Polyisobutylenes reactions

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... 

The susceptibihty of dialkyl peroxides to acids and bases depends on peroxide stmcture and the type and strength of the acid or base. In dilute aqueous sulfuric acid (<50%) di-Z fZ-butyl peroxide is resistant to reaction whereas in concentrated sulfuric acid this peroxide gradually forms polyisobutylene. In 50 wt % methanolic sulfuric acid, Z fZ-butyl methyl ether is produced in high yield (66). In acidic environments, unsymmetrical acychc alkyl aralkyl peroxides undergo carbon—oxygen fission, forming acychc alkyl hydroperoxides and aralkyl carbonium ions. The latter react with nucleophiles,... 

Polymerization. Polymerization reactions, which are addition reactions, are used to produce the principal products formed direcdy from butlylenes butyl elastomers polybutylenes and polyisobutylene (see Elastomers, synthetic Olefin polymers). 

Polyisobutylene has the chemical properties of a saturated hydrocarbon. The unsaturated end groups undergo reactions typical of a hindered olefin and are used, particularly in the case of low mol wt materials, as a route to modification eg, the introduction of amine groups to produce dispersants for lubricating oils. The in-chain unsaturation in butyl mbber is attacked by atmospheric ozone, and unless protected can lead to cracking of strained vulcanizates. Oxidative degradation, which leads to chain cleavage, is slow, and the polymers are protected by antioxidants (75). 

Cross-linking reactions for the polyisobutylene-type polymers depend on adding a reactive site, usually an aHyUc hydrogen or halogen. These reactive sites allow vulcanization with sulfur and accelerators or metal oxides (76,77). 

Although the effective functionality of CISi-PaMeSt was less than one, attempts were made to obtain block copolymers by coupling with living polyisoprenyllithium and a,w-disodium polyisobutylene glycolate. These particular coupling reactions were selected because it is known that Si-Cl bonds readily react with organolithium compounds and sodium alkoxides43 45 . 

This section concerns the synthesis of polyisobutylenes (PIB) bearing a Si-H head-group (HSi-PIB) by the use of Si-H containing functional initiator in conjunction with Me3Al coinitiator. First the effect of reaction conditions on the rate and molecular weight have been investigated and subsequently a H1 NMR method for the quantitative characterization of Si-H groups in HSi-PIB was developed. 

Paulo, C. and Puskas, J.E. Synthesis of hyperbranched polyisobutylenes by inimer-type living polymerization. I. Investigation of the effect of reaction conditions. Macromolecules, 34, 734, 2001. 

When the butyl rubber was compounded with up to 30 percent of polyisobutylene, which, lacking the unsaturated isoprene units, did not enter into the cross-linking reaction, the tensile strengths were, of course, considerably reduced. They were found nevertheless to be accurately represented by the same equation, (53), provided merely that Sa is taken as the fraction of the composite specimen consisting of network chains subject to orientation. Thus, in this case... 

The conductivity changes accompanying and following the polymerisation of five portions of norbornadiene added to an aluminium bromide solution at -63 °C are shown in Figure 6 (Experiment No. R4). The polymer, which was precipitated during the reaction, was subsequently found to be insoluble and therefore presumably crosslinked. Since this polymer was, therefore, unsuitable for radiochemical assay, another experiment (RIO) was done with norbornadiene in a mixture of methyl and ethyl bromide at -125 °C to prevent cross-linking. The polymer was soluble and the number of tritium atoms per molecule of polymer was much greater than for polyisobutylene. 

To ascertain whether tritium could have entered the polyisobutylenes by a process other than the hydrolysis of a carbon-aluminium bond, we tested the reaction of suitable polymers with aluminium bromide. The polyisobutylenes were dissolved in ethyl bromide, and phials of aluminium bromide were crushed into these solutions, which were subsequently kept at 0 °C for ca. 15 minutes, and then hydrolysed in the usual way with tritiated water. The three substances examined in this way were polyisobutylenes of high and low DP, and nonadecane. The polyisobutylenes contain approximately one double bond per molecule. The results in... 

