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Addition polymers and repeating units explained

Organic chemistry • Synthetic and natural polymers

Key concepts

What you'll likely be quizzed about

  • Addition polymerisation involves monomer molecules featuring a carbon-carbon double bond.
  • The pi bond opens, enabling each monomer to connect head-to-tail with its neighbors to create a long saturated carbon chain.
  • Unlike other types of polymerisation, no small molecules like water or HCl form as by-products.

Flashcards

Test your knowledge with interactive flashcards

What is head-to-tail addition?

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A common arrangement where one end of the monomer bonds to the next monomer's tail, creating a predictable pattern of substituents.

Key notes

Important points to keep in mind

Monomer must contain a C=C double bond for addition polymerisation.

The repeating unit equals the monomer structure with the double bond opened and shown inside brackets with 'n'.

Draw the monomer, break the double bond in diagrams, then show new single bonds linking units.

Side groups on the monomer remain attached to the same carbon atoms in the repeating unit.

Brackets and a subscript n denote repetition; dashes show linkage points to the chain.

Chain length depends on monomer concentration, initiator/catalyst, temperature, and termination events.

Termination via combination or disproportionation stops chain growth and limits molecular weight.

Head-to-tail addition results in a regular repeating pattern; head-to-head or tail-to-tail yields irregular substituent placement.

No small molecules form as by-products in pure addition polymerisation.

Impurities and chain-transfer agents reduce average polymer chain length.

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