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Part III.3: Transition in Polymers
- Level of Movement in the Amorphous Part of Polymer Chains
- Factors that influence Tg and Tm
- Transition at Tg and Tm
- The metastable amorphous state
- Changes in Tg and Tm of Copolymers
- Changes in Tg and Tm of Crosslinked Polymers
- Instrument for Thermal Analysis
OUTLINE
AE 449 TEPE: Cattaleeya Pattamaprom
Level of Movement in the Amorphous
Part of Polymer ChainsStep 1: -vibration of atoms at equilibrium
-movement of 1-2 carbon atoms
-happen below Tg of polymers
Step 2: -movement of 5-6 carbon atoms
or movement of side groups
-happen at around Tg
Step 3: -movement of 40-50 carbon atoms
-polymers become soft and rubbery
-happen above Tg
Step 4: -movement of the whole polymer chain
- polymers flow as in viscous melt
Factor that influences Tg
1. The free volume of the polymer (vf) vf = v – vs
vol. of solidly packed molecules free volume bulk specific vol. (ปริ�มาตริจำ�าเพาะของช่�องว่�าง)
vf more room to move around Tg
2. The attractive forces between molecules
difficult to move around
Tg
Factors that influence Tg
3. Steric hindrance more difficult Tg to move around
4. The stiffness of chain difficult to coil up and fold Tg
5. The chain length
Tg Tg
length
(con’t)
(bulky groups)
Factors that influence Tm
Melting Point (Tm) or so called “Crystalline melting
point”
Thermodynamics of melting
Gm = Hm - T Sm
energy needed to overcome crystalline bonding
at eqn Gm 0 Tm = Hm
Sm
- short chain S
- long chain S or stiff chain
Factors that influence Tm
Ex
O O O [ -O-C-N-(CH2)n-]X [-C-N--(CH2)n-]x [-N-C-N--(CH2)n-]x
H H H H
polyurethane polyamides polyureas
Tm < Tm < Tm
- Polyurethane: contains the -o- swivel high Sm most flexible low Tm
- Three polymers have comparable magnitude of hydrogen bonding
- Polyurea: with extra N-Hextra hydrogen bonding extra Hm high Tm
Example: Rank Tm of different polymers
(Ref.: S.L. Rosen, John Wiley&Sons 1993)
Transition at Tg
(Ref.: S.L. Rosen, John Wiley&Sons 1993)
Transition at Tm
(Ref.: S.L. Rosen, John Wiley&Sons 1993)
Low cp
High cp
Schematic of DSC curve
Example PET is cooled rapidly from (state 1) 3000C to
(state 2) room temp. Get perfectly transparent and rigid polymer
Then heat up to (state 3) 1000C and maintain at 1000C then cool down to (state 5) room temp. get rigid, translucent polymer
Question : 1. Sketch general specific volume (v) curve
2. Show DSC curve
1
5
42
3
Tg = 690 C
Tm = 2670 C
V (CC/g)
Temp.
Specific volume (v) curve
DSC curve
General Observation about Tg and Tm
• Polymers with symetric repeat unit
Tg/Tm ~ 1/2 (absolute temp)
n
Ex. Polyethylene Poly vinylidine chloride
Ex. Polypropylene Polychlorotrifluoride
• Polymers with asymetric repeat unit
Tg/Tm ~ 2/3 (absolute temp)
The metastable amorphous state
• metastable amorphous state :
–Occur when decreasing temperature of polymer melts quickly
–Produce transparent polymers
รู�ปที่�� 1 Amorphous polymer structure
The metastable amorphous state
• An example of metastable amorphous application
in polymer industries
– PET (soda bottles)
PET Bottle Resin – Before and After Annealing
PET After annealing(Cold Crystallization)
Pressed PET Bottle Resin
Effect of Heating Rate on Temperature of Cold
Crystallization in PETHeating RateAfter QuenchCooling
Tg
melt
Crystallization [kinetic event]
Volume changes of the metastable
amorphous state
•Study the changes in temperature and specific volume of crystallizable polymer
Ex. PET –Tm = 267 °C และ Tg = 69 °C –Molten PET at initial temp of 300 °C (state 1)
The metastable amorphous state
V (CC/g)
1
4
3
Tg = 690 C
Tm = 2670 C
Temp.
5
2
Fig. 8.5 Specific volume – temperature relation for
crystallizable polymer
State 2 = metastable amorphous, State 5 = semi-crystalline
(Ref.: S.L. Rosen, John Wiley&Sons 1993)
Changes in Tg and Tm of Copolymers
apparent Tg reduce / cannot
crystallize
less mobility hinder alignment
Effect of crosslinklightly crosslinked : same as before
heavily crosslinked : crosslink
Changes in Tg and Tm of Crosslinked Polymers
Summary crosslinking in polymers : leads to
(I) higher Tg (II) obstruct and reduce crystallization
Instrument for Thermal Analysis
• Two popular instruments in measuring
temperature response of polymers
- Differential Scanning Calorimeter (DSC)
- Thermogravimetric Analysis System (TGA)
DSC: Differential Scanning
Calorimeter
• This technique can analyze characteristic temperatures and heat flow from thermal transition of material with respect to temperature or time.
Differential Scanning Calorimeter
Heat flow vs. temp.Heat flow vs. time
DSC: Differential Scanning
Calorimeter
• DSC used to analyze :
– Temp and heat that makes polymers or ceramics
melt, crystalize or change phases
– Crytallinity of polymers
– Glass transition temperature (Tg) of polymers
– Heat capacity of materials
Main Parts of DSC
DSC: Differential Scanning
Calorimeter
DSC: Differential Scanning
Calorimeter
DSC Thermogram
DSC: Differential Scanning
Calorimeter
Endo
Exo
TGA: Thermogravimetric Analysis
• Use for analyzing
weight changes of
material when exposed
to heat by using
sensitive balances
(thermobalance)
รู�ปที่�� 3 แสดงเคริ��องThermogravimetric
Analysis
TGA: Thermogravimetric Analysis
• TGA can be used to analyze :
– Additives in plastic products
– Water or solvent in paints coatings adhesives
or ceramics
– Compositons of rubber products ex. Rubber
content, organic fillers, and inorganic fillers
TGA: Thermogravimetric Analysis
Main Parts of TGA
TGA: Thermogravimetric Analysis
TGA Thermogram
HW Chapter 8. Phase transition and Thermal properties of polymer
• Sketch scanning calorimeter traces upon heating from room
temperature for each of the following situations labelling
temperatures and exothermic/endothermic directions on each.
1. A 50/50 glassy crystalline polymer, Tg = 50 oC, Tm = 120 oC
2. A blend of two incompatible crystalline polymers with Tm’s of
90 oC and 160 oC
3. A 50/50 blend of two compatible glassy polymers with individual
Tg’s of 110 oC and 200 oC
4. A crystallizeable polymer which has been quenched from above
it’s Tm rapidly enough so that crystalline does not occur upon
cooling. (Tg = 100 oC, Tm = 250 oC)
5. Polyvinyl chloride plasticized 20% with dioctyl phthalate (DOP)?
(Tg of pure PVC = 85 oC)