Lower Critical Solution Temperature Behavior in Poly[2-(dimethylamino)Ethyl Methacrylate] Solutions

Poly[2-(dimethylamino)ethyl methacrylate] (PDMAEMA) is a water soluble, cationic, temperature responsive polymer which contains tertiary amine groups. Temperature responsive polymers are polymers whose physical properties change when undergoing an extreme change in temperature. When the polymer reaches a certain temperature, it can exist in two or more phases under a miscibility gap. Under normal circumstances, the lower critical solution temperature (LCST) – a temperature at which polymer solubility is rapidly reduced – lies somewhere between 30 °F and 50 °F depending on the molecular weight of the polymer. In order to observe changes in LCST, polymer solutions were characterized over a range of ionic strength (0.01M-0.5M), pH level (pH 8-pH 10), and salt structures (sodium chloride, acetate. sulfate, and phosphate) using dynamic light scattering (DLS). Based on the DLS experiments, PDMAEMA has an increased LCST when the pH increases due to the decrease in protonation causing the polymer chain to become more hydrophobic. Additionally, increasing ionic strength results in a decreased LCST due to the strong solvation of the salt ions, leading to earlier onset of hydrophobic character in the polymer. Testing these conditions allows for predicting material properties across a wide range of potential environments, including physiological conditions and seawater or brine. This information is important for developing applications in drug delivery, gene delivery, biosensors, surface coatings, membranes, and chromatography.