Abstract
A series of well-defined (polyisoprene)2(polystyrene), I2S, single graft copolymers with similar total molecular weights but different compositions, fPS, were blended with a low molecular weight polyisoprene homopolymer matrix at a constant concentration 2 wt%, and the micellar characteristics were studied by small-angle x-ray scattering. To investigate the effect of macromolecular architecture on the formation and characteristics of micelles, the results on the single graft copolymers were compared with those of the corresponding linear polystyrene-b-polyisoprene diblock copolymers, SI. The comparison reveals that the polystyrene core chains are more stretched in the case of graft copolymer micelles. Stretching turned out to be purely a result of the architecture due to the second polyisoprene block in the corona. The micellization of a (polystyrene)2(polyisoprene), S2I, graft copolymer was also studied, and the comparison with the results of the corresponding I2S and SI copolymers emphasizes the need for a critical core volume rather than a critical length of the core-forming block, in order to have stable micelles. Finally, the absence of micellization in the case of the I2S copolymer with the highest polystyrene volume fraction is discussed. For this sample, macrophase separation occurs, with polyisoprene cylinders formed in the copolymer-rich domains of the phase-separated blends.
Highlights
The profile corresponding to the graft copolymer I2 S−7 (Figure 1a) with the lower polystyrene volume fraction is featureless, signifying that there are no micelles formed in that mixture
The slightly increasing intensity at low wavevectors can be attributed to electron density fluctuations due to polystyrene blocks that are dispersed within the polyisoprene matrix
At lower fPS, the copolymer is miscible with the polyisoprene homopolymer matrix, whereas macrophase separation takes place for fPS = 0.90
Summary
To investigate the effect of macromolecular architecture on the formation and characteristics of micelles, the results on the single graft copolymers were compared with those of the corresponding linear polystyrene-b-polyisoprene diblock copolymers, SI. The micellization of a (polystyrene) (polyisoprene), S2 I, graft copolymer was studied, and the comparison with the results of the corresponding. The absence of micellization in the case of the I2 S copolymer with the highest polystyrene volume fraction is discussed. For this sample, macrophase separation occurs, with polyisoprene cylinders formed in the copolymer-rich domains of the phase-separated blends. The efficiency of the interfacial partitioning of diblock copolymers to the polymer/polymer interface can be severely affected by the formation of micelles within published maps and institutional affiliations
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