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
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 → shrinkage.
↑ Viscosity → entrapment of some monomer → residual monomer
(unreacted monomer inside the chain ”free monomer”).