The Two Percent Rule

for the Inventory description see the EPA Substance Registry Services Web site at http // iaspub.epa.gov/sor internet/registry/substreg/searchandretrieve/searchbylist/search.do and search the Inventory for CAS 25190-06-1. 

Polymers are generally described on the Inventory by their composition and starting materials. Therefore, a manufacturer may make or import a polymer with two percent or less of a starting material that is not listed as part of a polymer s Inventory description.As with most TSCA rules, the two percent rule cannot be summarized so neatly and there are exceptions and peculiarities to the rule. 

The two percent rule appears in two places in the regulations. First, it is embodied in 40 C.F.R. 720.45(a)(2) where it defines how a polymer must be described in a PMN and how the polymer will be described on the Inventory. 

The two percent rule also defines how broadly Inventory listings of polymers may be interpreted. The second place it makes its appearance is in the polymer exemption rule where it is used as part of the definition of polymers exempt from the PMN requirements of TSCA 5. ° 

When a manufacturer or importer files a PMN for a polymer, all of the starting materials must be described on the PMN form. The manufacturer must also list the percent by weight of each reactant. However, when the polymer is listed on the Inventory, it will only be listed by reference to the reactants that are either charged to the reaction vessel or incorporated into the final polymer at greater than two percent by weight unless the submitter chooses to list the reactants that are used at two percent or less. 

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This chapter discusses the regulatory effect for a substance meeting the polymer definition in these jurisdictions, and a discussion of several special topics the two-percent rule, post-reactions and devolvement of pre-polymers, and nomenclature issues involving epoxy polymers derived from hisphenol-A and epichlorohydrin. We shall also discuss the curious requirement under REACH that monomers and other reactants in reacted form must he registered even though the polymers manufactured from them do not, including consideration of confidential information which may he compromised through this provision. 

The two-percent rule has been used since the development of the TSCA Inventory in the determination as to which reactants must be included in naming the polymer for TSCA purposes. The two-percent rule means that monomers and reactants of a polymer that are used or incorporated at no more than 2 wt%, may be, but need not be, included in the considerations leading to the formal chemical description of a polymer manufactured from those precursors [3]. It is the submitter s choice as to whether he/she wishes to have these reactants considered or not considered in describing a polymer. There is no choice for precursors used or incorporated (whichever is less) at more than two weight percent. These precursors must be included in the information reported, and, ordinarily, they will be reflected in the name of the polymer. The two-percent rule has not meant that a precursor reflected in the description of a polymer must be used [4] or incorporated [5] at more than two weight percent. Therefore, any precursor reflected in description of a polymer can be used at any concentration greater than zero, but a precursor must not be completely omitted. These applications and interpretations of the two-percent rule also applied under the initial polymer exemption of 1983. 

Prior to 1995 the two percent rule only allowed measurement of the weight percent of reactants charged to the reaction vessel. Rule amendments in 1995 permitted the alternative of determining the weight percent of a reactant incorporated into the resulting polymer. 60 Fed. Reg. 16298 (Mar. 29, 1995) 60 Fed. Reg. 16316 (Mar. 29.1995). 

Additives that do not chemically react to become part of the polymer are disregarded for purposes of the two percent rule, and do not have to be named as part of the polymer. Examples of these additives include colorants and UV adsorbers, among others. Similarly, emulsifiers and plasticizers do not become part of the polymer s chemical composition and are not part of the polymer s description. Catalysts are not consumed in reactions and therefore do not have to be part of the polymer representation. 

If the PMN submitter uses the incorporated method of applying the two percent rule for polymers, it must keep records to support its determination, either by analysis or calculation. A theoretical calculation is only acceptable if the PMN submitter can document that analytical methods are either not necessary or not feasible. ... 

There are two situations in which the EPA will review several new chemicals together. The first is when up to six substances have similar chemistry, toxicology, uses, and expected manufacturing or importation quantities. The EPA will accept a single consohdated PMN that covers all of the substances, provided a Prenotice Coordinator has eigreed that the substances are sufficiently similar. There are reduced filing fees for consolidated PMNs. Consolidated PMNs can be filed on two related polymers, one with a specific monomer or other reactant above the two percent rule level so that monomer or reactant is part of the polymer s chemical identity and the other with the same monomer or other reactant below the two percent rule level so that monomer or reactant is excluded from the polymer s chemical identity. 

It is important to keep records of each exempt polymer. To do that, a manufacturer that changes its formulations must determine how the two percent rule is applied to define when it has made a distinct polymer. 

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