Polymer Chemistry CHEM 4364

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Polymer ChemistryCHEM 4364
Dr. Byron K. Christmas N - 809 (713)
221-8169 ChristmasB_at_uhd.edu 528 to 647 p.m.,
TTh A-425 Center for Applied Polymer Science
Research N-832/S-812 Polymer Science and
Technology Robert O. Ebewele
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Polymers The Gentle Giants of the Molecular
World An Introduction to Polymer Science
Chemistry - The study of the properties,
composition, and structure of matter, the
physical and chemical changes it undergoes, and
the energy liberated or absorbed during those
changes.
Polymer Chemistry - The study of the
properties, composition, and structure of
polymeric materials, the physical and chemical
changes they undergo, and the energy liberated or
absorbed during those changes.
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Polymer Science A marriage of Chemistry
and Material Science!
Material Science
Chemistry
Polymer Science
Chemical Compounds
Materials
Polymer Science
Molecular Structure
Bulk Properties
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Polymer Science uses Chemistry and Physics to
develop Technology.
What end-use properties are desired?
What chemical structure is required?
How do you prepare that structure?
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Understand the properties desired. Manipulate
the chemical composition and structure. Relate
the structure to observable properties. Make
useful articles and materials on a
commercial scale.
Chemistry and Engineering (Marketing!)
Chemistry
Chemistry and Physics
Engineering
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Polymer Chemistry in the Industrial Setting What
do Polymer Chemists Do??
A. Polymer Research - Research
Chemist 1. Knowledge Building Activities 2. Deve
loping new concepts and approaches to polymer
technology B. Product Development - Development
Chemist 1. Synthesis of New Polymers 2. Polymer
Characterization with end-use proper- ties in mind
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3. Takes new concepts and technology
from Research and develops commercially viable
products 4. Works with Applications Development
and Technical Service people to insure
desired properties are understood and
obtained C. Applications Development -
Applications Develop- ment
Chemist 1. Evaluate new polymers from Product
Develop- ment in specific end-use
applications 2. Develop a full understanding of
the end-use property advantages and weaknesses of
polymer products
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3. Find new applications for products
already being used in established
applications 4. Provide formulating expertise to
Product Development and Technical Service
people D. Technical Service - Technical Service
Chemist 1. Serve as liason between the
laboratory and Marketing and Sales
people. 2. Serve as technical expert in
helping customers use the products 3. Develop
detailed listings of properties of polymer
products for distribution to customers and
Target Accounts
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4. Carry out specific experiments requested by
Sales to assist customers with technical
problems. E. Process Development- Process
Development Engineer or Chemist 1. Develop
useful, economical processes for making new
polymer products from Product Development. 2. Ca
rry out initial phases of scale-up operations
for new products. 3. Assist Production people in
stream-lining and debottle-necking of current
pro- duction procedures used in the plant.
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3. Assist Production people in stream-lining and
debottle-necking of current pro- duction
procedures used in the plant.
F. Production - Production Engineer 1. Work
with Process Development to scale-up new
products to production quantities in
the plant. 2. Stream-line and debottle-neck
current production processes in order to
minimize cost of production and maximize yield
of products. 3. Supervise the production of
polymer pro- ducts to insure safe handling of
materials and that the product meets the
required specifications. 4. Design new
production equipment as necessary to produce
new products and to minimize production costs.
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Macromolecules - Very large molecules made up
of simple repeating chemical units known as
mers. Polymers - Materials consisting of
macromolecules many mers. Monomers -
Individual small molecules consisting of a single
chemical entity capable of combining with
other monomers to form polymers. Examples
Styrene Vinyl Acetate
Trimethylolpropane Triacrylate Lauryl
Acrylate 1,6-Hexanediol Diacrylate
Vinyl Chloride
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Dimers - Molecules consisting of two monomers
that are chemically bound together. Trimers -
Molecules consisting of three monomers that are
chemically bound together. Oligomers - Molecules
consisting of a few or several monomers bound
together. Since oligomers tend to have
relatively high viscosities, some materials which
have high viscosities are called oligomers even
though they do NOT consists of a few mers, e.g.
Acrylate ---DGEBA---Acrylate

