Aggregation phenomena of linear and miktoarm star copolymers of styrene and dimethylsiloxane: Influence of the architecture

The micellar behavior of PS-b-PDMS, PS-b-PDMS-b-PS linear block and (PS)2(PDMS) miktoarm star copolymers of polystyrene (PS) and polydimethylsiloxane (PDMS) is investigated in DMF, a selective solvent for PS. The linear PS-b-PDMS and star (PS)2(PDMS) copolymers exhibit different macromolecular architectures but similar compositions and total molecular weight, while the linear PS-b-PDMS-b-PS copolymer has the same composition as the diblock and miktoarm star but double their molecular weight. Static, dynamic light scattering and viscometry were used for the structural characterization of the micelles. Aggregation numbers were found to increase in the order PS-b-PDMS-b-PS < (PS)2(PDMS) < PS-b-PDMS. The corona thickness was dependent on the molecular weight of the soluble PS chains. In the case of (PS)2(PDMS), although the core area per PS chain, AC, was significantly lower than that of the linear copolymers, the coronal chains were not significantly stretched. This can be attributed to the stiff nature of the PS chains, which maintains the elongated form of the chains.