Free Radical Copolymerization Free Radical Copolymerization

Macromolecular Chemistry Macromolecular Chemistry

Lecture 09 Lecture 09

Michael Szwarc

Michael Szwarc

Free Radical Copolymerization Free Radical Copolymerization

What happens when we initiate a

polymerization in a mixture of monomers???

Random Copolymers

Random Copolymers MM_{1 1}MM_{2 2}MM_{1 1}MM_{1 1}MM_{2 2}MM_{2 2}MM_{2 2}MM_{1 1}MM_{1 1}MM₂₂ Block Copolymers

Block Copolymers MM_{1 1}MM_{1 1}MM_{1 1}MM_{1 1}MM_{2 2}MM_{2 2}MM_{2 2}MM_{2 2}MM_{2 2}MM₂₂ Alternating Copolymers

Alternating Copolymers MM_{1 1}MM_{2 2}MM_{1 1}MM_{2 2}MM_{1 1}MM_{2 2}MM_{1 1}MM_{2 2}MM_{1 1}MM₂₂

Two Two Homopolymers Homopolymers MM_{1 1}MM_{1 1}MM_{1 1}MM_{1 1} + M+ M_{2 2}MM_{2 2}MM_{2 2}MM₂₂

M M _{1 1} + M + M _{2 2} → → - - [( [( M M _{1 1} ) ) _{x x} - - (M (M _{2 2} ) ) _{y y} ] ] _{n n} - -

AIBNAIBN

A Few Cases to Remember…

3)

4)

F

f

Poly(styrene-alt-maleic anhydride)

O O

O

δ+ δ

O O

+ O

O O O

[ ]_n

Charge transfer complex

δ+

δ+ δ- δ-

Q and e Q and e

z Generalizations:

– This is a purely empirical relationship

– Q and e come from measurements of r

and r

– Ideal condition is same Q and e values

– Proceeds poorly if Q

and Q

are very different

– Tends toward alternating if Q’s are the same and

e’s are large but of opposite sign.

I+IV or II+III → alternating

I+III, II+IV and same → Statistical Copolymers

Χ

Χ

Copolymerization

Conclusions-radical copolymers

z

Co-polymers are important

– Properties depend on composition

z

In general, these materials are heterogeneous

z

Mayo equation allows calculation of composition knowing r

and r

z

Finemann Ross approach allows determination of r

and r

z

Alfrey – Price allows estimate of r

and r

We discussed A B type step growth polymers -ABABABA- If is the number of A molecules at the beginning of the polymerization and is the number if B molecules,

We define r, the stoichiometric imbalance as

What about step growth copolymers??

0

N

0

N

0 0

B A

N

r = N

DP is the number of monomer units divided by number of chains

⎥⎦⎤

⎢⎣⎡ + −

⎥⎦⎤

⎢⎣⎡ +

=

=

r p N

r r N

N DP N

A A r

1 2 2 1

1 2

0 0

Which luckily reduces to…

rp r

DP r

2 1 1

− +

= +

rp r

DP r

2 1 1

− +

= +

Note that if there is no stoichiometric imbalance, r =1 and we get…..

This is nice!!!

DP p

= − 1

1

When A is totally consumed (p =1) then….

r DP r

−

= +

1

1

rp r

DP r

2 1 1

− +

= + _{“A” is A-}

□-

□

B…..

A-□-A + B-□- B

B-□-B

A-□-B B-□-B

A-□-A + B-□- B

Equimolar

B’-□

Monofunctional

A-□-B B’-□

0 0

B A

N r = N

0 0

B A

N r = N

0 ' 0

0

2 _B

A

A

N N

r N

= +

0 ' 0

0

2 _B

A

A

N N

r N

= +

This illustrates the high precision required to achieve high molecular weights

!!!

DP

DP

r DP r

−

= +

1

1

Capping Trick

Often wise to use a capping agent than to use excess of one monomer

CH₂CH₂OH ⁺ CH₂CH₂O C O

CH₂CH₂O C O C

O

OH

CH₂CH₂O C O

Ph Ph

~

~ ~ ~

~ ~

“molecular weight stabilization”

Anionic polymerization

1914, Schlenk reacts Na with butadiene and styrene 1929, Ziegler proposes a mechanism

1952 Higginson, styrene, KNH₂ , kinetic study 1956 Szwarc, sodium naphthalene, Styrene,

living polymerization conception

60's, commercial products were available

90‘s, study on the living polymerization of polar monomers

History