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

Abstract

Thioether derivatives of brominated poly(isobutylene‐co‐isoprene) (BIIR) were prepared through base‐mediated nucleophilic substitution reactions of the elastomer with thiolate ions formed in situ from thiols. The characterization of the reaction products was accomplished with studies of a model compound, brominated 2,2,4,8,8‐pentamethyl‐4‐nonene, the reactivity of which was shown to be consistent with that of the polymer. The reaction of aliphatic thiols with the allylic bromide functionality of BIIR required a strong base, and base‐catalyzed air oxidation of the thiol to disulfide operated concurrently to reduce the yield of the desired substitution products. An efficient and direct method of coupling BIIR to silica with (3‐mercaptopropyl)trimethoxysilane improved filler dispersion, thereby overcoming problematic agglomeration of reinforcing siliceous fillers in these compounds. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2937–2944, 2002

Sulfuration and reversion reactions of brominated poly(isobutylene‐co‐isoprene)

“…The selectivity of BPMN for an allylic sulfide structure is more characteristic of accelerated sulfur cures of conventional rubbers that employ zinc salts as well as reagents such as MBTS 20. We have previously demonstrated the ease with which bromide is displaced from BPMN by thiolate nucleophiles at room temperature5 and by amine nucleophiles at 100 °C 4. The thioether and ammonium salts derived from these displacements are E , Z ‐endo isomers analogous to the sulfuration products observed in this work.…”

“…Direct comparisons between the kinetics of BIIR vulcanization and those of the model system are complicated by differences in viscosity/chain mobility, reagent concentrations, and the dielectric constant of the reaction medium. Nevertheless, the dynamics of BIIR reactions are consistent with those of BPMN with respect to isomerization, HBr elimination, and nucleophilic substitution 2, 4, 5. Therefore, having identified the principal vulcanization products in the model system, we have monitored their evolution over a range of reaction conditions to gain further insight into BIIR vulcanization.…”

“…Because of experimental challenges associated with the low allylic bromide concentration in BIIR and the insolubility of its crosslinked products, we have employed a model compound approach commonly adopted for studies of elastomer vulcanization. In this work, the reactive functionality within BIIR is represented by brominated 2,2,4,8,8‐pentamethyl‐4‐nonene (BPMN or 1 ), which has been used as a model for butyl rubber halogenation1, 3 as well as the thermal stability2 and nucleophilic substitution chemistry of BIIR 4, 5. The fractionation of BPMN cure products by high‐performance liquid chromatography (HPLC) and subsequent analysis by NMR and mass spectrometry (MS) have provided unique insights into the chemistry that underlies the BIIR vulcanization process.…”

Design of functional macromonomer derivatives of poly(isobutylene‐co‐isoprene)

“…This improvement is consistent with our previous work on silica-reinforced butyl rubber prepared by reaction of BIIR with mercaptopropyl trimethoxysilane to produce a thioether derivative. [13] The itaconate-based material of present interest is more attractive in some respects, as it is a sulphur-free, peroxide-curable alternative.…”

“…These include the grafting of trialkoxysilane functionality to bond the polymer to siliceous fillers, [13] the addition of poly(ethylene oxide) (PEO) side chains to generate amphiphilic copolymers, [14] and the introduction of polymer-bound ionic functionality to improve adhesive properties while conferring antimicrobial activity. [15] Each of these chemical modifications consumes allylic halide, putting one functionalization process at the expense of the other, since the electrophile content of the starting material is fixed.…”