What is the composition (base and accelerator pastes) of polyether?
Base paste:
- Low MW polyether with azridine rings
- Colloidal silica
- Cross-linking agent: Glycolether phthalate
- Triglycerides
Accelerator paste:
- Catalyst: Dichlorobenzene sulfonate
- Colloidal silica
- Cross-linking agent: Glycolether phthalate
What is the composition (base and accelerator pastes) of polysulfide?
Base paste:
- Polysulfide polymer
- Titanium oxide, zinc
- Sulfate, silica, copper carbonate
Accelerator paste:
- Lead oxide
- Sulfur
- Dibutyl phthalate
- Other additives: Magnesium stearate, deoderants, oxidising agents
What is the composition (base and accelerator pastes) of CPS?
Base paste:
- Silicone polymer
- Colloidal silica
Accelerator paste:
- Alkyl silicate
- Stannous octoate
What is the composition (base and accelerator pastes) of APS?
Base paste:
- Low MW silicone with terminal silane hydrogen
- Reinforcing filler
Accelerator paste:
- Low MW polymer with vinyl terminal groups
- Reinforcing filler
- Catalyst: Chloroplatinic acid
- Palladium black
Which is the only elastomeric impression material that is hydrophilic? (polysulfide, CPS, APS, polyether?)
Polyether
What are the respective setting times of polyether, CPS, APS and polysulfide?
Polyether: 3-6min
APS: 3-7min
CPS: 6-10min
Polysulfide: 10-16min
What is the setting reaction of polyether?
Polyether sets by an exothermic, addition polymerisation reaction.
Dichlorobenzene sulfonate in the accelerator paste catalyses the reaction by opening up the azridine rings in polyether. Cross-linking occurs between aromatic alkyl sulfonate and azridine rings.
What is the setting reaction of polysulfide?
Polysulfide sets by an exothermic, condensation polymerisation reaction. Condensation occurs between -SH groups in polysulfide polymer and lead oxide and sulfur, to produce disulfide links and water as a by product.
The reaction occurs in 2 steps.
- Chain lengthening confers viscosity to the set material
- Cross-linking confers elasticity to the set material
What is the setting reaction of CPS?
CPS sets by an exothermic, condensation polymerisation reaction. Condensation between terminal groups of silicone polymer and alkyl silicate in the presence of stannous octoate to form a 3D network. Ethyl alcohol is formed as a by-product, which evaporates and causes shrinkage to the material.
What is the setting reaction of APS?
APS sets by addition polymerisation. Cross-linking occurs between the terminal silane hydrogen groups and vinyl double bonds. If -OH groups are present, a secondary reaction occurs producing hydrogen gas.
