Topic 3

Question 1

How do we access large DPs?

Answer 1

Need to get to high conversion to access large DPs (i.e. high MW polymers)

Question 2

What are the two types of reactions in step growth polymerisation?

Answer 2

Type 1: AB + AB –> ABAB. Type 2: AA + BB –> AABB (assume [A] = [B]).

Question 3

How does the reactivity of an acid depend on the DP of the polymer it is attached to in a step growth polymerisation?

Answer 3

It is independent of DP. However, the availability of the end group might change - as polymers get longer the accessibility of the end group might reduce.

Question 4

What does an end capper do?

Answer 4

Lowers MW

Question 5

What is a stoichiometric imbalance?

Answer 5

When [A]0 does not equal [B]0 so we use the extended carothers equation

Question 6

Compare hyperbranched and crosslinked materials

Answer 6

Hyperbranched - 1 path, 1 ‘A’ end group; crosslinked - many paths, many ‘A’ end groups

Question 7

Why use crosslinked materials?

Answer 7

Heat resistant; chemically inert; higher MW (so can access larger DPs). But - hard to process and insoluble.

Question 8

What is the gel point?

Answer 8

Point at which polymer crosslinks i.e. MW approaches infinity. Conversion at which gelation occurs

Question 9

What is favg?

Answer 9

Average functionality factor. f = no of functional units on multifunctional monomer

Question 10

How does favg affect conversion?

Answer 10

As favg increases, conversion at which gelation occurs decreases due to gel point equation. So DP vs conversion plot for step growth polymerisation moves to the left whilst keeping the same shape.

Question 11

How is the conversion of a step growth polymerisation related to the average functionality of the monomers in the system?

Answer 11

It is proportional to 1/favg

Question 12

Why does addition of a multifunctional monomer lead to a narrowing of the dispersity of the resultant polymer in a step growth polymerization?

Answer 12

It leads to fewer chains so less coupling

Question 13

Why is the assumption that the propagation rate is the same at all points during a step growth polymerisation a poor assumption?

Answer 13

Propagation depends on availability of the polymer end group. The availability of the polymer end group will change during the polymerisation

Question 14

True or false - in a step growth polymerisation the first 95% conversion takes the same time as the last 2-3%

Answer 14

True

Question 15

True or false - Carother’s and Stockmayer’s gelation theory assumes that there are no intramolecular reactions during gelation

Answer 15

True

Question 16

True or false - the addition of monomers with more functional units leads to gel formation at lower conversion

Answer 16

True

Question 17

True or false - in a step growth polymerisation if one monomer is in excess, it is this monomer which determines the DP of a step growth polymerisation

Answer 17

False - limiting monomer determines this