2.1 Introduction:

There are some common names for polymers, for example:

The first two names reflect the source-based nomenclature. "Pyrrole" and "thiophene" are starting materials or monomers. the next two names are structure-based since the bivalent groups, "phenylene", "thienylene", and "vinylene" for

However, the linkage positions shown in the structures are not reflected in the names. Thus, the names corresponding to the structures should in fact be

"poly(1,4-phenylenevinylene)" and "poly(2,5-thienylenevinylene)"

The correct use of parentheses in the "poly" names is essential. In source-based names, the name of the monomer should be enclosed if it consists of more than one word, e.g., "poly(methyl methacrylate)".

In structure-based names, the constitutional repeating unit (CRU), also known as structural repeating unit (SRU), should always be enclosed in parentheses whether it consists of a single bivalent group or a combination of groups, e.g., "poly(2,5-pyrrolediyl)" and "poly(1,4-phenylenevinylene)".

These rules are made by International Union of Pure and Applied Chemistry (IUPAC):

2.2 IUPAC Rules

The steps involved in the complete process are:

1. Identification of the repeating unit
2. Orientation of the repeating unit
3. Naming of the complete repeating unit

Each of these three steps is now described in more detail.

1. Identification: draw a segment of the chain long enough to contain at least two complete units.

   For example: assume that a chain has seven different types of subunit, called (arbitrarily) P, Q, R, S, T, U, and V, and that they are bonded in the order: ..P-R-T-V-U-S-Q-P-R-T-V-U-S-Q-.. .

    

2. Orientation: A correctly oriented SRU has the senior subunit placed leftmost, and the rest of the subunits then read left to right.

   Start by placing a left square bracket through the single chain bond before the senior subunit in the chain. Read along the chain (from left to right) until you come to the next occurrence of the same type of subunit to the left of which you placed the left square bracket, and place a right square bracket through the single chain bond to the left of it. Place a sub-n outside the right square bracket. This identifies the SRU.

   For example: Assume v is the senior subunit  (a) Place a left square bracket somewhere near the left-hand end of the sequence, e.g. through the single chain bond between T and V. This creates ..P-R-T-[-V-U-S-Q-P-R-T-V-U-S-Q-.. .

   (b) Read along the chain (from left to right) as far as the next occurrence of V and place a right square bracket through the single chain bond to the left of it; this creates ..P-R-T-[-V-U-S-Q-P-R-T-]-V-U-S-Q-.. .

   (c) Add a sub-n outside the right square bracket; this identifies the SRU as -[-V-U-S-Q-P-R-T-]n- .

   Five important rules (A — E below) are needed.

• Rule A: the order of seniority among the types of subunits is:    ( ">" means "is senior to". )
•     (a) heterocyclic rings;
•     (b) acyclic hetero atoms;
•     (c) carbocyclic rings; and
•     (d) chain containing carbon atoms only.

• For chains containing more than one type of heterocyclic ring, there is a further set of rules, which are too complex to reproduce here, for determining seniority; one example only is given.

Example 2A5:3,5-pyridinediyl>2,5-thiophenediyl (nitrogenous heterocycle > non-nitrogenous heterocycle); therefore:

• For chains containing heteroatoms, seniority is as follows: O, S, Se, Te, N, P, As, Sb, Bi, Si, Ge, Sn, Pb, B, Hg.

For example:  How to identify and orient    -C-O-C-C-S-C-C-O-C-C-S-C-    ?

• For chains containing more than one type of carbocyclic ring, there is a further set of rules, which are too complex to reproduce here, for determining seniority. One example only is given.

• Rule B: from the senior subunit, as determined by rule A, proceed by the shortest path (smallest number of atoms) to (a) another occurrence of the same subunit (if present) within the SRU, then (b) to the next most preferred subunit, and so on. This rule thus indicates the direction in which to read along the chain after the senior subunit has been identified. Table 2 gives some examples.

If application of rule B results in more than one possible path, the situation is resolved by taking the most highly substituted path; nylon 66 is a good example (see table 3).

• Rule C: for any given arrangement of atoms in a subunit, unsaturation is senior to saturation.

• Rule D: if substituents are present, otherwise identical parent subunits in the SRU are chosen by the principles, in turn, of (a) maximum number, (b) lowest locants, and (c) earliest alphabetical order of substituents.

• Rule E: when defining an SRU, parentheses are never drawn through a multiple chain bond if they can be drawn through a single chain bond.

1. Naming: name the subunits in the order in which they occur in the oriented SRU (from left to right); write the names of the subunits in order (left to right); enclose them in parentheses or brackets; and preface the assembled subunits with "poly". Since CAS and IUPAC nomenclature differ somewhat, the examples given above in tables 1, 2, and 3 are repeated in table 6 with both CAS and IUPAC names for comparison.

