Polym. Chem, Part 2: Sec C Flashcards Preview

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Flashcards in Polym. Chem, Part 2: Sec C Deck (14):
1

3 main stages of chain growth polymerisation

*Initiation
*Propagation
*Termination

2

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

3

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

4

Define v

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

5

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)

6

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

7

What are network polymers ?

Are 3D networks made from trifunctional monomers

8

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

9

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.

10

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

11

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

12

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

Radical Initiator
Cationic
Anionic

13

*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

14

What is a crosslinked polymer

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