Design guide of amphiphilic crystalline random copolymers for sub-10 nm microphase separation

Sub-10 nm microphase separation of polymers is an important technology to create well-defined nanostructures in polymer materials and thin films for various applications. In this paper, we examined crystallization and microphase separation of amphiphilic random copolymers bearing hydrophilic poly(ethylene glycol) (PEG) or poly(propylene glycol) and hydrophobic octadecyl groups in the solid state. For this, we synthesized various amphiphilic crystalline random copolymers with different hydrophilic pendants, main chains, composition, monomer sequence, and molecular weight distribution via living or free radical copolymerization. Solid samples of the copolymers were analyzed by differential scanning calorimetry, X-ray diffractometry, and small angle X-ray scattering. From the systematic investigations, we found that, in spite of broad molecular weight distribution, a random copolyacrylate bearing hydroxyl terminal PEG chains and octadecyl groups induced crystallization of the octadecyl groups to form well-ordered lamellar structures with about 5 nm domain spacing. It should be noted that quite small lamellar structures are constructed by common random copolymers with broad molecular weight distribution that are easily obtained from free radical copolymerization. This sub-10 nm microphase separation system developed herein would bring innovation in creating functional polymer materials with precision nanostructures.