Self-assembly of dual-responsive amphiphilic POEGMA-b-P4VP-b-POEGMA triblock copolymers: effect of temperature, pH, and complexation with Cu2+

Abstract

Amphiphilic and stimuli-responsive triblock copolymers are an important class of smart materials due to their low critical micellar concentration in solution and capacity of self-assembly into different structures depending on the environment. In this context, the synthesis of a thermo-responsive poly(oligo(ethylene glycol) methyl ether methacrylate) (POEGMA) macro-RAFT using S,S′-bis(α,α′-dimethylacetic acid) trithiocarbonate (CMP) as a RAFT agent, followed by copolymerization with a pH-responsive poly(4-vinyl pyridine) (P4VP) is reported. The thermo- and pH responsiveness and critical micellar concentration of the POEG_xMA_y-b-P4VP_z-b-POEG_xMA_y copolymers in aqueous solutions were investigated by dynamic light scattering. Cryo-TEM images showed that the POEG₅MA₂₄-b-P4VP₃₆-b-POEG₅MA₂₄ copolymers self-assemble as spherical and interconnected micelles depending on the composition and environmental conditions. Nanostructures with a hydrodynamic radius (R_H) between 15 and 300 nm are formed. These nanostructures can encapsulate hydrophobic molecules, such as Nile red at pH ≥ 7 and 25 °C. Finally, the P4VP blocks of the triblock copolymer coordinate with Cu²⁺, generating a thermo- and pH-responsive nanogel whose R_H reduces from 90 to 25 nm by a thermo- or pH-induced deswelling.