? 1.2 x 106 cps
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Polymers - Large molecules consisting of many
simple repeat units from the Greek poly
meaning many and mer meaning parts or
units Polymer - Many parts or Many
units Examples Poly(vinyl acetate) -
PVA Polystyrene - PS Polycarbonate -
PC Poly(methyl methacrylate) -
PMMA Poly(ethylene terephthalate) -
PETE Poly(butyl acrylate)
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Classification of Polymeric Materials
Joe Mechada Polymer Chemistry Class Notes Spring
1990
Natural
Synthetic
Composites Plastics Fibers Synthetic Rubber
Coatings Adhesives Inks Liq. Crystal
Cellulose Protein Natural Rubber
Other
Other
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Polymeric Materials vs. Monomolecular Materials.
Examples of Each Type Monomolecular
Polymeric
H2O Cellulose CCl4 Rubber CH3CH2OH Nylon SO
2 Silicones Gasoline Epoxy
Glue BF3 Gelatin HCl Plastic
Wrap Air Guar Gum
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General Properties of Monomolecular
Materials A. Pure substances have distinct
melting boiling points. B. Liquids and solids
are essentially incompressible. C. Molecular
solids tend to be inflexible. D. For solids,
physical properties such as hardness, brittleness,
and flexibility tend to be independent
of temperature. E. Liquids and solutions tend
to have newtonian rheology.
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General Properties of Polymeric Materials A.
They do NOT have distinct melting points an
indica- tion that they really are a
mixture. B. They may be quite compressible in
the solid state.. C. Many polymeric solids are
quite flexible. D. Their physical properties are
quite dependent on temperature. E. Liquids and
solutions involving polymers tend to have
non-newtonian rheology.
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Why such differences? 1. Molecular
Differences A. Monomeric materials consist of
relatively small molecules of low molecular mass.
Polymeric materials consist primarily of
relatively large molecules of very high molecular
mass. B. Pure monomeric materials of the same
chemical composition contain molecules that are
essentially identical to one another. Polymeric
materials of a specific composition contain
molecules that are significantly different from
one another.
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2. Intermolecular Forces of Attraction A.
Primary Chemical Bonds - Both monomolecular and
polymeric materials may contain ionic,
pure covalent, polar covalent, and/or
coordinate covalent bonds. B. Secondary Bond
Forces - Both monomolecular and polymeric
materials may involve dipole- dipole,
dipole-induced dipole, hydrogen bonds, and/or
induced dipole-induced dipole (London Dispersion
Forces) interactions.
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Overview of Primary Bonding Types
Ionic Bonding - An ionic bond is a chemical bond
that results from an electrostatic
attraction among oppositely charged ions in a
compound. They form when electrons are
transferred from one atom to another to form ions.
Na Ne 3s1 Cl Ne 3s2 3p5
Na Ne Cl Ar-
Cl-
Na
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Overview of Primary Bonding Types
Covalent Bonding - A covalent bond is a chemical
bond that results from a sharing of electrons
among the atoms in a compound.
e-
e-



Energy
H H
e-
H2
e-


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Overview of Primary Bonding Types
Polar Covalent Bonding - A covalent bond
that occurs when the atoms unequally share one
or more pairs of electrons. This happens when
the atoms have different electronegativities.
e- e-
e- e-
F

H
e-
e-
Energy
e- e-
e- e-
e- e-
e- e-
d
d-
H
F
e- e-
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Overview of Primary Bonding Types
Coordinate Covalent Bonding (Dative) - A
dative bond is a covalent bond that occurs when
the two shared electrons are donated to the bond
by the same atom. The donating atom is the
donor or Lewis Base and the accepting atom is
the acceptor or Lewis Acid.
..
..
F
F
F BF F
..
..
..
..
..
..
..
F BF

..
..
..
..
..
F
Donor
..
..
Acceptor
Tetrafluoroborate ion
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2. Intermolecular Forces of Attraction A.
Primary Chemical Bonds - Both monomolecular and
polymeric materials may contain ionic,
pure covalent, polar covalent, and/or
coordinate covalent bonds. B. Secondary Bond
Forces - Both monomolecular and polymeric
materials may involve dipole- dipole,
dipole-induced dipole, hydrogen bonds, and/or
induced dipole-induced dipole (London Dispersion
Forces) interactions.
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Intermolecular Attractive ForcesSecondary
Bonding Types
Objective To review how intermolecular
inter- actions effect (create) the various states
of matter, particularly the liquid and solid
states.
Learning Goal To become knowledgeable
and conversant about the fundamental interactions
that occur among atoms, ions, and/or molecules
and how these interactions determine the
properties we observe for liquids and solids.
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Intermolecular Attractive Forces
Strongest
Minimal
Moderate
Solid
Liquid
Gas
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Intermolecular Attractive Forces
vs.Intramolecular Attractive Forces
Primary Bond
(Covalent Chemical Bond)
Secondary Bond
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• Types of Intermolecular Attractive Forces
• Instantaneous Dipole-Induced Dipole Attractions
• (London Dispersion Forces)
• Dipole-Dipole Attractions
• Hydrogen Bonding
• Ion-Dipole Attractions
• Others???

