Mixed Metal Compounds

Five research groups with expertise in the field summarize recent fascinating developments, including l,4-dUithio-1,3-butadienes and their transmetallated organo-di-metallic compounds, mixed dimers of lithium amide/alkyllithium, gem-diorganometallic compounds, alkali-metal mixed-metal ate compounds, and lithium zincates. 

Most commercial processes involve copolymerization of ethylene with the acid comonomer followed by partial neutralization, using appropriate metal compounds. The copolymerization step is best carried out in a weU-stirred autoclave with continuous feeds of all ingredients and the free-radical initiator, under substantially constant environment conditions (22—24). Owing to the relatively high reactivity of the acid comonomer, it is desirable to provide rapid end-over-end mixing, and the comonomer content of the feed is much lower than that of the copolymer product. Temperatures of 150—280°C and pressures well in excess of 100 MPa (1000 atm) are maintained. Modifications on the basic process described above have been described (25,26). When specific properties such as increased stiffness are required, nonrandom copolymers may be preferred. An additional comonomer, however, may be introduced to decrease crystallinity (10,27). 

Many methods for the conversion of acid copolymers to ionomers have been described by Du Pont (27,28). The chemistry involved is simple when cations such as sodium or potassium are involved, but conditions must be controlled to obtain uniform products. Solutions of sodium hydroxide or methoxide can be fed to the acid copolymer melt, using a high shear device such as a two-roU mill to achieve uniformity. AH volatile by-products are easily removed during the conversion, which is mn at about 150°C. A continuous process has been described, using two extmders, the first designed to plasticate the feed polymer and mix it rapidly with the metal compound, eg, zinc oxide, at 160°C (28). Acetic acid is pumped into the melt to function as an activator. Volatiles are removed in an extraction-extmder which follows the reactor-extmder, and the anhydrous melt emerges through a die-plate as strands which are cut into pellets. 

As will be shown in Section V, T -S mixing has so far been identified in reactions involving diradicals and in certain reaction of organo-metallic compounds. 

A number of mixed metalloxanes, R MOSnRrX (M = Hg, Tl, Si, Ge, or Pb), have similarly been synthesized from the stannoxanes (R2SnO) and the metal compounds R MX (250), and the borostannoxanes B(OSnRs)3 and (R0)2B0SnR20SnR20B(0R)2 have also been characterized (251, 252). 

---