3 main stages of chain growth polymerisation
- Initiation
- Propagation
- Termination
Provide generic chemical equations that illustrate all 3 main stages of chain growth polymerisation
*Initiation:
I —(Kd)—> 2R•
R• + M1 —(Ki)–> M1•
*Propagation:
M1• + M —(Kp)—> M2•
M2• + M —(Kp)—> M3•
M3• + M —(Kp)—> M4•
*Termination:
Cmbntn: My• + Mx• –(Ktc)–> M(y+x)
Dsprprtnatn: My• + Mx• –(Ktd)–> My + Mx
Provide mathematical expressions for each of the main stages of chain grown polymerization, and state any key assumptions.
- INITIATION: Rate of initiation(Ri) = 2fKd[I]
- 1st step is rate determining step
- 1st step is a unimolecular decomposition process
- Only a fraction(f) will react with monomers
- PROPAGATION: Rate of propagation(Rp) = Kp[M][M•]
- The reactivity of the radicals is independent of the chain length, THUS EACH STEP HAS THE SAME RATE CONSTANT
- The propagation step is a bimolecular reaction
- TERMINATION(Rt): Rate of termination(Rt) = 2Kt[M•]^2
- Can also occur via a mix of combination and disproportionation
- Termination processes are bimolecular, THUS 2ND ORDER RATE CONSTANTS
- Ktc and Ktd are additive
Define v
v = average number of monomers consumed for each radical that initiates a polymer chain.
What is the meaning of chain transfer in polymer production ? Briefly explain the uses of chain transfer in polymer productions.
Chain transfer is a chain breaking reaction leading to a decrease in the size of the propagating polymer. The active center is transferred from a growing chain to a different species.
Intramolecular reaction/backbiting(short chain branches) Intermolecular reaction(Long chain branches)
Explain the Trommsdoff-Norrish effect. How do you control the Trommsdoff-Norrish effect
Explanation:
- Sharp increase in P, as conversion of monomer increases
- Viscosity increase, mobility of polymer chain radical decreases
How to prevent:
- Viscosity can be kept low by addition of solvent
- Adding chain transfer agent
What are network polymers ?
Are 3D networks made from trifunctional monomers
What are resole type resins and provide chemical equations that illustrate the synthesis of such resins
resins of phenol formaldehyde that are produced from alkaline/basic conditions
What are novolac type resins and provide chemical equations that illustrate the synthesis of such resins
resins of phenol formaldehyde that are produced from acidic conditions.
What is a chain transfer agent and why would you use one in chain growth polymerizations?
It is a chain breaking reaction that results in a decrease of a polygating polymer chain. The active centre is transfered to another species.
it can be useful in:
- controlling the degree of polymerization
- the polydispersity of the polymer
- and molecular weight
list the typical types of monomers used in chain growth polymerization, and provide two examples of industrially important chain growth polymers
Molecules with a vinyl group or c=c within the structure
2 industrially important chain growth polymers: (any 2 of the following) *Polyethylene *Poly(vinyl chloride) *Polystyrene *Polypropylene
List 3 different types of intiators that can be used to synthesise a chain growth(or an addition) polymer
Radical Initiator
Cationic
Anionic
- What are elastomers and provide examples
* These polymers are viscoelastic. what does that mean ?
ELASTORMARS: These are polymers that are good insulators, withstand deformation and can easily be moulded into different shapes.
VISCOELASTIC:
- Have viscosity
- Have elasticity
What is a crosslinked polymer
A polymer consisting of chains linked together by covalent or ionic bonds.
