1. Ionic Polymerization

2. Anionic Polymerization
General Formula B-
Anionic active center;
Counter-ion

3. What monomer?
Electron withdrawing groups (ester, cyano) or groups with double bonds (phenyl, vinyl) are needed as the R groups because these can stabilize the propagating species by resonance.
Question:
What are the characteristic Q-e values for such monomers? (q1)

4. Anionic Initiation
For initiation to be successful, the free energy of the initiation step must be favorable. Therefore, it is necessary to match the monomer with the appropriate strength of initiator so that the first addition is "downhill."
Bottomline: Nucleophile agents

5. Concept of Living Polymerization
There are only
Initiation: Chains are initiated all at once
(fast initiation)
Propagation: All chains grow under
identical conditions; fast; generally
needs low temperature (why? q2).
BUT
Little or no termination (except purposeful)
Little or no chain transfer

6. Living Polymerization
Consequently,
Reaction rate
Degree of polymerization
[M-]: concentration of all anions in the system
[M]: concentration of the monomer
[C]: concentration of the initiator
n: the number of anions that an initiator molecule produces

7. MW in Living Anionic Polymerization
Poisson Distribution
Narrow distribution

8. Typical Products CASE 1 CASE 2
Mono-disperse Polystyrene: Gel Permeation Chromatography (GPC) standard
CASE 2
unlike conventional rubbers that are covalently crosslinked (vulcanized), these block copolymers can be processed thermally and molded.
One or more blocks of flexible, low Tg polymer, with other blocks of rigid, high Tg polymer. The polymer actually exhibits two glass transitions, one at high temperature and a second one below room temperature.

9. Answer
q2: ionic polymerizations necessarily carry along a counterion, and their rates are much more sensitive to reaction conditions (e.g., solvent polarity, temperature).
q1. monomers for anionic polymerization generally have
High Q or high e values

10. Cationic Polymerization
Initiation and Propagation
The mechanism of cationic polymerization is a kind of repetitive alkylation reaction
Propagation is usually very fast must often be run at low
temperatures cooling large reactors is difficult and expensive.
Trace of water kills reaction Careful drying of ingredients is
necessary

11. Cationic Polymerization: Monomer
Electron donating groups are needed as the R groups because these can stabilize the propagating species by resonance

12. Cationic Polymerization: Initiators
Proton acids with unreactive counterions
Lewis acid + other reactive compound

13. Cationic Polymerization: side reactions
Cationic vinyl polymerization is plagued by numerous side reactions, most of which lead to chain transfer.
It is difficult to achieve high MW because each initiator can give rise to many separate chains because of chain transfer.
These side reactions can be minimized but not eliminated by running the reaction at low temperature.

14. Review: Vinyl Polymer Tacticity
Vinyl polymers that have single substituents (e.g., propylene, the example below) or two unsymmetrical substituents (e.g., methyl methacrylate) have pseudoasymmetric carbon atoms in the backbone.
atactic polypropylene is a useless, gummy solid,
the isotactic version is a highly crystalline, tough plastic that can even be
made into fibers.

15. Coordination (Ziegler-Natta) Polymerization
Important discovery: R3Al + Lewis acids:
Another important discovery: tacticity control:
Results:
Nobel Prize in Chemistry for Zeigler and Natta (1963)
Multibillion $ industry

16. Overall Scheme of Coordination Polymerization
Limited to ethylene and other a-olefins like propylene.
(Actually, it is the only good way to polymerize these monomers.)
Produces linear polymer, with very few branches (e.g., high density
polyethylene, HDPE).
Capable of producing homo-tactic polymers.
Most commercial initiators are insoluble complexes or supported on
insoluble carriers. .

17. The mechanism is poorly understood because it takes place on the surface of an insoluble particle, a difficult situation to probe experimentally.
An approximation

18. Concept Check Questions
Styrene is almost a unique monomer, in that it can be polymerized by practically all methods of chain polymerization.
A. Free radical
B. Anionic
C. Cationic
D. Co-ordination (i.e., with a catalyst)
Which of these methods would you use to make isotactic polystyrene?
If you needed to synthesize a set of narrow molecular weight standards (i.e., with poly-dispersities close to 1), which of the above methods would you use?
Commercial atactic polystyrene is synthesized by which of the
above methods?

19. Concept Check Questions
4. What method would you use to synthesize a triblock copolymer?
A) Free radical polymerization
B) Anionic polymerization
C) Using a Ziegler Natta catalyst
D) By putting it into a bloody great pot and spitting on it to initiate polymerization
E) Condensation polymerization
5. Suspension free radical polymerization of styrene would be preferred over bulk polymerization to overcome the problem of
A) Branching
B) Cross-linking
C) Stereo-isomerism
D) Polymeric impurities
E) Temperature control during polymerization

20. Concept Check Questions
6. In emulsion polymerization, the principal place where the monomer polymerizes is
A) Monomer droplets
B) Aqueous phase
C) Surfactant micelles
D) Surface of reactor
E) Air-liquid interface
7. Polypropylene produced commercially using a Ziegler-Natta catalyst is predominantly
A) Atactic
B) Isotactic
C) Syndiotactic