After five minutes of vigorous stirring with an ultrasonic mixer (WELDER, Hiroshima, Japan) in a vacuum chamber (VB, Prague, Czech Republic) to homogenize and degass the reaction mixture prior to polymerization, this mixture was hardened in the mold and left to cure at 353±3 K for 4 h in a laboratory furnace XKL (France Etuves, Chelles, France).