The conductimetric, kinetic, and radiochemical experiments lead to the conclusion that alkenes, but not strainless alkanes, are aluminated by A1X2+. This and the balance of the number of C-Al bonds in our polyisobutylenes support Proposition 2 that initiation is by reaction (iii). 

In terms of chemistry, the potassium perchlorate is the oxidiser that oxidises the organic fuels (polyisobutylene, etc.) in exothermic reactions as discussed previously. 

The type of products depends largely on the reaction temperature (Thomaset al., 81). At the boiling point of the isobutylene (— 6°) polymerization in the presence of boron fluoride yielded an oil after a considerable induction period. On the other hand, if the isobutylene was precooled to — 80° an immediate reaction occurred with almost explosive violence, producing a polymer of a very much higher molecular weight. The molecular weight of the polyisobutylene molecule increased from... 

Isobutylene is polymerized under conditions where chain transfer to monomer is the predominant chain-breaking reaction. A 4.0-g sample of the polymer was found to decolorize 6.0 mL of an 0.01 M solution of bromine in carbon tetrachloride. Calculate the number-average molecular weight of the polyisobutylene. 

In the absence of substantial unsaturation and of active groups on the chain for either polymer, only linear block copolymers are formed, according to the initiation Reactions 1 and 4. Low density polyethylene and high molecular weight polyisobutylene are typical of polymers which form block copolymer fractions on intensive mechanical working. The composition of block copolymers is related also to the relative rates of reaction, (Reactions 2 and 3) which is determined by the relative radical reactivity. 

Berlin and coworkers (5,56) desired to obtain a material with an increased mechanical strength. They carried out a plasticization of bulk ami emulsion polystyrene molecular weight 80000 and 200000 respectively at 150-160° C, with polyisobutylene, butyl rubber, polychloroprene, polybutadiene, styrene rubber (SKS-30) and nitrile rubber (SKN 18 and SKN 40). The best results were obtained with the blends polystyrene-styrene rubber and polystyrene-nitrile rubber. An increase of rubber content above 20-25% was not useful, as the strength properties were lowered. An increase in the content of the polar comonomer, acrylonitrile, prevents the reaction with polystyrene and decreases the probability of macroradical combination. This feature lowers the strength, see Fig. 14. It was also observed that certain dyes acts as macroradical acceptors, due to the mobile atoms of hydrogen of halogens in the dye, AX ... 

The principal polyolefins are low-density polyethylene (ldpe), high-density polyethylene (hope), linear low-density polyethylene (lldpe), polypropylene (PP), polyisobutylene (PIB), poly-1-butene (PB), copolymers of ethylene and propylene (EP), and proprietary copolymers of ethylene and alpha olefins. Since all these polymers are aliphatic hydrocarbons, the amorphous polymers are soluble in aliphatic hydrocarbon solvents with similar solubility parameters. Like other alkanes, they are resistant to attack by most ionic and most polar chemicals their usual reactions are limited to combustion, chemical oxidation, chlorination, nitration, and free-radical reactions. 

When tested in other polymers, maleimides did not affect the rate of cross-linking in polydimethylsiloxane, polyisobutylene, and polyvinylchloride. In polyethylene, the addition of 5 wt.% of m-phenylene dimaleimide increased the G(X) from 1.8 to 7.2. In the polyvinylacetate the effect was even more pronounced the dose for gelation was reduced by about a factor of 50. Contrary to the cross-link enhancing effect found for m-phenylene dimaleimide, cross-linking was retarded in polyvinyl acetate by the addition of monomaleimides. When analyzing the mechanism of the reaction it was concluded that monomaleimides are not expected to affect cross-linking in saturated polymers. ... 

Upon irradiation, polyisobutylene and its copolymers tend to degrade. There are a large number of studies determining the nature of the process and mechanisms, and it was established that it involves formation and reaction of free radicals. The radical concentration increases linearly with a dose up to 100 Mrad (1,000 kGy). ... 

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