Effect of crystallinity on properties
Melting temperature
The morphology of most polymers is semi-crystalline. That is,
they form mixtures of small crystals and amorphous material and
melt over a range of temperature instead of at a single melting
point.
Specific volume (cc/g)

41
Melting temperature
42
Melting temperature
Factors that affect the melting temp. of polymer crystals
Intermolecular Interactions : Enthalpy change
- The enthalpy of fusion or heat of fusion is the change in enthalpy
resulting from heating a given quantity of a substance to change
its state from a solid to a liquid (Tm)
- The 'enthalpy' of fusion is a latent heat: The latent heat of fusion
is the enthalpy change of any amount of substance when it melts.
Why?
- The liquid phase has a higher internal energy than the solid
phase: energy must be supplied to a solid in order to melt it and
energy is released from a liquid when it freezes
→ Crystallinity!
- The enthalpy of fusion is almost always a positive quantity
Gf = Hf – Tm Sf = 0
Tm = Hf / Sf
→ Depends on Enthalpy change and Entropy changes
43
44
Melting temperature
Melting temperature
Intermolecular Interactions : Enthalpy change
Intermolecular Interactions : Enthalpy change
More polar →
Tm = Hf / Sf
45
Melting temperature
Tm = Hf / Sf
46
Melting temperature
Intermolecular Interactions : Enthalpy change
Intermolecular Interactions : Enthalpy change
- Nylon 66 has more hydrogen-bonding than nylon 6.
- Nylon 6,6 is tighter with less openings, making it the stronger and more
resistant to heat (m.p.) nylon 6,6 - 250oC, nylon 6 - 215~220 oC
47
- Nylon 66 has less amount of amorphous region and higher crystallinity than
nylon 6
48
Melting temperature
Melting temperature
Difference in properties
Intermolecular Interactions : conformational Entropy change

Nylon 6,6 shows
Stiffer polymer chains have less entropy changes between ordered crystal
state and unordered melt state : → Tm ↑
- Higher thermal properties : the preferred Nylon for temperature
performance products.
- Higher tensile strength in use.
- Excellent abrasion resistance.
Tg at 65% RH (oC)
Moisture regain (21oC, 65% RH)
Water shrinkage (%, 15mins; 98oC)
Melting point (oC)
Softening point (oC)
Nylon 6
60
4.0-4.5
10
215-220
170
Nylon 66
74
3.5-4.0
5.3
250
235
Tm = Hf / Sf
49
Melting temperature
50
Melting temperature
Chain flexibility and Entropy change
The effect of diluents

51
Diluents(low molecular weight
materials) increase the
entropy changes between
crystal and melt state → Tm ↓
52
Melting temperature
Melting temperature
The effect of copolymerization and M.W.

Stereoregulararity
Low M.W. → number of terminal group ↑ → Tm ↓

Stereoregular chain structure
→ more crystalline
→ Entropy change ↓ → Tm ↑
53
Motions of materials
Highly crystalline polymers Amorphous polymers:
Polypropylene
Poly(methyl methacrylate)
Syndiotactic polystyrene
Atactic polystyrene
Polyamide (Nylon 6, 66)
Kevlar와 Nomex
Polyketone
Polycarbonate
Polyisoprene
Polybutadiene
54
Movements of materials
Low molecular weight materials
Free volume

