Other Mixed-Bonded Polymers

Several early reports used otganometallic hydrides as an approach to forming polymers. The platinum-catalyzed addition of Si-H across carhon-carbon double 

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The PEG/water, PPG/water, and PVAL/water are among the most extensively studied water-soluble polymer solutions. These systems typically show a closed-loop phase behavior (Figure 16.4). Results for some ternary systems have been reported many of these data are for PEG/Dextran/water and PEG/water/salts and related systems, which are important for separating biomolecules such as proteins. Only few data for PEG or other hydrogen bonding polymer with mixed water solvents have been reported. 

Carbon in the carbonaceous chondrites does not exist as polymer or organic molecules alone. Carbonates are also present in relatively small amounts 20,23) and the same is true for elemental carbon. Elemental carbon seems to exist as carbynes (triple-bonded allotropes of carbon). At least three types of carbynes have been described in Murchison 341 but these results were questioned in 1982 by Smith and Buseck63). According to these authors, sheet silicates mixed with elemental carbon could be misidentified as carbynes in X-ray diffraction patterns. These particular carbonaceous phases (carbynes or otherwise) and other carbonaceous phases (polymer and amorphous carbon phases called C-oe and C- 3) are carriers of noble gases trapped in the chondritic material. Some of these carbynes seem to be condensates from the protosolar nebula while others are probably of presolar origin34 >. 

Phenolic and other formaldehyde condensation polymers are also important reactive adhesives. Powdered phenolic resin is mixed with abrasive grains and the mixture is compression molded to form grinding wheels. A B-stage phenolic (Chapter XX) in a solvent is used to impregnate tissue paper. The solvent is evaporated, and the dry sheets are placed between layers of wood in a heated press, where the resin first melts and then cures, bonding the wood to form plywood. Similarly, sheets of paper impregnated with a B-stage melamine-formaldehyde resin are laminated and cured to form the familiar Formica counter tops. 

Polymer/Polymer Complexes. PVP complexes with other polymers capable of interacting by hydrogen-bonding, ion-dipole, or dispersion forces. For example mixing of PVP with poly(acryHc acid) (PAA) in aqueous solution results in immediate precipitation of an insoluble complex (113). Addition of base results in dismption of hydrogen bonding and dissolution (114—116). Complexes with a variety of poly-acids (117) and polyphenols (118) have been reported. The interest in compatibiHty on a molecular level, an interesting phenomenon rarely found to exist between dissimilar polymers, is favored by the abiHty of PVP to form polymer/polymer complexes. 

Type AD-G is used in an entirely different sort of formulation. The polymer is designed for graft polymerisation with methyl methacrylate. Typically, equal amounts of AD-G and methyl methacrylate are dissolved together in toluene, and the reaction driven to completion with a free-radical catalyst, such as bensoyl peroxide. The graft polymer is usually mixed with an isocyanate just prior to use. It is not normally compounded with resin. The resulting adhesive has very good adhesion to plasticised vinyl, EVA sponge, thermoplastic mbber, and other difficult to bond substrates, and is of particular importance to the shoe industry (42,43). 

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