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Chemistry 367L/392N
Macromolecular ChemistryMacromolecular Chemistry
Lecture 17 Lecture 17
+++Cationic Polymerization+++
Mitsuo Sawamoto Joseph Kennedy
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Chemistry 367L/392N
Assignment 9Assignment 9
Read Odian 374-388 and 403-407
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Chemistry 367L/392N
Terminate Anionic PolymerizationTerminate Anionic Polymerization
Dr Ellison’s notes will be posted on the web site
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Reactivity of monomers
Group A:
Group B:
Group C:
Group D:CH2 CH CH CH2
CH 2 C(CN) 2 CH 2 C
CN
COOC 2H 5 CH 2 CH
NO 2
> >
CH 2 CHCN CH 2 C
CN
CH 3 CH 2 CH C
O
CH 3> >
CH 2 CH
CO OCH 3
CH 2 C CH 3
COO CH 3
>
CH2 CH CH2 C
CH3
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Anionic Polymerization in the Lab
Break seal vs Schlenk ApproachBreak seal is sure but complexSchlenk line is simpler but …..
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Break Seal Glassware
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In the laboratory
For making stars
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● Attack of the initiator or living end at the carbonyl group of the monomer may lead to termination
● Activation of the protons in the αααα position to the carbonyl group may lead to transfer
Potential problems with polar side groups
*
C
OO
CH3
H
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Chain transfer in acrylates
OMeO
CO2Me
CO2Me
O
CO2Me
CO2Me
Backbiting
C O
CO2Me
CO2MeOMe
O
CO2Me
CO2Me
Ketene formation
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Possible Termination Reactions
● Attack of Monomer Carbonyl Group
● Intermolecular Attack of Carbonyl Group
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Possible Termination Reactions
● Termination by backbiting
The efficiency of backbiting depends on the size of the Counteranion, the polarity of the solvent, and on monomer structure
Li+ > Na+ > K+ > Cs+ >
THP > THF > DME
Acrylates > methacrylates > methyl tert-butyl
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Additives for Anionic polymerization
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Alkoxy Alkoxides
Additives in Anionic Polymerization of Meth(acrylates)
● very inexpensive
● very fast polymerization even in non polar solvents
● no increase of termination reactions
● Well-controlled polymerization of primary acrylates
● Controlled block copolymerization of MMA with primary acrylates ( 2-ethyl acrylates, n-butyl-acrylates)
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For a series of para-substituted styrenes,
OCH3 > CH3 > H > Cl
Vinyl ethers
CH2 CHORR'+
R'CH2 CH OR+
R'CH2 CH OR+
XCH2 CH
X
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Protic acidswith bulky, non-nucleophilic anionse.g. H2SO4, HClO4, FSO3H, etc, etc
Lewis Acids are “co-catalysts”e.g SnCl4, AlCl3, BF3 when reacted with a nucleophile like water
BF3 OH2+ H+3BF OH
-
ORHAC
+
OR
HA
+
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are co-catalysts
…proton source
….cation source
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“onium salts”
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….much like anionic polymerization
Polar solvents favor free ions
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R+
R R
+
+
XCH2 CH2 C+
CH3
CH3
monomer CH2 CH2 C
CH3
CH3
CH2 CH CH
CH3
CH3X+
XCH2 CH CH
CH3
CH3
H:shift+