Study of the thermal properties and relaxation transitions in tetrafluoroethene-ethene copolymers

Copolymerization of tetrafluoroethene (TFE) with ethene (E) in water-alcoho l medium initiated by 2,2 ' -azo-bis-izobutyronitrile (AIBN) at 338 K and 4 .2 MPa was conducted in an autoclave by employing a semiflow procedure to f eed the comonomers. The thermal properties of the copolymers under both the static and dynamic conditions of thermal treatment in air (ageing) were st udied. The most pronounced changes in the initial temperature of destructio n were observed for the compositions containing more than 42 mol % TFE, whi ch corresponded to the formation of alternating copolymers. The reaction of thermal degradation was found to follow the first order kinetic equation, with the activation energy 174 kJ (.) mol(-1). The higher thermal stability of the alternating TFE-E copolymers was proved by IR spectroscopy and DTA analysis. Both the melting and crystallization DSC scans of copolymers of v arious compositions were analyzed. Monomodal peak of melting (and respectiv ely, crystallization) was observed in both scans for the alternating copoly mer, whereas the second peak appeared for the copolymer fractions with the higher content of ethylene block fragments and 30-40 mol % TFE units. The d ynamic-mechanical analysis showed three relaxation transitions (gamma, beta (1) and beta (2), alpha) in the temperature interval from 173-433 K, relat ed to the mobility of structural units of different type in the copolymers prepared. (C) 2001 John Wiley & Sons, Inc.