First Example of a Universal and Cost-Effective Approach: Polymers with Tunable Upper Critical Solution Temperature in Water and Electrolyte Solution

We present a powerful universal and versatile approach for the synthesis of polymers that show a UCST in water. Up to now only a few polymers were known that show an upper critical solution temperature (UCST) in water. This study establishes general requirements to obtain polymers with a UCST in water as well as electrolyte solution. It is demonstrated that old homo- and copolymer systems like poly(methacrylamide) and poly(acrylamide-co-acrylonitrile) can exhibit a UCST in water and how polymers with a tunable UCST can be synthesized by copolymerization of acrylamide and acrylonitrile, monomers that are industrially produced on large scales. Controlled increase of the UCST by copolymerization of acryamide with varying amounts of acrylonitrile was shown, and it could be varied between 6 and 60 °C. The hysteresis between the cloud point upon cooling and heating was very small with only 1–2 °C in most cases. The cloud points in pure water were similar to the cloud points measured in phosphate buffered saline. Also, it is possible to prepare highly concentrated thermoresponsive polymer solutions without gel formation.