Comb like Thermoresponsive Polymers with Sharp Transitions: Synthesis, Characterization, and Their Use as Sensitive Colorimetric Sensors

The synthesis and thermoresponsive behavior of two structural novel comblike polymers are presented, which are constituted by polymethacrylates main chain with dendritic oligoethylene glycol (OEG) side groups spaced with a linear hydrophobic alkyl [PG1(A)] or ION hydrophilic OEG unit [PG1(G)]. The design of this comblike architecture is to retain the unique thermoresponsive behavior of OEG-based dendritic polymers and, on the other side, to eliminate the tremendous synthesis effort for the dendronized polymer analogues. Their thermoresponsive behavior was investigated with UV/vis and temperature-varied (1)H NMR spectroscopy to determine their apparent LCSTs and follow chain dehydration process, respectively. These polymers show sharp and fast transitions with small hystereses. The phase transition temperatures are located in between 27 and 34 degrees C, which is in the vicinity of physiological temperature, and these transition temperatures are independent of polymer concentration. The thermoresponsiveness of these polymers is also compared with the corresponding macromonomers as well as the densely packed dendronized polymer analogues reported previously, focusing on chemical structure and architecture effects. It was found that the more hydrophobic polymer PG1(A) could form denser aggregates than that of the more hydrophilic polymer PG1(G). On the basis of the exceptional thermoresponsive behavior of these comblike polymers, this architecture is utilized for fabricating polymer sensors. Random copolymerization of the macromonomers with the monomer bearing solvatochromic dye moiety (Disperse Red 1) affords the thermoresponsive copolymers which act as sensitive dual-sensors for both temperature and pH value.