2- ethyl vinyl ether, cationic polymerization

The observation in 1949 (4) that isobutyl vinyl ether (IBVE) can be polymerized with stereoregularity ushered in the stereochemical study of polymers, eventually leading to the development of stereoregular polypropylene. In fact, vinyl ethers were key monomers in the early polymer Hterature. Eor example, ethyl vinyl ether (EVE) was first polymerized in the presence of iodine in 1878 and the overall polymerization was systematically studied during the 1920s (5). There has been much academic interest in living cationic polymerization of vinyl ethers and in the unusual compatibiUty of poly(MVE) with polystyrene. 

In 1970, a patent by Fukui and coworkers cited the cationic polymerization of ethyl vinyl ether in liquid C02 [85]. In these reactions, SnCl4 or ethyl etherate of boron trifluoride were employed as the catalysts and the polymerizations were conducted for 20 hours at room temperature to conversion of greater than 90% polymer. No molecular weight data or spectra for these polymers were reported in this work. 

This article reports on the synthesis of photosensitive polymers with pendant cinnamic ester moieties and suitable photosensitizer groups by cationic copolymerizations of 2-(cinnamoyloxy)ethyl vinyl ether (CEVE) (12) with other vinyl ethers containing photosensitizer groups, and by cationic polymerization of 2-chloroethyl vinyl ether (CVE) followed by substitution reactions of the resulting poly (2-chloroethyl vinyl ether) (PCVE) with salts of photosensitizer compounds and potassium cinnamate using a phase transfer catalyst in an aprotic polar solvent. The photochemical reactivity of the obtained polymers was also investigated. 

Most of the reported polyfvinyl ether) macromonomers have been prepared with a methacrylate end group which can be radically polymerized and which is non-reactive under cationic polymerization conditions [71-73]. Generally, the synthesis was based on the use of the functional initiator 30, which contains a methacrylate ester group and a function able to initiate the cationic polymerization of vinyl ethers. Such initiator can be obtained by the reaction of HI and the corresponding vinyl ether. With initiator 30 the polymerization of ethyl vinyl ether (EVE) was performed using I2 as an activator in toluene at -40 °C. The MW increased in direct proportion with conversion, and narrow MWD (Mw/Mn= 1.05-1.15) was obtained. The chain length could be controlled by the monomer to initiator feed ratio. Three poly(EVE) macromonomers of different length were prepared by this method Mn=1200,5400, and 9700 g mol-1. After complete... 

B. Living Cationic Polymerization of Ethyl Vinyl Ether with the... 

There is a scant data on the radical behavior of thianthrene radical cation [58]. As pointed out above, thianthrene radical cation couples with radicals. It shows little reactivity toward oxygen but this may be ascribed to its positive charge which should render it an electrophilic radical. It initiates the polymerization of styrene [59,60], a-methyl styrene [59], and ethyl vinyl ether [59,60],but not that of vinyl pyridine [61], vinyltrimethylsilane [59], methyl acrylate [59, 61], or acrylonitrile [59,61 ]. These results can be explained by cationic rather than radical polymerization. 

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. 

Cationic polymerizations of styrene in CO2 under dispersion conditions have also been demonstrated (51). The stabilizer was a block copolymer of 2-(A -propylperfluorooctanesulfonamido)ethyl vinyl ether (FVE) and methyl vinyl ether (MVE), which formed poly(FVE- >-MVE). The poly(FVE) segments served as the soluble block and the poly(MVE) segments served as the anchoring units of PS. These cationic dispersion polymerizations were sensitive to temperature, with the optimum temperature being 15" C, which seemed to prevent chain transfer to monomer. The polymerizations at 15" C and 4 wt % stabilizer resulted in approximately 95% yield and a molecular weight of 1.8 x 10" g/mol. 

Accordingly, N-vinylcarbcizole, ethyl vinyl ether, p-methoxystyrene (pMeOSt), and a-methylstyrene (aMeSt) are 17 400, 1380, 339, and 37 times more reactive than styrene (St). Due to this very large difference in cationic reactivity, different initiating systems bring about optimum polymerization for different monomers. This also explains why cationic statistical copolymerizations are less useful than the radical counterpart. 

As we have already reported, sequential living cationic polymerizations of functionalized vinyl ethers (8) readily give amphiphilic block copolymers (17). Such sequential living polymers are equally applicable to the star polymer synthesis. A typical example utilizes an AB living block copolymer ( ) that consists of 2-(acetoxy)ethyl vinyl ether and IBVE (10 and 30 units per chain, respectively). The... 

The cationic polymerization of 2-(A/-carbazolyl)ethyl vinyl ether with boron trifluoride etherate or ethylalu-minium dichloride as initiator has been described by several authors [177-180] (Scheme 11.9). Low molecular weight polymers were obtained with both catalysts [178]. In the case of boron trifluoride etherate... 

Nishikubo, T., Kameyama, A., Kishi, K., Kawashima, T., Fujiwara, T., and Hijikata, C., Synthesis of new photoresponsive polymers bearing norbomadiene moieties by selective cationic polymerization of 2- [ [ (3-phenyl-2,5-norbomadienyl)-2-carbonyl] oxy] ethyl vinyl ether and photochemical reaction of the resulting polymers. Macromolecules, 25,4469-4475,1992. 

Structures of the same type have also been prepared by cationic polymerization techniques, as can be seen in Scheme 16. Vinyl ethers having isobutyl-, ac-etoxy ethyl-, and malonate ethyl- pendant groups have been used. Hydrolysis of... 

Propenyl Ethers and Unsaturated Cyclic Ethers Propenyl ethers (CH3—CH=CH—OR R = ethyl, isobutyl, etc. cis- and trans-isomers) and 3,4-dihydrofuran are linear and cyclic a,/3-unsaturated ethers, that can be regarded as / -substituted vinyl ether derivatives. For these monomers a few controlled/living cationic polymerizations have been reported. The HI/I2 system is generally effective for both linear and cyclic monomers [181,182,183], whereas a recent study by Nuyken indicates that the IBVE-HI adduct coupled with nBu4NC104 is suited for 3,4-dihydrofuran (see Section V.A.4) [184]. A variety of mono- and bifunctional propenyl ethers can readily be prepared by the ruthenium complex-catalyzed isomerization of corresponding allyl ethers [185]. 

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