Thermal stability of brominated poly(isobutylene‐co‐isoprene)

Abstract

The thermal stability of brominated isobutylene–isoprene rubber (BIIR) was investigated through studies of the elastomer and a model compound that accurately represented the reactive functionality within the polymer. An analysis of commercial BIIR and reaction products of brominated 2,2,4,8,8‐pentamethyl‐4‐nonene (BPMN) by NMR demonstrated that bromination of isobutylene–isoprene rubber by 1,3‐dibromo‐5,5‐dimethylhydantoin yielded a kinetically favored exomethylene substitution product, 3‐bromo‐6,6‐dimethyl‐2‐(2,2‐dimethylpropyl)‐1‐heptene (2), as opposed to the more stable endo‐isomer, (E,Z)‐4‐(bromomethyl)‐2,2,8,8‐tetramethyl‐4‐nonene (3). The exposure of BIIR and the brominated model compound BPMN to vulcanization temperatures led to the isomerization of 2 to 3 at a rate strongly dependent on HBr concentration. The elimination of HBr from these allylic bromides to produce exo‐ and endo‐conjugated dienes proceeded concurrently with isomerization, and the kinetics of these processes could be rationalized on the basis of a polar reaction mechanism. The product distributions obtained from both the model system and BIIR were consistent, thereby justifying an extension of the model compound approach to an analysis of BIIR vulcanization chemistry. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2019–2026, 2001

Synthesis of thioether derivatives of brominated poly(isobutylene‐co‐isoprene): Direct coupling chemistry for silica reinforcement

“…Unlike the polymeric system, brominated 2,2,4,8,8‐pentamethyl‐4‐nonene (BPMN or 1 ) derivatives are amenable to chromatographic separation and unambiguous structural characterization by NMR and high‐resolution mass spectrometry (MS). Previous studies6, 7 of the halogenation chemistry and thermal stability of this model have shown that it behaves in a manner consistent with BIIR, and this work extends these comparisons to nucleophilic displacements of bromide by thiolate anions.…”

Thermally stable bromobutyl rubber with a high crosslinking density based on a 4,4′‐bismaleimidodiphenylmethane curing agent

“…The high loss modulus, extended fatigue life, and oxidative stability of butyl rubbers have made them favorite materials in mechanical damping applications. By investigating the thermal stability of brominated butyl rubber, Parent and coworkers 7,8 reported the fact that at elevated temperatures (at vulcanization temperatures), exomethylene isomers of bromobutyl rubber rearranged to the more thermodynamically stable bromomethyl isomers followed by dehydrobromination to provide a butyl rubber with a conjugated diene structure. 3,4 Even though the sulfur-cured system has often been accepted for the vulcanization of IIR, the sulfur-cured system exhibits poor vulcanizate properties and low curing compatibility with other diene-based elastomers, such as polybutadiene or styrene-butadiene rubber, mainly because of the low level of unsaturation.…”

Preparation of phenyl‐modified natural rubber in latex stage

“…Second, the resulting bromonium ion may react with H 2 O to form a bromohydrin group. Furthermore, the signals at 122.4 (C29) and 124.8 (C28) ppm were assigned to the tertiary carbons of the conjugated cis ‐1,4‐isoprene units generated by elimination reaction of bromine atoms (Figure ), based on Parent et al These results demonstrate that natural rubber is brominated with NBS in latex stage, according to mechanism shown in Figure . Consequently, it is proved that the bromine atom is introduced into the natural rubber at the allylic position of the cis ‐1,4‐isoprene units while the bromohydrin structure of BrDPNRlatex is formed since the reaction occurs in the water.…”