In the previous "Macromolecular Nomenclature Notes", we have presented the various recommendations of the Commission on Macromolecular Nomenclature of the International Union of Pure and Applied Chemistry (IUPAC).(1)
In December 1996, the Commission published the recommendations on basic terms in polymer science(2) and this is what we wish to discuss in this note. It might be of interest to provide first a brief historical background which highlights the early contributions of pioneers in polymer science to macromolecular nomenclature and terminology, and points out a long way towards universal and international acceptance and use.
As early as in 1949 there existed an IUPAC Subcommission on Nomenclature, whose first chairman was Maurice L. Huggins and second chairman Jan Joseph Hermans. The Subcommission was part of the IUPAC Commission on Macromolecules under the chairmanship of Herman F. Mark. The Commission included among its members other notable pioneers in polymer science: Otto Kratky, Harry W. Melville, and Georges J. Smets.
The Subcommission's official report(3) was adopted by IUPAC in September 1951 and published in 1952. It introduced a number of basic definitions starting with macromolecule, macromolecular substance, and high polymer, and proceeding to homopolymer, copolymer, graft copolymer, linear polymer, and branch polymer, as well as repeating unit, base unit, and monomeric unit (mer). The Report recognized that the practice in the field of small molecules of providing rigorous definitions is impractical for polymers which consist of molecules not necessarily exactly of the same size, chemical composition, or structure. The differences, of course, result from the presence of end groups, branches, variation in orientation of monomeric units, and irregularity in the sequence of different types of such units.
When the Commission on Macromolecules was elevated to become the IUPAC Division of Macromolecular Chemistry, which in turn established its Commission on Macromolecular Nomenclature in 1968, the work on basic definitions was continued and it culminated in the 1974 recommendations "Basic Definitions of Terms Relating to Polymers".(4)
Two broad sets of definitions were presented: one based on the structure of polymer and the other on the process by which polymeric substances come into being. Polymer was defined as
"a substance composed of molecules characterized by the multiple repetition of one or more species of atoms or groups of atoms linked to each other in amounts sufficient to provide a set of properties that do not vary markedly with the addition or removal of one or a few of the constitutional units".
These definitions provided the foundation of nomenclature recommendations that distinguished between structure-based names, derived from the knowledge of the detailed molecular architecture, and source-based names, derived from the knowledge of the components of the reaction mixture.
The 1996 recommendations(2) make it clear that in polymer science it is necessary to distinguish between the substance (the polymer) and the macromolecule of which it is composed.
Here is a selection of terms with their definitions from the new "Glossary". Some definitions were combined in order to cite more of them in this Note.
polymer is a substance composed of macromolecules, the structure of which essentially comprises the multiple repetition of units derived from molecules of low relative molecular mass.
homopolymer is a polymer derived from one species of (real, implicit or hypothetical) monomer, a substance composed of molecules which can undergo polymerization, thereby contributing constitutional units to the essential structure of a macromolecule.
constitutional unit is an atom or group of atoms (with pendant atoms or groups, if any) comprising a part of the essential structure of a macromolecule, an oligomer molecule, a block, or a chain.
constitutional repeating unit (CRU) is the smallest constitutional unit, the repetition of which constitutes a regular macromolecule, a regular oligomer molecule, a regular block, or a regular chain.
configurational unit is a constitutional unit having at least one site of defined stereoisomerism.
single-strand chain is a chain that comprises constitutional units connected in such a way that adjacent constitutional units are joined to each other through two atoms, one on each constitutional unit.
ladder chain is a double-strand chain consisting of an uninterrupted sequence of rings, with adjacent rings having two or more atoms in common.
spiro chain is a double-strand chain consisting of an uninterrupted sequence of rings, with adjacent rings having only one atom in common.
mesogenic monomer is a monomer which can impart the properties of liquid crystals to the polymers formed by its polymerization.
copolymer is a polymer derived from more than one species of monomer.
syndiotactic polymer is a polymer composed of syndiotactic macromolecules which are macromolecules essentially comprising alternating enantiomeric configurational base units, which have chiral or prochiral atoms in the main chain in a unique arrangement with respect to their constitutional units.
block polymer is a polymer composed of block macromolecules which are composed of blocks in linear sequence.
junction unit is a non-repeating atom or non-repeating group of atoms between blocks in a block macromolecule.
graft polymer is a polymer composed of graft macromolecules which are macromolecules with one or more species of block connected to the main chain as side-chains, these side-chains having constitutional or configurational features that differ from those in the main chain.
star polymer is a polymer composed of star macromolecules which are macromolecules containing a single branch point from which linear chains (arms) emanate.
comb polymer is a polymer composed of comb macromolecules which comprise a main chain with multiple trifunctional branch points from each of which a linear side-chain emanates.
ionomer is a polymer composed of ionomer molecules which are macromolecules in which a small but significant proportion of the constitutional units have ionizable or ionic groups, or both.
polymer blend is a macroscopically homogeneous mixture of two or more different species of polymer (Note: in most cases, blends are homogeneous on scales smaller than several times visual optical wavelengths; the use of the term polymer alloy for polymer blend is discouraged).
interpenetrating polymer network (IPN) is a polymer comprising two or more networks which are at least partially interlaced on a molecular scale but not covalently bonded to each other and cannot be separated unless chemical bonds are broken.
chain scission is a chemical reaction resulting in the breaking of skeletal bonds.
depolymerization is the process of converting a polymer into a monomer or a mixture of monomers.
REFERENCES
1.Polym. Prepr. 1991, 32(1), 655-656; 1992, 33(2), 6-7; 1993, 34(1), 6-9; 1994, 35(1), 6-9; 1995, 36(1), 6-9; 36(2), 6-9; 1996, 37(1), 6-9.
2.IUPAC. "Glossary of Basic Terms in Polymer Science". Pure Appl. Chem. 1996, 68, 2287-2311.
3.IUPAC. "Report on Nomenclature in the Field of Macromolecules". J. Polym. Sci. 1952, 8, 257-277.
4.IUPAC. "Basic Definitions of Terms Relating to Polymers". Pure Appl. Chem. 1974, 40, 477-491; reprinted as Chapter 1 in IUPAC "Compendium of Macromolecular Nomenclature" (The Purple Book), Blackwell Scientific Publications, Oxford, 1991, pp. 13-24.
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