Thermosensitive copolymers P1-P5 of N-isopropylacrylamide (NIPA) and poly(ethylene glycol) methyl ether methacrylates (PEGMEMs) were synthesized via surfactant-free precipitation polymerization (SFPP) using ammonium persulfate (APS) at 70 °C. The polymerization course was evaluated by the conductivity. The hydrodynamic diameters and the polydispersity indexes (PDI) of P1-P5 in the 18-45 °C range, which were assessed via dynamic light scattering (DLS), were at 18° (nm): 26.07 ± 0.54 (PDI 0.65 ± 0.03), 68.00 ± 1.10 (PDI 0.56 ± 0,02), 45.12 ± 0.57 (PDI 0.51 ± 0.03), 62.78 ± 0.40 (PDI 0.53 ± 0.003), and 92.95 ± 1.56 (PDI 0.60 ± 0.04), respectively. The lower critical solution temperatures ranged from 31 to 33 °C. The electrophoretic mobilities estimated the zeta potential in the 18-45 °C range, and at 18 °C, they were (mV): -4.64 ± 1.30, -6.91 ± 2.67, -5.85 ± 3.17, -2.28 ± 0.30, and -3.60 ± 0.96 for P1-P5, respectively. The polymers were characterized by Attenuated Total Reflectance Fourier-Transform Infrared spectroscopy (ATR-FTIR), H nuclear magnetic resonance (1H NMR), thermogravimetric analysis (TGA/DTA), Differential Scanning Calorimetry (DSC), and powder X-ray diffraction analysis (PXRD). Stable amorphous polymers were obtained. We conclude that the length of the co-monomer chain nonlinearly influences the properties of the obtained thermosensitive polymer nanostructures.
Keywords: N-isopropylacrylamide; ammonium persulfate; anionic initiator; controlled drug delivery; electrical conductivity; lower critical solution temperature; nanoparticles; poly(ethylene glycol) methyl ether methacrylate.