Polymer Synthesis

Question 1

What are the 2 main techniques used to synthesis polymers?

Answer 1

1. Chain growth polymerization (addition) (addition of monomers to a growing chain)
2. step-growth polymerization (condensation) (grow multiple chains at the same time and append them together)

Question 2

How do the speeds of the 2 methods of polymer synthesis compare?

Answer 2

• chain growth starts rapidly before plateauing while step growth starts slower but grows exponentially (both reaching roughly the same time to reach high molecular weights)

Question 3

What is Step-growth polymerization

Answer 3

• condensation reactions create chains (both ends must be able to condensate - bifunctional reactants) and water
• can be done with the addition of a single monomer group or with multiple polymers (polyaddition)
• polyaddition does not product any byproducts (same with self condensation and self addition - product already ready to react without creating water as a byproduct)

Question 4

Kinetics Overview (reaction rate)

Answer 4

• 2 different constants - diffusion constant and reaction constant
• reaction constant is dominant and constant past a certain chain length (n=8) since the increased diffusion is counteracted by the intermolecular forces that hold the particles together longer

Question 5

When is kinetics not ideal?

Answer 5

• if there are side reactions - they compete for chain ends
• if impurities or byproducts are produced as they can be bad for reactants

Question 6

What is Chain growth?

Answer 6

The addition of monomers to an activated chain
- propagates very quickly to gain high molecular weight very quickly

• most commonly done by producing a single highly reactive chain end from an active center
  **Monomers do not react with monomers

Question 7

What are the different classes of initiators for chain growth?

Answer 7

1. radicals
2. ionic groups
3. coordination
4. Living (gives more control to create specific polymers)

**3 and 4 are slower than 1 and 2

Question 8

What is Radical chain growth?

Answer 8

Performed in 3 steps:
1. Initiation - formation of a radical
2. Propagation - addition of monomer units to active chain (propagation technique dictates the tacticity of the created polymer)
3. Termination - removal of radical (either by reacting 2 chains together (combination) or by breaking 2 chains apart - 1 keeps the radical (disproportion))

*Rate of propagation&raquo_space; rate of initiation
**very fast and very exothermic (so need to worry about heat management)

Question 9

What is Ionic chain growth?

Answer 9

• has an ionic active site (these are sensitive to temp, solvent, and impurities)
• ionic active site can be cationic or anionic
• termination is more difficult than radical - use either dilution to separate chains or cool it down (but mostly just wait until everything reacts)
• easier to get side reactions in ionic chain growth

Question 10

What is the equal reactivity hypothesis and when is it not valid?

Answer 10

Reactivity of larger molecules does not depend on the size of molecules for n>8 as the time close together counteracts the longer diffusion time

This does not apply when side reactions occur or byproducts are created or impurities are present

Question 11

What is coordination Polymerization?

Answer 11

• common in olefins
• good for controlling tacticity
• inserts between initiator complex and next monomer unit
• gives high degree of stereoregularity (tacticity is controlled)

Question 12

What is Controlled Radical Polymerization?

Answer 12

• Living reaction
• can reversibly terminate radical propogation
• 3 widely used methods:
  – SFRP
  – ATRP
  – RAFT

*chain growth is reversible, reaction is slower (more linear than the other 2)

Question 13

Step Growth Example
- 90% of monomer consumed
What is the probability of finding a chain 30 units in length?
What is the probability of finding chains 60 units in length?

Answer 13

a) wx = 0.014

b) wx=0.0012