Configurational Mesophases in Amorphous–Azobenzene-Containing LC Block Copolymers: A15, Columnar Rectangular, and Highly Asymmetric Lamellar Phases

In strongly segregated block copolymers (BCPs), amorphous–liquid crystalline (LC) BCPs provide access to unconventional mesophases owing to the configurational anisotropy and conformational asymmetry (ε) between the two blocks. The BCPs of polydimethylsiloxane-b-poly((4(phenyldiazenyl)phenoxy)hexyl acrylate) (PDMS-b-PPHAs) are composed of amorphous and LC blocks containing side-chain azobenzene units. Various self-assembled morphologies were obtained by adjusting the volume fraction of the PPHA block and its photoisomerization. The trans-isomeric PDMS-b-PPHAs enable the π–π stacking of the azobenzene units in the PPHA block, that generates a variety of mesophases, including A15, columnar rectangular (Colr), columnar hexagonal (Colh), and lamellar (LAM) phases. The A15 and Colr phases are stabilized by the planar mesogenic packing of azobenzene units at low temperatures, and a Colr–Colh transition occurs upon heating. Particularly, the high ε between the two blocks leads to highly asymmetric LAM phase. However, the cis-isomeric PDMS-b-PPHAs show mostly the non-LC driven Colh phases with limited access to the highly asymmetric LAM phases. These findings highlight a versatile design platform for configurational mesophases using amorphous–LC BCPs, which, together with the discovery of a Colr phase with large microdomains, produces a new paradigm for self-assembled mesophases of side-chain LC BCPs.