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Luminescence spectral properties of the two symmetrical indocyanine dyes with different substituents near nitrogen atoms have been investigated in the polyurethane matrices. The analysis of the IR-spectra, measured for the product of a reaction between indolenine salt, being a terminal heterocyclic fragment in one of these dye molecules, and phenyl isocyanate, and this salt and isocyanate as single bulk compounds has shown possibility of covalent bonding between this indocyanine and polyurethane. Such covalent bonding of the dye with the polymer matrix results in improvement of its luminescence spectral properties, compared to the dye-polymer solutions. [ABSTRACT FROM AUTHOR]

The influence of modified hydrophobic aerosil on the formation, viscoelastic and mechanical properties of interpenetrating polymer networks (IPNs) of poly(methyl methacrylate)/polyurethane has been investigated. It was established that the introduction of a nanofiller directly into the reaction mixture and an increase in its concentration causes the slowdown of both reactions: polymerization and urethane formation. The process of phase separation that accompanies chemical reactions takes place in two stages. The nucleation mechanism is preferred at the first stage; the spinodal mechanism is preferred at the second one. The formation of the phase-separated morphology of the obtained structure is confirmed by the results of optical microscopy: at the nanofiller concentration of 1 % (by weight) interconnected periodic structures are formed, and at the concentration of 7 % (by weight) structures with non-uniform distribution of phases are formed. The established relationship between the values of impact strength and the mechanical loss modulus indicates a possible location of the nanofiller mainly in the interfacial region. It has been shown that IPN with 1 % (by weight) of hydrophobic aerosil has the best value of impact strength. It is assumed that the impact strength for the filled IPNs is determined by the coagulation structures formed by the aerosil nanoparticles. [ABSTRACT FROM AUTHOR]

This article is devoted to the study of the influence of the chemical nature of the components of polyurethane matrices (PU) on their optical and viscoelastic properties in order to obtain polymer materials that combine several different functional properties: high transparency, effective UV protection and high damping ability. PU matrices with different chemical structures of diisocyanate (aliphatic (hexamethylene diisocyanate) or aromatic (toluylene diisocyanate)) and oligodiol (oligoether (oligooxypropylene glycol) or oligoester (oligodiethylene glycol adipate)) were synthesized. PU matrices with different molecular weights of ester (800 and 1500) were synthesized too. It was established that all PU matrices have a fairly high (~90 %) transmission coefficient in the range of visible wavelengths and UV blocking. However, the range of UV absorption significantly depends on the PU components. Matrices based on aliphatic diisocyanate absorb UV up to 250-280 nm. The UV absorption of PU matrices based on aromatic diisocyanate, regardless of the nature of their oligoester component and its molecular weight, undergoes a shift to the long-wavelength region - up to 300-400 nm, which is due to the presence of aromatic rings. For PUs with an aromatic component, the highest absorption in the UV region is observed for PUs based on oligoesters, which is explained by the greater absorption ability of ester groups relative to ether ones. It was found that PU matrix based on oligoester has better elastic properties, but the PU matrix based on oligoether is characterized by a wider temperature range of effective damping. The replacement of aliphatic diisocyanate with an aromatic one shift s the area of effective damping of PU material towards positive temperatures. Therefore, by changing the nature of PU components, as well as the molecular weight of the PU oligoester component, it is possible to obtain transparent materials with a wide temperature range of effective damping in combination with high protection against UV radiation. [ABSTRACT FROM AUTHOR]

Influence of the curing temperature, the ratio prepolymer -- curing agent and the solvent content on the viscoelastic properties and the crosslink density of the spatial three-dimensional network of the polyurethane optically-transparent materials was studied. According to the viscoelastic properties data it was established, that increase of the curing temperature, as well as an increase of the concentration of NCO-groups in the reactionary mixture is favourable for forming of the more crosslink structure of the polymer material. The optimum concentration of the solvent for obtaining of the polyurethane optically-transparent material with the highest value of the crosslink density of the polymer was determined. [ABSTRACT FROM AUTHOR]