Polymerization of isobutene

Table 7.2-1 Polymerization of isobutene in the acidic ionic liquid [EMIMJCI/AICL (XjAICL)...

Table 7.2-4 Polymerization of isobutene to high molecular weight poly(isobutene)s in the ionic liquid [EMIM]CI/AICl3 under biphasic conditions [35].

Note added in proof. Marek and Chmelir [40b, c] found that the polymerization of isobutene in heptane by aluminium bromide is greatly accelerated by addition of titanium tetrachloride. They suggested that the polymerization by aluminium bromide only is initiated by a cation such as AlBr2+ which adds to the isobutene and which is formed by self-dissociation of the catalyst. The enhancement of the rate by titanium tetrachloride they attribute to an increase in the concentration of ions by the reaction... 

Another important feature is that all the terms are composite, and therefore it is not to be expected that the Arrhenius plots for the intercepts and slopes of the Mayo plots will be rectilinear. In fact, historically, the nonlinearity of such Arrhenius plots obtained for the polymerization of isobutene by titanium tetrachloride and water gave the first clue to the existence of simultaneous propagation by free ions and ion-pairs in that system [23]. 

In the present paper we are concerned principally with the initiation step. The new observations and suggestions regarding this step put forward by Polanyi and his collaborators [17-21] marked the first real practical and theoretical advance since the work of Whitmore. They found that in the polymerization of isobutene by TiCl4 or BF3, both at room temperature and at very low temperatures, the metal halide alone was inactive, and that a third component, the co-catalyst, was required to initiate the polymerization. The word co-catalyst was chosen for the substances concerned, by analogy with co-enzyme . It is to be preferred to the term promoter , often used by American workers, as this indicates a substance which speeds up a reaction which would also take place in its absence, and since the characteristic of co-catalysts is that they are essential to the reaction. The first co-catalyst to be discovered was water, but shortly afterwards certain alcohols and acids were found to act in a similar manner. 

The polymerization of isobutene is so far a repeatable but not a reproducible reaction. [A] Following on from the work of Seymour etal. in this department and work at I.C.I. and in America, we are attempting to elucidate the reaction mechanism of this polymerization. 

The form of (4.13) offers a ready explanation for the fact that the formal order of the polymerizations, d(ln R)ld(ln m), as shown by the bilogarithmic plots of Stannett et al., varies with m. Equation (4.13) is such that both the first derivative dRIdm and the second derivative d2R/dm2 can be zero the former applies to the polymerization of isobutene for which the R against m curves have a maximum (Figures 9 and 10), the latter to the VE and styrene, the R against m curves for which all show inflections. The pursuit of this... 

The increase in the rate of polymerization of isobutene as it is diluted with a polar solvent had been reported earlier by Popova et al. (1965). These authors found that for... 

Isobutylene is more reactive than n-butene and has several industrial uses. It undergoes dimerization and trimerization reactions when heated in the presence of sulfuric acid. Isobutylene dimer and trimers are use for alkylation. Polymerization of isobutene produces polyisobutenes. Polyisobutenes tend to be soft and tacky, and do not set completely when used. This makes polyisobutenes ideal for caulking, sealing, adhesive, and lubricant applications. Butyl rubber is a co-polymer of isobutylene and isoprene containing 98% isobutene and 2% isoprene. 

In 1957 Davison, Pinner, and Worrall (8) published data on the radiation polymerization of isobutene, which could best be explained as an ionic process. These initial findings were further confirmed by subsequent investigations (7, 9, 26, 27), Needless to say, these disclosures prompted reinvestigation of the question of radiation-induced ionic polymerizations in other systems. 

Vinyl-type addition polymerization can also be carried out with acidic catalysis such as boron tnfluoride or tin tetrachloride and with basic catalysis such as alkali melals or alkali alkyls. An example of the first ease is the low-temperature polymerization of isobutene, which gives Vistanex" and butyl rubber an example of the second type is the polymerization of butadiene with sodium, which leads to buna rubber. 

Dainton, F. S., and G. B. B. M. Sutherland Application of infrared analysis to elucidate the mechanism of the boron triflouride catalyzed vapor phase polymerization of isobutene at room temperature. J. Polymer Sci. 4, 37 (1949). 

