Photo-cross-linkable mixed micelles with dual response to pH and temperature

Abstract

Two photo-cross-linkable star amphiphilic triblock copolymers with thermo- and pH-responsive properties, respectively, star poly(ε-caprolactone)-b- poly(2-cinnamoyloxyethyl methacrylate)-b-poly(N-isopropylacrylamide-co-N,N-dimethylacrylamide) [SPCL-b-PCEMA-b-P(NIPAAm-co-DMAAm)] and star poly(ε-caprolactone)-b-poly(2-cinnamoyloxyethyl methacrylate)-b-poly(2-(diethyl-amino)ethyl methacrylate) (SPCL-b-PCEMA-b-PDMAEMA), were synthesized by stepwise reversible addition-fragment chain transfer (RAFT) polymerization of 2-hydroxyethyl methacrylate and 2-dimethylaminoethyl methacrylate or N-isopropylacrylamide monomers using star PCL macro-RAFT agent (SPCL-DDAT), followed by carbodiimide-mediated coupling of photo-cross-linkable cinnamate groups. The obtained two cinnamate-functionalized star copolymers with different weight ratios were used to construct mixed micelles with dual thermores and pH-responsive properties. Photo-cross-linking was performed by UV irradiation, resulting in the stabilization of the cross-linked mixed micelles. Dual stimuli–responsive behavior was investigated by combination of dynamic light scattering and optical transmittance. The results showed that the stimuli responses were tunable by varying the content of two star copolymers and cross-linking density. The structure stability and dual thermo- and pH-responsive properties endowed the mixed micelle with potential applications in biomedical fields, such as controlled drug release.