Polymers exhibit stimuli responsive solubility that depends on the polymer microstructure, the solvent, and a chemical or physical stimulus. For example, poly(N-isopropylacrylamide) (PNIPAM) is a common thermoresponsive polymers whose lower critical solution temperature derives from a favorable DH due to hydrogen bonding with water and an unfavorable DS due to the organization of solvents on the polymer. This work describes how H-bond solubilization can be used to generate chemically-reversible responsive solubility of a polar polymer like PNIPAM in nonpolar alkane solvents. The acid-assisted solubilization of PNIPAM was explored using carboxylic acids like acetic, valeric, octanoic and oleic acids. The results showed that the longer aliphatic acids are more effective on a mole:mole bases at effecting PNIPAM solubilization in hexane. Similar trend are seen for solubilization of PNIPAM in hydrocarbon oligomer solvents like poly(a-olefin)s (PAOs). In both cases, the PNIPAM that dissolves in the alkane solvents can be recovered by addition of base. Using dansyl-labelled PNIPAM with octanoic acid as a solubilization agent with NEt3 as the chemical agent for PNIPAM precipitation, we have shown that the process of solubilization/precipitation can be repeated through at least three cycles (Figure 1a). Ongoing studies are exploring this molecular recognition based solubilization with other solubilizing agents, other precipitation agents and exploring the use of this chemically responsive solubility both as a tool to prepare new solvent systems and new sorts of recyclable catalysts.

Stimuli-responsive solubility of poly(N-isopropylacrylamide) in nonpolar solvents

256th National Meeting (2018)

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