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Chemistry LibreTexts

The Preparation of Bakelite

[ "article:topic", "Fundamental" ]
  • Page ID
    3086
  • Chemical Concept Demonstrated

    • Thermoset plastics

    Demonstration

    Formaldehyde is added to the beaker inside a fume hood.

    Aniline hydrochloride (C6H5NH3Cl) is rapidly added.

    beaker.gif

    Observations

    The polymer expands out of the beaker, along with a prodigious amount of heat.

    Explanation

    This reaction is highly exothermic, but that is not why the plastic produced is referred to as "thermoset".

    Bakelite is a space-network polymer. Unlike linear and branched polymers, which are composed of long molecules that make them more or less crystalline, space-network polymers are highly and irregularly cross-linked throughout the structure. The sheer extent of the cross-linking means that a sample of the material is essentially one gigantic molecule.

    Although heat softens and melts linear and branched polymers, heating does not soften space-network polymers because such a softening would require the breaking of covalent bonds.  In fact, heating usually produces additional cross-linking in these polymers, making them harder.  It is for this reason that space-network polymers, such as bakelite, are called thermoset plastics.

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