PMMA Flashcards
types of PMMA
- self-curing (cold-curing)
- heat-curing
polymer
macromolecule formed by small repeating units called mers
PMMA
many methyl methacrylate units linked together
copolymerization
two or more different monomers polymerized at the same time
copolymer
dimer: polymer with 2 different mers
terpolymer: polymer with 3 different mers
powder PMMA
- pre-polymerized beads of PMMA
- initiator: benzoyl peroxide
- plasticizer: dibutyl phthalate (less brittle)
- inorganic particles (hardness)
- organic pigments and dyes
liquid PMMA
- monomer: MMA
- inhibitor: hydroquinone
- cross linking agent: glycol dimethacrylate
- activator (cold): dimethyl-p-toluidine
initiation with benzoyl peroxide
- exothermic polymerization
- double bond is reduced to single bond
cold-cure liquid
-activator: dimethyl-p-toluidine
heat-cure liquid
-activator: heat (>60 degC)
what happens when you add activator to PMMA and benzoyl peroxide
benzoyl peroxide is activated
what does activated benzoyl peroxide do to MMA
MMA is activated and polymerizes
degree of polymerization
number of mers in polymer molecule
polymers can vary in
degree of polymerization and molecular weight
function of inhibitors
- inhabitation of polmerization to increase storage stability
- retardation of polymerization to adjust working time
impurities in the monomer can cause
premature termination or retardation of polymerization
-react with activator initiator OR growing chain (affect initiation or propagation)
effect of oxygen on polymerization
- reacts with free radicals, causing:
1. decrease in rxn velocity
2. decrease in deg of polymerization
how to prevent oxygen effects
- cold-cure is under water
- trays that are cured in air have sticky surfaces
polymerization shrinkage caused by
- van der waals volume reduction
- free volume reduction
8 properties of PMMA
- colourless
- any shade
- radiolucent
- chemically stable
- knoop hardness # : 15 to 18
- Tg: 125 deg C
- absorb water
- low thermal conductivity
cons of adding barium salts to PMMA
- reduced strength
- reduced transluency and appearance
- expensive
5 properties of MMA
- transparent liquid
- dissolves PMMA particles
- Tg: -45deg C
- excellent organic solvent
- not chemically stable
