Cationic polymerization of isobutylene

Derivatives of polyisobutylene (6. in Figure 9.1) offer the advantage of control over the molecular weight of the polyisobutylene obtained by cationic polymerization of isobutylene. Condensation on maleic anhydride can be done directly either by thermal activation ( ene-synthesis reaction) (2.1), or by chlorinated polyisobutylene intermediates (2.2). The condensation of the PIBSA on polyethylene polyamines leads to succinimides. Note that one can obtain mono- or disuccinimides. The mono-succinimides are used as... 

TABLE 5-5 Monomer Transfer Constants in Cationic Polymerization of Isobutylene in CH2CI2... 

Consider the cationic polymerization of isobutylene using S11CI4 as the coinitiator and water as the initiator. Under certain reaction conditions, the polymerization rate was found to be first-order in SnCLj, first-order in water, and second-order in isobutylene. 

Cationic Polymerization of Isobutylene with Gaseous BF3 at Low Temperatures in Bulk... 

In the absence of monomers, trimethylaluminum (0.5 mol) reacts with t-butyl chloride (1.0 mol) at -78°C to give a quantitative yield of neopentane [22], Kennedy [23] found that aluminum trialkyls (AlMe3, AlEt3, A1Bu3) in the presence of certain alkyl halides are efficient initiators for the cationic polymerization of isobutylene, styrene, etc. 

The synthesis of A2B miktoarm star polymers has been discussed and exemplified using PIB as a component. The synthesis involves a quasi living cationic polymerization of isobutylene from a monofunctional cationic initiator. This initiator also contains a blocked hydroxyl group. Eventually, the blocked hydroxyl group of the initiator is deblocked, and functionalized with a branching agent. This activated reagent is then used for an atom transfer radical polymerization process of /erf-butyl acrylate (18). 

The cationic polymerization of isobutylene (12) and styrene (13) is initiated readily by Et2AlCl in the presence of an alkyl halide, RC1. The interaction of the catalyst and cocatalyst is presumed to produce the carbonium ion R+, which initiates polymerization, and the corresponding gegenion Et2AlCl2". Alkyl halides with low R-Cl bond dissociation energies—e.g. tertiary, substituted allylic, and benzylic halides—are among the most effective cocatalysts. 

The cocatalytic activity of alkyl halides in the cationic polymerization of styrene in the presence of stannic chloride (17), in the polymerization of butadiene with Et2AlCl-cobalt compound (10) and R3Al-cobalt compound (23) catalyst systems and in the cationic polymerization of isobutylene (12) and styrene (13) in the presence of Et2AlCl is well documented. It is reasonable to propose that a reaction between Et2AlCl and a labile chlorine atom on PVC results in the generation of a carbonium ion on the polymer backbone. 

Kennedy 441 reported the synthesis of a MACROMER on the basis of the cationic polymerization of isobutylene. 

The cationic polymerization of isobutylene (2-methylpropene) is shown in Section 8-16A. Isobutylene is often polymerized under free-radical conditions. Propose a mechanism for the free-radical polymerization of isobutylene. 

The mechanism given for cationic polymerization of isobutylene (Mechanism 26-2) shows that all the monomer molecules add with the same orientation, giving a polymer with methyl groups on alternate carbon atoms of the chain. Explain why no isobutylene molecules add with the opposite orientation. 

While the detailed mechanistic understanding of many cationic polymerization systems has not as yet been clearly established, there are some that are reasonably well understood. Let us consider the detailed progression of the cationic polymerization of isobutylene using a TiCl4/H20 catalyst system as an example. This system cannot be used as a general model for all cationic polymerizations as is possible for free radical-initiated systems, since there is a wider variety of mechanisms seen for cationic, than for free radical, systems. 

Scheme 1.26. Elementary reactions in the cationic polymerization of isobutylene initiated by boron...

Problem 8.22 Write equations to describe plausible termination reactions in cationic polymerization of isobutylene initiated by (a) BF3.OH2, (b) BCI3.OH2, (c)AlR3/(-butyl chloride, and (d) Al(C2H5)3/t-butyl chloride. 

Account for the fact that 1-butene can be used to control polymer molecular weight in cationic polymerization of isobutylene. 

Recently two ponderous papers appeared by Kriz and Marek which purported to be model studies of the cationic polymerization of isobutylene (11,12). In the first phase of their study (11) the authors chose 1,1 -dineopentyl ethylene, a trimer of isobutylene, as their model compound and worked with AlBr3, HBr (or DBr) in n-heptane at —70° (11). They mixed these reagents by the following sequence nC + HBr + trimer+AlBr3. The products were analyzed by gas chromatography, NMR (60 MHz), and mass spectroscopy. Useful, hard data of this research are as follows 1.1,1 -dineopentylethylene rapidly isomerizes... 

In 1970 Kennedy and Gillham (9) proposed a comprehensive scheme for the study of competitive reactions in cationic polymerization of isobutylene. Their scheme was based on reacting an initiator-coinitiator svstem with a nonpolymerizing olefin. In particular, they examined the t-BuO/Me3Al system with 2,4,4-trimethyl-1 -pentene, the model compound for isobutylene, using methyl chloride at — 78° C. The overall reaction scheme is shown in Fig. 1. 

Kennedy and Frisch (205) proposed the synthesis of polymerizable oligomers by cationic polymerization of isobutylene ... 

Reaction 10 depends on the selective removal of the tert-chloride ion and cationic polymerization of styrene in the first step. Subsequently and at higher temperatures the tert-bromide function is used to initiate the cationic polymerization of isobutylene (Reaction 11). 

The INBFER technique has been used for quasi living cationic polymerization of isobutylene. Bi- and tnfunctional initiators yield telechelics with two or three chlorine end groups (Scheme 6). ... 

Example 7.7 Explain why in the cationic polymerization of isobutylene, hquid ethylene or propylene at their boiling points are normally added to the reaction medium as a diluent. How wiU an increase in the dielectric constant of the reaction medium affect the rate and degree of polymerization ... 

Butyl rubber is a copolymer of isobutylene with a small amount (0.5 to 2.5 mol%) of isoprene, which provides the unsaturation sites necessary for vulcanization. Butyl rubber is produced by cationic polymerization of isobutylene and chloroprene in methyl chloride in the presence of Friedel-Crafts catalysts such as aluminum chloride at about -100°C. 

Chain transfer to monomer is also an integral step in the cationic polymerization of isobutylene, and it is this reaction which controls the molecular weight (Faust, 2012) ... 

The better results under fast chemical reactions carrying out in liquid phase can be obtained at conditions of use of "zone" model under dividing of reaction zones by shell-and-tube apparatus-condensers. The model of work is considered by the example of cationic polymerization of isobutylene (Table 4.3). 

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