Preparation and Characterization of Thermo-Responsive Rod-Coil Diblock Copolymers

In this study, we synthesized amphiphilic poly(2,7⁻(9,9⁻dioctylfluorene))⁻block⁻N,N⁻(diisopropylamino)ethyl methacrylate (POF⁻b⁻PDPMAEMA) rod-coil diblock copolymers by atom transfer radical polymerization (ATRP). The structure and multifunctional sensing properties of these copolymers were also investigated. The POF rod segment length of 10 was fixed and the PDPAEMA coil segment lengths of 90 and 197 were changed, respectively. The micellar aggregates of POF₁₀⁻b⁻PDPAEMA₉₀ rod-coil diblock copolymer in water showed a reversible shape transition from cylinder bundles to spheres when the temperature was changed from 20 to 80 °C or the pH was changed from 11 to 2. The atomic force microscopy (AFM) and transmission electron microscopy (TEM) measurements indicated that the temperature had also an obvious influence on the micelle size. In addition, since POF₁₀⁻b⁻PDPAEMA₉₀ had a lower critical solution temperature, its photoluminescence (PL) intensity in water is thermoreversible. The PL spectra showed that the POF⁻b⁻PDPAEMA copolymer had a reversible on/off profile at elevated temperatures, and thus could be used as an on/off fluorescent indicator for temperature or pH. The fluorescence intensity distribution of pH switched from "off⁻on" to "on⁻off" as the temperature increased. These results showed that the POF⁻b⁻PDPAEMA copolymer has a potential application for temperature and pH sensing materials.