Polymers

Question 1

Condensation

Answer 1

During condensation a small molecule like water is condensed out by the chemical reaction. As the chain grows the mixture becomes less mobile and inhibits further reaction. In many cases (but not nylon) the chains are cut short.

Question 2

Addition polymerisation

Answer 2

Rearrangement of bonding within the polymer units. There must be at least one double bond in the monomer, and the double bond is broken by the addition of an initiator, usually a free radical.

Question 3

Free radical

Answer 3

A species with an unpaired electron, which makes it very reactive.

Question 4

Free radical polymerisation

Answer 4

The initiator needs to be activated by heat, UV light or another chemical. Other methods of initiation can be used, such as cations or anions. The free radicals react with monomers until termination occurs via free radical combination, transfer or disproportionate reaction.

Question 5

Branching

Answer 5

A chain with a free radical may attach itself to the middle of another chain- one of the disadvantages of addition polymerisation. Can use ionic initiators to control branching.