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Instantaneous Dipole-Induced Dipole
Interactions (London Dispersion Forces)
Substances m.p. (K) b.p. (K) DHvap (kJ/mol)
Noble Gases
--- 24 84 116 160
He Ne Ar Kr Xe
4.2 27 87 121 166
0.081 1.76 6.52 9.03 12.63
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Instantaneous Dipole-Induced Dipole
Interactions (London Dispersion Forces)
Substances m.p. (K) b.p. (K) DHvap (kJ/mol)
Halogens
F2 Cl2 Br2 I2
50 172 266 387
85 239 332 458
6.5 20.4 29.5 41.9
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London Dispersion Forces
-
-
Attraction

• Due to instantaneous separation of charge in an
• atom or molecule.
• Effective only at very short range.
• Strength of force is dependent on the size of
  the atom
• or molecule and the number of electrons
  (Polarizability)

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Dipole-Dipole Attractions
m
Substances m.p. (K) b.p. (K) DHvap (kJ/mol)
H2 Cl2 CH4 CH3Cl CH2Cl2 CHCl3 CCl4 CF4
14 170 90 176 177 209 250 89
20 239 111 249 313 335 350 145
? 20.4 8.17 ? 28.1 29.2 29.8 12.0
D2 23.5 ?????
1.87 D
1.60 D
1.01 D
0.00 D
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Dipole-Dipole Attractions
Cl H C Cl H
Cl H C Cl H
d - d d - d
Attraction

• Due to a permanent charge separation in the
  molecule.
• Effective only at short to moderate range.
• Strength of force is dependent on the relative
  electro-
• negativities of the atoms and the molecular
  geometry.

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Hydrogen Bonding (H-bonding)
SnH4
Rn
GeH4
Xe
SiH4
Kr
Relative Boiling Points
CH4
Ar
Ne
He
Molecular Mass
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Hydrogen Bonding (H-bonding)
H2O
H2Te
HF
H2Se
SbH3
H2S
Relative Boiling Points
HI
NH3
HCl
AsH3
HBr
PH3
Molecular Mass
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Hydrogen Bonding
H H-N H
H H-N H
d
d -
d
d -
Attraction

• Special case of dipole-dipole attraction.
• Do to relatively large permanent charge
  separation in
• the molecule.
• Effective at relatively long range.
• Occurs when hydrogen is bound to a very
  electro-
• negative element (F, O, and N)

