Chemistry 5861 - Polymer Chemistry 1
Chemical Structure and Polymer Properties (Chapter 4 in Stevens)1
I Introduction - Materials & Fabrication Methods in Antiquity
Traditional Materials & Their Modern Analogues A)
1)
a)
b)
Rigid Thermoset Materials
Antiquity:
i)
ii)
iii)
iv)
i)
ii)
Stone
Nature’s Thermoset
Pottery/Ceramics
Made from natural/modified class
Most common & useful materials from antiquity to archeology
Concrete
Coliseum
Pilings
Plaster
Modern:
Phenol/Urea-Formaldehyde Resins
Bakelite
Plywood, Particle Board, Oriented Strand Board
Epoxy Resins
household
aircraft
1 The graphics in these notes indicated by “Figure/Table/Equation/Etc., x.x in Stevens” are taken from our lecture text: “Polymer Chemistry: An Introduction - 3rd Edition” Malcolm P. Stevens (Oxford University Press, New York,
©2002, Dr. Allen D. Hunter, Youngstown State University Department of Chemistry
Chemistry 5861 - Polymer Chemistry 2
2)
a)
b)
3)
a)
b)
Rigid Thermoplastic Materials
Antiquity:
i)
ii)
i)
ii)
i)
ii)
Metal
much more widely used than once suspected - recycling
Glass
much more widely used than once suspected - recycling
natural glass
obsidian
man-made glass
Modern:
Highly crosslinked polymers
Some high Tg polymers
Flexible Thermoset Materials
Antiquity:
Natural & Semi-synthetic materials
Bone & Horn
Sinew
Leather
Hair
Wood
Man-made materials
Animal glue based composites
Modern:
1999).
©2002, Dr. Allen D. Hunter, Youngstown State University Department of Chemistry
Chemistry 5861 - Polymer Chemistry 3
i)
i)
i)
Wire
Thermoset elastomers (medium and low crosslink density)
4)
a)
b)
B)
Flexible Thermoplastic Materials
Antiquity:
True Thermoplastics ???
Horn
Wood
Modern:
Most commercial thermoplastics
Traditional Processing Methods & Their Modern Analogues
1)
a)
b)
c)
2)
a)
b)
3)
a)
b)
c)
4)
5)
Molding:
Forging/Hammering/Compression
Injection/Reaction Injection
Blow Molding
Extrusion/Drawing:
Pipe
Casting:
Ceramics
Concrete
Reaction Injection
Machining of Preformed Objects:
Relative Energy, Labor, etc., Costs
©2002, Dr. Allen D. Hunter, Youngstown State University Department of Chemistry
Chemistry 5861 - Polymer Chemistry 4
II Fabrication Methods
A) Challenges With Polymers
1)
a)
b)
2)
a)
3)
B)
Viscosity
back pressure
shear
Melting
heat transfer without decomposition at edges
Throughput Considerations
Compression Molding
1)
2)
a)
b)
3)
a)
b)
Figure 4.1 in Stevens
Flow induced by applied pressure & heat
may use lower molecular weight pre-
polymer (B-Staging)
Common Uses
Thermoset polymers
i)
i)
cannot be melted once crosslinked
Composite (Fiber Reinforced) materials
e.g., fiberglass/epoxy & graphite/epoxy resins
©2002, Dr. Allen D. Hunter, Youngstown State University Department of Chemistry
Chemistry 5861 - Polymer Chemistry 5
C) Injection Molding
1)
2)
3)
a)
b)
D)
Figure 4.2 in Stevens
Thermoplastics
Screw Feed
⇒ pressure
⇒ heat
i)
ii)
heating coils
friction
Reaction Injection Molding, RIM
1)
2)
3)
E)
Figure 4.3 in Stevens
Thermoset Polymers
Polymerization-
Crosslinking occur in-situ
Blow Molding
1)
2)
3)
Figure 4.4 in Stevens
Thermoplastic
Common for both plastic and
glass bottles
©2002, Dr. Allen D. Hunter, Youngstown State University Department of Chemistry
Chemistry 5861 - Polymer Chemistry 6
F) Foam Production
1)
a)
b)
2)
a)
3)
4)
G)
Foaming Agent
Physical Blowing Agents
i)
ii)
iii)
i)
Dissolved liquid/gas in early stage
Gas in later stage
temperature change &/or
pressure change
Examples
halocarbons
hydrocarbons
N2, CO2, etc.
