Cooperative relaxations in semicrystalline fluoropolymers studied by thermally stimulated currents and ac dielectric

✍ Scribed by Bryan B. Sauer; Peter Avakian; Howard W. Starkweather Jr.

• Publisher: John Wiley and Sons
• Year: 1996
• Tongue: English
• Weight: 942 KB
• Volume: 34
• Category: Article
• ISSN: 0887-6266
• DOI: 10.1002/(sici)1099-0488(199602)34:3<517::aid-polb10>3.0.co;2-l

✦ Synopsis

Semicrystalline fluoropolymers including poly(tetrafluoroethy1ene) (PTFE), a 8 mol % hexafluoropropylene (HFP)/92% T F E random copolymer (FEP), and poly(viny1 fluoride) (PVF) were studied using thermally stimulated current depolarization (TSC), ac dielectric, and other thermal analysis techniques. The TSC thermal sampling (TS) technique is emphasized here for the detection of broad and weak "cooperative" relaxations with all three of the polymers studied exhibiting two cooperative (i.e., relatively high apparent activation energy) transitions. The well-studied low-temperature y relaxation in PTFE at ca. -100°C is characterized by this method as well as the y relaxation in the less crystalline F E P sample. Higher temperature cooperative glass transitions, associated with constrained noncrystalline regions, are found at ca. 100°C in PTFE and ca. 80°C in FEP at TSC frequencies. Comparisons with relaxation studies of linear polyethylene are made, and the effects of crystallinity on the various transitions are discussed. The unique characterization by the TSC-TS technique in the detection of multiple "cooperative" relaxations, even in the case of overlapping transitions, is emphasized here. An example is the low-temperature relaxation in FEP. Two cooperative transitions were detected in PVF. The higher temperature one at ca. 45°C is the glass transition, as is well known in the literature. More information is needed to confirm the molecular origin and the effects of crystallinity and chemical structure on the low-temperature cooperative transition in PVF.