Polyethers & Polysulphides

Question 1

What is the base paste of a polyether made up of? (6)

Answer 1

• Polyether polymer (terminal ethylene- imine groups)
• Fillers
• Plasticisers (high and low viscosity)
• Pigments
• Flavourings
• Triglycerides

Question 2

What is the catalyst paste of a polyether made up of? (4)

Answer 2

• Initiator (cationic starter - Sulphonium tetraborate salt)
• Fillers
• Plasticisers
• Pigments

Question 3

What is the role of inorganic fillers in polyethers? (2)

Answer 3

• High rigidity of the impression

- Help maintain dimensional stability

Question 4

What is the role of plasticisers in polyethers?

Answer 4

Adjust the viscosity of the paste

Question 5

What is the role of triglycerides in polyethers?

Answer 5

Increase the intrinsic viscosity

Question 6

In polyethers how does the material set?

Answer 6

Cationic (addition) reaction via. ring opening

Question 7

Give some advantages of impregum (3)

Answer 7

• Good dimensional stability in air
• Quick setting compared to polysulphide and reliable
• Clean to handle and odourless

Question 8

What is the commercial name for polyethers?

Answer 8

Impregum

Question 9

What is the benefit of impregum penta soft over normal impregum? (3)

Answer 9

• Easier removal
• Improved taste
• Optimal convenience and handling

Question 10

Give some disadvantages of impregum (4)

Answer 10

• Very stiff material
• Tearing on withdrawal possible
• Permanet deformation possible
• Material swells on prolonged contact with water

Question 11

What is the base paste of a polysuphide made up of? (3)

Answer 11

• Polysulphide polymer (Thiokol LP-2; contain S-S linkages)
• Filler (eg ZnS/TiO2)
• Plasticiser (usually a phthalate ester)

Question 12

What is the catalyst paste of a polysulphie made up of? (5)

Answer 12

• Lead dioxide (PbO2) (cross-linking agent)
• Filler (as in base)
• Plasticiser (as in base)
• Sulphur (~1%)
• Stearic or oleic acid

Question 13

In a polysulphide rubber what does the base paste react with?

Via what reaction?

Answer 13

The base paste reacts with PbO2 in catalyst paste via. a condensation reaction

Question 14

What is the byproduct of the polysulphide condensation reaction?

Answer 14

Water

Question 15

What is an advantage of a polysulphide rubber?

Answer 15

It is the strongest of all the impression rubbers

Question 16

What are some disadvantages of a polysulphide rubber? (4)

Answer 16

• Poor dimensional stability as shrinkage on setting
• Slow setting
• Dirty to handle and has an unpleasant smell
• Elastic recovery is not as good as the silicone and polyether materials