Table 6: Comparison of CAS 9CI and IUPAC Names for some Polymers

Ex. No.	Structure	CAS Polymer Namea	IUPAC Polymer Name
2A1		poly(2-5-thiophenediyloxy- 1,4-phenylene-1,2-ethanediyl)	poly(thiophene-2,5-diyloxy- p-phenyleneethylene)
2A2		poly(oxy-1,4-phenylene)	poly(oxy-p-phenylene)
2A3		poly(1,4-phenylenemethylene)	poly(p-phenylenemethylene)
2A4		poly(3,5-pyridinediyl -2,5-thiophenediyl)	poly(pyridine-3,5-diylthiophene -2,5-diyl)
2B1		poly(oxymethyl= eneoxy-1,2-ethanediyl)b	poly(oxymethylene= oxyethylene)b
2B2		poly(oxy-1,2-ethanediylthio -1,2-ethanediyl)	poly(oxyethylene= thioethylene)b

^b An equals sign, "=", is used to indicate that the name segment continues on the next line with no space or hyphen.

For guidance, a few examples only are included in table 7.

Table 7: Comparison of CAS 9CI and IUPAC Names for frequently encountered Bivalent Radicals

Ex. No.	Structure	CAS 9CI Name	IUPAC Name
1	-O-	oxy	oxy
2	-S-	thio	thio
3	-NH-	imino	imino
4	-N=	nitrilo	nitrilo
5	-CH2-	methylene	methylene
6	-CH=	methylidyne	methylidyne
7	-CH2-CH2-	1,2-ethanediyl	ethylene
8	-CH2-CH2-CH2-	1,3-propanediyl	propane-1,3-diyl
9	-CH2-CH2-CH2-CH2-	1,4-butanediyl	butane-1,4-diyl
10	-CH=CH-	1,2-ethenediyl	vinylene
11		1,4-phenylenea	p-phenylenea
12		(1,6-dioxo-1,6-hexanediyl)b	adipoyld
13		carbonyl-1,4-phenylenecarbonylc	terephthaloylc,d
14		iminocarbonylimino	ureylened

^aThe other two in this series are 1,2-phenylene (= o-phenylene) and 1,3-phenylene (= m-phenylene).

^bNames for others in this series may be safely deduced, e.g. (1,2-dioxo-1,2-ethanediyl) = oxalyl; (1,3-dioxo-1,3-propanediyl) = glutaryl; etc. Compound (i.e. "complex") expressions such as these, which contain substituents, must be parenthesized.

^cThe other two in this series are carbonyl-1,2-phenylenecarbonyl (= phthaloyl) and carbonyl-1,3-phenylenecarbonyl (= isophthaloyl).

^d IUPAC names such as adipoyl, terephthaloyl, ureylene, etc., are allowed only if they do not conflict with the orientation rule.

Table 8: Examples of Commercially Available Polymers

No.	SRU	Trivial Name; CAS Polymer Namea	Typical IUPAC Polymer Name
1		Polyethylene; Not structured or named as an SRU	poly(methylene)
2		Polypropylene; Not structured or named as an SRU	poly(1-methylethylene)
3		poly(oxy-1,2-ethanediyl)	poly(oxyethylene)
4		poly(oxy-1,4-butanediyl)	poly(oxybutane-1,4-diyl)
5		Poly(ethylene terephthalate) (PET); poly(oxy-1,2-ethanediyloxycarbonyl -1,4-phenylenecarbonyl)	poly(oxyethyleneoxyterephth= aloyl)
6		Nylon-6; poly[imino(1-oxo-1,6-hexanediyl)]	poly[imino(1-oxohexane-1,6-diyl)]
7		RYTON® PPS;c poly(phenylene sulfide); poly(thio-1,4-phenylene)	poly(thio-p-phenylene)
8		Elvanol®;c poly(vinyl alcohol); Not structured or named as an SRU	poly(1-hydroxyethylene)
9		Kevlar®;c poly(imino -1,4-phenyleneiminocarbonyl -1,4-phenylenecarbonyl)	poly(imino-p-phenyleneimino= terephthaloyl)
10		Kapton®;c poly[(5,7-dihydro -1,3,5,7-tetraoxobenzo[1,2-c: 4,5-c']dipyrrole-2,6(1H,3H) -diyl)-1,4-phenyleneoxy-1,4-phenylene]	poly[(5,7-dihydro -1,3,5,7-tetraoxobenzo[1,2-c: 4,5-c']dipyrrole -2,6(1H,3H)-diyl) -p-phenyleneoxy -p-phenylene]

2.3  Examples of naming new polymers.

1. An azidomethyl group-containing polyurethane was synthesized by the reaction of sodium azide with a bromomethyl group-containing polymer:

