Spherical Photonic Nanostructures from High Molecular Weight Liquid Crystalline Brushlike Block Copolymers

We demonstrate sequential ring-opening metathesis polymerization (ROMP) of norbornene bearing n-alkyloxycyanobiphenyl (NBCB12) and norbornene bearing poly(DL-lactide) (NBPLA) to synthesize low polydispersity ((D = 1.1-1.3), moderately high molecular weight (>265 kg/mol), liquid crystalline brushlike block copolymers (LCBBCs). The impact of (1) block composition, (2) PLA chain length, and (3) total molecular weight of the LCBBC on the thermal, morphology, and optical properties of the copolymers is explored. This LCBBC platform combines the rapid assembling kinetics of PLA brushes, good filmforming capabilities of liquid crystalline polymers, and abilities of high molecular weight brush copolymers to form large domain photonic nanostructures. The asymmetry in these copolymers impacts the interface between the LC and the brush block, resulting in large spherical domains even at 50 wt % of LC block composition as evidenced by scanning electron microscope of drop-tasted films. In these films, singular, additive-free, spherical 1D photonic polydisperse nanostructures in the 125-820 nm size range are formed but lack long-range order. Because of the polydispersity in the size of spherical nanostructures, this polymer platform (i) shows red, green, and blue reflections from the same sample due to which the films appear iridescent white with flecks of color that can be harnessed for white light-based LC displays and (ii) covers the spectral range from visible to near-IR wavelengths that can be exploited for optical devices and NIR reflector applications.