Influence of LC content on the phase structures of side-chain liquid crystalline block copolymers with bent-core mesogens

We report the phase structures of a series of poly(styrene-block-{3′- [4-(4-n-dodecyloxybenzoy- loxy)benzoyloxy]-4-(12-methacryloyloxydodecyloxy) benzoyloxybiphenyl}) (PS-b-PMAC) side-chain liquid crystalline block copolymers (SC LCBCP). The SC liquid crystalline polymer was formed by side attaching a bent- core mesogen to the polymer backbone using a 12-carbon spacer. The phase structure of the high and low f ^PMAC samples were investigated using differential scanning calorimetry, small-angle and wide-angle X-ray scattering, and transmission electron microscopy techniques. The PS coil block and PMAC LC block phase separate into a lamellar morphology in all of the samples investigated (volume fraction of PMAC f ^PMAC ∼ 0.31-0.65). However, both the LC phase and the orientation of the hierarchical structure under mechanical shear showed strong dependence on the LC content. Samples having a high f ^PMAC (0.5-0.65) showed a SmC ₂ LC phase (Smectic C denotes the LC molecules are tilted with respect to the layer normal, and 2 represents a bilayered structure), similar to that observed in PMAC homopolymers. Upon mechanical shear, these smectic layers oriented parallel to the shear plane and the BCP lamellae oriented perpendicular to the shear plane with the layer normal parallel to the vorticity direction. In samples having a lower f ^PMAC, the BCP lamellae laid parallel to the shear plane and the LC phase structure in these samples was columnar rectangular. A detailed structural and morphological study will be reported.