Polymers: linear and cross linked

What characteristic of alkene molecules allows them to form polymers?

• The presence of two carbon atoms joined together

• The presence of at least two hydrogen atoms

• The presence of a carbon-to-carbon double bond

• The presence of a single carbon-to-carbon bond

Answer explanation

The carbon-to-carbon double bond in an alkene molecule is broken and the electrons that are freed up are used to form a new bond to the next monomer.

Which one of the following is a natural polymer?

• Cellulose

• Polypropene

• Teflon

• Kevlar

Polymers can contain about how many carbon atoms linked together?

• 5000

• 500

• 50

• 5

Which of the following could represent the addition polymer formed from the following monomer?

• 
• 
• 
• 

Answer explanation

When the polymer is formed, the double bond becomes a single bond as electrons move to make new bonds with other monomers. The orientation of the monomers can vary as they attach to the chain.

What is an example of a natural condensation polymer?

• Cellulose

• 
  Polyethene

• PET

• Rubber

A piece of polymer was held over a heat source and, after a short while, it melted. From this it can be inferred that the polymer was

• 
  thermoplastic.

• thermosetting.

• 
  an elastomer.

• a copolymer.

In order to make a polymer more rigid, it is best to

• increase the length of the polymer chain.

• increase the amount of cross-linking between chains.

• increase the branching of the chains.

• reduce the temperature under which the polymer is formed.

Answer explanation

Thermosetting polymers are extensively cross-linked. The higher the amount of cross-linking, the more rigid the polymer produced.

Which of the polymer segments shown are from thermoplastic polymers?

• Polymer I only

• 
  Polymer II only

• Polymers I and III only

• Polymers II and IV only

Answer explanation

Covalent cross-links are represented in diagrams by solid lines. Thermoplastic polymers have no cross-linking.

Which of the polymer segments shown are from thermosetting polymers?

• I

• II

• III

• IV

Which of the following groups are all thermosetting polymers?

• Polythene, polyvinyl chloride, polytetrafluoroethylene

• Polypropylene, polyurethane, polystyrene

• Polyvinyl chloride, polystyrene, urea formaldehyde

• Urea formaldehyde, polyurethane, epoxy resin

Answer explanation

Urea formaldehyde, polyurethane, epoxy resin are thermosetting polymers that char rather than melt when heated.