Lecture 18
Lecture 18
Lecture 18
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Macromolecular Chemistry<br />
Mitsuo Sawamoto<br />
Joseph Kennedy<br />
+++Cationic Polymerization+++<br />
<strong>Lecture</strong> <strong>18</strong><br />
Chemistry 367L/392N
Classical Monomers for<br />
Cationic Polymerisation<br />
OR<br />
OR<br />
OR<br />
Chemistry 367L/392N
Initiation<br />
+<br />
E+<br />
+ CH 2 CR 2 ECH 2 CR 2<br />
Initiator mineral acid : H 2 SO 4 , H 3 PO 4<br />
lewis acid : AlCl 3 , BF 3 , TiCl 4 , SnCl 4<br />
Coinitiator<br />
BF 3 + H 2 O HOBF 3<br />
- H<br />
+<br />
AlCl 3 + RCl AlCl 4 - R +<br />
Chemistry 367L/392N
Rearrangement<br />
CH 3<br />
X + CH<br />
+ 3<br />
CH 2 CH CH<br />
XCH 2 CH CH<br />
H:shift<br />
CH 3<br />
CH 3<br />
XCH 2 CH 2 C + CH 3<br />
CH 3<br />
monomer<br />
CH 2 CH 2 C<br />
CH 3<br />
CH 3<br />
R R<br />
R + +<br />
+
Special case of β-elimination (E2)
A controversial claim made by Professor Sawamoto<br />
Sawamoto<br />
He successfully repeated the analog of the Szwarc<br />
experiment with vinylcabazole and HI. We will learn more<br />
about this from Rob Ono.
Living cationic polymerisation<br />
OR<br />
• using HI/I 2<br />
• shortly afterwards HI/ZnX 2 X= I, Br, Cl<br />
• M n ∝ [M]/[I]<br />
• Block copolymer by sequential addition<br />
• Mn increases linearly with conversion
Isomers of Polymers<br />
<br />
For example , polymer with structure<br />
unit -[ C 2 H 4 O-] n can be polyvinyl<br />
alcohol or polyethylene oxide<br />
[ CH2 CH ] n [ CH2 CH2 O ] n<br />
OH<br />
polyvinyl alcohol<br />
polyethylene oxide<br />
Chemistry 3<strong>18</strong>N
Natural Rubber (isomers matter)<br />
African Tree<br />
CH 2<br />
CH 3<br />
C<br />
C<br />
H<br />
CH 2<br />
Gutta Percha<br />
n<br />
harder<br />
CH 2<br />
CH 3<br />
C<br />
CH CH 2<br />
Isoprene<br />
South American tree<br />
CH 2 CH 2<br />
C C n<br />
CH 3 H<br />
Hevea<br />
softer<br />
Chemistry 3<strong>18</strong>N
Chemistry 3<strong>18</strong>N
Chicle (Manilkara zapota), native tree of Central America and the West Indies.<br />
Chemistry 3<strong>18</strong>N
Natural Rubber (isomers matter)<br />
African Tree<br />
CH 2<br />
CH 3<br />
C<br />
C<br />
H<br />
CH 2<br />
Gutta Percha<br />
n<br />
harder<br />
CH 2<br />
CH 3<br />
C<br />
CH CH 2<br />
Isoprene<br />
South American tree<br />
CH 2 CH 2<br />
C C n<br />
CH 3 H<br />
Hevea<br />
softer<br />
Chemistry 3<strong>18</strong>N
The synthetic rubber program<br />
How<br />
See web links for more history<br />
Chemistry 3<strong>18</strong>N
Polymer Macrostructure vs. Microstructure<br />
- Macrostructure: ‘what the whole molecule looks like’<br />
- Clearly, a huge influence on properties ---> viscosity, etc.<br />
- Microstructure: ‘how individual monomers or atoms are arranged’<br />
- One example: Alternating v. random copolymers…<br />
- Also: Stereochemical configurations<br />
Differences in microstructure can have a huge impact on polymer properties!<br />
Stereochemical configurations:<br />
-Polymerization of propylene…<br />
Same as…<br />
Stereogenic<br />
Center!<br />
CH 3<br />
CH 3<br />
n<br />
H<br />
n<br />
CH 3<br />
Conventional View<br />
There’s an H here, too…
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