PTFE relative molecular weight is larger, the lower is hundreds of thousands of, the height of more than 10 million, generally millions of (polymerization degree in 104 order of magnitude, and polyethylene only in 103). The general crystallinity is 90~95% and the melting temperature is 327~342℃. PTFE molecules in the CF2 unit by the sawtooth shape arrangement, because the fluorine atom radius is slightly larger than the hydrogen, so the adjacent CF2 unit can not completely press the opposite cross orientation, but forms a spiral twisted chain, the fluorine atom almost covers the entire polymer chain the surface. This molecular structure explains the various properties of PTFE.
When the temperature is less than 19 ℃, 13/6 spirals are formed, and in 19 ℃ the phase transition occurs, the molecule is slightly untied, forming 15/7 spirals. Although the carbon-carbon bond and the carbon-fluorine bond fracture need to absorb energy 346.94 and 484.88kj/mol separately in all fluorocarbon compounds, the PTFE solution generates 1MOL tetrafluoroethylene only energy 171.38kJ. So at high temperature pyrolysis, PTFE is mainly tetrafluoroethylene. The weight loss rate (%) of polytetrafluoroethylene at 260, 370, and 420 ℃ per hour is 1x10-4, 4x10-3 and 9x10-2 respectively. Visible, PTFE can be used in 260 ℃ for a long time.
Due to high-temperature pyrolysis also produces highly toxic by-products fluorine phosgene and total fluorine isobutylene, so special attention should be paid to safety protection and prevent PTFE contact open flame.