Polymers 1 Flashcards
What is the oilgemer
A short polymer chain of fixed number of units (2-10)
T ypes of Solids
A- According to type of bond
1- atomic ; 1 bond btwn the atoms
Strong and hard bond with a high tm
2- moulcular bond ; 1 btwn the atoms of the moulcues and the 2nd btwn the molcules
2nd bond determins the matirial proprties
Weak and soft with low tm
B- According to arrangement of atoms
Cryistaline - metals- low energy
Amorphes - ceramics and moulcules - high energy
Molecular bond
2nd bond determins the matiral proprties so ts weaker than the atomic
Type of bond
ļ The polymer is a molecular solid with the following:
1- ineratomic
Along the backbone of the chin and the sides
2-inter molecular
Between te 2 polymar chains
3-Entanglement:
Millions of the polymer chains can intertwine leading to
entanglement, like the spaghetti structure.
Classification
Acoording to: The origin
1-natural
Dna-rna
Protiens
Polysachried
Polyisoperine
2-synthetic
Bakelite
Nylon
PMMA
Polyvinyl chloride
Classification
Acoording to: 3- Thermal
Behaviour
1- thermoplast
Reversible
Physical reaction
Soft and sensitive to the heat
Polymer chain bonded to eache other by 2nd bond
( impression compound)
2-thermostat
Irreversible
Chemical reaction
No rebond or remelt
Acrilic resin
The physical state of polymer at room temperature
is determined by:
When thhe tg of the poly tm is higher than te mouth tm then the polyemer is hard - plastic, resin-
When the tg of the tm of the poly is less than the mouth tm then the poly is soft - elastomers
PolymersPreparation
Polymerizatioon reaction
Reaction by which the monemrs chemacily bonded to form the polymer
Types of polymarizition reaction
1- condensition poly
2- addition poly; free radical - ring opening
Condensation Polymerization [step reaction]
Formition of the poly by Repeated elemenition of the by product
- stepwise reaction
-short chain
-slow reaction - dif speciec of monemers
Exampels? Condinstian selecon - polysulfied rubber impres matirial
Addition Polymerization
[Chain growth polymerization reaction]
2.a. Free radical
Activaition of monemrs one by one
Polymrizition wo eleminition of byproducs
- rapid reaction
-long chain - gaint molcules
-the mono and polymers have the same emprical formula
-better dimnitional stability
-needs unsaturated groub monomers with double bond
There are four stages in the addition polymerization chain
reaction
-induction
-propgation
-chain transfer
-terminition
induction
The initiator needs to be activated to produce the free radical
initiator( pynzoyl peroxide)
Activitors - light-heat-chemicals
Then the free radical will attack the double bond of the monemr and transfer it into a free radical
II- Propagation:
II- Propagation:
- Linear growth of molecules.
- Shifting of free radical to the end of the growing chain ā shrinkage.
ā Viscosity ā entrapment of some monomer ā residual monomer
(unreacted monomer inside the chain āfree monomerā).
Chain Transfer
The free radical transfer from one chain to another molcule and then anew free radical will be formed
Termination:
Although chain termination can result from chain transfer,
addition polymerization reactions are most often terminated
either by:
1- 2 polymer chain compinition
2- hydogen transfer
2.bRing Opening Polymerization
Chain elongation > reduce the shrinkage of polymer but not
elimination, e.g. Silorane.
Factors associated with polymerization
reactions
1- shrinkage
2- evoulation of heat
3-residual monomer
Heat evolution
This is related to the energy released from the breakage of
the interatomic bonds during polymerization reaction.
Residual monomer
ā¢ The polymerization is never complete,
this means that not all the monomer
units are bonded into a polymer.
ā¢ There will be always residual
monomer due to: Viscosity of the
material during polymerization.
Inhibition of Polymerization
Anysubstance that will react with the free radicals will Inhibit Polymerization reaction
The precentace of these substance will decrease the initiition and increase the terminition
Applications of polymers in dentistry:
Applications of polymers in dentistry:
ā¢Prosthodontics: denture bases and teeth, soft liners, custom trays, impression
materials, core buildup materials, temporary restoratives, cementing/luting
materials, and maxillofacial prostheses.
ā¢Operative Dentistry: dentin bonding agents, cavity fillings, resin and glass-
ionomer cements, pit and fissure sealants, splinting materials, and veneers.
ā¢Orthodontics: brackets, bracket bonding resins and cements, and spacers.
ā¢Endodontics: gutta-percha points, root canal sealants, and rubber dams.
ā¢Equipment: mixing bowls and spatulas, mouth guards (sports equipment), and
protective eyewear.
Clinical significance
1-Addition of inhibiter to the monomer will inhibit the premature polymerization which will increase the shell life
2- The polymerization should not be conducted in open air but in
oxygen deficient environment to avoid retardation of
polymerization reaction.
Dental examples;
- Avoid air thinning of the bonding agent
- Use of a matrix during curing of the composite restorative
material
3- Eugenol must not be placed in contact with any polymerizing
material (e.g. resin composite), to avoid retardation of polymerization
reaction.
