Polymers 1 Flashcards

1
Q

What is the oilgemer

A

A short polymer chain of fixed number of units (2-10)

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2
Q

T ypes of Solids
A- According to type of bond

A

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

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3
Q

B- According to arrangement of atoms

A

Cryistaline - metals- low energy
Amorphes - ceramics and moulcules - high energy

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4
Q

Molecular bond

A

2nd bond determins the matiral proprties so ts weaker than the atomic

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5
Q

Type of bond
 The polymer is a molecular solid with the following:

A

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.

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6
Q

Classification
Acoording to: The origin

A

1-natural
Dna-rna
Protiens
Polysachried
Polyisoperine

2-synthetic
Bakelite
Nylon
PMMA
Polyvinyl chloride

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7
Q

Classification
Acoording to: 3- Thermal
Behaviour

A

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

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8
Q

The physical state of polymer at room temperature
is determined by:

A

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

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9
Q

PolymersPreparation
Polymerizatioon reaction

A

Reaction by which the monemrs chemacily bonded to form the polymer

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10
Q

Types of polymarizition reaction

A

1- condensition poly
2- addition poly; free radical - ring opening

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11
Q

Condensation Polymerization [step reaction]

A

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

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12
Q

Addition Polymerization
[Chain growth polymerization reaction]
2.a. Free radical

A

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
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13
Q

There are four stages in the addition polymerization chain
reaction

A

-induction
-propgation
-chain transfer
-terminition

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14
Q

induction

A

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

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15
Q

II- Propagation:

A

II- Propagation:
- Linear growth of molecules.
- Shifting of free radical to the end of the growing chain → shrinkage.
↑ Viscosity → entrapment of some monomer → residual monomer
(unreacted monomer inside the chain ”free monomer”).

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16
Q

Chain Transfer

A

The free radical transfer from one chain to another molcule and then anew free radical will be formed

17
Q

Termination:

A

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

18
Q

2.bRing Opening Polymerization

A

Chain elongation > reduce the shrinkage of polymer but not
elimination, e.g. Silorane.

19
Q

Factors associated with polymerization
reactions

A

1- shrinkage
2- evoulation of heat
3-residual monomer

20
Q

Heat evolution

A

This is related to the energy released from the breakage of
the interatomic bonds during polymerization reaction.

21
Q

Residual monomer

A

• The polymerization is never complete,
this means that not all the monomer
units are bonded into a polymer.
• There will be always residual
monomer due to: Viscosity of the
material during polymerization.

22
Q

Inhibition of Polymerization

A

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

23
Q

Applications of polymers in dentistry:

A

Applications of polymers in dentistry:
•Prosthodontics: denture bases and teeth, soft liners, custom trays, impression
materials, core buildup materials, temporary restoratives, cementing/luting
materials, and maxillofacial prostheses.
•Operative Dentistry: dentin bonding agents, cavity fillings, resin and glass-
ionomer cements, pit and fissure sealants, splinting materials, and veneers.
•Orthodontics: brackets, bracket bonding resins and cements, and spacers.
•Endodontics: gutta-percha points, root canal sealants, and rubber dams.
•Equipment: mixing bowls and spatulas, mouth guards (sports equipment), and
protective eyewear.

24
Q

Clinical significance

A

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.