importance, descriptive terminology was required. In the synthetic polymer field, the compounds from which the polymers were produced were, of course, known. In the ahsence of structural knowledge of the products, it was logical to invent names related to the source of the material. This was once a common practice in naming organic compounds; "acetylene tetrachloride" stems from the process by which the compound so named is produced. "Acetylene tetrachloride" owes its name to its sources, acetylene and chlorine. Source-based nomenclature for organic polymers is a parts, facile extension of the concept of "pdymer"-many with each part corresponding to a molecule of a "monomer" representing one part. The generic term is therefore "plymonomer." T o name an individual polymer, one needs only to know the name of the monomer. Thus, p l y styrene is the polymer made from styrene, poly(vinyl chloride) is the polymer produced by polymerizing vinyl chloride, and so on. As long as the polymerization process involved only the addition of monomer molecules to a growing polymer chain, hoth chain and name were straight. This system of nomenclature is by far the most common type in use today in polymer science. Even though the system is, in construction, inconsistent with the principles of good organic nomenclature, it would he acceptable if it generated unique unamhiguous names for the substances it purports to describe. Unfortunately, source-based polymer nomenclature shows weakness whenever a process other than addition is used to produce the polymer. In some cases, the addition process itself can follow more than one route. Since the need for unique and unamhiguous names for polymers is well-recognized, variants of source-based nomenclature have come into use. Occasionally, nomenclature systems were devised simply to give relatively short names. In rare
.
1) names hased on a hypothetical source: the structure of the re-
peating unit in -CH(OH)CH1-. suggests that it could he the polymer of the hypothetical monomer CHFCHOH, vinyl alcohol, leading to poly(viny1alcohol). 2) names based on an incorrect source or a hypothetical source where the name amears . . to bear some relations hi^ to the ~. o.l v mer repeatmg unit: puly(ethylenefumaratel. 3) names bared on a trivial name: polyterephthalylidrne 4) names hard on a trade name or a former trade name: Svlun.
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5) names based on afamily name: 6,6-polyamide
6) names based on repeating unit structure: palymethylene, poly(dimethylsiloxane);no reference is made in the name to the monomeric compounds from which the polymer is prepared. As might he imagined, some curious inconsistencies can result. The true source of "poly(viny1 alcohol)" made by the hydrolysis of poly(viny1 acetate) (a true source-based name) is poly(viny1 acetate) itself. An answer to the dilemma was to look a t the structure and guess a t a hypothetical monomer as the source. In this case, "vinyl alcohol" gets the nod, and poly(viny1 alcohol) is the resulting name. Never mind the fact that this polymer can also he made from acetaldehyde. Polymer reactions can lead to new polymers that are named by hybridizing nomenclature systems. For example, poly(p-lithiostyrene) can he made by the reaction of hutyllithium with poly(p-iodostyrene). The material is chemically a derivative of polystyrene; its name might be considered as being formed substitutively or it may he hased on a hypothetical source. The true source is again out of the question as the basis for a name. Even the name poly(p-iodostyrene) itself presents a prohlem: the substance could have been made from p-iodostyrene or by the iodination of polystyrene. The foregoing examples illustrate a common cause of collapse of a source-based system of polymer nomenclature: a given polymer can often be produced from more than one source. Resolution of the problem by looking at structure would he an answer if the reader knew when fact stopped and fiction began. The example of poly(viny1 alcohol) above represents fiction. For fact consider that either the self-condensation of a hromophenol or the thermal decomposition of a diazooxide leads to the same p l y mer: the common name is poly(pheny1ene oxide), a stmcture-based name. I t mizht well he concluded that the polymer was made from "phenylene oxide." If the generation of multiple names for the same suhstance is-not enough to bring about the end of sourcehased nomenclature for polymers, surely the fact that the system can lead to the same name for different polymers ought to finish the process. There are many monomers susceptible to polymerization through different functions depending on conditions. The monomers shown Volume 51, Number
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I CHa NCO CH=CH, can be polymerized in more than one way. The first, for example, could yield a substituted polystyrene or a polyisocyanate. Should they both be named "poly(4-vinylphenyl isocyanate)"? Similarly, a butadiene can be polymerized through either or both of the unsaturated linkages. Should all of the resulting individual polymeric products have the same name? When a polymer name is based on its source, i t might be thought that the process by which the polymer is made would come into consideration. Some of the difficulties have already been outlined. Consider polymer names in which both source and process are obscure. Examples are poly(ethylene terephthalate) and poly(bexamethylene adipamide). In each case, a monomer has been hypothesized, but unfortunately the names selected are those of cyclic compounds
