Study of the Thermal Properties and Relaxation Transitions in Tetrafluoroethene-Ethene Copolymers

摘要

Copolymerization of tetrafluoroethene (TFE) with ethene (E) in water-alcohol 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 feed the comono-mers. The thermal properties of the copolymers under both the static and dynamic conditions of thermal treatment in air (ageing) were studied. The most pronounced changes in the initial temperature of destruction were observed for the compositions containing more than 42 mol% TFE, which 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 various compositions were analyzed. Monomodal peak of melting (and respectively, crystalli-zation) was observed in both scans for the alternating copolymer, whereas the second peak appeared for the copolymer fractions with the higher content of ethylene block fragments and 30-40 mol % TFE units. The dynamic-mechanical analysis showed three relaxation transitions (#gamma#,#beta#_1 and #beta#_2 #alpha#) in the temperature interval from 173-433 K, related to the mobility of structural units of different type in the copolymers prepared.