SME
Organic Chemistry II · Problem type
Chain growth or step growth
Use this for “Is polystyrene made by chain growth or by step growth? And nylon-6,6?”
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How is each polymer made?
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Vinyl monomers with a C=C grow by chain growth; monomers with two reactive end groups grow by step growth.
Assumptions
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In chain growth, an initiator opens a monomer’s C=C, and the active end then adds one monomer after another, so long chains form early.
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In step growth, any two molecules with matching end groups can join, so the chains stay short until nearly every group has reacted.
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Step growth often loses a small molecule, such as water or HCl, at each link; a urethane forms by addition yet still grows step by step.
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