In preparing a fluorinated thermoplastic with good flex life, high thermal conductivity and low average spherolite diameter from tetrafluoroethylene and perfluoro n-alkyl vinyl ether, perfluoro 2-propoxyalkyl vinyl ether is additionally incorporated into the fluorinated thermoplastic. A semicrystalline, thermoplastically processable copolymer is prepared, made from units of the tetrafluoroethylene, from 2 to 10 % by weight of units of perfluoro n-propyl vinyl ether and from 0.1 to 6 % by weight of units of perfluoro 2-propoxypropyl vinyl ether. The novel copolymer preferably contains fewer than 70 unstable end groups per 106 carbon atoms, has thermal conductivity of at least 0.19 W/mK at 23 DEG C and has a smooth surface with an average spherolite diameter of 5 mu m. The novel terpolymer is suitable for extrusion of hose, in particular for heat exchangers, and also for ultrahigh-purity applications.
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