Effect of Rigidity of a Polymer Matrix on the Photochemical Transformations of Photochromic Compounds
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CTURE AND PROPERTIES
Effect of Rigidity of a Polymer Matrix on the Photochemical Transformations of Photochromic Compounds V. P. Gracheva,*, A. S. Dzhalmukhanovaa, M. L. Bubnovaa, S. A. Kurochkina,b, and S. M. Aldoshina a
Institute of Problems of Chemical Physics, Russian Academy of Sciences, Chernogolovka, 142432 Russia b Bauman Moscow State Technical University, Moscow, 105005 Russia *e-mail: [email protected] Received January 13, 2020; revised February 13, 2020; accepted March 19, 2020
Abstract—The thermal and thermomechanical properties of polyurethanes based on isophorone diisocyanate and polyfurit crosslinked using various curing agents are studied by differential scanning calorimetry and dynamic mechanical analysis. Two transitions are observed on thermograms in the temperature range from –100 to +150°С. The first transition detected at a temperature below –60°С corresponds to the glass transition temperature of soft ester segments. A broad endothermic region (near 100°С) is related to the melting of crystal-like ordered structures formed by strong hydrogen bonding between hard segments. The relationship between the spectral-kinetic behavior of the photochromic compound introduced into the polymer matrix and the properties of the polyurethanes is investigated. The rate of photochemical transformations of the photochromic compound covalently bonded to the matrix may depend on the stage of the polymerization process at which it is introduced into the polymer.
DOI: 10.1134/S1560090420040041
INTRODUCTION Prospects for using photochromic materials in various fields of engineering, specifically for creating sun-protection means, which automatically change their light transmission depending on illumination, and optical memory devices [1, 2], considerably depend on the properties of polymer matrices into which photochromic compounds are introduced. Owing to an insufficient molecular mobility in glassy polymer media, the achievement of a high light sensitivity and an acceptable rate of thermal relaxation of photochromic compounds is a major problem [3]. The efficiency of photochromic transformations of spiro compounds in glassy polymer matrices, for example, based on methyl methacrylate (MMA), may be improved by introducing into a polymer the additives of elastomers, which occur in the rubbery state (zones with a large free volume) at the exploitation temperature of the material [4, 5]. Finally, photochromic materials characterized by a high light sensitivity level and thermal relaxation rate can be produced using elastomers having a large free volume at the exploitation temperature, particularly polyurethanes, as a polymer matrix [6–8]. It is known that, along with free volume, the rate of photochemical transformations is substantially affected by the interaction of a molecule of photo-
chromic compound (PC) in the closed spyran form and, especially, in the open merocyanine form with the functional groups of the polymer chain [9, 10]. In order to decrease this effect of polymer chains, the authors of [8] made an
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