Chemical Blowing Agents
decompose and give off gas
growing gas bubbles
surface tension
Hard vs. Soft Foams
Open vs. Closed Cells
Filament Production & Winding
1)
2)
a)
b)
Figure 4.5 in Stevens
Extrusion of fiber
molten
in solution
©2002, Dr. Allen D. Hunter, Youngstown State University Department of Chemistry
Chemistry 5861 - Polymer Chemistry 7
c)
3)
a)
b)
c)
III
reaction in situ
i)
ii)
i)
ii)
iii)
i)
i)
ii)
crosslinks
fiber formation via monomer pyrolysis
graphite
Winding ⇒
increased alignment
increased crystallinity
increased strength/stiffness
Mechanical Properties
Dependence of Mechanical Properties on Molecular Weight A)
1)
a)
2)
a)
b)
Figure 4.5 in Stevens
trends in:
Viscosity/Processability
Properties
Working Range
MW Effects
end group concentration
negligible above ≈ 15,000
interchain forces
increase with MW
utility of increased chain length drops after total interchain forces are
greater than backbone strengths
©2002, Dr. Allen D. Hunter, Youngstown State University Department of Chemistry
Chemistry 5861 - Polymer Chemistry 8
3)
a)
B)
Chemical Structure effects
depend on type(s) of interchain bonding ⇒ required chain length
Mechanical Properties
1)
a)
b)
2)
a)
b)
c)
d)
3)
a)
b)
Strength & Modulus
Strength (Stress)
i)
i)
i)
i)
a measure of how much force must be applied to get the sample to change
by the desired amount (Strain)
Modulus
the resistance to deformation (≡ Stress/Strain)
Important Mechanical Properties
Tensile Strength & Modulus
Compressive Strength & Modulus
Flexural Strength & Modulus
Impact Resistance
toughness
Failure
Graceful vs. Catastrophic Failure
Fatigue
effects of repeated application of stress
©2002, Dr. Allen D. Hunter, Youngstown State University Department of Chemistry
Chemistry 5861 - Polymer Chemistry 9
C) Tensile Properties
1)
a)
b)
c)
2)
a)
b)
c)
3)
a)
b)
c)
4)
Tensile Stress, σ
a measure of how much force must be applied to get the sample to change by the
desired amount (Strain)
Tensile Stress ≡ Applied Force/Cross Sectional Area
σ = F/A
Tensile Strain, ε
a measure of sample stretching
Tensile Strain ≡ Change in Sample Length/Original Length
ε = ∆l/l
Tensile Modulus, E
the resistance to deformation
Tensile Modulus ≡ Tensile Stress/Tensile Strain
E = σ/ε
Stress-Strain Curves
a) Figure 4.7 & 4.8 in
Stevens
b)
c)
d
Brittle Material
i)
i)
high modulus
reversible before breakage
Fiber
lower or high modulus initially
epending on
©2002, Dr. Allen D. Hunter, Youngstown State University Department of Chemistry
Chemistry 5861 - Polymer Chemistry 10
degree of crystallinity
chemical structure
etc.
⇒ elongation
reversible
ii)
iii)
iv)
i)
ii)
iii)
iv)
critical stress
⇒ flow of polymer chains & untangling of chains
⇒ rapid lengthening
∴ drop in applied stress felt
irreversible
highly crystalline fiber
d)
Figure 4.7 in Stevens
often yields breakage soon after yield point
induced crystallinity in previously amorphous or low crystalline fiber
⇒ increased modulus
as in fiber drawing
often yields breakage soon after yield point
Elastomer
typically lower modulus overall
reversible flow
yield point
irreversible flow
©2002, Dr. Allen D. Hunter, Youngstown State University Department of Chemistry
Chemistry 5861 - Polymer Chemistry 11
5)
a)
Temperature Dependence of Modulus
Amorphous Thermoplastic
i)
ii)
iii)
i)
ii)
iii)
Figure 4.9 in Stevens
Tg
b)
rapid decrease of
modulus
mp
rapid decrease of modulus
Other Materials
Figure 4.10 in
Stevens
Regions of Curves
D)
Brittle-Glassy region
Rubbery/Plastic region
Liquid Region
Effects on Curves
MW Effects
Crosslink Density Effects
Crystallinity Effects
Time Dependent properties
1)
a)
Creep
cold flow
©2002, Dr. Allen D. Hunter, Youngstown State University Department of Chemistry
Chemistry 5861 - Polymer Chemistry 12
2)
E)
stress relaxation
Influences of Polymer Structure
1) Tables 4.1 & 4.2 in Stevens
©2002, Dr. Allen D. Hunter, Youngstown State University Department of Chemistry
Chemistry 5861 - Polymer Chemistry 13
IV Thermal Stability
A) Origins of Decomposition
1)
a)
b)
2)
3)
a)
b)
B)
Bond breakage
⇒ decreased materials properties
⇒ depolymerization with many polymers
i) this is especially true with vinyl polymers
Aromatization upon heating
Thermal Stability Criterion
decompose at ≥ 400 °C
retain useful properties near this
temperature
Thermally Stable Polymers
1)
a)
2)
a)
b)
c)
3)
Table 4.3 in Stevens
Inert atmosphere values
Primarily a function of bond energy
i.e., increased bond vibration ⇒
bond rupture
aromatics have advantage in that breaking one bond does not disrupt structure
this is especially true with ladder type polymers where there are no single atom-
atom interactions that solely hold together the polymer backbone
Thermooxidative Stability values
©2002, Dr. Allen D. Hunter, Youngstown State University Department of Chemistry
Chemistry 5861 - Polymer Chemistry 14
a)
b)
V
initial onset may be lower than those in inert atmospheres and the TGA curve will
typically be different
initial decomposition is still via bond rupture then new mechanism involving
oxidation may come into play
Flammability and Flame Resistance
A) Flammability Issues
1)
2)
a)
b)
c)
3)
a)
b)
4)
a)
b)
c)
d)
5)
a)
Mechanical Failure
Heat Induced Damage
direct heat effects on skin
high temperature gasses
hot “molten” materials on skin
Toxicity
evolved gasses
particulates
Relative Importance Varies for
Structural Components
Coatings
Fabrics
etc.
