Source-based representations

Example the source-based name poly(vinyloxirane) is ambiguous ambiguity about the structure is removed by writing either polyaUcyleneivinyloxirane to accompany the source-based representation,... 

CA s policy for naming acetylenic, acrylic, methacrylic, ethylenic, and vinyl polymers is to use the source-based method, and source-based representation is used to depict the polymers graphically thus, a synonym for polyethylene is polyethylene and not poly(1,2-ethanediyl) a synonym for polypropylene is polypropylene, and poly(vinyl alcohol) is named ethenol homopolymer although ethenol does not exist. Thus, these polymers are named and represented structurally by the source-based method, not the structure-based method. 

In Sgroups, repeating units are enclosed in square brackets and a subscript n is placed to the right of the closing bracket. The subscript blk indicates a block copolymer and mon a monomer in a source-based representation. Superscripts indicate the orientation of the repeating units (hh = head-to-head, ht = head-to-tail, eu = either unknown) in a structure-based description. Crossing bonds (bonds... 

There is no provision for structuring and naming end groups in source-based representations, except for ester-terminated polymers (see Table 14) and mixed polyalkylene glycols (see below). 

Expressions such as —(—O—CH2—) — and (H2N—(CH2)6—NH2 HO2C— (0112)4—C02H)x depict actual structures, not molecular formulae. Although expressions such as (CH20)n and (C6Hi6N2 C6Hio04)a are used by CAS to represent the molecular formulae of poly(oxymethylene) and nylon-6,6 respectively, these expressions are, per se, neither structure-based nor source-based representations of these two polymers. There is a link, however, between the full structural representation and its molecular formula. The subscript n is used consistently for both an SRU and its molecular formula similarly, the subscript x is used consistently for both a homopolymer (copolymer) structure expressed in terms of monomer(s) and its corresponding molecular formula. 

Seemingly random use of structure-based and source-based representations with no cross-referencing between them has resulted in decades of confusion. 

Until September 2002, searchers faced an essentially insolvable problem in a search for source-based representations for PET. A searcher might think of searching only for the two representations shown as Figures 3a and 3b the representation shown as Figure 3c, which represents PET synthesized by a modem, industrially significant route, would thus not be retrieved. 

A search for source-based representations for a polymer therefore depended upon a searcher s ability to surmise how it might be represented in other words, it was a guessing game. 

It must also be pointed out that neither structure-based nor source-based representation currently takes into account any structural irregularities. Real polymers, as synthesized, are seldom structurally perfect. Depending on the type of polymer, various kinds of structural irregularities may arise during a polymerization process. 

Structure-based versus Source-based Representation. There are no absolute rules that specify which types of polymers shall be represented as structure-based, which as source-based, and which by both methods. lUPAC makes no definitive statement about whether a polymer shall be represented as source-based or structure-based thus, polymers may be represented both ways, and many examples of this can be found in both lUPAC s publications (1,6-13) and the CAS Registry File. 

This is not limited to common polymers as long as the criteria are met (15), uncommon pol5uners are also registered with both structure-based and source-based representations. 

A comprehensive review of structiue-based and source-based representations for regular, single-strand, organic polsrmers has been published (17). 

Source-based Method. For source-based representations, CAS structures homopol5aners by an expression such as (A)x, where A is a monomer. A typical CAS source-based homopol5aner representation is shown as Figure 5. 

Structure-based Method. CAS does not generally index unterminated copolymers of SRUs by the structure-based method. Formats such as poly(oxyethylene)/poly(oxytetramethylene) or poly[(oxyethylene)/ (oxytetramethylene)] are not used. Instead, a source-based representation is used (see Fig. 9 below). 

Fig. 6. Source-based representation of p-vinylaniline/styrene copolymer.

Space limitations preclude more than an overview of these types aftertreated (post-treated), alternating, block, comb and graft, cross-linked, dendritic, hy-perbranched, hyper-cross-linked, star, and star-block. Comprehensive reviews of structure-based and source-based representations for them have been published (20,21). 

Fig. 7. Source-based representation of a three-component polyester.

For source-based representations, lUPAC recommends that alternating and periodic copolymer names contain the connectives -alt- and -per-, respectively. 

Fig. 8. Source-based representation of aniline/formaldehyde/phenol terpolymer.

CAS makes no distinction among ordered, segmented, and imordered block pol5uners. For source-based representation, block polymers are distinguished from random pol5uners by indexing as copolymers at the monomer names. The term block is cited in a special modification after all other structin-al information (2). 

Fig. 9. Source-based representation of poly(oxyethylene/oxytetramethylene) copolymer.

An lUPAC publication (11) discusses both structure-based and source-based representations of comb polymers acomb polymer is described as a macromolecule comprising a main chain with trifunctional points from which linear side chains emanate. If the subchains between the branch points of the main chain and the terminal subchains of the main chain are identical with respect to constitution and degree of polymerization, and the side chains are identical with respect to constitution and degree of polymerization, the macromolecule is termed a regular comb macromolecule. If at least some of the branch points are of functionalities greater than three, the macromolecule may be termed a brush macromolecule. 

Comprehensive reviews of nomenclatiu-e for structure-based and source-based representations for dendritic, hyperbranched, and hyper-cross-linked polymers (21,35-38), and for star and star-block polymers (21), have been published. 

Source-based representations of pol5miers are typically recorded as shown in... 

Source-based polymer representation preceded structure-based representation because polymers were made before they were structurally characterized. The introduction of structure-based representation, however, did not render source-based representation obsolete, and currently the two complementary systems coexist. Source-based representation continues to exist for several reasons ... 

Seemingly random use of structure-based and source-based representations with no cross-referencing between them has resulted in decades of confusion, and the diletruna is unlikely to be resolved in the near future. For even the simplest of polymers, a searcher is faced with three fundamental questions ... 

Figure 3 Different expressions for source-based representations of PET...

Over the last 50 years, two major organizations, CAS and lUPAC, have tackled the daunting task of how best to represent polymer structures, Their achievements are impressive, and the two organizations are in virtually complete agreement on structure-based and source-based representations of polymers, both on paper and in searchable online databases such as the CAS Registry File, However, much still remains to be done some aspects of copolymer representation need enhancement, and such newer areas as aftertreated (post-treated), comb, dendritic, and star polymers are handled inadequately. 

Structure-based Versus Source-based Representation... 

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