Synthesis of AMPSA Polymeric Derivatives Monitored by Electrical Conductivity and Evaluation of Thermosensitive Properties of Resulting Microspheres

Four stimuli-responsive polymers of N-isopropylacrylamide (NIPA) and 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPSA) and crosslinked derivatives by N,N′-methylene bisacrylamide (MBA) were synthesized: PNA, PAMPSA, PNAM, PAMPSAM. The effect of the cross-linker and methyl sulphonic acid (-CH(3)-SO(3)H) group on particle size, aggregation and volume phase transition temperature (VPTT) was investigated. Polymeric particles were synthesized via the surfactant free precipitation polymerization (SFPP) at 70 °C in the presence of cationic initiator 2,2′-azobis[2-methylpropionamidine] dihydrochloride (AMP) system. Chemical composition and morphology of investigated samples were evaluated using ATR-FTIR spectroscopy, (1)H-NMR spectrometry and SEM-EDS techniques. The hydrodynamic diameters (HD), zeta potential (ZP), and polydispersity index (PDI) in aqueous dispersions were assessed by dynamic light scattering (DLS) between 18–42 °C. HD values at 18 °C for PNA, PAMPSA, PNAM, PAMPSAM polymers were approx. 32, 730, 715, 665 nm, and ZP values were −1.36, −0.01, 8.90, −0.09 mV, respectively. The VPTT range was observed between 29 and 41 °C. PDI’s for PNA and PNAM were low and varied between 0.276 and 0.460, and between 0.119 and 0.056, respectively. PAMPSA and PAMPSAM were characterized by higher PDI in the range 0.728–0.959 and 0.658–0.836, respectively. The results confirmed the thermal sensitivity of the synthesized polymers and indicated a significant polydispersity and aggregation tendency of the resulting molecules. The conductivity results were applied for the interpretation of the polymerization process.