A branching point thermo and pH dual-responsive hyperbranched polymer based on poly(N-vinylcaprolactam) and poly(N,N-diethyl aminoethyl methacrylate)

Abstract

We report the design and synthesis of a branching point stimuli-responsive hyperbranched polymer based on poly(N-vinylcaprolactam) and poly(N,N-diethylaminoethyl methacrylate) through combined “A₂ + B_xC” (x > 2) double monomer polymerization and parallel click reaction. The results of ultraviolet-visible spectrophotometry and dynamic light scattering (DLS) indicated that the resultant hyperbranched polymer possesses thermo and pH dual-responsive properties and presents gradient phase transition behaviors under appropriate solution pH and temperature conditions. The dual-responsive properties are independent of the two grafted linear polymer components and hyperbranched structure. Interestingly, fluorescence spectrophotometry studies have revealed that hyperbranched polymer aqueous solutions show different encapsulation behaviors toward water-soluble methyl orange or oil-soluble lonidamine molecules below and above the critical micelle concentration (CMC). The different aggregation states of hyperbranched polymers with different encapsulation microenvironments, such as dot-like unimolecular micelles below CMC and spherical multimolecular micelles above CMC, were confirmed via DLS and transmission electron microscopy. The aggregation states directly indicated the level of encapsulation ability.