Halogenated poly(isobutylene-co-isoprene): influence of halogen leaving-group and polymer microstructure on chemical reactivity

Abstract

Brominated (BIIR) and chlorinated (CIIR) poly(isobutylene-co-isoprene) are commercially available materials commonly known as halobutyl rubbers. The effect of leaving-group ability on the reactivity of halogenated poly(isobutylene-co-isoprene) was studied to place iodobutyl rubber reactivity into context with these materials. The effect of microstructure on reactivity of existing commercial materials was studied through comparison to that of polymers containing rearranged halomethyl (r-CIIR, r-BIIR, and r-IIIR) microstructure (prepared from as-received BIIR). The effect of leaving group on both thermal stability and reactivity towards nucleophilic substitution with acetate, N-butylimidazole, and sulfur was examined. The material containing the iodomethyl microstructure (r-IIIR) readily underwent nucleophilic substitution at low temperatures; however, it was extremely sensitive towards dehydrohalogenation at temperatures above 65 °C. At temperatures between 100 and 135 °C, the material containing the bromomethyl microstructure (r-BIIR) demonstrated the greatest balance between reactivity toward nucleophilic substitution and elimination through dehydrohalogenation. Exceptional thermal stability at temperatures up to 190 °C was displayed by the material containing the chloromethyl microstructure (r-CIIR); however, its reactivity towards nucleophiles was variable and nucleophile dependent. Sulfur vulcanization studies showed a clear effect of microstructure on the ability to cure with sulfur. While commercial chlorobutyl rubber has no ability to cure with sulfur alone, when rearranged to its chloromethyl microstructure (r-CIIR), curing occurs readily. Both commercial (BIIR) and rearranged (r-BIIR) bromobutyl rubber readily vulcanize in the presence of sulfur; however, BIIR cures to a greater extent.

Synergistic effect of 4,4′-bis(maleimido) diphenylmethane and zinc oxide on the vulcanization behavior and thermo-mechanical properties of chlorinated isobutylene-isoprene rubber

“…On the other hand, the formation of conjugated diene butyl via dehydrochlorination of CIIR becomes faster in the presence of ZnO. As a result, the amount of conjugated diene butyl being produced at a given time and temperature will be higher than that produced by heating CIIR alone . This facilitates the Diels–Alder reaction to take place at a lower temperature while heating CIIR with ZnO in the presence of BMDM.…”

Isobutylene‐rich macromonomers: Dynamics and yields of peroxide‐initiated crosslinking

“…To accelerate the esterification process, we have used tetrabutylammonium carboxylate salts as toluene‐soluble nucleophiles, and we isomerized the exomethylene allylic bromide functionality in the starting material to more kinetically more reactive E,Z‐bromomethyl isomers by heating BIIR with Bu 4 NBr in toluene at 85 °C. The higher electrophilicity of the isomerized polymer, coupled with the use of soluble carboxylate nucleophiles, allowed esterifications to be completed in 1 h without complications associated with BIIR dehydrohalogenation . The resulting macromonomers contained 0.15 mmoles of reactive functionality per gram of elastomer, as measured by 1 H‐NMR spectrum integration.…”

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

“…31 It is a well-known fact that a conjugated diene and a dienophile, when heated at high temperature, follow a Diels-Alder reaction. The evolution of such a conjugated diene via dehydrobromination highly depends on the temperature and time.…”

“…The evolution of such a conjugated diene via dehydrobromination highly depends on the temperature and time. 31 It is a well-known fact that a conjugated diene and a dienophile, when heated at high temperature, follow a Diels-Alder reaction. 32 Hence, in our system, it was reasonable to believe that the conjugated diene formed in situ as a consequence of the dehydrobromination of BIIR at the vulcanization temperature (>160 8C) could react with the diene portions of the BMI to form a cyclic adduct; this would lead to a crosslinked structure, as depicted in Scheme 1.…”