P
P wo
NHCO
/\
(CHJe (CHA
\ /
NHW
Therefore, not only must a monomer be imagined but a pmcess, ring-opening, must be imagined as well to visualize the correct polymer. A name like poly(hexamethylene adipamide), even so, is far more descriptive than the more common Nylon-66. Names such as the latter have no place in scientific literature unless the object is to save wear and tear on typewriters. A few common polymer names are truly based on the chemical structure of the repeating unit of the polymer. Some examples are polymethylene, poly(oxyethyleue), and poly(1,l-difluoroethylene), although in the last case the structure- and one of the source-based names happen to he identical. With this kind of ambiguity and inconsistency in the present methods of naming relatively simple polymers, it is not difficult to imagine the near-impossibility of coining unambiguous names for the complex polymers resulting from current synthetic expertise and structural insight. For many polymers being synthesized in fact or imagination, none of the conventional nomenclature systems are adequate. One reason is that when a complex or unfamiliar polymer molecule is described, it is natural to describe the molecule and not its precursors or the process by which it was made. Another reason is that the names of the precursors themselves can often be quite long, and therefore a rational structural description can become attractive, however lengthy i t might be. Clearly, the requirements of polymer chemistry demand a set of rules by which any polymer can be described in terms a t least as precise as those for organic molecules. A rational nomenclature system for organic polymers clearly should be based on the structure of the polymer just as the names of organic molecules are based on their structures. If polymer structures are to be used in devising polymer names. some basic definitions will be rewired. The II:I'AC Macromolecular Nomenclature omm mission has recentlv' uodated earlier reoorts in the field of definition. Two sets oE definitions are presented: a "structure-based" series derived from a primary definition of polymer, and a "process-based" series linked to the primary definition through the terms polymerization and monomer. One version of the primary definition of polymer reads, "A substance composed of molecules characterized by the multiple repetition of many of one or a few species of constitu~~~
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tional units (atoms or groups of atoms), repetitively linked to each other such that the physical properties of the substance do not vary markedly with the addition or removal of one or a few of these constitutional units." Constitutional units are atoms or groups of atoms that are capable of linkina re~etitivelyto each other in a molecule. I t >s clear that $ the constitutional units are known and can be named, there exists a rational conceptual basis for a polymer nomenclature predicated on structure. Ordinarily, complete knowledge of the constitution or structure of a polymer molecule is not available. Most commercial polymers contain chemical units derived from more than one "monomer", and usually, but not always, these units are distributed in a random manner along the chain. Similarly, there may be present structural imperfections such & a few points of bsaturation in an otherwise saturated polymer chain or chain end-groups that have no chemical resemblance to the remainder of the chain. I t must be stressed that a polymer nomenclature based on structure must be almost entirely limited to features of structural regularity, and that in most instances this is an assumed regularity. This concept is not as strange as i t may at first seem: the label on the chloroform bottle often ignores the presence of an alcohol added as a stabilizer, and some of the 2-isomer is almost always present in a substance labelled l-methylnaphthalene. Indeed, the common source-based polymer names, such as polystyrene, also ignore the presence of chain irregularities, isomers, and impurities. Clearlv. the need exists for a rational oolvmer nomenclature ;Lough which, a t the minimum; any (assumed) regular polymer can be named. Within this restriction, a nomenclature system based on structure was devised and . ~ of inherent limitapublished twenty years a ~ o Because tions in detail but not inconcept, this system saw little application. Recently, this concept of regular polymer nomenclature has been brought within the framework of ordinary organic nomenclature principlesS and greatly extended' to cover most regular polymer structures that can be envisioned. The system is flexible and has been adopted for indexing purposes by Chemical Abstracts; it may be expected to see increasing use in a t least the fundamental polymer journals. In brief, in this nomenclature system a structural repeating unit for a given polymer is identified, oriented, and the constituent parts named in order. The resulting bivalent group name, prefixed by "poly," becomes the name of the polymer. A few examples will serve to illustrate the system
Because of its importance to polymer chemistry, this structure-based nomenclature s$stim for regular singlestrand polymers will be examined in detail in Part 11. 1 "Basic Definitions of Terms Relating to Polymers," KUF'AC Information Bulletin, Appendices an Tentative Nomenclature Symbols, Units, and Standards, No. 13,February 1971. 5.Polymer Sei., 8,251(1952).
