Details

Autor(en) / Beteiligte

• Jeon, K J

Titel

Solubility of homopolymer in block copolymer

Erscheinungsjahr

1994

Quelle

Alma/SFX Local Collection

Beschreibungen/Notizen

• The solubility limit of polystyrene homopolymer in the styrene blocks of styrene-butadiene diblock copolymer was determined from light scattering measurements. Two symmetric diblock copolymers (M sub n =25 000 and M sub n =47 900, respectively) and polystyrene homopolymers ranging in molecular weight (M sub n ) from 14 600-45 500 were used in the measurements. The solubility limits obtained in lamellar microdomains here were compared with the results calculated from Meier's model, and from Tucker and Paul's model. The solubility limit depended on the molecular weight ratio of the homopolymer to the corresponding block of the copolymer. The observed solubility limit showed a large difference from predictions by both models. The solubility limit of homopolymer in lamellar microdomains was found to be larger than that in spherical or cylindrical microdomains by others. The change in the morphological size of lamellar microdomains in mixtures of block copolymer and homopolymer with increasing homopolymer concentration was investigated from small angle x-ray scattering measurements. The lamellar microdomain thicknesses for all mixtures were found to be larger than that for the pure diblock copolymer. The lamellar thickness increased linearly with polystyrene homopolymer concentration. The expansion of the lamellar microdomain thickness was affected by the amount of homopolymer but independent of the molecular weight of homopolymer. From the results of the axial change and the lateral change in lamellar microdomains of mixtures, it was predicted that the polystyrene homopolymer was completely segregated into the middle region of the microdomains. The thickness of boundary layer between microdomains was evaluated from comparison of the experimental small angle x-ray scattering profiles and the calculated profiles. The estimated interfacial thickness for pure block copolymer or mixture of block copolymer and homopolymer was found to be 3.0 plus/minus0.5 nm. Transmission electron microscopy was employed to observe the macrophase beyond the solubility limit, and to identify the morphologies which developed in a series of mixtures of block copolymer and homopolymer. The microdomain morphology for the mixture of block copolymer (M sub n =47 900) and polystyrene (M sub n =24 500) changed from lamellar to catenoid-lamellar, to strut, to disordered cylindrical, and then to cylindrical micelles with increasing amount of polystyrene.