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The impact of the acrylic acid neutralization degree and binding agent on the properties of polyacrylate systems. Part II

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Methods of infrared spectroscopy forfrustrated total internal reflection (FTIR), electron spectroscopy of diffuse reflection (ESDO), and terahertz (THz) spectroscopy were used to analyze the influence of acrylic acid (0–100%) neutralization degree  with 14 n NaOH solution and the amount of MBAA crosslinking agent (0.1 to 1.0%, wt.) on the optical properties of the sodium polyacrylate. A comprehensive comparative analysis of dry and swollen hydrogels of polymerization products by spectral methods and by the method of swelling solutions for reaction systems confirmed the possibility of two structurally different systems in the synthesis of the crosslinked polymer compositions. A crucial role is played by the degree of acrylic acid neutralization. The transition boundary is the presence of sodium hydroxide (50–60%)in the reaction system, which results in the low swelling of the investigated samples and bathochromic shift in the long-wave branch of the global maximum in the electronic spectrum with increasing absorption of the medium intensity series in the range of 250–350 nm. The use of ESDO method showed that the swelling of dry powdered samples with a degree of acrylic acid neutralization of to 50% is accompanied by a short-wavelength shift and a sharp decrease in the long-wave branch of global absorption bands. The increase in swelling of the samples neutralized over 60% can be seen in hypochromic shift of the maximum only with the stabilization of discrete bands’ absorption in the range of 250–350 nm, which indicates the absence of the C=O functional group in plagiarizing processes during the swelling.Analysis of the data obtained by THz-spectroscopy revealed that refractive index of the samples increases with their swelling, and confirmed the formation of two systems with different mechanism of structure formation  depending on the acrylic acid neutralization degree.

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