2. An irregular polyester containing sequences of units derived from 1,1'-binaphthyl-4,4'-diol (BND) and 2,6-naphthalenedicarboxylic acid (NDA), and from 6-hydroxy-2-naphthoic acid (HNA) is best represented by showing the repeating units not connected to each other to avoid an implication that these are block sequences, since the authors clearly state that "6-oxy-2-naphthoate" units have a random distribution:

2.4. Another example of source and structure based naming

Chemical Abstracts Service (CAS) assigned the 13 millionth CAS Registry Number, 155827-99-9, to a polymer, represented as a regularly repeating structural (constitutional) unit, as was reported in the October 1994 issue of the Divisional Newsletter on page 6:

a) SOURCE-BASED NOMENCLATURE

The polymer was obtained by polycondensation of "2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride" with "m-benzenediamine containing tri(tetrafluoroethene) segments". The two starting materials or monomers were:

the name of the copolymer is constructed by citing the names of the constituent monomers after the prefix "poly", and by placing between the names of each pair of monomers an italicized connective denoting the kind of the sequence arrangement, if known.

Thus, the name of the copolymer is:

CAS, registers, indexes, and names polymers on the basis of monomers by using systematic CA Index names and conforming to the requirements of alphabetically arranged "inverted" names in the CA Chemical Substance Index. Thus, the monomer-based index entries for the polymer illustrated above:

b) STRUCTURE-BASED NOMENCLATURE

It is useful to draw first a larger segment of the chain containing two or more repeating units:

The repeating unit is readily identified and there are a number of them, as shown by brackets of different size.

Each method of naming polymers has its own merit and should be used when appropriate.

Homework problems: (write the structure based name)

poly(benzo[1,2-d:5,4-d']bisoxazole-2,6-diyl-1,4-phenylene)

d. What is the correct name of the following polymer  ?

    1) polyvinyl chloride 2) polyvinylchloride 3) poly(vinyl chloride).

e. The IUPAC name of polystyrene is __________________________

f. The IUPAC name of poly(methyl methacrylate) is ____________________

g. What is the IUPAC name of the following polymer?

       pyridine     triazole

h.  the IUPAC name of the following polymer is                    

2.5. Block and graft copolymers:

Block copolymers are macromolecules which contain a linear arrangement of blocks or portions of a polymeric macromolecule that have at least one constitutional or configurational feature which is absent from the adjacent portions. For example, block copolymers made up of A and B structural units can have the following sequence arrangements

where the sequences -AAAAAAAA-, -BBBBBBBB- constitute blocks. The corresponding polymers are named

A systematic source-based nomenclature for copolymers identifies the constituent monomers and provides a description of the sequence arrangement of the different types of monomeric units present. The structural diagrams, on the other hand, show the constitutional repeating units linked in a head-to-tail arrangement.

Below are listed some examples of block copolymers:

1. Polystyrene-block-poly(dimethyl-t-butylsilyl vinyl ether)

2. what is the name of the following?

3. Poly[w-methoxyocta(oxyethylene) methacrylate]-block-poly(4-vinylpyridine)

Note: Don't confuse the block polymers with random polymers
(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.

For example:

   and   

GRAFT COPOLYMERS

Graft polymers are macromolecules that have blocks of one or more species connected to the main chain of a macromolecule as a side chain. These side chains have constitutional or configurational features that distinguish them from those in the main chain. In graft copolymers (as opposed to graft polymers) the distinguishing feature of the side chains is constitutional, i.e. the side chains are derived from at least one species of monomer that is different from the monomers which make up the main chain. For example, the arrangement

would be given the name

      polyA-graft-polyB

where the monomer named first (A) is that which makes up the backbone or main chain and the monomer named second (B) makes up the side chain. The designation (X) denotes a modified constitutional repeating unit of the main chain to which the side chain is attached or a junction unit usually derived from a macromonomer.

Below are some examples of graft copolymers taken from several different papers in the symposium:

1. Poly(ethyl acrylate)-graft-poly(vinylidene fluoride)

2. Poly(1,1-dihydroperfluorooctyl acrylate)-graft-poly(ethylene oxide)

This name reflects the polymeric chains only. The junction unit derived from a macromonomer, as shown on the structural diagram, can be named as a trivalent group: 1-(4-methylenephenyl)ethylene

3. Polypropylene-graft-poly(methyl methacrylate)

This name reflects the polymeric chains only. The junction unit derived from a macromonomer, as shown on the structural diagram, can be named as a trivalent group: 1,2,6-hexanetriyl

Copolymer Nomenclature

Table 11. Short Sequence Copolymer Nomenclature

Table 12. Long Sequence Copolymer Nomenclature

*Some authors use -inter-

2.7. REGULAR DOUBLE-STRAND ORGANIC POLYMERS (Ladder and Spiro)

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;          poly(l.2-dihydrocyclobuta[b]-naphthalene-1,2:5,6-tetrayl)

(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)

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

(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.

