Vinyl trifluoroacetate

Attempted reduction of vinyl acetate yields a mixture containing 8% ethyl acetate and 3% ethyl trifluoroacetate after 10 hours. The amounts of the two esters change to 13% and 12%, respectively, at reaction times beyond 60 hours.234 Vinyl trifluoroacetate does not undergo reduction under these conditions, even after 75 hours.234... 

Figure 6.10 Active sites of lipase (1), triflinctional (thio)urea derivatives (38 39) mimicking the acive site of serine hydrolases (2), and acetyl-catalyst intermediate of the biomimetic transesterification between vinyl trifluoroacetate methanol and 2-propanol, respectively (3).

Figure 7.15 XPS spectrum of poly(vinyl trifluoroacetate) (a) C Is and (b) O Is with monochromatic AlKaexcitation. (Reproduced with permission from D. Briggs and J.T. Grant, Surface Analysis by Auger and X-ray Photoelectron Spectroscopy, IM Publications and Surface Spectra Ltd, Chichester. 2003 IM Publications.)...

Exploration of the template controlled free-radical oligomerization of other activated olefins began with standard monomers utilized in bulk polymer synthesis and the template 63. Vinyl acetate and acrylonitrile led only to uncontrolled polymerization, while vinylene carbonate did not react under the standard experimental conditions. More exotic monomers, such as vinyl trifluoroacetate and rert-butyl acrylate, were also unsuccessful. Only methyl acrylate polymerization was arrested by template 64 to provide the macrocyclized product 96 in modest yield as a mixture of five diastereomers (Scheme 8-25). Subsequent studies with the more effective thiophenyl-bearing template 63 at lower temperatures improved this yield to 35%. The diastereomer distribution was reminiscent of the methyl methacrylate-derived product, although no stereochemical assignments were made in this case either. 

Un-cross-linked semicrystalline poly vinyl alcohol) hydrogels were prepared by solvolysis of the corresponding vinyl trifluoroacetate polymers and copolymers. The relationships between polymer crystallinity, hydrogel structure, and mechanical properties in the subject hydrogels were examined. Evidence was presented that comonomers acted to disrupt crystal structure and increase water content. The effects of copolymer structure on surface characteristics important to biomedical applications were examined, and the importance of hydrogel nonionic character was demonstrated through protein binding studies. 

The rationale for this approach further involved the hypothesis that swelling in water occurs by virtue of water uptake in the amorphous regions of the polymers with network structure provided by relatively water-insensitive crystallites in the polymers. In this approach, vinyl trifluoroacetate was polymerized or copolymerized to provide highly syndiotactic thermoplastic polymeric intermediates that were converted to the corresponding syndiotactic PVA homopolymers or copolymers by solvolysis with mild nucleophilic reagents in media that were not solvents for both starting and end-product polymers. 

Materials. Vinyl trifluoroacetate monomer was prepared by the reaction of acetylene with trifluoroacetic acid in the presence of HgO catalyst and small amounts of trifluoroacetic anhydride as a water scavenger. An adaptation of the procedure of Howk (12) was used to obtain very high purity monomer. Vinyl acetate (Aldrich Chemical Company) was distilled before use maleic anhydride (Aldrich Chemical Company) was used as received. 

Vinyl trifluoroacetate (VTFA) monomer was readily prepared by the vinyl-ation of trifluoroacetic acid. Purification was difficult because of the very similar boiling points of the monomer (39 °C) and trifluoroacetic anhydride (38-39 °C). An effective procedure involved the titration of the anhydride with water to form the more readily separable carboxylic acid (b.p. is 72 °C). By using this approach, VTFA monomer of very high purity (>99.8%) has been routinely prepared. Monomer stability was excellent if cold, dark, dry conditions were maintained. 

Table IV presents additional data about the amount of head-to-head, tail-to-tail sequencing not only for the case of poly(vinyl acetate) but also for polymers of vinyl formate and of vinyl trifluoroacetate. The amount of the abnormal sequence in these vinyl esters is said to be related to the inductive effect of the acid portion of the ester [50].

Figure 20-9. Influence of the relative permittivity of the solvent on the cross-over step activation enthalpy differences for the free radical polymerization of vinyl trifluoroacetate. A, Alkanes E, esters K, ketones , bulk polymerization. (From data of Matsuzawa et al.)...

FIGURE 13.7 Molecular structures of (a) poly(vinyl acetate-sfaf-vinyl trifluoroacetate) and... 

PVdF Poly(vinylidene fluoride) PVMK Poly(vinyl m yl k ne) PVTFA Poly(vinyl trifluoroacetate)... 

Saa et al. presented remarkable examples for the tri-fluoroacetic acid (TFA)-promoted cyclization of 5, 6, and 7-alkynals (Scheme 24.72). Alkynals 291 having an internal triple bond were converted into the corresponding 5, 6, and 7-membered cyclic enones 293. On the other hand, the cyclization of terminal alkynal 294 afforded the cyclohexenone compound 296. The authors suggested that the observed formation of each enone compound would involve aldol-type reactions of vinyl trifluoroacetate intermediates 292 and 295, formed by the addition of TEA to terminal or internal alkynes, respectively. 

Scheme 7.13 Methanolysis of vinyl trifluoroacetate catalyzed by Sakai s trifunctional catalyst 56...

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