Hypothesis: This study aims to investigate the effect of monomer ratio and synthesis conditions on the properties and phase transition behavior of acrylamide-acrylonitrile copolymers (AAm-co-AN). The upper critical solution temperature (UCST) is expected to be affected by changing the ratio of acrylamide to acrylonitrile and the amount of solvent.
Methods: (AAm-co-AN) copolymers were synthesized by free radical polymerization under two different conditions: using pure DMSO with various monomer ratios and varying the DMSO/water ratio with a constant monomer ratio. The polymers composition was investigated by Fourier-transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (¹H-NMR). The phase transition behavior and UCST were studied by turbidimetry and changes in particle size by dynamic light scattering (DLS).
Findings: FTIR analysis confirmed the successful synthesis of (AAm-co-AN) copolymers. Increasing the mole percentage of acrylonitrile from 23% to 30% led to an increase in UCST from 40°C to 65°C, while for copolymers synthesized in a DMSO/water co-solvent, increasing the water volume from 0.15 mL to 0.45 mL resulted in a decrease in UCST from 43°C to 25°C. In other words, the presence of water in the reaction medium reduces the reactivity of acrylonitrile and reduces its amount in the copolymer composition. The ¹H-NMR results indicate a direct correlation between the acrylonitrile fraction in feed and its incorporation in the copolymer structure. Furthermore, it was determined that increasing the ratio of water in the reaction medium leads to a decrease in the acrylonitrile content in the final copolymer structure. DLS analyses showed that the hydrodynamic radius of the particles decreases with increasing temperature. It undergoes a sharp change at a certain temperature, which corresponds to the UCST. It is different from the UCST temperature obtained by the turbidity method by about 7℃, which is probably due to the shorter retention time in DLS analysis.