Terminology
Nonflammable
i) e.g., PVC
©2002, Dr. Allen D. Hunter, Youngstown State University Department of Chemistry
Chemistry 5861 - Polymer Chemistry 15
b)
c)
B)
Self-Extinguishing
i)
i)
ii)
iii)
iv)
v)
i)
e.g., polycarbonates
Flammable
Mechanism of Flames
1)
2)
a)
b)
c)
3)
a)
b)
e
Figure 4.11 in Stevens
Flame Components
Pyrolysis Zone
Diffusion Zone
Combustion Zone
Kinetic & Thermodynamic Processes
Heat Transfer/Loss
generated by ignition source
generated by combustion
causes pyrolysis
heating of gasses
radiative loss
Mass Transfer
diffusion of fuel molecules
CO
C2H2
H2
tc.
©2002, Dr. Allen D. Hunter, Youngstown State University Department of Chemistry
Chemistry 5861 - Polymer Chemistry 16
ii)
iii)
i)
ii)
iii)
i)
ii)
iii)
diffusion of oxygen molecules
diffusion of combustion products
4)
a)
b)
CO2
H2O
etc.
Flame resistance/retardent strategies
starve flame for fuel
decrease pyrolysis
insulating/impermeable crusts
char formation
phosphorous containing materials in cellulosic fibers
cool pyrolysis zone
Al2O3.3H20
NaHCO3
inhibit heat flow to pyrolysis zone
must slow combustion
Free Radical Scavengers (Radical Traps)
halogens
toxicity
phosphorous compounds
increased amounts of spectator gasses
their heat capacity lowers flame temperature
©2002, Dr. Allen D. Hunter, Youngstown State University Department of Chemistry
Chemistry 5861 - Polymer Chemistry 17
VI Chemical Resistance
A) Morphology Influence
1)
a)
b)
c)
2)
a)
b)
VII
For most reactions, chemical reagents must diffuse into bulk polymer
∴ deduced diffusion ⇒ reduced reactivity
decrease pore size/volume
make polymer and chemical incompatible so that they repel each other
i)
i)
ii)
i)
i)
ii)
iii)
e.g.,
hydrophobic polymers
fluoropolymers
Chemical Reactivity
Polymers react similarly to their discrete molecule analogues
albeit often slower
∴ choose polymers that chemically are expected to be unreactive
e.g.,
Ozone converts C=C into carbonyls
Electrical Conductivity
Band Structure & Conductivity A)
1)
a)
Relationship of Molecular Orbitals to Bands
Hückel Orbitals for Aromatics
Benzene
Naphthalene
Anthracene
©2002, Dr. Allen D. Hunter, Youngstown State University Department of Chemistry
Chemistry 5861 - Polymer Chemistry 18
iv)
i)
ii)
iii)
iv)
i)
ii)
iii)
i)
ii)
Graphite
b)
2)
a)
b)
c)
B)
Structural Isomers of PAHs
Anthracene & Phenanthrene
changes to HOMO-LUMO Gap
Nature of HOMO
etc.
