Microphase Separation with Sub-3 nm Microdomains in Comb-Like Poly( n -alkyl acrylate) Homopolymers Facilitated by Charged Junction Groups between the Main Chains and Side Chains.

The phase structure with a small domain size in polymers is expected to provide a template for lithography to fabricate electronic devices, while the uniformity and thermal stability of the phase structure are vital in lithography. In this work, we report an accurately microphase-separated system of comb-like poly(ionic liquid) (PIL)-based homopolymers containing imidazolium cation junctions between the main chain parts and the long alkyl side chains, poly(1-((2-acryloyloxy)ethyl)-3-alkylimidazolium bromide) (P(AOEAI-Br)). The ordered hexagonally packed cylinder (HEX) and lamellar (LAM) structures with small domain sizes (sub-3 nm) were successfully achieved. Since the microphase separation was induced by the incompatibility between the main chain parts and the hydrophobic alkyl chains, the microdomain spacing of the ordered structure was independent of the molecular weight and molecular weight distribution of P(AOEAI-Br) homopolymers and could be precisely regulated by changing the length of the alkyl side chains. Importantly, the microphase separation was promoted by the charged junction groups; thus, the phase structure and domain size of P(AOEAI-Br) exhibited excellent thermal stability.