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C. So why the differences? The polymer molecules
are much larger in general and the individual
molecules may be quite different in size and
shape from their neighbors. Because of this, the
total forces of attraction are much larger and
the molecules are capable of entangling with one
another. This helps explain why ethylene monomer
is a gas under ambient conditions while
polyethylene is a solid. They have identical
compositions but their structures and molecular
masses are completely different. Thus, their
physical and chemical proper- ties are completely
different.
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Variables Affecting the End-Use Properties of
Polymeric Materials
1. Chemical Composition Changing the monomers
or their relative amounts will fundamentally
change the end-use properties. 2. Relative
Order of the Monomers in the back bone of the
polymer A. Homopolymers - Only one order is
possible. -A-A-A-A-A-A-A-A-A-A-A-A-A-A-A-
B. Copolymers - Several different arrangements
are possible.
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1) Alternating Copolymer -A-B-A-B-A-B-A-B-A-B
-A-B-A-B-A-B-
2) Random Copolymer -A-B-B-B-A-A-B-B-A-B-A-B-
B-A-A-B- 3) Block Copolymer -
B-B-B-B-B-B-A-A-A-A-A-A-B-B-B-B- 3. Spatial
Arrangement of Atoms A. Conformation - The
arrangement of atoms that can be changed simply
by rotating groups of atoms around a single bond.
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H H H-C -- C - H Cl Cl
H Cl H-C -- C - H Cl H
Free
Rotation
1, 2 - Dichloroethane
Because of relatively free rotation about the
carbon- carbon single bond, these are NOT isomers.
B. Configuration - The arrangement of atoms that
can be changed only by breaking and reforming
primary chemical bonds. (cis- and
trans-isomers and d- and l-forms)
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CH2 CH2 C C
CH3 H
CH2 H C C CH3
CH2
trans-1,4- polyisoprene
cis-1,4-poly- isoprene
4. Macromolecular Structure A. Linear Chains -
A-A-A-A-A-A-A-A-A-A or
H H H H H H C - C - C - C - C
- C or CH2-CH2 H H H
H H H
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B. Branched Polymers -
A-A-B-A-A-A-A-A-B-A-A-A-A A A A
A A A A A
CH2-CH-CH2-CH2-CH2-CH2-CH-CH2-CH2 CH2
CH2 CH2 CH2 (CH2)x
(CH2)y CH2 CH2 CH3 CH3
Low Density Polyethylene (LDPE)
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C. Graft Copolymers -
A-A-B-A-A-A-A-A-B-A-A-A-A C C C
C C C C C
D. Network (Crosslinked) Polymer -
A-A-B-A-A-A-A-A-B-A-A-A-A A A A
A A-A-B -A-A-A-A-A-B -A-A-A-A-A A
A A A
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In Network (Crosslinked) Polymer, the polymer
chains are held together with primary chemical
bonds.
5. Morphology
A. Definition - The overall structure of order
of a polymeric material how the molecules are
oriented with respect to one another.
B. Amorphous Polymer - The molecules are
randomly oriented. They tend to have lower
overall inter- molecular attractive forces (lower
cohesive energy densities) than polymers of
similar chemical composi- tion but a more ordered
structure.
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C. Microcrystallinity - While most polymers have
a ran- dom morphology, many have regions within
the bulk structure that are highly ordered.
These are referred to as microcrystalline
regions or domains.
As microcrystallinity increases, what properties
change?
1. Opacity increases (transparency decreases).
2. Density increases. 3. Glass transition
increases (for amor- phous polymers). 4.
Tensile strength increases. 5. Modulus
increases, etc., etc., etc.,.
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D. Crystalline Polymers - Some polymers are
highly ordered in their morphology although some
random structure is always present. Fibers are a
class of materials with a high degree of
crystallinity.
E. Stereochemistry - In cases where different
configura- tions are possible due either the
presence of multiple bonds or significant steric
hinderance, different morph- ologies can be
obtained. 1. Isotactic 2. Syndiotactic 3.
Atactic
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Tacticity
ISOTACTIC
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ISOTACTIC
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6. Polymer Blends
Polymeric materials that consist of blends
or mixtures of polymers with different
chemical composition and/or structure will give
properties that are different from the individual
polymers making up the blend.
However, many polymers are Incompatible with one
another!
7. Molecular Mass and Molecular Mass
Distribution (MWD)
Virtually all polymers consist of mixtures of
macro- molecules with different molecular masses.
The molecular mass is said to be polydisperse
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The Physical State of Polymers Basic Concepts
1. The physical state of a polymer is affected
by the temperature and the intermolecular
attrac- tive forces (Secondary bond forces). 2.
The cohesive energy is the total energy
neces- sary to remove a polymer
macromolecule from a liquid or a solid. The
larger the inter- molecular attractive forces,
the higher the cohesive energy.
CED (DHv RT)/Vl d 2
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Cohesive Energy Density of Linear Polymers
Polyethylene CH2-CH2 259
J/cm3 Polyisobutylene CH2 -C(CH3)2 272
J/cm3 Polystyrene CH2-CH(C6H5) 310
J/cm3 Poly(vinyl acetate) CH2-CH(OC-CH3) 368
J/cm3 O Poly(vinyl
chloride) CH2-CHCl 381 J/cm3
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3. Volatility and Molecular Mass A. Larger
molecules will tend to have higher inter-
molecular attractive forces, higher
cohesive energy densities, and, thus, higher
melting points and boiling points. B. Most
polymers will decompose before their cohesive
energy densities can be overcome sufficiently to
boil. C. Some polymers decompose before they
melt.
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4. Miscibility and Solubility ?G ?H - T
?S A. For a substance to dissolve in another
substance, the ?Gsoln must be negative. B. For
a polymer to dissolve, the cohesive
energy energy density must be overcome. C. To
favor solution, the intermolecular
attractive forces between the polymer and the
solvent should be large. D. Even if they are
not as large as the cohesive energy density,
solution may occur if the tempera- ture and
entropy factors are sufficiently high.
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E. The intermolecular attractive forces in a
crosslinked polymer system are, in fact,
primary chemical bonds! Therefore,
crosslinked, 3-dimensional network polymers are
NOT soluble in solvents because for them to
dissolve would require breaking chemical bonds.
Thus, a chemical reaction would be occurring,
not a dissolution.
Virtually ALL practical UV/EB-polymerizable
systems are crosslinked systems. Therefore, they
are NOT soluble in solvents. HOWEVER,
non-crosslinked components may be soluble in
specific solvents.
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F. Critical Chain Length, Zc - The length of
a polymer chain necessary to allow for
ENTANGLE- MENT of polymer chains. Without
entanglement useful polymer PROPERTIES are not
obtained.
For polymers with higher intermolecular
attractive forces, lower Zc values are
obtained Polymer Zc PMMA 208 PS 730 Polyiso
butylene 610
?melt a Zc 3.4 ?melt K Zc3.4 K f(T)
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log ?melt log K log Z 3.4 log ?melt
log K 3.4 log Z log ?melt 3.4 log Z
log K
Y m X b
log ?melt
m (often 3.4)
log K
log Z
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Commercial Polymer Range
Tensile Strength
Impact Resistance
Property
Melt Viscosity
Molecular Mass
Different Polymers have different Zc values.
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http//www.instron.us/wa/home/default_en.aspx
Instron Tensile Tester
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s F/A
Fiber

