CO2-driven vesicle to micelle regulation of amphiphilic copolymer: random versus block strategy

Abstract

Precise morphological control over self-assemblies is attractive due to their promising applications, especially in biotherapy. Block copolymer is a common choice for morphological control, since the geometry of self-assemblies can be easily predicted by the hydrophilic volume fraction. However, random copolymers are rarely taken into consideration. Here, starting from the same hydrophilic segment poly(ethylene oxide) (PEO), and using CO₂-responsive 2-(diethylamino)ethyl methacrylate (DEAEMA) and hydrophobic styrene (St), we designed and synthesized a random and an entire block copolymer with similar polymerization degrees but different monomer sequences: PEO₄₅-b-(DEAEMA₉₀-r-St₆₆) (P_r) and PEO₄₅-b-DEAEMA₉₃-b-St₆₆ (P_b). In aqueous solution, the two polymers both aggregate into vesicles. Upon CO₂-stimulus, however, the vesicle of the random copolymer P_r transforms into a spherical micelle, whereas that of the triblock copolymer P_b shows an expansion instead of a morphological transition. The restricted hydration in the random structure of P_r accounts for such a morphological transition, and the random strategy in polymer design might be useful in self-assembly regulation.