Classes of Conductors
Metallic Conductors
Semiconductors
thermal population
photoconductors
n-type & p-type doped semiconductors
Insulators
Polymeric Conductors/Semiconductors
1)
a)
Structural Features for Conductivity
Delocalization usually required
conjugation of π system
Molecules 20-23 in Stevens
poly(sulfur nitride)
polyacetylene
exceptions via charge transfer between pendant groups
poly(N-vinyl-cabazole), 19
©2002, Dr. Allen D. Hunter, Youngstown State University Department of Chemistry
Chemistry 5861 - Polymer Chemistry 19
b)
c)
2)
a)
b)
c)
poly(vinyl ferrocene)
Dopants
Morphology
Mechanism of Conductivity
Interchain Electron Transfer!
Valence & Conduction band populations
Solitons
i)
i)
ii)
i)
ii)
i)
Figure 4.14 in Stevens
d) Doping
Molecules 23a in Stevens
3)
a)
b)
p-type doping
n-type doping
Property Changes on Doping
thermal stability
oxidative stability
processability
Measuring Conductivity
Units of conductivity, σ
siemens (S)/cm
siemen = 1/ohm
Classes
Insulators
σ < 10-8 S/cm
©2002, Dr. Allen D. Hunter, Youngstown State University Department of Chemistry
Chemistry 5861 - Polymer Chemistry 20
ii)
iii)
i)
ii)
Semiconductors
c)
10-8 < σ < 102 S/cm
Conductors
σ . 102 S/cm
Examples
poly(sulfur nitride), 20
100 S/cm
superconductive at about 0.3 K
polyacetylene (undoped)
1.7 x 10-9 S/cm for cis, 22
4.4 x 10-5 S/cm for trans, 23
doped materials are conductive in metallic range
Molecules 23a in Stevens
doping converts cis to trans isomers
C) Conjugated Organic Polymeric Conductors
1) Examples of Conjugated Organics
a) Molecules 24-28 in Stevens
b) polyaniline, 24
c) polypyrole, 25
d) polythiophene, 26
e) poly(para-phenylene), 27
f) poly(para-phenylenevinylene), 28
©2002, Dr. Allen D. Hunter, Youngstown State University Department of Chemistry
Chemistry 5861 - Polymer Chemistry 21
2) Experimental Conductivities
a)
b)
3)
a)
b)
c)
d)
e)
4)
Table 4.5 in Stevens
Typically less than those of polyacetylene
i)
ii)
i)
ii)
iii)
sufficient for commercial application
better stabilities
Applications
anti-static materials
light weight batteries
thin film transistors
light-emitting diodes
molecular electronics
Ionic Conductors/Electrolytes
a) Molecules 29 & 30 in Stevens
b) poly(ethylene oxide), 29
c)
d)
polyphosphazenes, 30
Key properties
highly amorphous
low Tg
⇒ highly mobile ions
e.g., Li+
©2002, Dr. Allen D. Hunter, Youngstown State University Department of Chemistry
Chemistry 5861 - Polymer Chemistry 22
VIII Nonlinear Optical, NLO, Properties
Non-Linear Optical Behavior A)
1)
a)
2)
a)
b)
c)
3)
a)
b)
4)
a)
b)
c)
1st Order (linear) behavior
refraction, etc., typically see in our lives
2nd Order behavior, χ2
frequency doubling
requires molecular dipoles on Chromophores
i)
ii)
i)
ii)
iii)
i)
increases with
extended conjugation
π donor/acceptor strength
called β values in solution
requires that they be aligned
Poling of polymeric solids
non-centrosymmetric single crystals
host-guest complexes
3rd Order behavior, χ3
frequency tripling
requires polarizable materials on Chromophores
2nd & 3rd order effects
interaction of electric fields of light with those of sample
⇒ electro-optic interactions
⇒ electrical-light signal converters
⇒ optical-optical interactions
©2002, Dr. Allen D. Hunter, Youngstown State University Department of Chemistry
Chemistry 5861 - Polymer Chemistry 23
i)
i)
ii)
iii)
iv)
v)
vi)
i)
⇒ all optical device elements
IX Additives
Turn Polymers into Plastics A)
1)
2)
a)
b)
3)
a)
b)
B)
Found in almost all commercial plastics
Purposes
Alter polymer properties
pigments
oderants
stability
mechanical property modification
crosslinking agents
etc.
Improve processability
lubricants
Interactions with Polymers
Miscible
Immiscible
Commercial Additives
109 kg used per year in US 1)
2) Classes
a) Table 4.6 in Stevens
©2002, Dr. Allen D. Hunter, Youngstown State University Department of Chemistry
Chemistry 5861 - Polymer Chemistry 24
©2002, Dr. Allen D. Hunter, Youngstown State University Department of Chemistry
3) Examples
a)
b)
Table 4.7 in Stevens
Plasticizers
i)
ii)
iii)
permanence
“new car smell”
solubility parameters
toxicity
di-2-ethylhexyl phthalate, 33