CO2-Triggered and temperature-switchable crystallization-driven self-assembly of a semicrystalline block copolymer in aqueous medium

Abstract

The synthesis of a semicrystalline block copolymer comprising a hydrophilic poly(acrylic acid) (PAA) pure block and an amphiphilic poly(acrylic acid)-r-poly(octadecyl acrylate) (PAA-r-PODA) random block by nitroxide-mediated polymerization (NMP) is reported. The aggregation behavior of the copolymer in aqueous medium was studied by using a MicroCal VP differential scanning calorimeter (VP-DSC) and dynamic light scattering (DLS) and transmission electron microscopy (TEM). The copolymer directly self-assembled into large compound micelles (LCMs) which are composed of small micelles. Upon CO₂ stimulus, the LCMs transformed into bigger crystalline LCMs, which was confirmed by wide angle X-ray diffraction (WAXD) and small angle X-ray scattering (SAXS). Reversible morphological transformation was realized by raising the temperature to 50 °C above the melting point. Our research provides a new way to manipulate the assembly of the semicrystalline block copolymer with a reversible micellization–crystallization method using CO₂ and temperature.