2.8 CASCADE (DENDRITIC) POLYMERS

These macromolecules are highly symmetrical, discrete organic molecules possessing well defined repeat units. Many researchers in this field have coined trivial class names that reflect the arborescent branching of these molecular structures (e.g., arborols, dendrimers, molecular fractals).

Cascade polymers are macromolecules prepared by the attachment of a branched repeat unit to a central initiator core; larger macromolecules are derived by the addition of another layer (generation) of branched repeat units to the termini of an existing macromolecule. The nth generation of a symmetrical cascade polymer has the general line formula:

where C is the formula for the initiator core; Nc is the branch multiplicity of the initiator core; R_i is the formula for the formula of the ith generation repeat or branch unit; N_bi is the branch multiplicity of the ith repeat unit; and T is the formula for the terminal moiety.

The need for a convenient and accurate nomenclature to describe cascade polymers was apparent from the difficulty and time required to name even the simplest of these structures using the rules for organic molecules. For example, the 36-Micellanol^TM and 36-Micellanoic Acid^TM cascade polymers were named 22,22-bis[21-hydroxy-9,9-bis[12-hydroxy-9,9-bis(3-hydroxypropyl)dodecyl]-18,18-bis(3-hydroxypropyl)heneicosyl]-13,13,31,31-tetrakis[12-hydroxy-9,9-bis(3-hydroxypropyl)dodecyl]-4,4,40,40- tetrakis(3-hydroxypropyl)-1,43-tritetracontanediol and 4,4,40,40-tetrakis-(propylcarboxy)-13,13,31,31-tetrakis[12-carboxy-9,9-bis(3-propylcarboxy)dodecyl]-22,22-bis[21-carboxy-18,18-bis(propylcarboxy)-9,9-bis[12-carboxy- 9,9-bis(propylcarboxy)dodecyl]heneicosyl]tritetracontanedioic acid, respectively. These names obscure the number and type of terminal moieties, the constituency of the initiator core, and the structural similarity of the two molecules.

36-Micellanol^TM Cascade(left), 36-Micellanoic Acid^TM cascade(right)

The cascade (dendrimer) name begins with information detailing the number of terminal moieties (Z) and the molecular class descriptor ("cascade") , followed by name fragments that describe, in order, the initiator core, each of the branch repeat units, and finally the terminal functionalities. The majority of cascade macromolecules reported to date possess symmetrical branches and are easily described by this approach. Further descriptors are required to accommodate cascade macromolecules possessing: repetitions of combinations of repeat branch units (i.e., a block cascade polymer), nonidentical branches, or distinct segments emanating from the core (i.e., a segmental block cascade polymer).

The initiator core and terminal unit names resemble conjunctive nomenclature. Multiplicity of branching from the core is indicated by a bracketed numeral following the core unit name; any necessary locants are also enclosed within the brackets after the multiplicity numeral, separated by a hyphen.

A branch repeat unit consists of the molecular fragment extending from (but not including) a branch atom (or group) through the next cascade branching site. The parent chain of an intermediate (or terminal unit) always terminates at a cascade branching site. Example repeat branch units (and names) are shown below with branch multiplicities of two (2) and three (3). The illustrated replacement nomenclature is easy to use and readily indicates the length of the repeat unit, but masks the functionality. Alternatively, a repeat unit name [e.g., (3-methoxypropanamido)methylidyne] may be used; however, this approach indicates the functionality but obscures the chain length. The choice between styles for the repeat (or core or terminal) unit name has not been dictated and does not affect the general form of the proposed cascade nomenclature.

(1,4-diaza-5-oxoheptylidene) Repeat Unit (left), (3-oxo-6-oxa-2-azaheptylidyne) Repeat Unit (right)

The second generation alcohol- and acid-terminated Micellane^TM polymers shown earlier are named 36-cascade:methane[4]: (nonylidyne)2:propanol and 36-cascade:methane[4]:(nonylidyne)2:propanoic acid, respectively, via the proposed nomenclature. Multiple generations of a cascade polymer family can be easily described via a general name. A series of acid-terminated polyamido cascades (1: Z = 36; G = 2) have been prepared and are readily described by the family name: Z-cascade:methane[4]:(3-oxo-6-oxa-2-azaheptylidyne):(3-oxo-2-azapentylidyne)G-1:propanoic acid, where Z is the number of terminal acid groups, and G is the number of generations. Furthermore, obvious structural similarities are easily noted for macromolecules where only the terminal functionalities differ. For example, 36-cascade:methane[4]:(3-oxo-6-oxa-2-azaheptylidyne):(3-oxo-2- azapentylidyne):propanoic acid (2) and 36-cascade:methane[4]:(3-oxo-6-oxa-2-azaheptylidyne):(3-oxo-2-azapentylidyne)G-1:propylamine (3).

