Poly(N-isopropylacrylamide) Soluble Polymer Supports in Catalysis and Synthesis

Abstract

Co- and terpolymers of N-isopropylacrylamide exhibit inverse temperature solubility in water with the polymer's lower critical solution temperature (LCST) being dependent on the polymer's microstructure and the concentration of salt in the water solvent. This solubility behavior has been used to prepare “smart” recoverable homogeneous catalysts and substrates. These catalysts' activity reversibly turns first off and then on as the temperature is first raised and then lowered due to changes in the polymer support's solubility. Such catalysts can be recovered by heating the aqueous solution or by adding brine. Catalysts prepared include both phosphine-ligated transition metal catalysts and acid catalysts. The transition metal catalysts are active in alkene hydrogenation, C−C coupling, and allylic substitution reactions. The acid catalysts are active in acetal hydrolysis. Substrates can be attached to these polymers and their activity likewise can be turned off and on by heating or cooling. Substrate activity on such supports can equal that of a low molecular weight analogue. NMR spectroscopic studies show that a vinyl group bound to PNIPAM has peaks whose line widths in 1H NMR spectroscopy are like those of a low molecular weight compound when a nine-carbon tether chain is used to attach the vinyl group to PNIPAM.

A Novel Route to the Preparation of Poly(N‐isopropylacrylamide) Microgels by Using Inorganic Clay as a Cross‐Linker

“…The temperature sensitivity of the microgels was examined by means of dynamic light scattering (DLS) and UV-vis spectrophotometers, and the chemical structure and morphology were determined by Fourier-transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), and scanning electron microscopy (SEM) as well. 4 Na 0.66 : layer size ¼ about 30 nm in diameter and 1 nm in thickness; cation exchange capacity ¼ 104 mequiv. per 100 g) was used after washing with ethanol/water (90:10 w/w) and freeze-drying.…”

“…Since the first preparation of monodispersed colloidal microgels based on N-isopropylacrylamide (NIPAM) and N,N 0 -methylenebis(acrylamide) (MBA) by Pelton and Chibante in 1978, [1] the responsive microgel particles ranging in diameter from 10 to 1 000 nm have attracted considerable attention due to their potential applications in numerous fields, including drug delivery, [2,3] catalysis, [4] chemical separation, [5,6] and optical devices. [7,8] Over the past two decades, the poly(N-isopropylacrylamide) (PNIPAM) microgels have been extensively studied.…”

Synthesis of Poly(<em>N</em>-isopropylacrylamide) Janus Microhydrogels for Anisotropic Thermo-responsiveness and Organophilic/Hydrophilic Loading Capability

“…Microparticles made of environmentally responsive hydrogels are fascinating candidates for application in drug delivery, 16,17 catalysis, 18 sensing, 19,20 and photonics. 21 Traditional synthetic methods including emulsion polymerization, are used to produce hydrogel microparticles with polydispersity.…”

Surface design with self-heating smart polymers for on–off switchable traps

“…Their properties can be changed by external stimuli such as temperature [1,2], light [3,4], electric and magnetic fields [5][6][7], ionic strength [8], pH [9] and chemicals [10,11]. Therefore, smart polymers are used in biotechnology, medicine and engineering, in such applications as drug delivery systems [12][13][14], chemical separation [15,16], sensors [17] and actuators [18,19].…”