Effects of Side-Chains on Polymers

Chemistry: Cambridge International A Level, topic 3.8.3

Side-chains & intermolecular forces can impact the properties of polymers. Two examples are PTFE and Kevlar.

Polytetrafluoroethylene (PTFE) is a polymer of tetrafluoroethylene.
Fluorine is a very electronegative atom, which reduces the strength of the van der Waals forces between neighbouring PTFE strands.
This is because the electrons are held closely to the fluorine atom.
Each monomer subunit is also symmetrical. This eliminates any overall charge across the molecules.
This makes PTFE non-polar.

PTFE molecules have small side chains. The side chains are just individual fluroine atoms.
This allows PTFE strands to pack closely together.
Even though the strength of the van der Waals forces is reduced in PTFE, many forces can form between the closely packed strands.
This means PTFE has a fairly high melting point.
Together the high melting point and hydrophobic nature make PTFE a useful non-stick material in cookware.

Kevlar is a very strong polyamide made from benzene-1,4-dicarboxylic acid and 1,4-diaminobenzene monomers.
Neighbouring strands of kevlar can form hydrogen bonds.
These bonds occur between the CO group of one monomer and the NH group of the monomer on a different chain.
Kevlar has a high tensile strength-to-weight ratio (it is about 5 times stronger than an equal weight of steel).
This makes it useful for many applications from bicycle tires to sails to body armour.

Test yourself on Effects of Side-Chains on Polymers