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

Abstract

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 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 1H 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 °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.

Thermoresponsive dendronized polymeric sensors

“…Around the T cp s of the copolymers, both the structures of the aggregated copolymers and the solution pH conditions contribute significantly on the state transition of the dye moieties. Shift of λ max with temperature for PG1 is similar to the case for comb‐like OEG‐based polymers, and thus, there is no abnormal state transition of the dye around its T cp . While for the G2 dendronized copolymers, the greatly enhanced blue‐shift of the λ max at the initial stage of the aggregation, irrespective of solution pH values, indicates that the dye is still wrapped in the hydrophobic media of dehydrated and collapsed OEG phase.…”

“…The tiny influence of solution pH conditions on T c p s of the copolymers suggests the DR1 moieties may not be protonated even at very acidic conditions within the media of OEG‐based dendronized polymers. This phenomenon resembles very much the case for DR1 decorated comb‐like OEG‐based copolymers . DLS measurements were performed to follow the thermally‐induced aggregation of these dendronized copolymers.…”

“…They are therefore supposed to be nice vehicles for the construction of temperature sensors, and may lead to different sensory behavior. Based on this anticipation, we recently developed OEG‐based comb‐like thermoresponsive polymeric sensors, which were proven to be efficient sensors . To make use of the characteristic bulky structures of dendronized polymers, we here report on the synthesis and characterization of first ( G1 ) and second generation ( G2 ) of dendronized polymethacrylates sensors bearing solvatochromic dye DR1 (Fig.…”

Dendronized Copolymers

“…The obtained results suggested that the dencopols acted as a molecular concentrator in which substrates were being driven into the interior. In addition, Zhang and coworkers efficiently synthesized two solvatochromic dye-modified dencopols via free radical polymerization of methacrylate monomers oligo (ethylene glycol) dendron and solvatochromic dye through macromonomer strategy [20]. The dencopol solutions exhibited big red l max shift upon minor increase of solution temperature at acidic conditions, which made them as highly sensitive sensors.…”

Ionic liquid-based fluorescein colorimetric pH nanosensors

“…In this regard, various metal nanoparticles based colorimetric pH sensors have been reported, including modification of gold or silver nanoparticles with DNA, 8 protein antigens, 9 and polymers. 10 Although several nanomaterials have been designed toward this end, most of these materials involve multistep and very sophisticated synthetic procedures. Thus, a facile, cost efficient design in this direction would be extremely advantageous.…”