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Phenol and formaldehyde react readily, but heated in an open vessel they foam and fill with bubbles, as Leo Baekeland's own patent explains. He worked out how to control that reaction and turn it into a hard, useful material. This post covers who he was, the chemistry and the engineering trick, a worked calculation, and what his career teaches.
Who was Leo Baekeland?
The Science History Institute biography gives his dates as 1863 to 1944. He took his doctorate at the University of Ghent in Belgium and taught there for several years. In 1889, aged 26, he travelled to New York on a fellowship, and Charles Chandler of Columbia University persuaded him to stay in the United States.
His first big success was in photography. Working as an independent consultant, he invented Velox, a photographic paper that could be developed under gaslight instead of sunlight. In 1899 Eastman Kodak bought the invention for a reputed $750,000. That money let him pick his next problem freely.
Why phenol and formaldehyde?
The Science History Institute says Baekeland was frank that he chose synthetic resins deliberately, "looking for a way to make money". His first target was a replacement for shellac, which at the time was made from lac insects. His first product, a soluble resin called Novolak, did not sell. He then looked for a phenol-formaldehyde binder that could be moulded with fillers, in place of hard natural rubber.
The core problem is in his patent US 942,699, granted on 7 December 1909. He describes reacting phenol with formaldehyde to get an intermediate that heat can turn into "an insoluble and infusible body", and then doing that conversion "by the combined action of heat and pressure". The reason is spelt out: above about 90 to 100 °C, if the vessel is open, "vapors of formaldehyde and the like escape causing foam and air bubbles", and the proportions of the reagents are thrown off.
So the trick was not a new reaction but control: heat to drive the reaction, pressure in a closed vessel to stop the volatile parts boiling off and foaming. The Science History Institute shows his original pressure vessel, the "Bakelizer", used from 1907 to 1910. He published the chemistry in 1909 in a paper titled "The Synthesis, Constitution, and Uses of Bakelite".
What is the chemistry?
Formaldehyde (HCHO) links phenol rings at the positions next to and opposite the –OH group. Each link is a –CH₂– bridge between two rings. To make one bridge, one formaldehyde molecule and two ring hydrogens are used, and one water molecule is released. A reaction that joins monomers and gives off a small molecule is a condensation polymerisation.
Because each phenol ring can be linked at up to three positions, the chains branch and cross-link into a network. The early, lightly linked stage is still soluble; the fully cured network is hard and insoluble, matching the two stages in the patent.
Worked example: how much water comes off?
Problem. Suppose 10.0 mol of phenol (C₆H₆O) react with 10.0 mol of formaldehyde (CH₂O), and every formaldehyde makes one –CH₂– bridge. Find the mass of water released and the mass of resin left. Use C = 12.011, H = 1.008, O = 15.999.
Molar masses: phenol = 94.11 g/mol; formaldehyde = 30.03 g/mol; water = 18.02 g/mol.
Mass of reactants: 10.0 × 94.11 + 10.0 × 30.03 = 941.1 + 300.3 = 1241.4 g.
One water per bridge, and 10.0 bridges: water = 10.0 × 18.02 = 180.2 g.
Resin = 1241.4 − 180.2 = 1061.2 g.
Check with the repeat unit: phenol + CH₂O − H₂O = C₇H₆O, molar mass 106.12 g/mol. Ten moles of that is 1061.2 g. The two methods agree.
About 15% of the starting mass leaves as water. If that water and any spare formaldehyde boil off inside a setting solid, you get the bubbles Baekeland's patent describes.
Common mistakes:
Calling Bakelite an addition polymer. Water is lost at each link, so it is condensation.
Forgetting that the cured material is cross-linked, which is why it is a thermoset.
Losing track of hydrogens when building the repeat unit. Each bridge takes one H from each of two rings.
Is Bakelite on the syllabus?
The JEE (Advanced) 2026 syllabus lists Polymers, naming Bakelite along with natural rubber, nylon, Teflon and PVC. The JEE (Main) 2026 syllabus has no polymers unit. Check your own year's document. Our post on addition and condensation polymers covers the exam side, and the story of Hermann Staudinger explains how chemists came to accept that polymers are giant molecules, something still unclear when Baekeland began.
What happened next?
The Science History Institute notes that Bakelite found many uses in the growing car and radio industries. Baekeland retired in 1939 and sold his company to Union Carbide and Carbon Corporation.
What can a student learn from Baekeland?
Read failure as information. Foam and bubbles told him gas was escaping, which pointed to a closed vessel.
Control the conditions, not just the reagents. The same two chemicals gave junk or a useful plastic depending on temperature and pressure.
Pick problems with a clear use. He chose a known need, a shellac substitute and a mouldable binder, and worked backwards.
If condensation and cross-linking are hard to picture, the Fermi Concept Library has a lesson for each concept in chemistry, and the Fermi Problem Library has worked problems with a step-by-step solver for the mass calculations.
Try this: repeat the worked example with 15.0 mol of formaldehyde, all forming bridges, and find the water released (answer: 270.3 g).
