Abstract
The aim of the study was to monitor the influence of increasing initiator concentrations on the properties of poly-N-isopropylacrylamide (polyNIPA) nanoparticles obtained via surfactant free precipitation polymerization (SFPP). In all studied systems P-001 to P-1, the same amount of monomer was used, and increasing amounts of potassium persulphate (KPS). The course of each reaction was monitored by measuring the conductivity of the whole system. The resulting composition of products was confirmed by attenuated total reflectance within Fourier transformed infrared spectroscopy (ATR-FTIR) measurements. The hydrodynamic diameters with polydispersity index (PDI) and zeta potential (ZP) were measured in aqueous dispersions of the synthesized polymers in dynamic light scattering (DLS) device (λ = 678 nm), and were found to be for P-1: 20.33 nm (PDI = 0.49) and −7 mV, for P-05: 22.24 nm (PDI = 0.39) and −5 mV, for P-01: 50.14 nm (PDI = 0.49) and −3 mV, for P-005: 62.75 nm (PDI = 0.54) and −3 mV and for P-001: 509.4 nm (PDI = 0.61) and −12 mV at 18 °C, respectively. Initiator concentration affects the size and ZP of particles. The hydrodynamic diameter decreases with initiator concentration increase, whereas the time of the reaction decreases when the initiator concentration increases. This fact is reflected in the observed values of conductivity in the course of the performed reaction. Evaluated volume phase transition temperature in the range of 32 °C enables further research of the nanoparticles as thermosensitive drug carriers.
Highlights
The potential application of N-isopropylacrylamide (NIPA) derivatives in controlled release of active pharmaceutical ingredients (API) is presently intensively studied [1]
During the surfactant free precipitation polymerization (SFPP) of NIPA derivatives, the radical polymerization is initiated by free radicals, and the oligomer chain grows
These results indicate that size of poly-NIPA particles can be adjusted by the concentration of the initiator, and indirectly conforms, that the conductivity measurements well correspond with the
Summary
The potential application of N-isopropylacrylamide (NIPA) derivatives in controlled release of active pharmaceutical ingredients (API) is presently intensively studied [1]. Some interesting potential applications include the controlled release of: doxorubicin [2], mesenchymal stem cells [3], basic fibroblast growth factor [4], theophylline [5], epirubicin [6], prodigosin [7], and simvastatin [8]. The NIPA derivatives may act as “smart” polymers, sensitive to a temperature factor, releasing the API, when the temperature increases locally [9,10,11]. In the course of the particle growth, the chains obtain—after a specified time—high molecular mass, at which the turbidity is usually observed [12]. The initial initiator level has a crucial influence on the number and molecular mass of synthesized nanoparticles
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