Microphase separation of hybrid dendron-linear diblock copolymers into ordered structures

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Hybrid copolymers with dendritic-linear blocks are shown to exhibit many of the classic microphase-separated structures of linear-linear block copolymers. Transmission electron microscopy (TEM), small-angle X-ray scattering (SAXS), and small-angle neutron scattering (SANS) were used to evaluate the morphology of a sixth generation (G6) poly(benzyl ether) dendron covalently bonded to linear polystyrene (PS) at the dendron focal point. Increasing the fraction of the linear block, øPS, through an increase in the molecular weight of the PS block revealed morphologies evolving from disordered to ordered lamellar to hexagonally close-packed dendron cylinders. Significantly, the observed morphologies are distinct from those expected for analogous linear-linear blocks at equivalent volume fraction, although the direction of progression follows expectation. Quantitative analysis suggests substantial molecular deformation or shape change in the dendritic phase. The possible role of conformational entropy in determining the overall free energy is suggested to be important for this class of block copolymer.