Polym. Chem, Part 2: Sec C

Question 1

3 main stages of chain growth polymerisation

Answer 1

• Initiation
• Propagation
• Termination

Question 2

Provide generic chemical equations that illustrate all 3 main stages of chain growth polymerisation

Answer 2

*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

Question 3

Provide mathematical expressions for each of the main stages of chain grown polymerization, and state any key assumptions.

Answer 3

• 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

Question 4

Define v

Answer 4

v = average number of monomers consumed for each radical that initiates a polymer chain.

Question 5

What is the meaning of chain transfer in polymer production ? Briefly explain the uses of chain transfer in polymer productions.

Answer 5

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)

Question 6

Explain the Trommsdoff-Norrish effect. How do you control the Trommsdoff-Norrish effect

Answer 6

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

Question 7

What are network polymers ?

Answer 7

Are 3D networks made from trifunctional monomers

Question 8

What are resole type resins and provide chemical equations that illustrate the synthesis of such resins

Answer 8

resins of phenol formaldehyde that are produced from alkaline/basic conditions

Question 9

What are novolac type resins and provide chemical equations that illustrate the synthesis of such resins

Answer 9

resins of phenol formaldehyde that are produced from acidic conditions.

Question 10

What is a chain transfer agent and why would you use one in chain growth polymerizations?

Answer 10

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

Question 11

list the typical types of monomers used in chain growth polymerization, and provide two examples of industrially important chain growth polymers

Answer 11

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

Question 12

List 3 different types of intiators that can be used to synthesise a chain growth(or an addition) polymer

Answer 12

Radical Initiator
Cationic
Anionic

Question 13

• What are elastomers and provide examples

* These polymers are viscoelastic. what does that mean ?

Answer 13

ELASTORMARS: These are polymers that are good insulators, withstand deformation and can easily be moulded into different shapes.

VISCOELASTIC:

• Have viscosity
• Have elasticity

Question 14

What is a crosslinked polymer

Answer 14

A polymer consisting of chains linked together by covalent or ionic bonds.