Polyamidocascades Synthesized using modular Building Blocks

2.9 Summary of non-linear polymers

The following italicized qualifiers can be used as both prefixes (e.g., blend-, net-) and infixes (connectives) (e.g., -blend-, -net-) to designate the skeletal structure of non-linear macromolecules or macromolecular assemblies:

cyclic: cyclo
branched, unspecified: branch
short-chain-branched: sh-branch
long-chain-branched: l-branch
branched with branch point of functionality f: f-branch
comb: comb
star: star
star with f arms: f-star
network: network
crosslink: i (Greek iota)
polymer blend: blend
interpenetrating polymer network: ipn
semi-interpenetrating polymer network: sipn
polymer-polymer complex: compl

In naming non-linear homopolymer molecules, the italicized prefix for the skeletal structure of the macromolecule is placed before the source-based name of the constituent linear chain.

Comb macromolecule is a macromolecule comprising a main chain with multiple trifunctional branch points from each of which a linear side-chain emanates.

Examples:

polystyrene-comb-polyacrylonitrile
(equivalent to polystyrene-graft-polyacrylonitrile)

polystyrene-comb-[polyacrylonitrile; poly(methyl methacrylate)]
(polystyrene with polyacrylonitrile and poly(methyl methacrylate) side chains)

Star macromolecule is a macromolecule containing a single branch point from which linear chains (arms) emanate.

Examples:

4-star-polystyrene
(a four-armed star of polystyrene)

star-(polyA-block-polyB-block-polyC)
(star copolymer molecule, each arm of which consists of the same block-copolymer chain)

star-(polyA; polyB; polyC)
(a variegated star copolymer molecule consisting of arms of polyA, arms of polyB, and arms of polyC)

star-(polyacrylonitrile; polystyrene) (M_r 100,000:20,000)
(star macromolecule consisting of arms of polyacrylonitrile of a total M_r (relative molecular mass) = 100,000 and arms of polystyrene of a total M_r = 20,000)

Network is a highly ramified macromolecule in which essentially all constitutional units are connected to all other constitutional units and to the macroscopic phase boundary by many permanent paths through the macromolecule. In a covalent network all the permanent paths are formed by covalent bonds. In a physical network, some of the bonds are formed by physical interactions. A micronetwork contains cyclic structures and of colloidal dimensions.

Examples:

net-polystyrene-i-divinylbenzene
(polystyrene crosslinked with divinylbenzene to form a network)

net-poly[styrene-alt-(maleic anhydride)]-i-(ethylene glycol)
(alternating copolymer of styrene and maleic anhydride crosslinked with ethylene glycol to form a network)

Polymer blend is a macroscopically homogeneous mixture of two or more different species of polymer. The general use of the term "polymer alloy" is discouraged.

A polymer blend is defined as a macroscopically homogeneous mixture of two or more different species of macromolecule.The term miscibility is defined as the capability of a mixture to form a homogeneous single phase that is thermodynamically stable with respect to phase separation at least in a certain range of temperature, pressure, molar mass distribution, and composition.

Examples:

polystyrene-blend-poly(2,6-dimethylphenol)

poly(methyl methacrylate)-blend-poly(n-butyl acrylate)

Semi-interpenetrating polymer network (SIPN) is a polymer comprising one or more networks and one or more linear or branched polymers characterized by the penetration on a molecular scale of at least one of the networks by at least some of the linear or branched macromolecules.

Example:

(net-polystyrene)-sipn-poly(vinyl chloride)
(SIPN of a polystyrene network and a linear poly(vinyl chloride)

Interpenetrating polymer network (IPN) is a polymer comprising two or more networks which are at least partially interlaced on a molecular scale but are not covalently bonded to each other and cannot be separated unless chemical bonds are broken.

Example:

[net-poly(styrene-stat-butadiene)]-ipn-[net-poly(ethyl acrylate)]
(IPN of two networks)

Researchers in the field of multicomponent polymer materials are urged to look up, as this abstract cannot do justice to the full document.

2.10. Inorganic and Organometallic Polymers

constitutional repeating unit (CRU). Once a CRU is identified, it has to be oriented in such a way that the subunit of the highest seniority is selected as the left terminal and other subunits are placed sequentially according to specified criteria.

