Polyisobutylene physical properties

The most important physical properties of the elastomeric polyisobutylenes are those exhibited by vulcanised compounds, especially high loss modulus and low permeabihty air. 

It is possible to cross-link polyisobutylene and poly(isobutylene-isoprene) and chlorobutyl rubber by means of certain additives however, the physical properties of the vulcanizates prepared by conventional curing methods cannot be attained. The most promising results were obtained with chlorobutyl compounds containing thioether polythiols as prorads. ... 

Following quantitative methylation of the co-fert-chloro site by trimethyl aluminum, the methylated polyisobutylene methacrylate macromonomer was co-polymerized with MMA by Group Transfer Polymerization [87]. PMMA-g-PIB graft copolymers with controlled MW and composition were obtained. The structure and physical properties were determined by the [MMA]/[MA-PIB] and [MMA]/[Initiator] ratios. 

The regions that are not crystalfine are called amorphous regions. Crystalline regions render a polymer hard and durable, while amorphous regions render a polymer flexible. The degree of crystallinity of a polymer, and therefore its physical properties, greatly depends on the steric requirements of the substituent(s) present in the repeating unit of the polymer. For example, compare the structures of polyethylene and polyisobutylene. 

While dispersant hydrocarbon backbones are currently dominated by conventional polyisobutylene, many more backbones are on the horizon with the potential to provide improved properties, processing, overall performance per cost, and the ability to optimize properties to respond to specific engine performance characteristics. Some of these (Fig. 8) include high vinylidene PIB, olefin copolymers (OCP) and poly-alpha olefins (PAO). Each of these will be discussed in terms of their structure and reactivity, physical properties and how these translate into strengths and weaknesses in the final application. 

Kramer,O., Greco,R., Ferry,J.D. Viscoelastic properties of butyl rubber networks containing reptating polyisobutylene. Paper presented at the San Diego meeting of the American Physical Society, March, 1973. 

The connectivity indices therefore have different values for many polymers which have the same value of N. They thus enable distinctions to be made between polymers which have equal values of N but different structures, and different physical and chemical properties. Some examples of such polymers include polyisobutylene, polybutadiene, polyacrylonitrile, poly(vinylidene chloride) and poly(dimethyl siloxane), all of which have N=4. 

The physical, chemical, and compounding properties of the isobutylene family of polymers will vary with molecular weight, amount of unsaturation, the minor constituents in the polymer and, in certain instances, chemical modification. With proper allowance for gross differences in molecular weights, butyl and polyisobutylene can often be used interchangeably in cement and adhesive compositions that will not be cured. 

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