Ketene, polymerization with

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). 

In a similar way the complex (TPP)Al-0-C(C4H9) =CH-CH2-C2H5 was prepared [116] from A1(TPP)(C2H5) and rm-butyl vinyl ketene together with poly-ferf-butyl methacrylate. Every step of propagation in the photoinduced polymerization is conditioned by light absorption and includes the photoinsertion of an unsaturated molecule [115]. 

Cyclic orthoeslers. The cycloaddition of ketene acetals with epoxides can be effected by catalysis with ZnCl2, which does not promote polymerization. Some useful transformations of the resulting cyclie orthoesters are formulated. Examples ... 

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. 

Thus the lactam polymerization with strong bases can be strongly accelerated by addition of activators such as, for example, acyl lactams. Additionally, the acyl lactam may be formed in situ by adding acetic anhydride or ketenes to the polymerization mixture. 

Racemic and optically active a- and 3-substituted poly(3-propiolactones) can be synthesized by the current methods of pol5rmerization. However, the synthesis of a-substituted 3-propiolactones usually involves the ring closure of 3-substituted acids and they are often polymerized with anionic initiators. In contrast, the synthesis of 3-substituted 3-propiolactones is often made by the reaction of ketenes with carbonyl compounds (in the presence of a chiral base to obtain optical purity) and their polymerization proceeds with a cationic or coordinated initiator. 

Group transfer polymerization is the most suitable polymerization mechanism for methacrylates. Propagation involves reaction of a terminal silyl ketene acetal with a monomer by Michael addition during which the silyl group transfers to the added monomer thus creating a new terminal silyl ketene acetal group. In this kind of polymerization it is common to... 

Ring-opening polymerizations and copolymerizations also offer novel routes to polyesters and polyketones. These polymers are not otherwise available by radical polymerization. Finally, ring-opening copolymerization can be used to give end-functional polymers. For example, copolymerization of ketene acetals with, for example, S, and basic hydrolysis of the ester linkages in the resultant copolymer offers a route to a,co-difunctional polymers. 

The second method involves end-quenching of living polymers with appropriate nucleophiles. Although this approach appears to be more attractive than the first one, in situ end funaionali-zation of the living ends is limited to nucleophiles that do not react with the Lewis add coinitiator. Because the ionization equilibrium is shifted to the covalent spedes, the concentration of the ionic active species is very low. Quantitative functionalization can only be accomplished when ionization takes place continuously in the presence of nudeophile. Quenching the vinyl ether polymerization with the malonate anion,certain silyl enol ethers " and silyl ketene acetals have been successfully used to synthesize end-functionalized poly(vinyl ethers). Alkyl amines, " ring-substituted anilines, " " alcohols, " and water " have also been used to quench the vinyl... 

When living poly(methyl methacrylate) (PMMA) prepared by group transfer polymerization (GTP) is used as a macroinitiator for the ROP of cyclic carbonates, a site transformation from the silyl ketene acetal (GTP-mechanism) to an alcoholate (anionic ROP-mechanism) with a metal-free counterion occurs (Scheme 12.5). The GTP of PMMA was initiated with l-methoxy-l-trimethylsilyloxy-2-methyl-l-propene (MTS) in combination with catalytic amounts of tetrabutyl ammonium cyanide in THF as solvent. Towards the end of the reaction, DTC is dissolved in the reaction mixture and lequiv. of fluoride anions (e.g. tris(dimethylamino) sulfonium difluorotrimethylsilicate TASF), with respect to the active species, is added. In this way, good yields of the respective block copolymers were obtained. A model experiment for this site transformation is the polymerization of DTC with MTS as the initiator and TASF as the desilylating agent. The fluoride anion promotes desilylation of the silyl ketene acetal with formation of an enolate, which reacts as a carbon-centered nucleophile with the carbonyl carbon of DTC, thereby... 

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. 

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. 

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. ... 

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. 

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. 

Ketenes, which are even more reactive than isocyanates, afford ketenimines at or below room temperature [62CRV247 84JOC2688 89JCS(P1)2140]. At elevated temperatures, dimerization or polymerization occurs (21HCA887). Although N-aryl- and A-vinyliminophosphoranes react smoothly with ketenes, strong acceptor substituents on the nitrogen hamper the reaction thus V-acyliminophosphoranes do not react with ketenes. Vinylketenimines such as 2-aza-l,3-dienes prepared in this way from... 

An interesting bifunctional system with a combination of In(OTf)3 and benzoyl-quinine 65 was developed in p-lactam formation reaction from ketenes and an imino ester by Lectka [Eq. (13.40)]. High diastrereo- and enantioselectivity as well as high chemical yield were produced with the bifunctional catalysis. In the absence of the Lewis acid, polymerization of the acid chloride and imino ester occurred, and product yield was moderate. It was proposed that quinine activates ketenes (generated from acyl chloride in the presence of proton sponge) as a nucleophile to generate an enolate, while indium activates the imino ester, which favors the desired addition reaction (66) ... 

Monomers with cumulated double bonds, such as substituted allenes and ketenes, produce a great variety of structures. Stereoisomerism is found both at the saturated (iso- or syndiotacticity) and at the unsaturated carbons where the substituents in the plane of the chain can be oriented in either direction (forward or backward). With regard to 1,3-disubstituted allenes, four stereoregular strac-tures, 43-46 (Scheme 10), are predicted. Porri, Rossi, and Ingrosso succeeded in polymerizing 2,3-pentadiene (1,3-dimethylallene) samples of different optical purity (87). In their experiments they recognized the existence of sequences 43. 

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. 

The first route relies on the ROP of cyclic ketene acetals [1-3]. The electron-rich double bond is prone to react with radicals and electrophiles. Therefore, this class of monomers undergoes cationic and radical polymerization. For example, radical initiators react with the double bond to provide a new tertiary radical (Fig. 2). Two distinct mechanisms of polymerization can then take place direct vinyl polymerization or indirect ring opening of the cycle accompanied by the formation of a new radical, which is the propagating species (Fig. 2). The ester function is formed... 

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