A branched isobutylene-styrenic elastomer with a broad molecular weight distribution is disclosed comprising an interpolymer of an isoolefin monomer as isobutylene, a styrenic monomer such as p-methylstyrene, and a multiolefin such as divinylbenzene. The elastomer has improved green strength, relaxation characteristics, and processability in melt processing, while retaining excellent aging characteristics and barrier properties, and can be used in a blend with a linear isobutylene-p-alkylstyrene elastomer to improve processability of the linear elastomer. Also disclosed are a method for processing the linear elastomer with an effective amount of the branched elastomer to improve processability, and nanocomposites, curable compositions, cured compositions and useful articles formed from the branched elastomer and the linear-branched elastomer blends.