Polymerization ketene

The submitters have not been successful in isolating tert-butylcyanoketene by any method. If the solvent is removed, the ketene polymerizes. The spectral properties of the product are as follows infrared (benzene) cm.-1 2220 (C=N), 2130 (C=C=0) proton magnetic resonance (benzene) <5, multiplicity, assignment 0,75 [singlet, C(CH3)3],... 

It is a gas that liquefies at —56°. It bears the same relation to acetic acid that carbon suboxide does to malonic acid it adds water directly and is thereby converted into acetic acid. The double bond which it contains is a very active one. Ketene polymerizes readily and adds directly to a number of elements and compounds. It unites with alcohol and forms ethyl acetate, and with ammonia to form acetamide. 

StericaHy hindered or very electrophilic substituted ketenes, such as diphenylketene, di-Z rZ-butylketene [19824-34-17, and bis(trifluoromethyl)ketene, are quite stable as monomers. Ketenimines tend to polymerize. The dimerization of thioketenes results in 1,3-dithiacyclobutanones (6) (45), a type of dimer not observed with ketenes. 

Other Rea.ctions, The photolysis of ketenes results in carbenes. The polymeriza tion of ketenes has been reviewed (49). It can lead to polyesters and polyketones (50). The polymerization of higher ketenes results in polyacetals depending on catalysts and conditions. Catalysts such as sodium alkoxides (polyesters), aluminum tribromide (polyketones), and tertiary amines (polyacetals) are used. Polymers from R2C—C—O may be represented as foUows. 

Polymerization of methacrylates is also possible via what is known as group-transfer polymerization. Although only limited commercial use has been made of this technique, it does provide a route to block copolymers that is not available from ordinary free-radical polymerizations. In a prototypical group-transfer polymerization the fluoride-ion-catalyzed reaction of a methacrylate (or acrylate) in the presence of a silyl ketene acetal gives a high molecular weight polymer (45—50). 

The anionic polymerization of methacrylates using a silyl ketene acetal initiator has been termed group-transfer polymerization (GTP). First reported by Du Pont researchers in 1983 (100), group-transfer polymerization allows the control of methacrylate molecular stmcture typical of living polymers, but can be conveniendy mn at room temperature and above. The use of GTP to prepare block polymers, comb-graft polymers, loop polymers, star polymers, and functional polymers has been reported (100,101). 

Group-Transfer Polymerization. Living polymerization of acrylic monomers has been carried out using ketene silyl acetals as initiators. This chemistry can be used to make random, block, or graft copolymers of polar monomers. The following scheme demonstrates the synthesis of a methyl methacrylate—lauryl methacrylate (MMA—LMA) AB block copolymer (38). LMA is CH2=C(CH2)COO(CH2) CH2. 

Reaction in a Centrifugal Pump In the reaction between acetic acid and gaseous ketene to make acetic anhydride, the pressure must be kept low (0.2 atm) to prevent polymerization of ketene. A packed tower with low pressure drop could be used but the required volume is very large because of the low pressure. Spes (Chem. Ing. Tech., 38, 963-966 [1966]) selected a centrifugal pump reactor where... 

Diketene polymerizes violently in the presence of alkali. Distd at reduced pressure, then fractionally crystd by partial freezing (using as a cooling bath a 1 1 soln of Na2S203 in water, cooled with Dry-ice until slushy, and stored in a Dewar flask). Freezing proceeds slowly, and takes about a day for half completion. The crystals are separated and stored in a refrigerator under N2. See ketene on p. 276. 

Faster addition results in some polymerization of the dichloro-ketene which darkens the precipitate. 

The ring-opening polymerization of ketene acetals (45, X=0) provides a novel route to polyesters and many examples have now been reported (Scheme 4.27). " "7 A disadvantage of these systems is the marked acid sensitivity of the monomers which makes them relatively difficult to handle and complicates characterization. This area is covered by a series of reviews by Bailey ct a/.177 228 ... 

