Ringopening of cyclic ethers

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Ring-opening of cyclic ethers
Common monomers and their repeat units
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Epoxides

• Polymerizable by both anionic and cationic means
• Highest value of ring strain
• Many commercial examples

Anionic polym
Usually opens at methylene
Cationic polym
Often opens at both methylene and methine
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Stereoregular polymers
Racemic monomers like PO can give isotactic
microstructure-with catalysts such as ZnEt2/H2O,
Fe oxide, AlEt3/H2O. Either 1)An asymmetric
catalyst is responsible- enantiomorphic catalyst
site control or 2) A growing polymer chain of a
given configuration reacts preferentially with
one enantiomer
The two enantiomers of PO
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E.g.
Or optically active polymer can be made by using
an optically active catalyst
An optically active alcohol
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Polytetrahydrofuran

• cationic polymerization
• often see monomer/polymer equilibrium

A COMMON SYSTEM INVOLVES INITIATION BY THE ESTER
OF A SUPER ACID
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Initiators
1) A proton or acidic groups adds directly to
the monomer
Etc.
Produces polymers with OH ends
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2) A group other than H adds
E.g.
3) Hydride transfer