Addition silicones (polyvinyl siloxane) Flashcards Preview

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Flashcards in Addition silicones (polyvinyl siloxane) Deck (6)
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1
Q

base paste

A
  • polyethyl hydrogen siloxane
  • other siloxane prepolymers
  • fillers to give bulk and viscosity
2
Q

accelerator paste

A
  • divinyl polysiloxane
  • inert oils and fillers(forms bulk of paste)
  • platinum salt (chloroplatinic acid)
  • palladium or hydrogen absorber
  • retarders
  • fillers
3
Q

setting rxn

A
  • addition polymerization
  • vinyl groups of base paste react w/ silane groups of accelerator paste and cross-linking occurs
  • if in improper proportion, H gas may evolve during setting rxn
  • Palladium is added to absorb H to prevent dimensional change
  • time: 5-9 min
  • mix: 45 sec
4
Q

other characteristics

A
  • excellent surface detail reproduction
  • high dimensional stability among elastomers
  • lowest curing shrinkage-0.17%
  • good tear strength 3000 gm/cm
  • extremely hydrophobic
  • low flexibility
  • electroplated w/ copper and silver
  • shelf life 1-2 years
5
Q

advantages

A
  • short setting time
  • adequate tear strength
  • extremely high accuracy
  • minimal distortion on removal
  • dimensionally stable even after 1 week
  • if hydrophilic, good w/ gypsum
6
Q

disadvantages

A
  • may cause dimensional change
  • hydrophobic
  • expensive