When appropriate energy is
added, molecules can move
through free volume among
molecules
Glass Transition
Temperature (Tg)
55
56
Movement of polymer chains
Glass Transition Temperature, Tg
Motion in polymers – The dynamics of polymer chains
A. Definition of Glass Transition Temperature.
Free volume
a. The temperature at which the glassy state(brittle crystalline) is
changed into the rubbery state.
b. The glassy state: short-range vibrational and rotational motion
of atoms → hard, rigid and brittle.
Heating : increased kinetic energy of molecules
At Tg, 20-50 chain atoms are involved
in the segmental movement →
c. The rubbery state: long-range rotational motion of segments (2050 atoms) → soft and flexible.
Remember! Tg has to do with free
volume increase
57
Glass Transition Temperature, Tg
58
Glass Transition Temperature, Tg
Greater local
motion
V
Restricted
local motion
Free
volume
Tg
Brittle glass
T
Melt, tough polymer
or “other”
59
60
Glass Transition Temperature, Tg
Glass Transition Temperature, Tg
The amorphous state - *Rheology
Limited molecular
motion :
very short range
vibration and rotation
B. Change of physical properties at Tg.
a. Specific volume : increase free volume above Tg.
Segmental motion
(conformational
freedom)
b. Enthalpy(∆H) change : kinetic energy of segmental motion.
c. Refractive index : change of density.
d. Modulus : glass → rubber
Above Tm
e. Heat conductivity : free volume.
Below Tg
*Rheology : Science of deformation and flow
61
Glass Transition Temperature, Tg
62
Glass Transition Temperature, Tg
Factors affecting Tg of polymers
Factors affecting Tg : 1. MW
1. Molecular weight
2. Chain flexibility
3. Substituents
a. Steric effect
b. Flexibility (plasticizing effect)
c.
Chain length (entanglement; side chain crystallization)
d. Branching
4. Polarity (intermolecular interaction)
5. Crosslinking
6. Crystallization
7. Diluents
8. Stereochemistry
Ex) PS
63
Tg = 40 C for Mn = 3,000
100 C for Mn = 300,000
64
Glass Transition Temperature, Tg
Glass Transition Temperature, Tg
Factors affecting Tg : 2. Chain flexibility
Factors affecting Tg : 2. Chain flexibility
Flexible chain : low Tg
Rigid chain : high Tg
65
Glass Transition Temperature, Tg
66
Glass Transition Temperature, Tg
Factors affecting Tg : 3. Steric effect
Factors affecting Tg : 3. Steric effect
Bulkier substituent → Less rotational freedom → higher Tg
67
68
Glass Transition Temperature, Tg
Glass Transition Temperature, Tg
Factors affecting Tg : 3. Steric effect
Factors affecting Tg : 4. Polarity
Tg ↑ with polarity of pendant group ↑
69
Glass Transition Temperature, Tg
70
Glass Transition Temperature, Tg
Factors affecting Tg : 5. Cross-linking
Factors affecting Tg : 6. Crystallization
Cross-linking ↑ → chain movement ↓ → Tg ↑
Crystallization↑ → amorphous chain movement ↓ → Tg ↑
71
72
Glass Transition Temperature, Tg
Glass Transition Temperature, Tg
Factors affecting Tg : 7. Diluents
Factors affecting Tg : 7. Diluents
Diluents↑ → free volume ↑ (Plasticizing effect)→ Tg ↓
Diluents↑ → free volume ↑ (Plasticizing effect)→ Tg ↓
73
Glass Transition Temperature, Tg
74
Glass Transition Temperature, Tg
Factors affecting Tg : 7. Diluents
Factors affecting Tg : 8. Stereochemistry
Diluents↑ → free volume ↑ (Plasticizing effect)→ Tg ↓
75
76
Kinetics, Crystallization and Glass Transition
Kinetics, Crystallization and Glass Transition
(ABJK) Amorphous polymers :
the more rapidly cooled polymer
Observed behavior depends on:
Glass transition appears at
higher temp. (Tg’)
• Structure
• Cooling rate
• Crystallization Kinetics
(ABDG) low molecular weight compound : transition at single temp. (Tm)
(ABCEFG) partly crystalline, partly amorphous polymer: crystallization begins at
Tm. trailing off between C & E cf. low molecular weight comp.
(ABHI) Amorphous polymers : No discontinuity at Tm
The change in slope between EF and FG occurs at Tg.
the change occurs in slope over a range of temp. (~20oC) (Tg)
HI is the glassy state, and the threshold for its appearance is Tg
BH is said to be supercooled
77
Tg and Tm
78
Liquid Crystal
A. Definition of liquid crystallinity
a. Liquids which exhibits anisotropic behavior.
b. Molecules are ordered in liquid.
c. The ordered regions in the liquid are called mesophases.
a state of matter intermediate between liquid and solid.
Ex. Gelatin, lipid bilayers of cell membranes
B. Two types of liquid crystal molecules.
a. Low molecular weight liquid crystals which have been studied since 1960.
b. Polymeric liquid crystals which have been studied since 1970s.
79
80