Examples

1. Polyphosphazenes

preferred CRU IUPAC inorganic name: catena-poly[(diethoxophosphorus)-m-nitrido] common name: poly(diethoxyphosphazene)

According to the rules for linear organic polymers, this polymer would be reoriented and named: poly[nitrilo(diethoxyphosphoranylidyne)]

2. Polysiloxanes

IUPAC inorganic name: catena-poly[(methylphenylsilicon)-m-oxo] common name: poly(methylphenylsiloxane)

According to the organic polymer rules: poly[oxy(methylphenylsilylene)

b. An aminophenyl-terminated poly(dimethylsiloxane) is named:

a-[(4-aminophenyl)dimethylsilyl)-w-(4-aminophenyl)poly(oxy(dimethylsilylene)]

3. Polysilanes

IUPAC inorganic name: catena-poly[(diethylsilicon)(dimethylsilicon)]

According to the organic polymer rules: poly(1,1-diethyl-2,2-dimethyldisilanylene)

The structure and the name represent an ideal alternating copolymer, assuming that the alternating units, diethylsilylene and dimethylsilylene, came from two different monomers.

One might be tempted to indicate that in a structure-based name, e.g.,

poly(diethylsilylene-alt-dimethylsilylene),

but this would be contrary to the current nomenclature rules. The connective "alt" (alternating) is meant to be used with the source-based names only. Secondly, for a regular single-strand polymer, the largest regularly repeating constitutional unit is selected in constructing a structure-based name. Thus for a copolymer such as

-A-B-A-B-A-B-A-B-

the structure-based name is "poly(A-B)", rather than "poly(A-alt-B)". In our case, "disilanylene" is the proper "parent" bivalent group, rather than two consecutive "silylene" bivalent groups.

b. The source-based nomenclature for copolymers would indicate the starting monomers and what is known about the polymer, e.g., an alternating sequence:

poly(dichlorodiethylsilane-alt-dichlorodimethylsilane)

If other monomers or starting reactants were used to arrive at the same polymer, the source-based names would reflect that, e.g.,

poly(diethylsilane-alt-dimethylsilane)
poly(1,2-dichloro-1,1-diethyl-2,2-dimethyldisilane)
poly(1,1-diethyl-2,2-dimethyldisilane)

The source-based names do not indicate the type of reaction which would have to take place such as reductive coupling with sodium, dehydrogenative coupling with a catalyst, or anionic polymerization.

Some of the above monomers are hypothetical, yet are useful to illustrate the naming process for polymers. Incidentally, the potential polymerization of disilenes to form linear polysilylenes has been discussed, and the anionic polymerization of masked disilenes to form highly ordered alternating polysilylene copolymers has been successful.

c. The structure-based nomenclature for irregular copolymers would indicate individual constitutional units not joined together:

poly(diethylsilylene/dimethylsilylene)

d. The corresponding source-based name for a copolymer of unspecified sequence would be:

poly(dichlorodiethylsilane-co-dichlorodimethylsilane)

e. If the copolymer has regular blocks with unspecified sequential arrangement of the blocks, the structure and the name would be:

poly[poly(diethylsilylene)/poly(dimethylsilylene)]

Homework questions: What type of polymer are these following copolymer structures?

Polymer I: solid line                Polymer II: dashed line

from left: a, b, c, d

from left: e, f, g

Appendix 1: GLOSSARY OF BASIC TERMS IN POLYMER SCIENCE

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.

Appendix 2:  NOMENCLATURE AND STRUCTURE REPRESENTATION FOR DENDRITIC POLYMERS

The last 15 years have witnessed such a rapid development of comb, crosslinked, dendritic, graft, star, star-branched, and other types of non-linear polymers that nomenclature for these has received little attention. Understandably, both chemists and nomenclature experts disagree on how to classify and name the bewildering variety of novel structures.

Structure-Based versus Source-Based Representation for Dendritic Polymers
Structure-based representation for a polymer is generally acknowledged to be superior to source-based representation because it conveys structural information that is omitted by the latter. While it is possible to draw source-based representations for some dendritic polymers, e.g. polyamides or polyesters, discussion here will be confined to the problems of structure-based representation and nomenclature.

Relationship between Nomenclature and Structure-Based Representation
For virtually all synthetic polymer types encountered prior to the discovery of dendritic polymers, also called dendrimers, structure has essentially ruled nomenclature. Thus, a name for a constitutional repeating unit (CRU) is created based upon its structure; both CAS structural repeating unit (SRU) nomenclature rules and IUPAC CRU nomenclature recommendations are published.

 the two most pertinent to this discussion are:

• To determine the head atom or senior bivalent radical of the CRU, subunit seniority is: (1) heterocyclic rings; (2) heteroatoms in chains; (3) carbocyclic rings; (4) carbon chains.
• For situations where a heteroatom in the chain is the CRU head atom, the most senior atom is O, followed in turn by S, Se, Te, N, P, As, Sb, Bi, Si, Ge, Sn, Pb, B, etc.

International rules need to be established on how dendrimer structures are to be represented. Depending upon these new rules, the existing nomenclature rules, which work well for linear polymers, may need to be modified to accommodate dendrimers. The question is: should existing nomenclature rules be allowed to influence dendrimer structure representations, or should dendrimer structure representation rules be created independently of existing nomenclature rules for linear polymers, and new nomenclature rules then be created to accommodate the novel structures? This question may not be easy to answer.

