Nylon, Teflon and epoxy resin

Nylon and Teflon are different polymers

Nylon 6,6 is a polyamide made by condensation polymerisation of hexamethylenediamine (6 carbons) and adipic acid (6 carbons) at about 250 °C under pressure:

n H₂N(CH₂)₆NH₂ + n HOOC(CH₂)₄COOH → [–NH(CH₂)₆NH–CO(CH₂)₄CO–]ₙ + 2n H₂O

The repeating unit has the amide (–CONH–) link. (Nylon 6 is made from caprolactam by ring-opening polymerisation.)

Teflon (PTFE, polytetrafluoroethylene) is made by free-radical addition polymerisation of tetrafluoroethylene (TFE) using a persulphate initiator under pressure:

n CF₂=CF₂ → [–CF₂–CF₂–]ₙ

TFE itself is obtained by heating chlorodifluoromethane (CHClF₂) at 600–800 °C.

Preparation and uses of epoxy resin

Epoxy resins are thermosetting polymers containing epoxide (oxirane) groups. They are made by condensing bisphenol-A with epichlorohydrin in presence of NaOH (about 50–60 °C):

HO–R–OH + 2 ClCH₂–CH–CH₂   --NaOH, –2HCl-->
(bisphenol-A)      \ /
                    O  (epichlorohydrin)

CH₂–CH–CH₂–O–R–O–CH₂–CH–CH₂    (n = 0)
  \ /                 \ /
   O                   O
where R = C₆H₄–C(CH₃)₂–C₆H₄
Higher polymers: more –CH₂–CH(OH)–CH₂–O–R–O– units inside.

The product is a liquid or low-melting prepolymer with epoxide end groups. It is cured (hardened) by adding a hardener such as a polyamine (ethylenediamine, triethylenetetramine) or an acid anhydride, which opens the epoxide rings and forms a cross-linked network.

Uses:

• Strong adhesives (Araldite) for metal, glass and ceramics.
• Surface coatings, paints and protective linings for tanks and pipes.
• Electrical insulation and potting of electronic components; glass-epoxy laminates for printed circuit boards.
• Matrix of fibre-reinforced composites (aircraft, boats, sports goods).
• Flooring, castings, moulds and tools.