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Addition polymers Knowledge-Based Study

Chemistry · Organic Chemistry · Chemistry · Polymers & Biomolecules

Chemistry topic explanations on Addition polymers.

Study notes

  1. Addition polymerisation is a reaction in which many unsaturated monomer molecules join together to form a single long-chain macromolecule without the formation of any by-products.

    Key Features of Addition Polymers

    • Monomer Structure: Monomers must possess an unsaturated bond, typically an alkene carbon-carbon double bond (C=C).
    • Atom Economy: Because no atoms are eliminated during the chain growth, the atom economy of addition polymerisation is 100%.
    • Composition: The repeating unit in the polymer contains the exact same atoms as the monomer; hence, the empirical formula of the polymer is identical to that of the monomer.

    The general equation can be represented as: n CH2=CH(R) → –[CH2–CH(R)]n–, where R represents a hydrogen atom or a substituent group.

    A variety of commercial plastics are manufactured through addition polymerisation by varying the substituent group attached to the vinyl group.

    • Polyethene (Polyethylene): Formed from ethene (CH2=CH2). Depending on reaction conditions, low-density polyethene (LDPE, branched) or high-density polyethene (HDPE, linear) is produced.
    • Polypropene (Polypropylene): Formed from propene (CH2=CH–CH3). The methyl side group gives increased stiffness and thermal resistance.
    • Polychloroethene (PVC): Formed from chloroethene (vinyl chloride, CH2=CH–Cl). Rigid PVC is used in construction pipes, while plasticised PVC is used for flexible coverings.
    • Polytetrafluoroethene (PTFE): Formed from tetrafluoroethene (CF2=CF2). The strong C–F bonds impart high thermal stability and non-stick properties.
    • Polyphenylethene (Polystyrene): Formed from phenylethene (styrene, CH2=CH–C6H5), commonly used for insulation and packaging.

    Determining the relationship between monomer and polymer requires identifying the continuous two-carbon backbone segment.

    From Monomer to Polymer

    1. Draw the monomer structure by flattening the C=C bond horizontally.
    2. Orient all substituent groups vertically above and below the two alkene carbons.
    3. Convert the double bond into a single bond and draw extending single bonds through surrounding square brackets with a subscript n.

    From Polymer to Monomer

    1. Identify the continuous chain and isolate the two-carbon repeating unit.
    2. Remove the extending end bonds and regenerate the carbon-carbon double bond between those two carbon atoms.
    3. Verify that the total atom count and substituent positions match the target structure.