# Intermolecular Forces in Teflon vs Polyethylene

From Wikipedia, polyethylene has a melting point of around $400K$, while Teflon (polytetrafluoroethylene) has a melting point of $600 K$, which is much higher. Besides the increased London Dispersion Forces caused by the larger fluorine atoms, could the stronger bonding in Telfon be explained by Teflon molecules being polar?

The $\ce{C-F}$ bond is strongly polar, so there is definitely a dipole there. However, whether a molecule is polar or not depends on whether or not the individual dipole vectors cancel. The flexibility of $\ce{C-C}$ single bonds allow for the polymer to behave like any other saturated alkane: free rotation to produce a molecule that more resembles a noodle than a pencil.

When we imagine an individual molecule of Telfon without Van Der Waal forces, we see that it is statistically the case that the molecule is twisted and is thus polar, as the vectors don't cancel. However, when we take into account these dipole-dipole attractions (and the London Dispersion Forces) between molecules, the molecules line up and straighten (for it is more energetically favorable). However, once they straighten up, line up, and pack, the dipole-forces/polarity are gone. Thus, do dipole-dipole forces exist and play a role in the stronger bonding in (polytetrafluoroethylene) as compared to polyethylene?

• PTFE chains form a helix in the crystalline state, afaik. So i guess there might be some polar interaction inside each strand. But I'd chalk up most of the melting point difference to teflon being just much heavier. Btw.: The perfluorated C-C bond is rather stiff, compared to a regular polyethylene backbone. – Karl Apr 30 '16 at 20:11
• Teflon has LOWER intermolecular forces. Teflon has a super-low self friction and gekos hate it, perfluorohexane boils at a lower temperature than hexane, etc. – Kevin Kostlan Apr 27 '18 at 17:18