The crystallization of a copoly(chlorotrifluorethylene-vinylidene fluoride) from the amorphous rubbery state
Abstract
A random copoly(chlorotrifluorethylene-vinylidene fluoride) in the ratio of 3 : 1 was annealed at the temperature range of Tg < T < Tm. The copolymer slowly crystallizes, attaining a rather low ultimate degree of crystallinity, depending on the annealing temperature, in the form of randomly distributed ribbonlike lamellae. The crystallites' melting temperatures are much lower than those of the corresponding homopolymers, increasing with annealing temperature and time. The crystallization kinetics, analyzed using the Avrami equation, indicates the formation of small, low-ordered crystallites. The crystallization process results in a dramatic increase in the elastic modulus at T > Tg. Annealing of stretched samples results in oriented crystallization at much higher rates than in the unstretched material, without markedly affecting the ultimate degree of crystallinity. The oriented crystallites, distributed in an isotropic amorphous matrix, exhibit lower thermal stability than the corresponding unoriented crystals. Their melting temperatures increase with annealing time; however, they decrease with the extent of stretching, suggesting a strong kinetic effect on the crystallites' degree of order.