As examples of this problem, consider the Frechet dendrimer from 5-(bromomethyl)resorcinol (3,5-dihydroxy-benzyl bromide) (Figure 1) and the Tyler and Hanson dendrimer from 3,5-bis(bromomethyl)phenol (Figure 2).

The question arises: how should their CRU representations be drawn?

For the resorcinol of figure 1, figures 3, 4, and 5 show the logical possibilities. These are "phase-shift" variants of one another, i.e. all possible variants of the same intellectual CRU are drawn, but in each new figure the left and right-limiting brackets are moved one atom to the right from the previous one until all possibilities are covered. It is logical to create a rule that the single crossing bond of A2B, A3B, etc. CRU representations are always drawn on the left. "Illogical" CRUs, e.g. figure 6 as a variant of figure 5, are excluded from discussion.

A fundamental difference is now observed between representations of linear polymers versus dendrimers. For a linear polymer, regardless of whether a CRU is drawn correctly or incorrectly phased per CAS and IUPAC rules, its molecular formula (MF) is invariable; in contrast, as shown in figures 3, 4, and 5, the MF of a dendrimer changes with CRU phasing. Therefore, what rules shall be used to select the "correct" CRU from the representations shown as figures 3, 4, and 5?

If the assumption is made that figures 3, 4, and 5 are all representations of regular polymers, as defined by IUPAC, application of the IUPAC definition of a CRU to figures 3, 4, and 5 results in selection of figure 3 because it has the "smallest MF", i.e. the fewest number of atoms, and therefore represents the "smallest CRU".

Application of the CRU head atom rules cited above also lead to selection of figure 3 as the correct representation. Thus, the "smallest CRU" and "head atom" rules for determining a CRU all lead to the same selection. The IUPAC name for this CRU could be oxymethylenebenzene-1,3,5-triyl, and the corresponding polymer could be named poly(oxymethylenebenzene-1,3,5-triyl).

Analogous treatment of the phenol of figure 2 results in three possible CRUs; these are shown as figures 7, 8, and 9.

However, when the rules applied above to figures 3, 4, and 5 above are now applied to figures 7, 8, and 9, a conflict arises; the "smallest CRU" rule leads to selection of figure 7 as the "correct" CRU, whereas the "head atom" rules lead to selection of figure 8.

There is currently no basis for selection of figure 7 versus figure 8 as the "correct" CRU. Compare possible names for the polymers corresponding to the CRUs shown as figures 7 and 8:

Figure 7: poly(methyleneoxybenzene-1,3,5-triyl)
Figure 8: poly[oxybenzene-1,3,5-triyl-3,5-bis(methylene)]

CAS rules and IUPAC recommendations state that a CRU must be defined before it can be named; ergo, a concise name, however tempting, should theoretically not be allowed to influence the creation of a CRU structure. It is very tempting to select the CRU of figure 7 in preference to that of figure 8 because (a) it follows the "smallest CRU" rule, and (b) the names of the CRU and its corresponding polymer are more concise.

This temptation is reinforced by the example shown as figure 10, which illustrates Tomalia's dendrimer from a bicyclic ether and pentaerythritol.(28)

The CRU possibilities are shown as figures 11 through 14. Note that the right-hand crossing bonds in figure 11 are three single bonds, not one triple bond.

As in the previous example, a conflict arises; the "smallest CRU" rule leads to selection of figure 11 as the "correct" CRU, whereas the "head atom" rules lead to selection of figure 12.

Plausible names for polymers corresponding to the CRU representations of figures 11 through 14 are as follows:

Figure 11: poly(methyleneoxyethane-1,2,2,2-tetrayl)
Figure 12: poly[oxypropane-1,2,2,3-tetrayl-2,2-bis(methylene)]
Figure 13: poly[propane-1,2,2,3-tetrayl-2,2-bis(methyleneoxy)-3-oxy]
Figure 14: poly[ethane-1,1,1,2-tetrayl-1,1-bis(methyleneoxymethylene)-2-(oxymethylene)]

These examples suggest strongly that as the molecular formula and degree of branching increase in dendritic CRUs, nomenclature quickly becomes complex to the point of confusion. Therefore, for dendrimers, would nomenclature considerations and use of the "smallest CRU" rule be preferable to rigid adherence to "head atom" rules? Once established, the new rules could be used also for hyperbranched polymers, in spite of their greater degree of imperfection versus dendrimers. Readers are invited to submit their suggestions, with supporting arguments, for choosing either the "smallest CRU" rule or the "head atom" rules as the principle by which dendritic and hyperbranched CRUs should be represented.

