Curing of Vinylidene Fluoride Based Fluoroelastomers

Vinylidene fluoride based fluoroelastomers have remarkable resistance to flames, chemicals, solvents, heat and oxidation. These fluorolastomers can be cured either by bis-nucleophiles such as bis-phenols or diamines or by peroxides. The bis-phenol curable stocks provide excellent processability and compression set resistance. In addition to the bis-phenol, an accelerator such as a quaternary phosphonium or ammonium salt and a metal oxide or hydroxide such as Ca(OH)2 or MgO are required. The mechanism involves base attack on the polymer backbone to generate olifinic unsaturation through HF elimination, followed by nucleophilic attack on these double bonds. Compared to nucleophilic cures, peroxide cures provide advantages in acid and steam resistance but require a cure site on the polymer such as a bromine or iodine atom that is susceptible to radical attack. In addition to an organic peroxide, a radical trap, such as triallylisocyanurate or cyanurante, and an acid acceptor such as a metal oxide are needed. The mechanism of curing involves peroxide decomposition to generate polymeric radicals to the trifunctional radical trap to form a crosslinked network.