A general strategy for the preparation of well-defined diblock copolymers combining a random cascade-branched dendritic (i.e., hyperbranched) and a linear block has been developed. The strategy is based on a linear poly(styrene-b-butadiene) (PS-b-PB) diblock copolymer with high molecular weight PS block and short, functional 1,2-PB block, prepared by conventional anionic polymerization. The functional PB block is used for the grafting of branched AB2-type carbosilane monomers, resulting in the attachment of a hyperbranched structure to the backbone. Slow addition of the methyldi(undecenyl)silane monomers using Karstedt's catalyst permits control of the molecular weight of the hyperbranched block, resulting in high molecular weight linear-hyperbranched diblock copolymers. Molecular weights of the block copolymers ranged between 72 800 and 106 400 g/mol for M n, and polydispersity M̄ w/M̄ n was low (typically below 1.1), as predicted by theory for slow monomer addition. Morphological studies by TEM, AFM, and SAXS on these systems demonstrate that various microdomain structures typical for microphase-separated block copolymers can be obtained upon increasing the size of the hyperbranched block with respect to the linear one, despite the strong architectural asymmetry of the linear-hyperbranched macromolecules. However, due to the hyperbranched structure and the crowding of the interface, an asymmetry of the phase diagram is observed. The linear-hyperbranched PS520-b-[PB47-hb-PCSi142] sample with 49 wt % of the hyperbranched component displayed the most unusual morphological behavior

We have investigated the roles of liquid crystallinity (LC) and substrate interactions on the ordering of isotropic cylindrical microdomains in thin films of two hybrid isotropic/LC triblock copolymers. Each copolymer consists of polystyrene (PS) end blocks and a side-chain LC midblock that exhibits either a nematic or smectic mesophase up to temperatures beyond the glass transition temperature (T g) of PS. In thin films measuring on the same order as the lattice period, the orientation of the cylinders relative to the substrate is sensitive to the interactions of the mesogens at internal microdomain boundaries and external interfaces. Upon annealing such copolymer films at temperatures below the LC → isotropic transition but above the PS T g on a neutral NaCl substrate, the PS cylinders within the nematic matrix adopt a long-range parallel orientation, whereas those within the smectic matrix lie perpendicular to the substrate and exhibit liquidlike order. After long annealing times, the cylinders residing near the film surface within the smectic matrix reorganize from perpendicular to parallel orientation due to surface tension at the film/air interface. On a polished Si substrate that promotes homeotropic mesogen anchoring, the perpendicular cylindrical orientation within the smectic mesophase remains stable.

We have synthesized a series of liquid crystalline/isotropic block copolymers with narrow molecular weight distribution and with well-defined chemical structure. Block volume fractions were varied systematically. The domain structure of these compounds was determined by means of small-angle X-ray scattering. Spherical, cylindrical, and lamellar morphologies were observed with the liquid crystalline (LC) block in the matrix or in the domain, respectively. The polymers are strongly segregated, and no order-to-disorder transition is found up to 170 °C. DSC and polarized microscopy data reveal that the mesomorphic behavior of LC blocks is only slightly influenced by copolymer composition and is basically characterized by the sequence g/∼35 °C/n/∼120 °C/i. The rotational dynamics over a broad temperature and frequency range was studied using dielectric spectroscopy. The LC block reveals two cooperative modes assigned to the segmental relaxation (α process) and to the side chain rotation as a whole (δ process). A confinement effect is visible in the shift of both relaxation times to lower values for domain sizes less than 20 nm. The effect is stronger for 2D than for 1D confinement geometry. It is small compared to similar effects found for free-standing thin polymer films. For copolymers with alternate lamellae or LC cylindrical microdomains, a Maxwell−Wagner polarization was observed in addition to the α and δ processes.

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