Safety. Since organic peroxides can be initiated by heat, mechanical shock, friction or contamination, an enormous problem in safety presents itself. Numerous examples of this problem have already been shown in this article. Additional examples include the foilowing methyl and ethyl hydroperoxides expld violently on heating or jarring, and their Ba salts also are extremely expl the alkylidene peroxides derived from low mw aldehydes and ketones are very sensitive and expld with considerable force polymeric peroxides of dimethyl ketene, -K>-0-C(CH3)2C(0)j-n, expld in the dry state by rubbing even at —80° peroxy acids, especially those of low mw, and diacetyl, dimethyl, dipropkmyl and methyl ethyl peroxides, when pure, must be handled only in small amts and... 

All attempts to isolate efficient process giving a white solid polymer which appears to have repeating keteneimine units. This assignment is consistent with the very strong absorption at 2140 cm.-1 in the infrared spectrum. ... 

The previous two systems resemble in some way the interesting group-transfer polymerization discovered by the DuPont team 13). The initiator, asilyl ketene acetal, l,... 

The controlled polymerization of (meth)acrylates was achieved by anionic polymerization. However, special bulky initiators and very low temperatures (- 78 °C) must be employed in order to avoid side reactions. An alternative procedure for achieving the same results by conducting the polymerization at room temperature was proposed by Webster and Sogah [84], The technique, called group transfer polymerization, involves a catalyzed silicon-mediated sequential Michael addition of a, /f-unsaluralcd esters using silyl ketene acetals as initiators. Nucleophilic (anionic) or Lewis acid catalysts are necessary for the polymerization. Nucleophilic catalysts activate the initiator and are usually employed for the polymerization of methacrylates, whereas Lewis acids activate the monomer and are more suitable for the polymerization of acrylates [85,86]. 

Diels-Alder reactions [31] and 1,3-dipolar cycloadditions [32, 33] have been performed by use of this methodology. For example, Diaz-Ortiz described the hetero-Diels-Alder and 1,3-dipolar cycloaddition reactions of ketene acetals. The reactions were improved and products were isolated directly from the crude reaction mixture without polymerization of the ketene acetals [34],... 

In an attempt to avoid the polymerization/depolymerization equilibrium that occurs during melt polycondensation, Albertsson and Lundmark (1988) also studied the irreversible reaction of adipic anhydride with ketene. However, they reported very little difference in molecular weights when two ketene syntheses were compared to melt polycondensation and ringopening polymerization using a zinc catalyst (Albertsson and Lundmark, 1988). 

The column and apparatus should not be washed with acid cleaning solution because the glass surface is left acidic and it then catalyzes the polymerization of ketene acetal.4 A thin coating of the polymer on the walls of the apparatus is not detrimental. If polymer must be removed, it is best done by dissolving it in a 10 per cent solution of hydrochloric acid in acetone a deep red solution results. 

In the fashion of the established German school of organic chemistry, Staudinger studied a wide range of materials we now know to be polymeric. His shift in research interest was quite courageous as it caused a stir in Germany. He was, as a result of his work which included the discovery of ketenes, an established, reputable synthetic organic chemist. 

Related work had shown that the nitrogen analogs of the cyclic ketene acetals were readily synthesized and would polymerize with essentially 100% ring opening. For this reason their copolymerization with a variety of monomers was undertaken (6). 

Since the cyclic ketene acetal V will undergo free radical polymerization to produce an ester group, a study was undertaken to see if... 

On this basis it was reasoned that a benzyl group in a ketene acetal should greatly increase the extent of cleavage during polymerization and, therefore, should increase the efficiency of chain transfer. That in fact is what occurred when an equimolar mixture benzyl methyl ketene acetal (XIV) and styrene was heated at 120°C in the presence of di-tert-buty1 peroxide an oligomer with 80% styrene units and capped with a carbomethoxy group was obtained. 

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