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.

We report the derivatization of hyperbranched poly(acrylic acid) (PAA) films with a wide range of amino- or alcohol-terminated molecules. These molecules can include moieties such as pyrene, ferrocene, poly(ethylene glycol), 15-crown-5, and a dye. To derivatize PAA films, we activate their carboxylic acid groups with isobutyl chloroformate and allow them to react with amine- or alcohol-containing molecules. Infrared spectroscopy demonstrates the formation of amide and ester bonds upon coupling as well as the presence of the derivative functional groups. Excimer fluorescence from pyrene-containing films implies a high density of pyrene groups. However, we can control the amount of pyrene in the film (and obtain monomer fluorescence) by varying the concentration of Py(CH2)3CONH(CH2)2NH2 in the derivatization solution. Cyclic voltammetry of ferrocene-containing films shows an electrochemically addressable ferrocenyl surface coverage of (6 ± 3) × 10-9 mol/cm2 in three-layer PAA films. PAA films and their derivatives are stable under sonication, Soxhlet extraction, and acidic and basic conditions. PAA films also respond to external stimuli. The ellipsometric thickness of PAA films increases by ≈45% upon deprotonation of the film's carboxylic acid groups and returns to its original thickness after acidification. Using surface acoustic wave mass sensors, we observed that pure PAA films adsorb or absorb volatile organic compounds (VOCs), although the amount is in the monolayer range. Fluorination of PAA films increases the amount of polar VOCs absorbed by an order of magnitude.

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This paper describes a high-throughput method for characterization of the temperature-dependent folding of poly(N-isopropylacrylamide), PNIPAM, using dark field microscopy to measure this thermoresponsive polymer's lower critical solution temperature (LCST). The effect of ionic solution components (halide and alkali metal ions) on the polymer precipitation temperature follows the Hofmeister series whereas solution isotopic effects using D2O give rise to a roughly linear increase in the LCST with the mole fraction of D2O added. The polymer structure itself was also varied through the synthesis of N-alkylacrylamide copolymers. It was found that replacement of the isopropyl N-alkyl pendant groups of PNIPAM with varying amounts of N-n-propyl groups results in a monotonic decrease in the LCST. Repeated analyses of the same sample and of separately prepared samples show that this type of analysis is quite precise and that investigations of subtle effects of polymer microstructure and solvation are feasible even when the difference in LCST temperatures is <1 °C. Such effects may be difficult to study by other methods.