Patent ID: 7514512
Filing Date: 2009-04-07
Classification: C07C,C08F

Abstract:
1. Cured fluoroelastomers comprising VDF-based curable fluoroelastomers, said fluoroelastomers comprising the monomer of formula (a) CF 3 OCF 2 OCF═CF 2 , said fluoroelastomers having a glass transition temperature lower than −35° C., an improved combination of mechanical and compression set properties at range of temperatures up to 250° C., high thermal resistance, high molecular weight, and an amount of —COF end groups lower than the sensitivity limit of the method described herein: at the end of the polymerization, the polymer is isolated by coagulation by freezing and subsequent defrosting; it is washed twice with demineralized water and is dried in a stove until a constant weight; the —COF end groups are determined by FT-IR spectroscopy, wherein on a polymer film having a thickness from 50 to 300 micron a scanning between 4,000 cm −1 and 400 cm −1 is initially carried out, the film being then kept for 12 hours in an environment saturated with ammonia vapours, and recording the IR spectrum under the same conditions of the initial IR spectrum; elaborating the two spectra by subtracting to the signals of the spectrum of the untreated specimen (initial spectrum) the corresponding signals of the specimen spectrum after exposure to ammonia vapours, drawing the difference spectrum, normalized by the following equation: the optical densities related to the —COF end groups, reacted with the ammonia vapours, are measured; the optical densities are converted into mmoles/kg of polymer by using the extinction coefficients reported in Table 1, page 73 of the report by M. Pianca et Al. “End groups in fluoropolymers”, J. Fluorine Chem. 95 (1999), 71-84; obtaining the concentrations of the residual —COF end groups expressed as mmoles of end groups —COF/Kg of polymer: in the fluoroelastomer spectrum no bands related to COF groups (1900-1830 cm −1 ) are detectable, the method sensitivity limit being 0.05 mmoles/Kg.