Metals initiated

The use of alkaU metals for anionic polymerization of diene monomers is primarily of historical interest. A patent disclosure issued in 1911 (16) detailed the use of metallic sodium to polymerize isoprene and other dienes. Independentiy and simultaneously, the use of sodium metal to polymerize butadiene, isoprene, and 2,3-dimethyl-l,3-butadiene was described (17). Interest in alkaU metal-initiated polymerization of 1,3-dienes culminated in the discovery (18) at Firestone Tire and Rubber Co. that polymerization of neat isoprene with lithium dispersion produced high i7j -l,4-polyisoprene, similar in stmcture and properties to Hevea natural mbber (see ELASTOLffiRS,SYNTHETic-POLYisoPRENE Rubber, natural). 

Cationic polymerization with Lewis acids yields resinous homopolymers containing cycHc stmctures and reduced unsaturation (58—60). Polymerization with triethyl aluminum and titanium tetrachloride gave a product thought to have a cycHc ladder stmcture (61). Anionic polymeriza tion with lithium metal initiators gave a low yield of a mbbery product. The material had good freeze resistance compared with conventional polychloroprene (62). 

Plating T anks. An electroless plating line consists of a series of lead-lined (for plastics etching) or plastic-lined tanks equipped with filters and heaters, separated by rinse tanks (24). Most metal tanks, except for passivated stainless steel used for electroless nickel, cannot be used to hold electroless plating baths because the metal initiates electroless plating onto itself. Tank linings must be stripped of metal deposits using acid at periodic intervals. 

The most important reaction with Lewis acids such as boron trifluoride etherate is polymerization (Scheme 30) (72MI50601). Other Lewis acids have been used SnCL, Bu 2A1C1, Bu sAl, Et2Zn, SO3, PFs, TiCU, AICI3, Pd(II) and Pt(II) salts. Trialkylaluminum, dialkylzinc and other alkyl metal initiators may partially hydrolyze to catalyze the polymerization by an anionic mechanism rather than the cationic one illustrated in Scheme 30. Cyclic dimers and trimers are often products of cationic polymerization reactions, and desulfurization of the monomer may occur. Polymerization of optically active thiiranes yields optically active polymers (75MI50600). 

Fig.. 86. Photograph of the metal initiation zone of a lap joint preptired from hot-dipped galvanized. steel substrates showing the six locations where small-area XPS spectra were acquired. Reproduced by permission of John Wiley and Sons from Ref 411.

It is essentially a phase diagram which consists of a family of isotherms that relate the equilibrium pressure of hydrogen to the H content of the metal. Initially the isotherm ascends steeply as hydrogen dissolves in the metal to form a solid solution, which by convention is designated as the a phase. At low concentrations the behaviour is ideal and the isotherm obeys Sievert s Law, i.e.,... 

Another application of the concept of fractional valence bonds has been made in the field of metals and alloys. In the usual quantum mechanical discussion of metals, initiated by W. Pauli (Z. Physik, 41, 81 (1927)) and Sommerfeld (Naturwiss., 15, 825 (1927)), the assumption was made that only a small number of electrons contribute significantly to the binding together of the metal... 

The titan cup was the source of zinc atoms. It contained the metal initially melted in hydrogen atmosphere and distilled. The operational temperature of the cup was maintained at the level of 185°C which provided the high percentage of the content of single zinc atoms in the flux. 

Yasuda, H. and Ihara, E Rare Earth Metal-Initiated living Polymerizations of Polar and Nonpolar Monomers, VoL 133 pp. 53-102. 

Soluble heavy metals initially added to arid soils were quickly transferred from the soluble and exchangeable form into the carbonate bound fraction. Within the first hour from the start of the saturation incubation, and/or during the first step of the SSD procedure, the metals in the freshly salt contaminated arid soils were predominately transferred from the EXC fraction into the CARB fraction (82% for Cd, > 50% for Ni and Cr, 40-85% for Zn, and 30% for Cu) (Han and Banin, 1997). Similarly, under the field... 

Rare Earth Metal-Initiated Living Polymerizations... 

Rare Earth Metal-Initiated Polymerizations of Polar Vinyl... 

Rare Earth Metal-Initiated Polymerization of Polar Vinyl Monomers... 

Rare Earth Metal-Initiated Living Polymerizations of Polar and Nonpolar Monomers 61... 

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