Isopropyl vinyl ether polymerization

TABLE 5-8 Effect of Solvent on kp in Radiation Polymerization of Isopropyl Vinyl Ether at 30° C ... 

The energies of activation of vinyl ether polymerizations are much larger isobutyl and isopropyl vinyl ether E = 21 kJmol-1 ethyl vinyl ether Ea 54 kJ mol This indicates that carbenium ions of vinyl ethers are less reactive, probably due to an equilibrium with dormant oxonium ions formed by an intramolecular cyclization [Eq. (67)]. The overall activation energies should also increase to more positive values if formation of the active carbenium ions is endothermic. 

Where both donor and acceptor molecules are vinyl monomers then the generation of radical ions might be expected to polymerize both species. This appears to be so [see reaction (9)] when unsaturated ethers, such as / -dioxene, dihydropyran, ethyl vinyl ether, isopropyl vinyl ether, and ketene diethylacetal, are each mixed with vinylidene cyanide. Cycloadducts are also important... 

The principal features of this radiation initiated ionic polymerization as understood at the present time has been recently presented and will not be repeated here. The unequivocal free ion nature of the polymerizations gives us an opportunity to study such reactions and compare the results with those obtained with, for example, chemical initiation with stable carbonium ion salts. This paper will describe the results of such studies with cationic polymerization and be limited to two vinyl ethers, ethyl vinyl ether, EVE, and isopropyl vinyl ether IPVE which behave in somewhat different ways. In particular, methods of estimating the rate constants for propagation will be presented and the results obtained discussed with particular emphasis on the effect of solvents on these values. 

Estimated Propagation Rate Constants and the Activation Energies by the Radiation and Chemically Initiated Polymerization of Ethyl and Isopropyl Vinyl Ethers at 30°C. 

Some chemicals are susceptible to peroxide formation in the presence of air [10, 56]. Table 2.15 shows a list of structures that can form peroxides. The peroxide formation is normally a slow process. However, highly unstable peroxide products can be formed which can cause an explosion. Some of the chemicals whose structures are shown form explosive peroxides even without a significant concentration (e.g., isopropyl ether, divinyl acetylene, vinylidene chloride, potassium metal, sodium amide). Other substances form a hazardous peroxide on concentration, such as diethyl ether, tetrahydrofuran, and vinyl ethers, or on initiation of a polymerization (e.g., methyl acrylate and styrene) [66]. 

Fig. 10. Kinetic curves of phenylglycidyl ether polymerization (7.0 mol I-1) under the action of dimethylbenzylamine (0.25 mol 1 ) in the presence of isopropyl alcohol (0.25 mol I"1) and in the accumulation of hydroxyl and vinyl groups in the system at 353 K 149 1501...

It is reported that methyl acrylate, allyl acetate, vinyl acetate and dimethyl maleate give only low yields of oligomers with butyllithium under all experimental conditions (31). Furukawa and coworkers (32) confirm that vinyl acetate will not polymerize and that n-butyl-vinyl-ether will not either. High polymers can be formed from isopropyl acrylate (39) in toluene at —70° and from t-butyl acrylate (65). The reported failure of methyl acrylate and butyl acrylate to yield high polymers could reflect a genuine difference in behaviour connected with the side group or. could simply result from failure to choose the most favourable conditions for polymerization. Vinyl acetate can be polymerized by lithium metal (49) but co-polymerization experiments suggest that the polymer is formed by a radical mechanism. 

Commercial polymers have been produced from methyl, ethyl, isopropyl, n-butyl, isotubtyl, t-butyl, stcaryl, benzyl and trimethylsilyl vinyl ethers. The polylmethyl vinyl ether) called PVM or Resyn is produced by the polymerization of the monomer by boron trifluoride in propane at —40°C in the presence of traces of an alkyl phenyl sulfide. The polymer may have isotactic, syndiotactic or stereoblock configurations depending on the solvent and catalyst used. 

Polymerization activity was obtained with a variety of catalyst compositions. The best stereospecific catalyst was the split pretreated type (357) in which one mole of VC14 was reduced by a stoichiometric amount of an alkyl metal (0.34 mole AlEt3) in heptane at room temperature and heated 16 hours at 90° C. to obtain the purple crystalline VC13-1/3 A1C13. This reduced transition metal component was then treated with two moles of (i-Bu)3Al tetrahydrofuran complex for 20 hours at room temperature to obtain a chocolate-brown catalyst consisting predominantly of divalent vanadium with 0.21 Al/V and 1.4 i-Bu/Al. Polymerizations at 30° C. gave crystalline polymers from methyl, ethyl, isopropyl, isobutyl, tert.-butyl, and neopentyl vinyl ethers. 

The rate constants of propagation in bulk polymerizations of several alkenes initiated by y-rays are presented in Table 15. The rate constant of propagation of isobutene is estimated to be 1000 times lower in chlorinated solvents than in bulk [134]. The rate constant of vinyl ether propagation decreases a few times by adding only 1 mol% of methylene chloride [238]. This may be due to either an error in the estimate of Gh or to specific interactions between growing carbenium ions and solvent molecules both explanations assume that much less reactive, but still conducting carbenium ions are formed. Nevertheless, recently determined rate constants of propagation of isopropyl and isobutyl vinyl ethers initiated with trityl salts [217] are within a factor of 2 of those calculated from y-irradiated systems. 

A wide variety of anionic initiators [352] can also affect the polymerization of vinyl ketones. Crystalline poly(alkyl vinyl ketones) were prepared by precipitation polymerization using metallic lithium or alkyl lithium catalysts. Thomas [342] reported that lithium dust initiation at — 25°C produced two types of poly(isopropyl vinyl ketone). The ether-soluble crystalline fraction was unstable. The highest crystalline samples melted to a... 

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