Quaternary ammonium elastomeric ionomers by melt-state conversion

Quaternizations of benzyl bromide units in brominated poly(isobutylene-co-p-methylstyrene), or BIMS, elastomers with tertiary amines can be readily accomplished either by solution techniques or by melt reactive mixing. At temperatures of 130 °C and above, the nucleophilic substitution of benzyl bromide with ammonium bromide occurs instantaneously in an internal mixer. The conversion is around 95% for both dimethyl alkyl and dialkyl methyl amines. Suppressions in loss tangent measured in dimethyl alkyl amine melt quaternized BIMS indicate that molecular weight amplifications as a result of ionic association in these ionomers are in line with that obtained from solution quaternized BIMS. These melt quaternized BIMS ionomers become gels when their molecular weight amplification factors are greater than 1.5. Viscosity of BIMS can be raised significantly through quaternization to facilitate its mixing with thermoplastics. BIMS ionomers can also be added into bromobutyl innerliner compounds to enhance their green strengths. The efficiency in promoting ionic associations during melt mixing of BIMS with only 0.1 mol equiv. of dimethyl alkyl amines allows residual benzyl bromide units for subsequent curing.