Polymerization Flashcards
Polymers are the _________ because their __________ is the ______ rather than a ________.
It is held together by _________.
most diverse class of materials
unit structure is the molecule rather than a crystal lattie
Covalent Bonds
Not all monomer reacts. What happens ?
Residual monomer is trapped in the polymer
What are the 3 ways to trigger polymerization?
Heat Cure
Chemical Cure
Light Cure
High degrees of polymerization leads to ________ and less ___________.
Is this good or bad?
more rigid, less soluble
GOOD
High degree of polymerization have ______ long polymer chains.
FEWER
What are the three chemical stages of bonding?
- Initiation by activation of monomer
- Propogation by chain growth
- Termination by reaction completion
What is addition polymerization?
Are there by-products?
Free radical (highly reactive molecule with FREE electron) is formed.
These are initiators.
NO co-generation of by-products.
What are advantages of addition polymerization?
Preferred Clinically
No risk of leaching of by-product intraorally
Prevents increase shrinkage
Toxic Reactions to the patient
What is crosslinking?
Link between polymer chains by adding cross-linking agent.
Amount of agent controls final properties.
What can the amount of cross-linking agents control?
Melting temp
Strength
Flexibility
Increased wear resistance
Degradation from Solvents such as alcohol
What are copolymers?
Two or more different types of monomers in polymer network
What are homopolymers?
Polymer is made of one monomer.
What are fillers?
Solid particles that change their optical or physical properties.
Ex. Adding substance to increase resistance
What are plasticizers?
Modify interactions between polymer strands.
Liquid becomes rubber
Fillers and plasticizers are _____________ to the polymer network. They can two do things. What are they?
Chemically linked
Increase Wear Resistance
Decrease Shrinkage
Dentures and fake teeth are made of _______.
PMMA
What is the Glass Transition Temperature?
What two thinks are decreased at this temperature?
Temperature at which a significant loss of modulus or STIFFNESS occurs.
A significant loss of volume occurs.
What property changes at the Glass Transition Temperature?
Chemical or Mechanical?
Mechanical
Thermoplastic polymers have ______ and _____ structures made of ___________ bonded together ___________ which makes them easy to _______.
They ______ when heated and ____ when cooled. This process is ________ and can be ______.
The heating and cooling process __________ a significant change on the polymer properties.
linear and branched , long main chain of carbon atoms bonded together COVALENTLY.
Easy to fabricate
soften/harden - reversible and can be repeated
does NOT HAVE
What are 3 examples of thermoplastics?
Polystyrene
PMMAcrylate
PVAcryilic
Thermoplastics can always be remelted back to ________ unlike ________ which remains in a ______.
liquid
thermoset; permanent solid state
Thermoset polymers require _______ to permanently set the ________.
They are formed into shape by ______________.
Once hardened, the structure will _________ upon heating
If heated at a high temperature, _______
heat, plastic
temporarily disabling the cross linking
not soften
degraded or decomposed
Thermoset polymers are _____ and _____ than thermoplastics.
Harder and stronger
What are 3 examples of thermosets?
Silicones
X-linked PMMA
Polyisoprene
