Polymerization Flashcards
Why is the polymer molecular weight advised?
Polymers with a molecular weight less than 10^4 have poor thermal and mechanical properties
Polymers with a molecular weight higher than 10^7 are very difficult to process
Formula for the molecular weight of a polymer.
Molecular weight of repeating unit* degree of polymerization
Benefits of increasing the dp of a polymer?
It improves the tensile strength and wear resistance of the polymer.
What are the three methods of creating a polymer?
There are three ways polymerization reactions can occur:
1. Opening a double bond.
2. Opening a ring structure.
3. Replacing a functional group of a molecule with two functional groups
What are the three classification of polymerization reactions?
- Addition or chain growth polymerization
- Condensation or step-growth polymerization
- Co-polymerization
What is addition polymerization?
Addition polymerization is the process where unsaturated monomers containing double bonds (usually vinyl monomers of the ethylene family) react to create a polymer without the formation of any byproducts.
Before polymerization can occur an active site for polymerization must be present. List the ways this active site can be created.
- By thermal initiation.
- Use of initiators (free radical generators)
- Use of catalyst:
a. Typically this are peroxides or acids and require high temperature and pressure to occur.
b. The exemption is the Ziggler nattler method which uses transition metals and doesn’t require high temperature or pressure. This is also known as coordination polymerization - Ionic polymerization
Significance of coordination polymerization
- Can produce isotactic polymers unlike traditional methods which produce atactic polymers
- Produces linear polymers.
- Allows selective synthesis of polymers
Differences between high pressure free radical processes and low pressure free radical processes?
- High pressure systems require tabular or autoclave reactors but low pressure requires fluidized bed or stirred bed reactors.
- High pressure systems require high pressures of around 3400 atm compared to 20 atm.
- High pressure systems require temperatures of around 300 Celsius compared to 80 -110 Celsius.
- High pressure systems are higher cost.
- High pressure systems require more energy.
- High pressure systems produce only Low Density Polymers while low pressure systems can create LDP and HDP
- High pressure systems are homomonomers while low pressure systems are co-polymers.
What is condensation polymerization?
Condensation polymerization refers to the polymerization that occurs between monomers with bi or poly functional groups. This reaction leads to the formation of some byproducts like HCl, H2O hence the name condensation.
The monomers must have at least two functional groups else polymerization won’t occur.
Important types of functional groups formed?
OH + COOH = Polyesters
NH2 + COOH = Polyamides
OH + OCN = Polyurethanes
Types of polymers based on number of functional groups.
Di + Di = linear polymers
Di + Tri = possibilty of cross linked, branched or network polymers
Tri + Tri = network polymers
Di/Tri + Mono= nothing, doesn’t work
Effect of medium on condensation polymerization?
The pH of the medium can influence the functional behavior of the monomers.
Eg:
In the presence of a basic medium phenol behaves like a bifunctional monomer but in acidic medium it behaves like a trifunctional monomer
Urea in acidic, neutral and basic behaves like a trifunctional, monofunctional and bifunctional respectively.
Differences between addition and condensation polymerization?
1.Addition polymerization doesn’t leave byproducts.
2. Addition polymerization requires monomers with double bonds but condensation requires monomers with 2 or more reactive functional groups
3. Addition polymerization forms homopolymers but condensation polymerization forms heteropolymers.
4. Addition polymerization has 100% atom efficiency but condensation polymerization has less than 100% atom efficiency.
What are biopolymers?
This are polymers that are biodegradable.
