Temperature Sensitivity, The Ph Response Of Porous Hydrogel Synthesis And Catalytic Reaction Applications

The synthesis and application of hydrogel,especially for intelligent hydrogel is reviewed.Firstly,a porous hydrogel ofpoly(N-isopropylacrylamide)-co-poly[2-methacrylic acid 3-(bis-carboxymethylamino)-2-hydroxypropyl ester] (PNIPAM-co-PMACHE),which contains a thermoresponsive segment of PNIPAM and a zwitterionic,pH-responsive and chelating segment of PMACHE,is synthesized. The PNIPAM-co-PMACHE hydrogel is thermoresponsive with a volume-phase-transition temperature at 32℃.The PNIPAM-co-PMACHE hydrogel is also pH-responsive,which swells at a confined pH range and deswells out of this pH range due to the zwitterion-like segment of PMACHE.The deswelling kinetics of the PNIPAM-co-PMACHE hydrogel is studied and the results suggest that the hydrogel deswells faster at higher temperature,especially in acidic or basic aqueous solution.Furthermore,the PNIPAM-co-PMACHE hydrogel is demonstrated to be a suitable scaffold,within which metal cation or nanoparticle can be stabilized.Then,PNIPAM-co-PMACHE hydrogel is used as both a reaction medium and the Pd catalyst support for organic synthesis.Organic synthesis within the PNIPAM-co-PMACHE hydrogel is demonstrated to have three merits.Firstly, organic reactions such as Suzuki and Heck reactions within the hydrogel can be accelerated due to the enriched concentration of the Pd catalyst and reactants within the hydrogel by the reversible deswelling/swelling of the intelligent hydrogel. Secondly,organic synthesis within the PNIPAM-co-PMACHE hydrogel,which holds about～300 times of water and is similar to the environmentally benign reaction medium of water,can be performed efficiently without surfactant or cosolvent being added.Thirdly,both PNIPAM-co-PMACHE hydrogel itself and the therein-immobilized Pd catalyst can be easily recycled since the hydrogel/Pd composite can reversibly swell/deswell.Lastly,synthesis of size-controlled Au nanoparticles for aerobic alcohol oxidation within the porous,chelating and intelligent hydrogel of PNIPAM-co-PMACHE is studied.The PNIPAM-co-PMACHE hydrogel is demonstrated to be a suitable scaffold,within which Au nanoparticles with size ranging from 2.6 to 6.3 nm are synthesized by reducing the Au precursor with different reducing agents.The synthesized composite of the hydrogel and the encapsulated Au nanoparticles can reversibly deswell/swell at the volume-phase-transition temperature(VPTT) and the encapsulated Au nanoparticles keep stable during the reversible deswelling/swelling.The catalyst of the encapsulated Au nanoparticles for aerobic alcohol oxidation with molecular oxygen is tested.It is found that the activity of the Au nanocatalyst is strongly dependent on the size of the encapsulated Au nanoparticles,and the reversible deswelling/swelling of the hydrogel composite provides great convenience for the reuse of the Au nanocatalyst.Besides,it is found that the catalyst of 2.6-nm Au nanoparticles encapsulated within the PNIPAM-co-PMACHE hydrogel is highly efficient for aerobic alcohol oxidation partly due to the concentrated reagents within the deswelled hydrogel and partly due to the activated alcohol through the strong hydrogen bonding between the alcohol molecules and the PNIPAM segment.