Polymer Terms Links

The way to think of them all is as Si04 tetrahedra (or, in polymer terms, monomers) linked to each other either directly or via a metal ion (M) link. When silica is combined with metal oxides like MgO, CaO or AI2O3 such that the ratio MO/SiOj is 2/1 or greater, then the resulting silicate is made up of separated Si04 monomers (Fig. 16.4a) linked by the MO molecules. (Olivene, the dominant material in the Earth s upper mantle, is a silicate of this type.)... 

Chapman et al. [131] reported the synthesis of poly(ethylene oxide) (PEO) supported dendritic f-BOC-poly(a, c-L-lysines). These dendritic polymers termed as hydramphiphiles formed foams possessing good temporal stability in aqueous solution. Scrimin et al. [132] synthesized a three-directional polypeptide having uses in membrane permeability modulation. Decapeptide fragments were linked to TREN [tris(2-aminoethyl)amine] core. 

The sorption coefficient (K) in Equation (2.84) is the term linking the concentration of a component in the fluid phase with its concentration in the membrane polymer phase. Because sorption is an equilibrium term, conventional thermodynamics can be used to calculate solubilities of gases in polymers to within a factor of two or three. However, diffusion coefficients (D) are kinetic terms that reflect the effect of the surrounding environment on the molecular motion of permeating components. Calculation of diffusion coefficients in liquids and gases is possible, but calculation of diffusion coefficients in polymers is much more difficult. In the long term, the best hope for accurate predictions of diffusion in polymers is the molecular dynamics calculations described in an earlier section. However, this technique is still under development and is currently limited to calculations of the diffusion of small gas molecules in amorphous polymers the... 

The stereoselectivity of cyclopropane ester formation could also be effected by using reagents supported on linear or cross-linked polymers. The most important effects were noted with chloromethylated polymers cross-linked with divinylbenzene. The role of hyperconjugation in determining the stereochemistry of nucleophilic cyclopropanation of electrophilic alkenes has been studied and predicted In terms of equation 57 the... 

Polymers are frequently classified in terms of bonding in one dimension versus bonding in two or three dimensions. Bonding in one dimension results in linear polymers with single-strand chains. Bonding in two or three dimensions results in cross-linked polymers having infinite sheets or three-dimensional networks. Linear polymers are produced by addition polymerization if the reactant has only one double bond or by condensation polymerization if the reactant or reactants each have two reactive sites. Such polymers are usually soluble in suitable solvents. Since they also tend to soften when heated, they are called thermoplastic polymers. Cross-linked polymers may be produced by addition polymerization if the reactant has more than one double bond, or by condensation polymerization if the reactant or reactants each have more than two reactive sites. Such network polymers are usually insoluble and Infusible and are called thermosetting polymers. 

We must warn the reader of the terminological subtleties on this point. In chemical literature, the term monomers is frequently reserved for the relatively small molecules employed as the initial building blocks in purposeful making, or preparation, of polymer chains. In this language, the units of a polymer, or links of a polymer chain, are sometimes referred to as monomer residues (because monomers typically loose some chemical groups, such as OH, when combined into chains). We will discuss these issues in somewhat more details in Chapter 3, but mostly we will follow the tradition of physics literature and use the simple word monomer for the units of already prepared molecular chains. 

The ideal, classical, rubbery properties are displayed by polymers cross-linked by valence bonds (main-chain bonds or sulphur bridges, see Introduction, Fig. 0.1) these are termed chemical cross-links. Physical cross-links are also important in many useful rubbery materials. In physical cross-linking the chains are not chemically attached one to another, but are effectively pinned together in one of three ways ... 

Originally, vulcanization implied heating natural rubber with sulfur, but the term is now also employed for curing polymers. When sulfur is employed, sulfide and disulfide cross-links form between polymer chains. This provides sufficient rigidity to prevent plastic flow. Plastic flow is a process in which coiled polymers slip past each other under an external deforming force when the force is released, the polymer chains do not completely return to their original positions. 

The four regions of behavior shown by the polymers in Fig. 3.9 are fairly typical of high molecular weight un-cross-linked polymers. Let us examine the four regions of behavior, this time in terms of what is happening at the molecular level ... 

We noted above that the presence of monomer with a functionality greater than 2 results in branched polymer chains. This in turn produces a three-dimensional network of polymer under certain circumstances. The solubility and mechanical behavior of such materials depend critically on whether the extent of polymerization is above or below the threshold for the formation of this network. The threshold is described as the gel point, since the reaction mixture sets up or gels at this point. We have previously introduced the term thermosetting to describe these cross-linked polymeric materials. Because their mechanical properties are largely unaffected by temperature variations-in contrast to thermoplastic materials which become more fluid on heating-step-growth polymers that exceed the gel point are widely used as engineering materials. 

Haward et al.t have reported some research in which a copolymer of styrene and hydroxyethylmethacrylate was cross-linked by hexamethylene diisocyanate. Draw the structural formula for a portion of this cross-linked polymer and indicate what part of the molecule is the result of a condensation reaction and what part results from addition polymerization. These authors indicate that the crosslinking reaction is carried out in sufficiently dilute solutions of copolymer that the crosslinking is primarily intramolecular rather than intermolecular. Explain the distinction between these two terms and why concentration affects the relative amounts of each. 

CLAIMS COMPREHENSIUE (subscriber access only) further enhances the UNITERM indexing from 1964 with roles for aH iadexed compounds and polymer class terms and with links and negation codes for the fragment terms describiag chemical compounds (94). 

Surfactants evaluated in surfactant-enhanced alkaline flooding include internal olefin sulfonates (259,261), linear alkyl xylene sulfonates (262), petroleum sulfonates (262), alcohol ethoxysulfates (258,261,263), and alcohol ethoxylates/anionic surfactants (257). Water-thickening polymers, either xanthan or polyacrylamide, can reduce injected fluid mobiHty in alkaline flooding (264) and surfactant-enhanced alkaline flooding (259,263). The combined use of alkah, surfactant, and water-thickening polymer has been termed the alkaH—surfactant—polymer (ASP) process. Cross-linked polymers have been used to increase volumetric sweep efficiency of surfactant—polymer—alkaline agent formulations (265). 

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