MELTING AND CRYSTALLIZATION OF TETRAFLUOROETHYLENE-ETHYLENE COPOLYMERS

The melting and crystallization of copolymers of tetrafluoroethylene w ith ethylene, synthesized in bulk and in suspension by semi-flow metho d, were studied by DSC. X-ray diffractions and infrared spectra of the copolymers were measured and new crystalline reflections, different f rom those of the homopolymers were observed. The melting temperature o f the copolymers synthesized in bulk depends strongly on the compositi on and exhibits several maxima. A certain small decrease in the meltin g temperature within the range of the alternating composition is obser ved. For alternating copolymers synthesized in suspension, the peaks a re monomodal indicating a higher structural and chemical homogeneity o f the copolymer. The nonisothermal crystallization kinetics in the tem perature interval from 260 to 255-degrees-C of the alternating copolym er prepared in suspension can be described by a modified Avrami equati on. The mechanism of nucleation and nuclei growth during the nonisothe rmal crystallization of the tetrafluoroethylene-ethylene copolymer is close to that of polyethylene.