A process for producing a high impact polystyrene having a high swell index may include feeding at least one vinyl aromatic monomer and at least one elastomer to at least one polymerization reactor to form a reaction mixture. The process may include polymerizing the reaction mixture, combining a chain transfer agent to the reaction mixture leaving the at least one polymerization reactor to form a combined mixture, and sending the combined mixture to a devolatilization zone. The process may include obtaining a HIPS product having a high swell index.