THERMODYNAMICS, MORPHOLOGY AND DYNAMIC-MECHANICAL PROPERTIES OF POLYURETHANE AND NANOCOMPOSITES BASED ON IT, CONTAINING HYDROXY-POSS

Abstract

Nanocomposites based on polyurethane matrix consisting of an adduct of trimethylolpropane with toluene diisocyanate and a bifunctional polyester of poly(diethylene glycol) adipinate with mol. weight 2000, and contained 1,2-propanediolisobutyl-POSS with the amount of 1–10 %, were synthesized. The thermodynamic compatibility, dynamic-mechanical properties and morphology of the created nanocomposites were investigated. For the purpose of calculations the thermodynamic parameters of interactions between the components of POSS-containing nanocomposites, a study of the isothermal sorption of methylene chloride vapors by the created systems was conducted. The sorption of methylene chloride vapors by the samples of the native PU, POSS-containing nanocomposites and nanofiller was studied using a vacuum instalation with McBean balances. The values of the free energy of polyurethane and POSS mixing during the formation of the nanocomposites were calculated based on the concentration dependences of Ägm - the average free energy of mixing of individual components (polyurethane and POSS) and nanocomposites with methylene chloride, according to the thermodynamic cycles proposed by A.A. Tager. It is shown that polyurethane and hydroxy-POSS demonstrate thermodynamic incompatibility during the formation of nanocomposites. The free energy of mixing polyurethane and hydroxy-POSS have positive values at all concentrations of the nanofiller. By the method of dynamic-mechanical analysis investigations it was shown that the introduction of POSS into polyurethane matrix led to a shift of the tan δ maximum in the direction of increasing temperatures. The temperature values of the tan δ peak for nanocomposites with increasing POSS content increased from 38 to 47 °C for PU1 and PU10, respectively. With the introduction of the POSS nanofiller into the polyurethane matrix, the intensity of the tan δ peak also decreased. Therefore, it was shown that the introduction of hydroxy-POSS into the polyurethane matrix leads to suppression of segmental motions in polyurethane, to an increase in the glass transition temperature of nanocomposites, and to an increase in the modulus of elasticity of nanocomposites compared to the native matrix. It is assumed that this happens due to the fact that the part of hydroxy-POSS, which was not incorporated into the polyurethane chain, is concentrated in the flexible segments of polyurethane as a nanofiller. When studying the morphology of the created nanocomposites using scanning electron microscopy, it was found that starting from a content of 3 % of hydroxy-POSS, it forms agglomerates of nanoparticles in the polyurethane matrix, which increase in size when the content of hydroxy-POSS increases.