Test 2

Question 1

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

Answer 1

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 2

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

Answer 2

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 3

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

Answer 3

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 4

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

Answer 4

Radical Initiator
Cationic
Anionic

Question 5

For the following industrially important polymers, provide a general overview on the properties and uses, and the chemical structure of the repeat unit:

a) Polycarbonates
b) Polyurethenes

Answer 5

POLYCARBONATES

1. Properties: relatively tough, transparent
2. Uses: used as an engineering plastic
3. Chemical structure

1. Properties: made with alcohols with two or more hydroxyl groups(-OH) per molecule and isocyanates with more than one reactive isocyanate group per molecule(-NCO)
2. Uses: foam, shoes, automotive parts etc.
3. Chemical structure:

Question 6

List the different types of industrial scale reactors and give the importance of each reactor type

Answer 6

1. BATCH REACTOR: Reactors in which no flow of mass across the reactor boundaries, once the reactants have been charged.
   -ADV: all components react for the same length of time
   DISADV:: stop-start operation wastes time
2. TUBULAR REACTOR: Consist of a pipe or tube in which reactants are pumped
   - ADV: can continuously operate for extended periods of time
   - DISADV:: reactor temp. difficult to control
3. CONTINUOUS STIRRED TANK REACTOR: are open systems which allow materials to enter or exit the system
   - ADV: cheap to construct
   - DISADV: conversion of reactant to product per volume of reactor is small compared to other flow reactors