The Influence of Initiator Concentration on Selected Properties of Thermosensitive Poly(Acrylamide-co-2-Acrylamido-2-Methyl-1-Propanesulfonic Acid) Microparticles.

Agnieszka Gola,Andrea Bernardi,Witold Musiał,Gianfranco Pasut

doi:10.3390/polym13070996

Abstract

Thermosensitive polymers PS1–PS5 were synthesized via the surfactant free precipitation polymerization (SFPP) using 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPSA), and potassium persulfate (KPS) at 70 °C in aqueous environment. The effect of KPS concentrations on particle size and lower critical temperature solution (LCST) was examined by dynamic light scattering (DLS). The conductivity in the course of the synthesis and during cooling were investigated. The structural studies were performed by attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), H nuclear magnetic resonance (1H NMR), thermogravimetric analysis (TGA/DTA) and powder X-ray diffraction (PXRD). ATR-FTIR, 1H NMR and PXRD data confirmed the polymeric nature of the material. TGA/DTA curves demonstrated thermal stability up to approx. 160 °C. The effect of temperature on the hydrodynamic diameter (HD) and zeta potential (ZP) were evaluated by dynamic light scattering (DLS) and electrophoretic mobility (EM) in 18–45 °C range. The LCST values were between 30 and 34 °C. HD and polydispersity index (PDI) of aqueous dispersions of the synthesized polymers PS1–PS5 at 18 °C were found to be 226 ± 35 nm (PDI = 0.42 ± 0.04), 299 ± 145 nm (PDI = 0.49 ± 0.29), 389 ± 39 nm (PDI = 0.28 ± 0.07), 584 ± 75 nm (PDI = 0.44 ± 0.06), and 271 ± 50.00 nm (PDI = 0.26 ± 0.14), respectively. At 18 °C the ZPs of synthesized polymers suspensions were −13.14 ± 2.85 mV, −19.52 ± 2.86 mV, −7.73 ± 2.76 mV, −7.99 ± 1.70 mV, and −9.05 ± 2.60 mV for PS1–PS5, respectively. We found that the initiator concentration influences the physicochemical properties of products including the size of polymeric particles and the LCST.

Highlights

Polymeric micro- and nanoparticles have a broad application in the pharmaceutical industry and medicine [1,2,3,4,5]
The color disappeared with time, and reaction mixtures remained colorless until the end of the synthesis and even after the systems were cooled to room temperature
The schematic diagrams illustrating the suggested major stages of radical polymerization of 2-acrylamido-2-methyl-1-propanesulfonic acid and potential reactions of radicals and ions produced by potassium persulfate decomposition in water are presented in Figure 1 [23,24,25,26,27,28]

Summary

Introduction

Polymeric micro- and nanoparticles have a broad application in the pharmaceutical industry and medicine [1,2,3,4,5]. There are numerous environmental factors, such as temperature, pH, light, and electric field, to which stimuli-responsive materials respond with changes in shape, volume, solubility, conductivity, and conformation [6,7]. Due to the ability to control and fine-tune the smart polymer sensitivity, they are extensively studied for controlled drug delivery systems [8]. The thermosensitive polymers have been widely and extensively studied. They are well characterized due to the relatively uncomplicated control of the stimulus via external heating or cooling [9]. In some biomedical applications, such as tumor-specific delivery, multi-responsive polymers that combine the lower critical solution temperature (LCST) with another response triggered by another factor, for example, pH, are of particular interest [13,14]

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