Polymerization of ketones and isocyanates

In spite of many attempts to prepare useful polymers from ketones, this has so far not been very successful. Acetone polymerizes with the aid of magnesium. 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. Infrared spectra show the 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 

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 struc- 

Polar solvents increase formations of ether groups. Nonpolar solvents, used with lithium, magnesium, or aluminum counterions, yield products that are high in ketones. The same solvents, used with sodium or potassium counterions, form polymers with predominately polyester units.  

Isocyanates polymerize through the carbon-to-nitrogen double bonds by anionic mechanism. Reactions can be catalyzed by sodium or potassium cyanide at-58 °C. N,N -dimethylformamide is a good solvent for this reaction. Other anionic catalysts, ranging from alkali salts of various carboxylic acids to sodium-naphthalene, are also effective. In addition, polymerizations can be carried out by cationic, thermal, and radiation-induced methods. 

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Development of molecularly imprinted enantioselective hydrogenation catalysts based on immobilised rhodium complexes was reported by Gamez et al. [29]. The imprinted catalysts were prepared by polymerising Rh(I)-(A,A -dimethyl-l,2-diphe-nylethanediamine) with di- and tri-isocyanates, using a chiral alkoxide as the template (9). The imprinted polymer, after removal of the template, was tested for the reduction of ketones to alcohols. An enhanced enantioselectivity was observed in the presence of the imprinted polymeric catalyst, in comparison to the control polymer. 

A great percentage of the sand binders used by the foundry industry are made of phenol- and urea-formaldehyde resins, phenolic- and oil-isocyanate resins, and furan resins. Almost all these binders and their decomposition products such as ketones, aldehydes and ammonia are toxic. The principal effect on man is dermatitis, which occurs not so much from completely polymerized resins, but rather from the excess of free phenol, free formaldehyde, alcohol or hexamethylenetramine used as... 

Other examples include the free radical polymerization of vinyl isocyanate with subsequent anionic polymerization of the isocyanate side groups, as well as the corresponding polymerization of acrylonitrile or poly(acrylonitrile). Free radical and anionic polymerizations are to be preferred over those initiated by cations, since cationic polymerization frequently tends to give rise to transfer reactions which interrupt the transannulation. For example, in the cyclization of natural rubber with the aid of concentrated acids or Lewis acids, an average of only three transannular rings is obtained [see Equation (25-9)]. The intermolecular elimination of water from poly(vinyl methyl ketone) only produces single, double, and triple rings ... 

A very versatile polymeric scaffold for site-specific double PPM is poly( 1 -aceto-l-pentalluorophenoxycarbonyl-2-vinylcyclopropane) [poly(APVCP)] (see Scheme 8) [139]. In this case, the two-step modification is performed in a sequential batch process. Following aminolysis by treatment with various primary amines, the ketone can be converted in the presence of hydrazide or hydroxylamine derivatives. Fmthermore, the ketone can be reduced to the secondary alcohol, which is subsequently converted into the ester or carbamate through the use of different acyl halides and isocyanates. 

Reactivity. Flammable polymerizes violently in the presence of trace amounts of metals or acids can react violently with acid anhydrides, alcohols, ketones, phenols, ammonia, hydrocyanic acid, hydrogen sulfide, halogens, phosphorus, isocyanates, strong alkalis and amines (American Conference of Governmental Industrial Hygienists, 1991)... 

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