Mansoor Ahmed presented on the topic of thermal transitions in polymers to Miss Habiba Taj Sahiba on July 23, 2020 at the University of Balochistan in Quetta. The presentation discussed glass transition temperature (Tg), crystalline melting point (Tm), and factors that affect Tg and Tm such as polymer structure, molecular weight, and intermolecular interactions. It also described techniques for analyzing polymer thermal behavior including differential scanning calorimetry and thermogravimetric analysis.

1. NAME: MANSOOR
AHMED.
S/O: HAJI BARI DAD.
ROLL NO: 20
PRESENTATION: PHYSICAL CHEMISTRY-V
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PRESENTATION
CONTACT NO: 0300-8061972
23-07-2020 Mansoor Ahmed Mamtaz. UoB Quetta.
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2. PRESENTATION TOPIC:
THERMAL TRANSITIONS OF
POLYMERS
 PRESENTED TO: MISS HABIBA TAJ SAHIBA.
 DATE OF PRESENTATION: 23-07-2020
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23-07-2020 Mansoor Ahmed Mamtaz. UoB Quetta.

3. UNIVERSITY OF BALOCHISTAN
QUETTA
 DEPARTMENT: CHEMISTRY
 PROGRAM OF STUDY: M.Sc
 SEMESTER NO: 3RD
 SESSION: 2019-20
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23-07-2020 Mansoor Ahmed Mamtaz. UoB Quetta.

4. 23-07-2020 Mansoor Ahmed Mamtaz. UoB Quetta.
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5. CONTENTS
Glass transition temperature
Crystalline melting point
Factors affecting Tg
Factors affecting Tm
Thermal methods of polymer analysis
23-07-2020 Mansoor Ahmed Mamtaz. UoB Quetta.
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6. THERMAL TRANSITIONS OF POLYMERS
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7. Thermal Transitions Of Polymers
Completely amorphous
polymer: Tg only
Completely Crystalline: Tm
Semi-crystalline: Both Tg & Tm
23-07-2020 Mansoor Ahmed Mamtaz. UoB Quetta.
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8. AMORPHOUS POLYMERS
Temperature LOW MW HIGH MW
LOW Glassy solid Rubbery:
1. rigid solid – rubber
2. rubber – liquid
HIGH Viscous fluid
23-07-2020 Mansoor Ahmed Mamtaz. UoB Quetta.
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9. Semicrystalline Polymers
Two major types of thermal transitions:
Crystalline melting point, Tm, at which the crystalline
domains melt.
•Above this temperature, polymer is liquid.
•Below this temperature, polymer forms flexible crystalline solid.
Tg, glass transition temperature.
•Below this, polymer exists as hard, rigid glassy solid.
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10. Factors Affecting Tg
• Nature of polymerbackbone.
• C-C and C-O bonds are flexible.
• Nature of groups directly attached
to the backbone (due to repulsion
and tendency to form H-bonding).
• Flexibility enhanced by methylene
groups.
• Flexibility reduced by ring
structures
• phenylene and amide
• substitutionof H atoms by HC
groups
• eg. Tg: PTFE > PE
Chain
flexibility,
interactions &
structure
23-07-2020 Mansoor Ahmed Mamtaz. UoB Quetta.
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11. …Cont’…Factors Affecting
Tg
Inclusion of double bond stiffens it but increases
flexibility of adjacent bonds.
Segmental rotation is affected by other chains in the
same region (mainly dipole interaction and hydrogen
bonding).
• Tg: PVC > PE (more polar).
• Tg: polyvinylidene < PVC (less polar due to symmetrical
substitution.
• Hydrogen bonding also significantly increases Tg.
23-07-2020 Mansoor Ahmed Mamtaz. UoB Quetta.
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12. Factors Affecting Tm
Same factors affect both Tg & Tm.
Usually high Tg & high Tm are found together and vice versa.
Asymmetrically structured polymershave higher Tm
• Eg PVC vs polyvinylidene
High polarity and hydrogen bonding increases Tm.
Molecular symmetry leads to high Tm.
• Eg PE has high Tm due to tightly packed crystals although Tg
is low due to flexibility of the chain.
23-07-2020 Mansoor Ahmed Mamtaz. UoB Quetta.
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13. Values Of Tg & Tm
Polymer Repeating Unit Tg (˚C) Tm (˚C)
Polyethylene -CH2CH2- -125 137
Natural rubber -CH2C(CH3)=CHCH2- -73 28
Polypropylene -CH2CH(CH3)-- -13 176
Polyvinylchloride -CH2CHCl- 81 273
Polystyrene -CH2CHØ- 100 240
Polymethylmethacrylate -CH2C(CH3)(CO2CH3)- 105 200
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14. Thermal Analysis Of
Polymers
Technique Quantity measured Applications
Differential Scanning
Calorimetry (DSC)
Heat flow Reaction kinetics,
purity analysis,
polymercures
Differential thermal
analysis (DTA)
Temperature
difference
Thermal stability,
phase diagram
Thermogravimetric
analysis (TGA)
mass Thermal stability,
compositional
analysis
23-07-2020 Mansoor Ahmed Mamtaz. UoB Quetta.
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15. Differential Scanning Calorimetry
(DSC)
 Polymer and reference samples are heated in such a way that they are
kept at the same (increasing) temperature.
 When a thermal transitionoccurs thermal energy is suppliedto the
polymer or reference.
 The energy transferred is equivalent to the energy absorbed or evolved
in the transition.
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16. DSC Plot
 The resulting plot of differential rate of heating Vs temperature
can be studied to measure heat capacity, melt enthalpy and
transition temperature.
23-07-2020 Mansoor Ahmed Mamtaz. UoB Quetta.
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17. Characteristics of a DSC
Curve
Each substance has
a characteristic
DSC curve that can
be used for
qualitative
identification.
Endotherms
generally represent
physical changes
while exotherms
indicate
crystallization,
polymerization,
curing,
decompositionetc.
The area under the
peak (trough) is
proportional to the
heat evolvedor
absorbed during
the reaction.
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18. Applications Of The DSC
Curve
• % Crystallinity =  Hf,x/ Hf
= Heat of fusion of sample/heat of
fusion of 100% crystal
% Crystallinity
• Height of peak is proportional to rate
of reaction
• Heat of reaction = Heat absorbed or
emitted/No. of moles
Rate of reaction
• Manifests as a change in baseline.
• A sharp increase is typical of Tg.
Change in heat
capacity
23-07-2020 Mansoor Ahmed Mamtaz. UoB Quetta.
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19. Melting Point From DSC Curve
 Can determine the exact melting point as the temperature at
which melting is complete.
 The actual melting of the polymer takes place at a range of
temperature.
On-set
Mid
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20. Thermogravimetric Analysis
TGA
Measurement of the mass vs temperature.
Plotted as mass vs time or mass vs temperature.
Characteristics
• Unique shape for each substance.
• Temperature at which changes occur.
• Each plateau indicates stable state & any deviation or
changes shows the presence of a reaction.
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21. TGA Curve
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22. THE END
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