Polymerization of isobutyl vinyl ether

At -50°C Mn s remained unchanged (Mn % 3 x 10, [p-DCC]Q = 0.50 mM) with increasing Wjgyg and Mw/Mn % 2.0. The polymerization is no longer quasiliving but follows a conventional chain-transfer-dominated course. Nonpolar media are evidently unsuitable for quasiliving polymerization of isobutyl vinyl ethers. 

A number of publications purport to give values for the absolute propagation rate constant kp for the polymerization of isobutyl vinyl ether (Table 2). The values of Okamura et ah, are derived by techniques and arguments which are of doubtful validity [54a] and they seem much too small. Eley s value, derived from an analysis of non-stationary kinetics, is four orders of magnitude smaller than the kp deduced from studies of radiation... 

Table 5-1 shows the various kinetic parameters, including k+ and kp, in the polymerization of styrene initiated by triflic acid in 1,2-dichloroethane at 20°C. Data for the polymerization of isobutyl vinyl ether initiated by trityl hexachloroantimonate in methylene chloride at 0°C are shown in Table 5-2. Table 5-3 shows values for several polymerizations initiated... 

TABLE 5-2 Kinetic Parameters in (t)3C+SbCl6 Polymerization of Isobutyl Vinyl Ether in CH2CI2 at 0°C ... 

Stronger Lewis acids such as SnCLi, TiCLt, and CH3AICI2 yield fast but uncontrolled polymerization with broad PDI. LCP of vinyl ethers can be achieved if the other components and reaction parameters are appropriately adjusted by various combinations of lower reaction temperature, added nucleophile, added common salt, and solvent prolarity. For example, polymerization of isobutyl vinyl ether using HC1 as the initiator (or one can use the preformed adduct of monomer and HC1) with SnCLt or TiCLj in CH2CI2 is non-LCP... 

Fig. 5-2 Dependence of M and MwfMn on conversion for the polymerization of isobutyl vinyl ether by HI/I2 in CH2C12 at - 15°C. [M] = 0.38 M at beginning of each batch [HI] = 0.01 M [I2] = 0.02 M (A), 0.001 M ( ), 0.005 M (o). After Sawamoto and Higashimura [1986] (by permission of Huthig and Wepf Verlag, Basel and Wiley-VCH, Weinheim).

The first reported instance of stereoselective polymerization was probably the cationic polymerization of isobutyl vinyl ether in 1947 [Schildknecht et al., 1947]. A semicrystalline polymer was obtained when the reaction was carried out at —80 to —60°C using boron tri-fluoride etherate as the initiator with propane as the solvent. The full significance of the polymerization was not realized at the time as the crystallinity was attributed to a syndiotactic structure. X-Ray diffraction in 1956 indicated that the polymer was isotactic [Natta et al., 1956a,b], (NMR would have easily detected the isotactic structure, but NMR was not a routine tool in 1947.)... 

Cationic Polymerization of Isobutyl Vinyl Ether with BFj-Etherate at Low Temperatures... 

Tanabe el al. studied in detail the catalytic action and properties of metal sulfates most of the sulfates showed the maximum acidity and activity by calcination at temperatures below 500°C, with respect to the surface acidity and the acid-catalyzed reaction (118, 119). Other acid-catalyzed reactions were studied with the FeS04 catalyst together with measurement of the surface acidity of the catalyst the substance calcined at 700°C showed the maximum acidity at Ho s 1.5 and proved to be the most active for the polymerization of isobutyl vinyl ether, the isomerization of d-limonene oxide, and the dehydration of 2-propanol (120-122). It is of interest that the catalyst calcined at a slightly higher temperature, 750°C, was completely inactive and zero in acidity in spite of the remarkable activity and acidity when heat treated at 700°C. 

Ueno et al. (35) have reported similar behavior for styrene. In their work, at 30°C. and a dose rate of 2.42 X 1014 e.v. cc. 1 sec. 1, there was an approximate inverse linear relationship between the rate of polymerization of styrene and the concentration of triethylamine, between 10 6 and 10 4M amine. Ammonia and amines have also been observed to inhibit the polymerization of isobutyl vinyl ether (6) and a-methvl-styrene (17). 

Use of triphenylmethyl and cycloheptatrienyl cations as initiators for cationic polymerization provides a convenient method for estimating the absolute reactivity of free ions and ion pairs as propagating intermediates. Mechanisms for the polymerization of vinyl alkyl ethers, N-vinylcarbazole, and tetrahydrofuran, initiated by these reagents, are discussed in detail. Free ions are shown to be much more reactive than ion pairs in most cases, but for hydride abstraction from THF, triphenylmethyl cation is less reactive than its ion pair with hexachlorantimonate ion. Propagation rate coefficients (kP/) for free ion polymerization of isobutyl vinyl ether and N-vinylcarbazole have been determined in CH2Cl2, and for the latter monomer the value of kp is 10s times greater than that for the corresponding free radical polymerization. 

