Polymerization of Ketones and Isocyanates

In spite of many attempts to prepare useful polymers from ketones, so far, this is not very successful. Acetone polymerizes with the aid of magnesium [364]. The reaction requires high vacuum. Vapors of magnesium metal and dry acetone condense simultaneously in vacuum on a surface cooled by liquid nitrogen. The white elastic polymer that forms possesses a polyketal structure:

Like low molecular weight ketals, the polymer is unstable and decomposes even at room temperature. Acetone also polymerizes upon irradiation in a frozen state under high vacuum. The product is a yellow, rubbery material [364]. Infrared spectra show presence of both, C-O-C linkages and carbonyl groups. Monobromoacetone polymerizes in the same manner, by irradiation in the frozen state. The hard resinous polymer that forms is more stable than polyacetone [364].

Polymerizations of ketenes yield varieties of structures because monomer placements are possible through either the carbon-to-carbon double bond or through the carbon to oxygen double bond. Dimethylketene polymerizes by anionic mechanism to a polymer with the following structures [46]:

Polar solvents increase formations of ether groups. Non-polar solvents, used with lithium, magne- sium, or aluminum counterions, yield products that are high in ketones [46]. The same solvents, used with sodium or potassium counterions, form polymers with predominately polyester units [46]. Isocyanates polymerize through the carbon to nitrogen double bonds by anionic mechanism. Reactions can be catalyzed by sodium or potassium cyanide at -58°C [365]. N,N'-dimethyl- formamide is a good solvent for this reaction. Other anionic catalysts, ranging from alkali salts of various carboxylic acids [344] to sodium-naphthalene, are also effective [367]. In addition, polymerizations can be carried out by cationic [368], thermal [369], and radiation-induced [369] methods. Although anionic polymerizations yield very high molecular weight polymers, there is a tendency to depolymerize at high temperatures. The products of anionic polymerization are substituted polyamides [365].

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مواضيع ذات صلة

Group Transfer Polymerization

Copolymerizations by Ionic Mechanism

Polymerizations of Di Aldehydes

Polymerization of Unsaturated Aldehydes

Anionic Polymerization of Aldehydes

Polymerization of Aldehydes

Isomerization Polymerizations with Coordination Catalysts

Reduced Transition Metal Catalysts on Support

Post Ziegler and Natta Coordination Polymerization of Olefins

Steric Control in Polymerization of Conjugated Dienes

Steric Control with Homogeneous Catalysts

Homogeneous Ziegler–Natta Catalysts