Appendix 3:   HYPERBRANCHED POLYMERS

While it is possible to register hyperbranched polymers by source-based methods (i.e. in terms of the monomers), structure-based registration is superior in conveying structural information that is omitted from source-based registration.

A brief overview is presented here of the method devised for structure-based representation of hyperbranched polymers and their accompanying systematic nomenclature. These are not ladder polymers; successive units of the generic structural repeating unit (SRU; see structure 1.1 and Note) fit together as shown in structure 1.2, not as shown in structure 1.3.

Symmetrical "I"-Shaped Hyperbranched Polymers
Virtually all symmetrical three-crossing-bond SRUs, e.g. structure 2.1 (currently unregistrable by the CAS Registry System), can be "doubled" to create a four-crossing-bond SRU with two left- and two right-crossing bonds. A crossing bond is a bond that passes though the limiting parentheses or brackets of the SRU. This creates a symmetrical "I"-shaped SRU (see example 2.1 below).

The general structure rules are: the original SRU is "doubled"; intellectually superfluous atoms are eliminated; the bridge formed is kept as short and as unsubstituted as possible, oriented vertically, and placed as far to the left as possible; the new SRU is oriented with the head atom in the top leftmost position. The nomenclature rules are: the moiety in the center of the bridge is named; the doubling prefix "bis" is added; the rest of the SRU is named. If the bridge has a unitary name it is used. The method is described in detail elsewhere. Three examples are given.

Example 2.1 - hyperbranched poly-1,3,5-benzenetriyl15 (structure 2.1) "doubled" to poly-3,3',5,5'-biphenyltetrayl

Asymmetrical "I"-Shaped Hyperbranched Polymers
This type presents additional difficulties, both in structuring and nomenclature. For SRUs for which "doubling" is possible, the general structure rules are as for symmetrical hyperbranched polymers (see above).

There is an inherent difficulty in creating a nomenclature system for asymmetrical "I"-shaped SRUs, namely, how to deal with a junction moiety or unit, whether it is a ring or a single atom. Whether the complete name of the SRU begins with a linear moiety or atom sequence that connects to a junction unit, or with a central junction unit itself, merely naming the remaining moieties that emanate from the central junction unit is insufficient to indicate in which direction they go. Nomenclature must therefore include indications of directions. Two examples illustrate the method, which is described in detail elsewhere.

Example 3.1 - polymerization of diamines and dihalo compounds

Condensation of diamines and dihalo compounds produces mixtures of linear, branched, and hyperbranched SRUs; for this polymer class, CAS uses source-based registration.17 However, structure-based registration provides appreciably more information. Thus, for the condensation of 1,6-hexanediamine with a,a'-dichloro-p-xylene, five SRUs are possible (see structures 3.1a through 3.1e); one of the four-crossing-bond SRUs (structure 3.1e) is asymmetrical and needs novel nomenclature.

The complete polymer is named by alphabetizing the SRUs and separating them with oblique strokes: poly[1,6-hexanediylbis(nitrilomethylene-1,4-phenylenemethylene)/iminomethylene-1,4-phenylenemethyleneimino-1,6- hexanediyl/(<-L)nitrilo(R;D)-(R)(methylene-1,4-phenylenemethylene)(R->)-(D)(methylene-1,4-phenylene- methylenenitrilo)(L;R)-(L<-)-(R)1,6-hexanediyl(R->)/1,4-phenylenebis(methylenenitrilo-1,6-hexanediyl)/1,4-phenylenebis(methylenenitrilomethylene-1,4-phenylenemethylene)]

New directional symbols created for this novel nomenclature are:
(<-L) a bond enters the SRU as a crossing bond through a left-limiting bracket
(L<-) a bond exits as a crossing bond through a left-limiting bracket
(->R) a bond exits as a crossing bond through a right-limiting bracket
(D) a bond emanates downward from a junction point
(L) a bond emanates to the left from a junction point
(R) a bond emanates to the right from a junction point

A junction point always has at least two directions cited after it, e.g. (R;D). Rings that function as junction points need locants in addition to letters, e.g. (6R;4D). The symbol (R;D) following a junction point indicates two separate bonds that emanate to the right and downward. After the first junction point, which is always in the upper linear strand of the SRU, the rest of the upper strand is named before the vertical bridge and the lower linear strand.

Three-crossing-bond (i.e. branched) structures cannot, per se, be registered, but "intellectual mixing" of structures 3.1a through 3.1e can create them in the mind's eye.

Example 3.2 - this polymer is named: poly[(<-L)2,6,4-pyridinetriyl(6R;4D)-(R)(methylene-1,4-phenylenemethyl- ene)(R->)-(D)1,3,5-benzenetriyl(3L;5R)-(3L<-)-(5R)(methylene-1,4-phenylenemethylene)(R->)]