Definition of Polymers

The definition of polymer thermal stabiUty is not simple owing to the number of measurement techniques, desired properties, and factors that affect each (time, heating rate, atmosphere, etc). The easiest evaluation of thermal stabiUty is by the temperature at which a certain weight loss occurs as observed by thermogravimetric analysis (tga). Early work assigned a 7% loss as the point of stabiUty more recentiy a 10% value or the extrapolated break in the tga curve has been used. A more reaUstic view is to compare weight loss vs time at constant temperature, and better yet is to evaluate property retention time at temperature one set of criteria has been 177°C for 30,000 h, or 240°C for 1000 h, or 538°C for 1 h, or 816°C for 5 min (1). 

There are many definitions of polymer compatibility. On one hand, compatible polymers are the polymer mixtures that have desirable physical properties when... 

Because proteins are not composed of identical repeating units, but of different amino acids, they do not fall within the formal definition of polymers given at the start of this chapter. They are nevertheless macromolecular and techniques developed for the study of tme polymers have been applied to them with success. However, for the most part they are outside the scope of this book and accordingly will receive very little attention in the chapters that follow. 

In an effort to optimize the solvent-containing passive sampler design, Zabik (1988) and Huckins (1988) evaluated the organic contaminant permeability and solvent compatibility of several candidate nonporous polymeric membranes (Huckins et al., 2002a). The membranes included LDPE, polypropylene (PP), polyvinyl chloride, polyacetate, and silicone, specifically medical grade silicone (silastic). Solvents used were hexane, ethyl acetate, dichloromethane, isooctane, etc. With the exception of silastic, membranes were <120- um thick. Because silicone has the greatest free volume of all the nonporous polymers, thicker membranes were used. Although there are a number of definitions of polymer free volume based on various mathematical treatments of the diffusion process, free volume can be viewed as the free space within the polymer matrix available for solute diffusion. 

For a definition of polymer supported reagents and scavengers, see http //www. biotage.com/DynPage.aspx id=24303 (accessed date 10-23-2007). 

Most countries with chemical inventories have excluded by-products, small product tests and laboratory quantities, and naturally occurring substances from their reporting schemes. One of the issues associated with inventories is the definition of a chemical. The definition of polymers is a complex issue that will vary depending upon the nature of the chemicals from which they are formed, their relative proportions, the order of reaction, and reaction conditions (duration, temperature, catalysts, etc.).14 Most inventories include polymers and treat all different polymeric substances and monomers as individual chemicals. Some countries, including the United States, have decided not to require updated reporting on the production of such polymers. None of the national chemical inventories include formulated mixtures, or preparations, such as paints and household cleaners, or articles such as automobiles, computers, and paper. 

Polymers are exempt from notification, unless they contain in combined form of any non-EINECS list new substance. The EC definition of polymer is the same as that agreed by the OECD. Basically a polymer must have molecular weight (MW) spread and consist of at least 50% by weight of molecules which are a chain of 3 (or mwe) monomer units linked to at least one other unit (which may be a monomer or another moiety). This essentially means that at least 50% of a polymo- must be of 4 units or more. It does not matter how many types of monomer are present. 

This chapter addresses nomenclature issues involving polymers, including generic definitions of polymers how polymers are named (generally by reactants) how other reactants such as free-radical initiators are considered and how polymers will be treated under REACH along with the confidentiality issues resulting from the need to register monomers and other reactants used to manufacture polymers. 

The definition of polymer under the TSCA polymer exemption is the same as that used in the EU, but there are two other criteria required to qualify under the PMN exemption. These are that the polymer meets one of three exemption criteria, and that it not be rendered ineligible due to one of five exclusions. 

Under EINECS, polymers were exempt from EINECS listing provided that they did not contain new monomers or other reactants. Under REACH, polymers meeting the EU definition of polymer are also exempt from registration, but the monomers and other reactants used to manufacture them must be registered even if the polymer is imported into the EU and these components are never present in unreacted form. This leads to complex issues involving normal business practices and confidentiality that are addressed in this chapter. 

The basic definition of polymer used in many countries, including the US under the TSCA polymer exemption and Canada under CEPA, is the one first developed in Europe under the Sixth Amendment to Directive 67/548/EEC and retained in REACH. This definition provides as follows ... 

The other elements of the polymer definition address the distribution of mers, and stipulate that no one molecular weight component of the polymer can be present at >50%, and that at least 50% of the polymeric product must meet the definition of polymer, i.e., they must contain at least three repeat monomer units bonded to one other monomer or reactant. 

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. °... 

Many chemicals that a chemist would consider to be polymers do not meet this exemption definition of polymer. For example, enzymes are polymers made of amino acid monomers, but they do not meet the exemption definition of a polymer because all of the enzyme molecules will have the same chain length and molecular weight. The EPA explained its logic in a Q A ... 

The second condition for the polymer exemption is that the substance cannot be specifically excluded. In practical terms, this means that once a person determines that the substance meets the definition of polymer, he or she must also check the list of exclusions to be certain that the substance is not excluded from the polymer exemption. If the substance is excluded, then no one can manufacture or import it without going through the PMN process. 

Once a polymer has met the polymer exemption definition of polymer, and is not specifically excluded from the polymer exemption, it still must meet one of the three criteria contained in the regulations to qualify for the polymer exemption. 

Phenol acts as the initiator of the ethoxylation reaction, and shall be regarded as an other reactant since it cannot react with itself or an opened epoxide. The molecule depicted in Figure 2.3 would therefore qualify for the definition of polymer molecule whenever n>3. 

A broad definition of polymer materials which encompasses both natural and synthetic polymers is that they are materials made up of large molecules, some of the properties of the materials arising from or being affected by the large molecular size. This is an awkward description it leaves unclear what should be considered as a molecule, and it is too all-embracing for most purposes. It would include crystalline proteins and also inorganic three-dimensional structures such as zeolites [18]. 

The definitions of polymer chirality are also closely connected with the clear description of stereoisomerism in macromolecules. The sites of isomerism in vinyl... 

Multicomponent polymeric materials consist of polymer blends, composites, or combinations of both. A polymer blend has two definitions The broad definition includes any finely divided combination of two or more polymers. The narrow definition specifies that there be no chemical bonding between the various polymers making up the blend. Table 2.5 and Section 2.7 summarize the basic types of polymer blends based on the broad definition primarily these are the block, graft, star, starblock, and AB-cross-linked copolymers (conterminously grafted copolymers), interpenetrating polymer networks, as well as the narrow definition of polymer blends. More complex arrangements of polymer chains in space can be shown to be combinations of these several topologies. 

Fig. 13.19. Microscopic definition of polymer contribution to stress on a plane, as the stress exerted by the dumbbell bead above the plane on the bead below the plane.

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