Bakelite is which kind of plastic?

Thermosetting phenol-formaldehyde condensation resin

Which catalyst and ratio gives the novolac prepolymer?

Acid catalyst and excess phenol

Base catalyst and excess formaldehyde

Acid catalyst and excess formaldehyde

Which property explains non-stick use of PTFE?

Very low coefficient of friction and chemical inertness

2073 Bhadra · 2.5+2.5 marks

Short notes: Bakelite and Teflon

Short answer

Bakelite: thermosetting phenol–formaldehyde resin made by condensation polymerisation, cross-linked 3D network, hard, heat-resistant, used for electrical switches and handles. Teflon (PTFE): addition polymer of tetrafluoroethylene, chemically inert, very low friction, heat-resistant to 260 °C, used for non-stick coatings, insulation, and seals.

Write short notes on Bakelite and Teflon.

Bakelite

Bakelite is a phenol–formaldehyde resin, the first fully synthetic thermosetting plastic. It is made by condensation polymerisation of phenol and formaldehyde (methanal).

Phenol reacts with formaldehyde (acid or base catalyst) to give o- and p-hydroxymethyl phenols: C₆H₅OH + HCHO → HOCH₂–C₆H₄–OH
These condense with more phenol with loss of water, forming a linear, low molecular mass prepolymer (novolac with an acid catalyst and excess phenol; resole with a base catalyst and excess formaldehyde).
On heating with a hardener (hexamethylenetetramine for novolac) or just heat for resole, –CH₂– bridges form between the rings at the o- and p-positions, giving a hard, cross-linked three-dimensional network.

   OH         OH         OH
   |          |          |
  (C₆H₃)–CH₂–(C₆H₃)–CH₂–(C₆H₃)–   (rings joined by –CH₂–;
         |            |            more CH₂ bridges cross-link
        CH₂          CH₂           the chains in 3-D)

n C₆H₅OH + n HCHO → [C₆H₃(OH)–CH₂]ₙ + n H₂O (simplified)

Bakelite is hard, rigid, heat resistant, a good electrical insulator, and does not soften on reheating. Uses:

Electrical switches, plugs, sockets, switch-boards and insulating parts of computers and appliances.
Handles of cookers, pans and irons.
Laminates (e.g. phenolic printed circuit boards), brake linings, and adhesive for plywood.
Telephone cases, radio cabinets, billiard balls, gears and bearings.

Teflon

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.

PTFE is chemically inert, heat resistant (up to 260 °C, m.p. 327 °C), has a very low coefficient of friction and is an excellent electrical insulator. Uses: non-stick coating on cookware, gaskets and seals, insulation of wires and cables, lining of chemical equipment, bearings, valves and surgical implants.

✓ Answer checked by Claude Opus 5.5 (high effort)

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