Thermal characterization of copolymers obtained by radiation grafting of styrene onto poly(tetrafluoroethyleneperfluoropropylvinylether) substrates: thermal decomposition, melting behavior and low-temperature transitions

Differential scanning calorimetric (DSC) and thermogravimetric analysis (TG A) have been used to study the thermal decomposition, the melting behavior and low-temperature transitions of copolymers obtained by radiation-induced grafting of styrene onto poly (tetrafluoroethylene- perfluoropropylvinylet her) (PFA) substrates. PFA with different contents of perfluoropropylvinyle ther (PPVE) as a comonomer have been investigated. A two step degradation p attern was observed from TGA thermograms of all the grafted copolymers, whi ch was attributed to degradation of PSTY followed by the degradation of the PFA backbone at higher temperature. One broad melting peak can be identifi ed for all copolymers, which has two components in the samples with higher PPVE content. The melting peak, crystal-crystal transition and the degree o f crystallinity of the grafted copolymers increases with radiation grafting up to 50 kGy, followed by a decrease at higher doses. No such decrease was observed in the ungrafted PFA samples after irradiation. This indicated th at the changes in the heats of transitions and crystallinity at low doses a re due to the radiation effects on the microstructure of PFA (chain scissio n), whereas at higher doses the grafted PSTY is the driving force behind th ese changes. (C) 2001 Elsevier Science Ltd. All rights reserved.