Dimethylketene polymerization

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-... 

The /3-lactone dimer of dimethylketene can be prepared by pyrolysis of its polyester, which is formed by the base-catalyzed polymerization of dimethylketene.3"6 In addition to the rearrangement of the normal dimer described above,6 the direct dimerization of dimethylketene in the presence of aluminum chloride3 or trialkyl phosphites7 leads to the /3-lactone dimer. 

In the presence of catalytic amounts of sodium methoxide, dimethylketene /3-lactone dimer is polymerized at moderate temperature to a polyester.3 At higher temperatures (above 100°), disproportionation to the cyclic trimer, hexamethyl-1.3,5-cyclohexanetrione, takes place.9 Addition of a stoichiometric amount of sodium methoxide to the lactone dimer generates the sodium enolate of methyl 2,2,4-trimethyl-3-oxovalerate. This reaction provides a convenient entry into certain ester anion chemistry that formerly required the use of a strong base like tritylsodium.10... 

It has been known for some time that dimethylketene produces three different types of polymers with polyketonic (47, X = Y), polyacetalic, 48, and polyester, 49, structures (88-90) (Scheme 11). The use of nonsymmetric ketenes like methylisopropylketene should produce an iso-syndio stereoisomerism in the ketonic form (47, X Y, only one of the possible stereoisomers is shown) and an orientational isomerism in the polyacetalic form, 48 in the polyester form, 49, there would be a combination of the two possibilities, analogous to those described for polyallenes. 4-Methylpentamethyleneketene offers the reverse possibilities iso-syndio isomerism in the polyacetalic form, 50, orientational isomerism in the polyketonic form, 51, and the combination of the two in the polyester form, 52 (Scheme 12). The three polymeric forms (ester, acetal, ketone) of 2- and 3-methylpentamethyleneketene each show both of these types of isomerism, one along and the other perpendicular to the chain. 

Dimethylketene has been polymerized by anionic initiators. Three different repeat units are formed (XLVII, XLVIII, XLIX) corresponding to polymerization through the alkene... 

Dimethylketene rapidly forms an extremely explosive peroxide when exposed to air at ambient temperatures. Drops of solution allowed to evaporate may explode. Inert atmosphere should be maintained above the monomer [1], The peroxide is polymeric and very sensitive, exploding on friction at —80°C. Higher homologues are very unstable and unisolable [2]. 

Linemann [1] prepared polydimethylketene by the Friedel-Craft cationic polymerization of dimethylketene using AlBrs. 

The lactone dimer of dimethylketene has been polymerized, a polyeater of the same struotuie... 

Vinyl monomers containing P-lactam groups were prepared by ketene-imine [2 - - 2] cycloaddition followed by modification of the side chains, and by free radical polymerization gave polyacrylate P-lactams (Scheme 4.41). Cationic polymerization of dimethylketene catalyzed by aluminum tribromide with tetra- -butylammonium bromide in dichloromethane... 

A nonionic way of polymerizing MVK is the group transfer polymerization (GTP) with dimethylketene methyl trimethylsilyl acetal as intiator and the MegSiFa anion delivered from tris(dimethylamino)sulfonium difluorotrimethylsilicate (TASF2SiMe3)... 

A, A-Dialkylacrylamides also undergo group-transfer polymerization to provide polymers in good to quantitative yields. Sogah and Webster have reported that the polymerization of DMA can be initiated with dimethylketene methyl trimethylsilyl acetal in THF (Sogah et al, 1987). Poly(DMA) was quantitatively obtained, while the number-average molecular weight was apparently lower than the theoretical one and the MWD was fairly broad = 1.62). On... 

However, mention should be made of the use of a trimethylsilyl methyl acetal of dimethylketene as an initiator for addition polymerization " and characterization or detection of compounds with Si=Si or Si=C bonds or containing divalent silicon or interchanges between these species. The chemistry of reactive intermediates in organosilicon chemistry has been reviewed by Barton."... 

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