Abstract
The thermal stress-cracking properties of ethylene-chlorotrifluoroethylene copolymer (E/CTFE copolymer, marketed as Halar® by Ausimont USA Inc.) has been improved considerably by using 2 to 6 wt% hexafluoroisobutylene (HFIB) as a termonomer. This improvement arises from the increased flexibility of the polymer molecule in the presence of HFIB units, which also reduces the average lamellar repeat from 300–400 Å for the copolymer to 135–185 Å for the terpolymer. We postulate that crystalline lamellae consist entirely of alternating units of ethylene and chlorotrifluoroethylene, while the HFIB substituted E/CTFE segments are segregated in the interlamellar amorphous regions. These structural features are used to explain the role of HFIB in enhancing the resistance of the terpolymer to environmental stress-cracking.
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