Abstract
The thermosensitive polymers of N-vinylcaprolactam P1, P2, P3, P4, and P5 were synthesized via the surfactant free precipitation polymerization (SFPP) at 70 °C in the presence of cationic initiator 2,2’-azobis[2-methylpropionamidine] dihydrochloride (AMPA). The influence of various concentrations of initiator AMPA on particle size, aggregation and lower critical temperature solution (LCST) was investigated by dynamic light scattering (DLS) measurement. The conductivity was measured in the course of the synthesis and during temperature decrease of the reaction mixtures. The polymers were characterized by Attenuated Total Reflectance-Fourier Transform Infrared spectroscopy (ATR-FTIR), 1H NMR, and thermogravimetric analysis. Thermal parameters of the degradations process were investigated using thermogravimetric analysis (TGA/DTA) under non-isothermal conditions in N2 atmosphere. The samples were characterized by powder X-ray diffraction analysis (PXRD).The hydrodynamic diameter (HD), polydispersity index (PDI) and zeta potential (ZP) were measured in aqueous dispersions of the synthesized polymers in temperature 18–45 °C. HD and PDI values at 18 °C were 137.23 ± 67.65 nm (PDI = 0.53 ± 0.18), 83.40 ± 74.46 nm (PDI = 0.35 ± 0.08), 22.11 ± 0.29 nm (PDI = 0.45 ± 0.05), 29.27 ± 0.50 nm (PDI = 0.41 ± 0.04), 39.18 ± 0.57 nm (PDI = 0.38 ± 0.01) for P1, P2, P3, P4, and P5, respectively. The aqueous solutions of the obtained polymers at 18–45 °C had a positive charge. ZP’s for P1, P2, P3, P4, and P5 polymers at 18 °C were 11.64 ± 4.27 mV, 12.71 ± 3.56 mV, 3.24 ± 0.10 mV, 0.77 ± 0.28 mV, 1.78 ± 0.56 mV respectively. The LCST range was between 32 and 38 °C. We conclude that the concentration of initiator affects the size of obtained polymeric spheres and theirs LCST.
Highlights
Despite continuous advances in pharmacotherapy, there are still many factors that limit effective pharmacological treatment, including drug instability in pH conditions of the gastrointestinal tract, low bioavailability, short half-life time, low drug selectivity, and adverse reactions in healthy cells, e.g., in the treatment of cancer [1]
The present work focuses on the synthesis of five types of polymeric nanoparticles, derivatives of NVCL (P1, P2, P3, P4, and P5), via surfactant-free precipitation polymerization (SFPP), and on the physicochemical study of the synthesized, thermally-responsive systems, both in aqueous solutions and in solid form
Surfactant-free precipitation polymerization in an aqueous environment at 70 ◦C degrees is an effective method of synthesis the polymer of N-vinylcaprolactam
Summary
Despite continuous advances in pharmacotherapy, there are still many factors that limit effective pharmacological treatment, including drug instability in pH conditions of the gastrointestinal tract, low bioavailability, short half-life time, low drug selectivity, and adverse reactions in healthy cells, e.g., in the treatment of cancer [1]. Important aspects include the reduction of the side effects, increases in stability, and the development of controlled release mechanisms of the drug under the influence of the pathophysiological factors. These effects may be obtained by using stimuli-sensitive nanocarriers [2,3,4,5,6,7]. The polymer may precipitate from the solution, increase or decrease its volume, and release the drug substance. These polymers are, ideal candidates for the role of "intelligent" drug carriers, i.e., for proteins and nucleic acids
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