PMMA

Question 1

types of PMMA

Answer 1

• self-curing (cold-curing)

- heat-curing

Question 2

polymer

Answer 2

macromolecule formed by small repeating units called mers

Question 3

PMMA

Answer 3

many methyl methacrylate units linked together

Question 4

copolymerization

Answer 4

two or more different monomers polymerized at the same time

Question 5

copolymer

Answer 5

dimer: polymer with 2 different mers
terpolymer: polymer with 3 different mers

Question 6

powder PMMA

Answer 6

• pre-polymerized beads of PMMA
• initiator: benzoyl peroxide
• plasticizer: dibutyl phthalate (less brittle)
• inorganic particles (hardness)
• organic pigments and dyes

Question 7

liquid PMMA

Answer 7

• monomer: MMA
• inhibitor: hydroquinone
• cross linking agent: glycol dimethacrylate
• activator (cold): dimethyl-p-toluidine

Question 8

initiation with benzoyl peroxide

Answer 8

• exothermic polymerization

- double bond is reduced to single bond

Question 9

cold-cure liquid

Answer 9

-activator: dimethyl-p-toluidine

Question 10

heat-cure liquid

Answer 10

-activator: heat (>60 degC)

Question 11

what happens when you add activator to PMMA and benzoyl peroxide

Answer 11

benzoyl peroxide is activated

Question 12

what does activated benzoyl peroxide do to MMA

Answer 12

MMA is activated and polymerizes

Question 13

degree of polymerization

Answer 13

number of mers in polymer molecule

Question 14

polymers can vary in

Answer 14

degree of polymerization and molecular weight

Question 15

function of inhibitors

Answer 15

1. inhabitation of polmerization to increase storage stability
2. retardation of polymerization to adjust working time

Question 16

impurities in the monomer can cause

Answer 16

premature termination or retardation of polymerization

-react with activator initiator OR growing chain (affect initiation or propagation)

Question 17

effect of oxygen on polymerization

Answer 17

• reacts with free radicals, causing:
  1. decrease in rxn velocity
  2. decrease in deg of polymerization

Question 18

how to prevent oxygen effects

Answer 18

• cold-cure is under water

- trays that are cured in air have sticky surfaces

Question 19

polymerization shrinkage caused by

Answer 19

• van der waals volume reduction

- free volume reduction

Question 20

8 properties of PMMA

Answer 20

• colourless
• any shade
• radiolucent
• chemically stable
• knoop hardness # : 15 to 18
• Tg: 125 deg C
• absorb water
• low thermal conductivity

Question 21

cons of adding barium salts to PMMA

Answer 21

• reduced strength
• reduced transluency and appearance
• expensive

Question 22

5 properties of MMA

Answer 22

• transparent liquid
• dissolves PMMA particles
• Tg: -45deg C
• excellent organic solvent
• not chemically stable