Thermoresponsive Behavior of Poly(acrylic acid-co-acrylonitrile) with a UCST

Poly(acrylic acid) is water soluble but can be converted into a thermoresponsive polymer possessing an upper critical solution temperature (UCST) by copolymerizing with acrylonitrile. The copolymers showed a UCST in water under ambient conditions, driven by the combined effect of hydrogen bonding between the carboxylic acid groups and hydrophobic interaction among the acrylonitrile moieties. The cloud point of the copolymers can be tuned by changing the copolymer composition, concentration, pH, and ionic strength of the solution. The dynamic light scattering results indicate that the amphiphilic copolymer chains are solubilized in the form of micelles through interchain hydrophobic interaction and the micelles may also form small aggregates through hydrogen bonding at temperatures below the UCST. This work demonstrates a new strategy for the design of thermoresponsive polymers from comonomers that are not known to produce thermoresponsive polymers but can be made into such polymers through the synergetic effect of different interactions that contribute to the enthalpic and entropic changes of mixing in the aqueous systems.