Polyethers & Polysulphides Flashcards
What is the base paste of a polyether made up of? (6)
- Polyether polymer (terminal ethylene- imine groups)
- Fillers
- Plasticisers (high and low viscosity)
- Pigments
- Flavourings
- Triglycerides
What is the catalyst paste of a polyether made up of? (4)
- Initiator (cationic starter - Sulphonium tetraborate salt)
- Fillers
- Plasticisers
- Pigments
What is the role of inorganic fillers in polyethers? (2)
- High rigidity of the impression
- Help maintain dimensional stability
What is the role of plasticisers in polyethers?
Adjust the viscosity of the paste
What is the role of triglycerides in polyethers?
Increase the intrinsic viscosity
In polyethers how does the material set?
Cationic (addition) reaction via. ring opening
Give some advantages of impregum (3)
- Good dimensional stability in air
- Quick setting compared to polysulphide and reliable
- Clean to handle and odourless
What is the commercial name for polyethers?
Impregum
What is the benefit of impregum penta soft over normal impregum? (3)
- Easier removal
- Improved taste
- Optimal convenience and handling
Give some disadvantages of impregum (4)
- Very stiff material
- Tearing on withdrawal possible
- Permanet deformation possible
- Material swells on prolonged contact with water
What is the base paste of a polysuphide made up of? (3)
- Polysulphide polymer (Thiokol LP-2; contain S-S linkages)
- Filler (eg ZnS/TiO2)
- Plasticiser (usually a phthalate ester)
What is the catalyst paste of a polysulphie made up of? (5)
- Lead dioxide (PbO2) (cross-linking agent)
- Filler (as in base)
- Plasticiser (as in base)
- Sulphur (~1%)
- Stearic or oleic acid
In a polysulphide rubber what does the base paste react with?
Via what reaction?
The base paste reacts with PbO2 in catalyst paste via. a condensation reaction
What is the byproduct of the polysulphide condensation reaction?
Water
What is an advantage of a polysulphide rubber?
It is the strongest of all the impression rubbers