3Macromolecules, 1,193 (1968). 4 "Nomenclature of Regular Single-Strand Organic Polymers,"
ILJF'AC Information Bulletin, Appendices on Tentative Nomenclature, Symbols, Units, and Standards, No. 29, November 1972.
Functional Derivatives of Inorganic Acids When one speaks of carbon dioxide as carbonic anhydride, one is not so much using a name for a compound as speaking of a function performed by a compound. While functional nomenclature is still used in connection with derivatives of acids, this usage is not recommended. Acid Halides. The names of acid halides are formed from the name of the corresponding acid radical if this has a special name: nitrosyl chloride, NOCI; phosphoryl chloride, POC13. In other cases these compounds are named as halide oxides: molybdenum dichloride dioxide, MoOzCIz. Anhydrides. Anhydrides should he given names as oxides. Thus N ~ O Jis dinitrogen pentoxide, not nitric anhydride or nitric acid anhydride. There is a group of compounds which are sometimes called mixed anhydrides because they furnish two different acidsupon hydrolysis. N~0s.2SOs 0NOS020SOzON0 mixed anhydride of disulHSO&.NO
HOSOaONO
furic and nitrous acid pktial anhydride of sulfuric acid with nitrous acid
However, the customary and acceptable names are not constructed on this functional basis dinitrosyl disulfate and nitrosylsulfuric aeid or nitmsyl hydrogen sulfate. Esters. The names for inorganic esters a? constructed in the same way as those for salts: dimethyl sulfate, diethyl hydrogen phosphate, trimethyl phosphite. Amides. The names for amides are derived in either of two ways: 1) replacing "acid" hy "amide" in the acid
names and 2) using acid-radical names with amide, diamide, triamide, etc. sulfuricdiamide or sulfonyl diamide SOa(NHd2 PO(NH4a phosphoric triamide or phasphoryl triamide. Many compounds exist in which only some of the hydmxyl groups have been replaced by NH2 groups. Again, two patterns are in use: 1)names ending in amidic acid and 2) abbreviated coordination names NH2SOaH . sulfamidic acid or amidosulfuric acid NHzPO(0H)z phmphoramidic acid or amidophosphoric acid (NH2)*PO(OH) phosphomdiamidieaeid or diamidophm. phoric acid Abbreviated names (sulfamide, phosphoramide, sulfamic acid) have the advantage of brevity hut do not follow any general pattern. Nitriles. Although the suffix -nitrile has been 'used in the names of a few inorganic compounds, e.g., (PC1zN)a trimeric phosphonitrile chloride, systematic names are preferable. (PChNIs KIOaNO3)
trimeric phosphorus dichloride nitride potassium nitridotrioxoosmate(Vm,or potassium nitridutrioxuasmate(1-) but nut potassium
The IUPAC Commission sees no reason for retaining the name nitrile in purely inorganic names.
W. C. Fernelius Kurt Loening Roy M. A d a m s
Volume 51, Number
1, January 1974
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