DM.5 Flashcards
polymers and polymerisation
What are the following:
a) Homopolymer
b) Regular copolymer
c) Block Copolymer
a) (one monomer)
b) repeating pair or sequence of monomers
C) alternating segments of different polymer compositions,
What type of reaction forms copolymers?
condensation polymerization
What is formed by condensation polymerization?
copolymers
What type of reaction forms homopolymers?
addition polymerization
What is formed by addition polymerization?
homopolymers
How many products are there in an addition reaction?
1
How many products are there in an condensation reaction?
Condensation reactions system have a bi-product e.g. water, CO, CO2, H2.,
1) what are the distinctive reaction stages of addition polymerisation?
2) what is required for it to occur?
1) activation, initiation, propagation, termination
2) active species such as an ion or radical (molecule with a spare electron)
What properties is required of the free radicals we use:
- must be activated by something e.g. energy, , light
2. reasonable stable, can be stored for a certain amount of time
Why don’t we use heat to activate free radicals?
2) What do we do instead?
we would possible have to heat to 60 degrees.
2) Instead we use light. We can also use another chemical to activate with a benzene ring e.g. N, N dimethyl-p-toluidine
What type of bond to we break usually when activating a free radical?
ones with low bond enthalpy. O-O,
What safety issues are there with polymerisation:
heat produced,
monomers can be toxic when not in polymer form
what happens in the activation step of polymerisation?
free radical formed
What happens in the initiation step of polymerisation?
free radical reacts with monomer (added to it)
What happens in the propagation step of polymerisation?
monomer bonded to radical reacts with another monomer
What happens in the termination step of polymerisation?
monomer bonded to radical reacts with monomer bonded to radical, or radical with radical
What happens when you mix the monomers?
2) Why do we have to be careful no to over add initiator?
1) polymer is formed and viscocity increases. eventually reaction will terminate as no frequency of collisions decreases
2) initiator will react with itself
What sort of monomer forms cross-links when polymerised?
2) are polymers that are cross-linked the same as polymers that are not? (if made up of same monomer)
3) do we want linear or non-linear polymers in dentiistry?
1) di or tri-functional monomer
2) properties change
3) Linear polymers flow apart in lquid, like spaghetti in water. Therefore, liner polymers will soften and aren’t useful in the mouth. The solution joining the chains together.
1) Give an example of a bulking agent used in dentures:
2) what do bulkers do?
3) What properties does it give the material?
4) What would happen if too much was added?
1) Ethylene Glycol dimethacylate, is added to the bulk polymer (methy methacrylate) making up dentures,
2) act as cross-linkers to form a copolymer.
3) harder to deform
4) brittle.
What is Bis-GMA?
2) What is it used in?
3) what are its properties and what about it gives it this property?
1) bulking agent
2) Bis-GMA is used in composite filling materials,
3) viscous due to large size (it has aromatic rings)
naturally forms cross-links (mathymathacrylate group)