Radiation-induced polymerization of isobutyl vinyl ether in bulk leads to an estimate (42) for kp of 10+5M 1 sec.-1 at 30 °C. with Ea = 6 kcal./mole. This value, extrapolated to the temperatures used in the present work, yields an estimate of kp within one order of magnitude of that now reported. Considering the experimental problems in these vastly different techniques, and the fact that different solvents are involved, such agreement is remarkable and provides support for the assumptions made to evaluate kp. 

When protonic acids are used as the initiators, nucleophiles do not complex oxyanions and therefore only form onium ions. The kinetic scheme of triflic acid initiated polymerizations of isobutyl vinyl ether in the presence of sulfides is presented in Eq. (80) [58,133]. The rate of polymerization described by Eq. (81) takes into account propagation by both carbenium kp ) and sulfonium ions ( /). 

Since the discovery of the first controlled/living cationic polymerization of isobutyl vinyl ether [IBVE CH2=CH OCH2CH(CH3)2 ] with the HI/... 

Figure 25 The total concentration of living end ([P ]/[HI]0 P active + dormant species) as a function of time in the polymerization of isobutyl vinyl ether with the HI/I2 initiating system in toluene (A) and CH2CI2 (B) at temperatures 0 to -40° C [M]0 = 0.38 M [HI]0 = 10 mM [I2]o = 5.0 mM (in toluene) or 0.20 mM (in CH2CI2). [P ] is determined by quenching the reaction with the sodium salt of ethyl malonate followed by H NMR end group analysis of the product. The vertical arrows indicate the time for 100% conversion at each temperature. (From Ref. 85.)...

In some systems it is necessary to add a large amount of salts to obtain polymers with low polydispersities. This happens when salts participate in ligand/anion exchange (special salt effect) and when they enhance ionization of covalent compounds through the increase of ionic strength. The special salt effect may either reduce or enhance ionization. Strong rate increases observed in the polymerization of isobutyl vinyl ether initiated by an alkyl iodide in the presence of tetrabutylammonium perchlorate or triflate can be explained by the special salt effect [109]. The reduction in polymerization rate of cyclohexyl vinyl ether initiated by its HI adduct in the presence of ammonium bromide and chloride can be also ascribed to the special salt effect [33]. The breadth of MWD depends on the relative rate of conversion of ion pairs to covalent species and is affected by the structure of the counterions. 

Table 4 shows typical reaction conditions and results of the living cationic polymerization of isobutyl vinyl ether (IBVE) with the HCl/ZnCh [127] and the CFjCC H/ZnCL [227] initiating systems. The former system is now among the most convenient for the synthesis of poly(alkyl vinyl... 

During the polymerization of isobutyl vinyl ether, macromolecules grow about 10 times more rapidly than the chains of poly(tetramethylene oxide) (PTHF) from tetrahydrofuran (THF) (at the same temperature and with the same initiator, PhjC SbCI ). Therefore it is possible, even by relatively rough methods, to record the change in lenght of PTHF macromolecules during the reaction, whereas with poly(isobutyl-vinyl-ether) this is not possible, even by sensitive and rapid methods. Nevertheless, both chain types grow by stepwise monomer addition to carboxonium or oxonium centres, respectively. 

S. Kwon, H. Chun, and S. Mah, Photo-induced living cationic polymerization of isobutyl vinyl ether in the presence of various combinations of halides of diphenyliodonium and zinc salts in methylene chloride. Fibers Polymers, 2004, 5(4), 253-258. 

S. Kwon, et al., Living cationic polymerization of isobutyl vinyl ether (II) Photoinduced living cationic polymerization in a mixed solvent of toluene and diethyl ether. J. Appl. Polym. Sci. 2006, 101(6), 3581-3586. 

M.U. Kahveci, M.A. Tasdelen, and Y. Yagci, Photochemically initiated free radical promoted living cationic polymerization of isobutyl vinyl ether. Polymer 2007, 48(8), 2199-2202. 

M. Kamigaito, M. Sawamoto, and T. Higashimura, Living cationic polymerization of vinyl ethers by electophile lewis acid initiating systems. 6. Living cationic polymerization of isobutyl vinyl ether by RCOOH/lewis acid initiating systems effects of carboxylate ions and lewis acid activators. Macromolecules 1991, 24(14), 3988-3992. 

All previously discussed examples of living cationic polymerization of vinyl ethers were based on homogeneous polymerization media. In 2007, Oashima and coworkers demonstrated the living polymerization of isobutyl vinyl ether in the presence of iron(III) oxide as heterogeneous catalyst and ethyl acetate or dioxane as base [58]. The major advantage of this heterogeneous catalytic system is the easy removal of the metal oxide catalyst. In addition, it was demonstrated that the iron(III) oxide could be reused for at least five times without a decrease in activity. 

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