Morphologies and photonic properties of an asymmetric brush block copolymer with polystyrene and polydimethylsiloxane side chains

Abstract

Asymmetric brush block copolymers (BBCPs) with polystyrene (PS) and polydimethylsiloxane (PDMS) side chains, gPS-b-gPDMS, were synthesized by ring-opening metathesis polymerization of corresponding norbornene macromonomers. The morphologies of the BBCP were systematically investigated with small-angle X-ray scattering and scanning electron microscopy. As the volume fraction of PS increases, the polymer self-assembles into spherical, cylindrical, and lamellar structures. Due to the shape asymmetry of the BBCP macromolecule, nanostructures with curved interfaces are easily formed. With a large d-spacing, most samples self-assemble into photonic crystals that selectively reflect ultraviolet light. Simulations have been conducted to calculate the photonic band structures of the two-dimensional photonic crystals. It is found that this system shows a wider partial band gap than other polymer systems with smaller refractive index contrast.