polymerisation mechanisms and monomer structure — VCE chemistry, live

Polymerisation mechanisms and monomer structure

Polymers are long chains built from small molecules called monomers, joined in one of two ways. In addition polymerisation the C=C double bond of each alkene monomer opens and the monomers link through new C–C bonds, so every atom ends up in the polymer. In condensation polymerisation each monomer has two functional groups, and every link that forms (amide, ester or –O–) releases a small molecule, usually water. This is the real knowscape from knowhere, not a picture of one. Drag it. Watch what actually changes.

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A polymer is one small molecule's decision repeated ten thousand times. Addition keeps every atom and just opens double bonds; condensation pays for each link with a water molecule. Chain by chain, those two moves — and how the chains then pack — decide whether you get a shopping bag, a rope or a benchtop.

Pick a monomer and add units: addition monomers open their C=C bond and lose nothing, while condensation monomers release one water at every link. A second picture packs addition-polymer chains so you can change the side group, chain length and branching and see how they pack.

what examiners catch — Students lose marks by drawing an addition polymer with the C=C still double, by leaving out the water in a condensation equation, or by calling a branched polymer stronger. Show the repeating unit in brackets, write n − 1 H₂O for condensation, and link packing to the strength of the forces between chains.

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Addition polymers form from monomers with a C=C double bond, such as ethene, chloroethene, propene and tetrafluoroethene; the bond opens and no atoms are lost.

Condensation polymers form from monomers with two functional groups; each new amide, ester or –O– link releases a small molecule, usually water, so n monomers lose n − 1 water.

Natural polymers such as proteins (from amino acids) and starch and cellulose (from glucose) are condensation polymers; manufactured ones include nylon 6,6 and PET (condensation) and polyethene, PVC and PTFE (addition).

The monomer sets the side group: Cl in PVC adds dipole–dipole forces and stiffness, CH₃ in polypropene and F in PTFE change the forces and the uses.

Longer chains mean more dispersion forces and more tangling, so the plastic is stronger and softens at a higher temperature.

Fewer branches let chains pack closely (HDPE: denser, stiffer); more branches hold chains apart (LDPE: less dense, softer, more flexible).

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This concept has no prerequisites in knowhere's map — it is a root. Everything in the topic is built from here.

this conceptpolymerisation mechanisms and monomer structurePick a monomer and add units: addition monomers open their C=C bond and lose nothing, while condensation monomers release one water at every link.

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why this one carries the topic.

five things, not forty.

nothing. this is where it starts.

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they don't read it. they run it.