Influence of the molar masses on compatibilization mechanism induced by two block copolymers in PMMA/PS blends

Abstract

The compatibilization mechanism of poly(methylmethacrylate) (PMMA)/polystyrene (PS) blends induced by PMMA-b-PS block copolymers of different molar masses (30 and 104 kg/mol) was studied. The blend morphologies with and without copolymers were observed by scanning electron microscopy. The rheological behavior was studied performing small amplitude oscillatory shear experiments. The experimental results were compared to Palierne's model predictions. Shear induced coalescence tests were also conducted. Contrary to what was expected, adding block copolymers did not result in a refinement of the droplet size. However, it induced Marangoni stresses, a decrease in interfacial tension and an inhibition of coalescence of the dispersed phase. During coalescence tests, a decrease in the relaxation time due to Marangoni stresses with time was revealed. This interesting behavior contradicts previous works on the subject, and is believed to be due to a migration of block copolymers to the interface during the tests rather than droplets' coalescence. As such, the morphology was explained by the fact that block copolymers are not entirely at the interface initially. Also, the block copolymer with a higher molecular mass was shown more efficient at inhibiting coalescence, indicating that the compatibilization mechanism is a combination of Marangoni stresses and steric hindrance.