Fig. 3.54. Carbenium ion additions to isobutene as key steps in the cationic polymerization of isobutene. The dashed arrow corresponds to the overall reaction.

Intermolecular additions of carbenium ions to olefins give polymers. Such a reaction is used in industry, for example, in the cationic polymerization of isobutene (Figure 3.43). One of the rare cases of an intermolecular carbenium ion addition to an olefin without polymer formation occurs in the industrial synthesis of isooctane (Figure 3.44). 

An artificial rubber may be made by cationic polymerization of isobutene using acid initiation with BF3 and water. What is the mechanism of the polymerization, and what is the structure of the polymer ... 

If initiation is faster or comparable to propagation and termination is negligible, kinetic plots are straight in semilogarithmic coordinates. Initiation is faster than propagation and not kinetically detectable in polymerizations of isobutene and styrene initiated by cumyl derivatives because the initiator is more easily ionized than the propagating species. However, if the initiator is less easily ionized than the propagating species as in a-methyl-styrene polymerizations initiated by cumyl derivatives, and in isobutene polymerizations initiated by /-butyl derivatives (cf., also Section III. A.5), then initiation may be incomplete and the overall polymerization rate will increase continuously. 

The rates of initiation and propagation are comparable when the covalent initiator and dormant chain ends have similar structures. Therefore, 1-phenylethyl precursors are useful initiators for styrene polymerizations, but are poor initiators for a-methylstyrene and vinyl ether polymerizations. Similarly, cumyl derivatives are good initiators for isobutene and styrene, but are poor initiators for vinyl ethers their initiation of a -methylstyrene is apparently slow [165]. 1-Alkoxyethyl derivatives are successful initiators for vinyl ethers, styrenes, and presumably isobutene polymerizations [165,192]. /-Butyl derivatives initiate polymerization of isobutene slowly [105]. This is mirrored in model studies that show that /-butyl chloride undergoes solvolysis approximately 30 times slower than 2-chloro-2,4,4-trimethylpentane [193]. This may be due to insufficient B-strain in monomeric tertiary precursors [194]. In contrast, monomeric and dimeric or polymeric structures of secondary esters and halides apparently have similar reactivity. 

The common ion effect does not influence the kinetics of collapse of the ion pairs to dormant covalent species since it is a unimolecular reaction. In this case, however, deactivation of the ion pair can be increased by using less stable and more nucleophilic counteranions. The nucleophi-licity of both pure halides and complex anions with halide ligands increases in the order FOther examples of polymerizations which are well behaved because the equilibrium is favorable due to nucleophilic counteranions include Hl/I2 initiated polymerizations of vinyl ethers and polymerizations of isobutene and styrene using acetate-based initiators in the presence of BC13. 

The exo double bond is formed first in polymerizations of a-methylstyrene, but is later isomerized by protonic acid to the more stable endo isomer [14]. Carbocationic polymerizations initiated by protonic acids with extremely basic counteranions, as in triflic acid-initiated polymerizations of isobutene, produce predominantly the unsaturated dimer [285]. The exo dimer forms first and then isomerizes to the more stable endo isomer [Eq. (90)]. 

However, halide is not transferred directly in polymerization of isobutene. Instead, the propagating ion pair first reacts unimolecularly to form a covalent species with regeneration of the Lewis acid [Eq. (105)], which can then activate the inifer [306],... 

Terminal unsaturation favors termination by formation of carbo-cations which are additionally stabilized by double bonds. This can be illustrated by /3-proton elimination and subsequent loss of methide in polymerization of isobutene [Eq. (121)]. 

In 1986, Kennedy and Faust published a similar controlled/living polymerization of isobutene by the cumyl acetate/boron trichloride [C6H5C(CH3)20C(0)CH3/BC13] and related binary initiating systems [35,62],... 

In 1986 Faust and Kennedy reported the first example of controlled/living cationic polymerization of isobutene, which was initiated by a cumyl ace-... 

Table 3 Initiating Systems for Controlled/Living Polymerization of Isobutene A Reference List ...

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