dental material

1. POLYMER

2. 1)
2)
3)
4)
polymers
Monomer
Classification of polymers
Preparation of polymers
a) types of polymerization
b) inhibition of polymerization
c) factors affecting properties of polymers
d) physical state of polymers
e) stress- strain behavior of polymer

3. Polymers :
Are long chain molecules consisting of many
repeating units.
Monomer :
Is the smallest repeating unit in the polymer chain
e.g. ethylene monomer.

4. Classification of polymers
1)
2)
3)
According to the basis of their origin.
According to the basis of structural or spatial
configuration.
According to the basis of their thermal behavior.

5. 1. according to the basis of their origin: a)
natural polymers. *
proteins ( polyamide of polypeptide ). *
polyisoprenes, e.g. rubber & gutta percha. *
polysaccharide, e.g. starch,cellulose,agar,alignate *
polynucleic acids, such as DNA and RNA b)
synthetic polymers. Are
produce industrially or laboratory by chemical
reactions .
Dental examples: *
acrylic resin. *
elastomeric.

6. *
*
2. According to structural or spatial configuration *
linear
branched
Cross - linked polymer

7. *
*
*
*
*
*
*
3. According to thermal behavior :
a) thermoplastic resin
shaped by heat and after cooling they maintain their
shape.
Secondary bonds
Mechanical properties sensitive to heat
Dissolve in organic solvents
b) thermosetting polymers
permanent shape and set by a chemical reaction.
Cannot remelted and reformed into another shape.
Primary covalent bonds

8. Preparation of polymers
1.
2.
3.
4.
5.
Type of polymerization.
Inhibition of polymerization.
Factors affecting properties of polymer.
Physical state of polymers.
Stress - strain behavior of polymers.

9. I. Type of Polymerisation
The conversion of monomer
molecules into poly- mers may
proceed by either an addition reaction
or a condensation reaction

10. Addition
polymerisation
An addition reaction simply involves the joining together
of two molecules to form a third, larger molecules
without by products.
For example, ethylene reacts with bromine under the
correct conditions to form dibromoethane, as follows
CH2 =CH2 +Br2
→CH2Br−CH2Br

11. 1.
Type of addition polymerization :
Free radical mechanism.
2. Ring opening ( ionic and cationic reaction )

12. The polymerisation processes follow a well-
documented pattern which consists of four main
stages – activation, initiation, propagation and
termination
Activatio
n
thermal activation (heat), chemical activators or
radiation

13. Initiation
The polymerisation reaction is initiated when
the radical, formed on activation, reacts with a
monomer molecule.
Propagation
Following initiation, the new free radical is
capable of reacting with further monomer
molecules

14. Terminatio
n
It is possible for the propagation reaction to
continue until the supply of monomer molecules
is exhausted. In practice however, other reactions,
which may result in the termination of a polymer
chain, compete with the propagation reaction.
These reactions produce dead polymer chains
which are not capable of further additions

16. 1.
2.
3.
*
1.
2.
e.g.
Ethylene imine group in poly ether rubber
impression material .
Epoxy resin.
Siloranes.
The monomers are rings and the reactive
material ring open.
advantages:
Less polymerization shrinkage
Less heat evolution
Ring opening

18. Condensation
polymerisation
A condensation reaction involves two
molecules reacting together to form a third, low
molecule with the production of a byproduct
which is nor- mally a small molecule such as
water.

19. example
organic acid and an alcohol react together to form
an ester with the evolution of water. This reaction
may be illus- trated by the reaction between acetic
acid and ethyl alcohol to form ethyl acetate
CH3CO2H + C2H5OH → CH3CO2C2H5
+ H2O
In dentistry polysulphide rubber impression material ,
water and lead sulfide are by products of this reaction.

20. A simple generalized reaction sequence
for condensation polymerisation for two
monomers, X − M1 − X and Y − M2 − Y,
with reactive groups X and Y can be
written as follows:
X−M1 −X+Y−M2 −Y→ X−M1 −M2 −Y+XY
X−M1 −M2 −Y+X−M1 −X→ X−M1 −M2
−M1 −X+XY
X − M1 − M2 − M1 − X + Y − M2 − Y → X −
M1 − M2 − M1 − M2 − Y + XY etc.

21. II. Inhibition of polymerization
Can be inhibited by the presence of any material that we'll react with a
free radical.
* lead to :
1. Decrease rate of initiation
2. Increase rate of termination
e.g. Small amount of hydroquinone added to methyl methacrylate to
prolonged shelf life.
eugenol or oxygen inhibition polymerization .

22. 1.
2.
3.
4.
5.
6.
7.
8.
9.
Molecular weight and degree of
conversion.
Cross - linking.
Co - polymerization.
Plasticizers.
Spatial structure.
Polymer crystallinity .
Rate of loading.
Temperature.
Addition of filler.
III. Factor affecting properties of polymer

23. 1. Molecular weight and degree of conversation :-
Degree of polymerization (DP): M.W of a polymer
M.W of a mer
M.W ( molecular wight )
* Effect on properties :-
1. Large M.W are strong and more resistance to thermal and
mechanical stresses.
2. Growth of the chains (faster).

24. Chemical compound with two double bonds per molecule can act as a
cross- linking agent.
* Effect of cross - linking :-
1. Increase the strength , hardness, rigidity .
2. Decrease water sorption .
3. Extensive cross-linking lead to brittleness material.
2. Cross - linking

25. Containing two or more different type
of monomeric unite.
3. Co - polymerization
*Effect of co - polymerization :-
Block and graft polymers often improved impact strength.

26. a. External plasticizers: it is penetrates between the polymer chains.
b. Internal plasticizers : it is part of the polymer main chain.
* Effect of plasticizers :
1. Reduce softening or fusion temperatures.
2. Reduce the strength and hardness
N.B :- Glass transition temperature ( Tg )
Is the temperature at which polymer starts to soften, below Tg polymer
very rigid, hard, glass . Above Tg polymer viscous, soft, rubber.
4. Plasticizers

27. 5. Spatial structure :
Cross - linking flow at higher TP, lower water sorption, stronger, rigid,
than linear or branched.
6. Polymer crystallinity :
Crystalline polymer have higher density, stronger, and more resistant to
dissolution and softening by heat.
7. Rate of loading :
Slow rate of loading they ductility, high rate of loading they brittle
8. Temperature :
They soften are the heat near glass transition temperature.
9. Addition of fillers :
To improve the properties of material e.g. Composite restorative
materials.

28. IV. Physical state of polymers
1. Hard amorphous structure .
2. Hard partially crystalline structure.
3. Rubbers consist
4. Fibers e.g. Nylon.

29. V. Stress - strain behaviour of polymers
1.
2.
3.
Brittle polymer.
Plastic polymer.
Elastomers.

30. Thank you