Preparation and characterization of temperature/pH/CO2-triple-responsive homopolymers and their substituent determined response

Abstract

Three novel temperature/pH/CO₂-triple-responsive homopolymers namely P(Et-N-EO₂MA), P(THP-N-EO₂MA) and P(Ph-N-EO₂MA) were prepared by reversible addition–fragmentation chain transfer (RAFT) polymerization. They have the same backbone structure but different types of end substituents i.e., ethyl, tetrahydropyran, and the benzene ring, respectively. Subsequently, their responsive properties were studied. P(Et-N-EO₂MA) has a lower critical solution temperature (LCST)-type cloud point (CP) in aqueous solution and is affected by many factors such as the molecular structure and weight, concentration, additives, pH and CO₂. P(THP-N-EO₂MA) is soluble in water, but in different buffer solutions, it shows a soluble–LCST–insoluble transition, and its LCST-type CP can also be adjusted by molecular weight and concentration. P(Ph-N-EO₂MA) is insoluble in water, but reversible phase transformation can be achieved by adjusting the pH of the solution or injecting CO₂, and it also shows different properties in buffer solutions and an upper critical solution temperature (UCST)-type CP in n-butanol. In addition, since P(Ph-N-EO₂MA) is amphiphilic, it can be self-assembled in solution, and the release of Nile Red (NR) can be achieved under the stimulation of acid. The different properties of these homopolymers show the effect of substituents on the responsiveness of multistimuli-responsive polymers, which provides ideas for the design of stimuli-responsive polymers, and have good application prospects in the fields of self-assembly and controlled release.