Regioselective Synthesis of Cellulosic Janus Bottlebrushes with Polystyrene and Poly (Ε-Caprolactone) Side Chains and Their Solid-State Microphase Separation

In this article, we describe the synthesis and self-assembly of novel Janus bottlebrushes with cellulose as a polymeric backbone. The cellulosic Janus bottlebrushes, bearing poly(ε-caprolactone) (PCL) and polystyrene (PS) branches at the C-2,3 and C-6 positions of anhydroglucose units, respectively, were successfully prepared using a bulky p-methoxytrityl protecting group and by combining the “grafting-from” ring-opening polymerization of ε-caprolactone with the “grafting-to” click chemistry of PS. The degree of substitution of PCL at the C-2,3 positions was estimated to be 1.5, whereas values of 0.64–0.84 were estimated for the C-6 position of PSs with different molecular weights (number-average molecular weight = 4.0, 9.2, or 16 kg mol−1), depending on the length of the PS graft. The Janus bottlebrushes (PS/PCL = 50:50 v/v) self-assembled to form a lamellar microdomain structure comprising three layers (amorphous PCL, crystalline PCL, and amorphous PS layers), as characterized by small-angle X-ray scattering and transmission electron microscopy. The interlamellar distance was approximately 30 nm, depending on the length of the PS graft. The results illustrate that cellulosic polymeric backbones for Janus bottlebrushes can exhibit microscale morphologies, potentially leading to the development of polymers with new morphologies and functionalities.