• Dl/l

Brittle Plastic

• s/e

Stress s
Elastomer
Strain e
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s F/A

• Dl/l

Elongation at Break

• s/e

Elongation at Yield
Stress s
Ultimate Strength
Yield Stress
Strain e
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G. Flexibility- The Glass Transition
Temperature, Tg
A characteristic temperature at which
glassy amorphous polymers become flexible or
rubber-like because of the onset of
segmental motion in the macromolecules.
Specific Volume
Tg
Temperature
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Tg
Glassy
Thermoset
Modulus
Rubbery
Thermoplastic
Flow
Temperature
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Differential Scanning Calorimeter (DSC)
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Differential Scanning Calorimetry (DSC)
Heat of Crystallization
Tg
Crosslinked polymers dont melt. They
decompose!
Endotherm Exotherm
Tm
Temperature
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Dynamic Mechanical Analysis (DMA)
66
Dynamic Mechanical Analysis (DMA)
67
Dynamic Mechanical Analysis (DMA)
68
Representative DMA Thermogram
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• Amorphous Rubbery
  Polymer
• Solid Tg Elastic Tm
  Melt
• Temperature
• At the Tg
• 1. Greater Rotational Freedom
• 2. Increase in specific volume
• 3. Enthalpy change (endothermic)
• 4. Modulus (stiffness) decreases
• 5. Refractive index changes
• 6. Thermal conductivity changes

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Factors that Influence the Tg
1) Method of measurement - Different methods
give different results. 2) Aging of the Polymer
- Changes occur with time including oxidation, UV
degradation, etc. 3) Molecular Mass - Results
in lower concentration of chain ends and lower
free volume. Polystyrene w/MN 3000 u/molecule
Tg 33oC Polystryene w/MN 300 000 u/molecule
Tg 100oC
100oC is a limiting value. Chain-end effects on
free volume are negligible at this molecular mass.
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4) Chemical Structure - By far the most
important.
a. Given that the Tg is a function of
the rotational freedom, a restriction of
this, particularly in the backbone, should give
a higher Tg.
H
CH3
H
H
H
H
- 70oC
- 120oC
H
H
H
H
H
CH3
R R
R R
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• Plasticizing Effect of Pendant Side Groups
• Longer side groups reduce secondary bond
• forces among the polymer chains but at a certain
• size, molecular entanglements or side-group
• crystallization becomes important, causing an
• increase in Tg.

CH2-CH R
R Tg (oC)
CH3 - 5 CH3CH2 -24 n-C3H7 -40 n-C4H9 -50 n-C
5H11 -31 n-C10H21 - 6
However! n-C8H17 - 41!
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c. Polarity of Pendant Side Groups More polar
side groups tend to produce a higher Tg.
CH2-CH R
R Tg (oC)
H - 120 CH3 - 10 Cl 87 OH
85 CN 103 C(O)O-CH3 3 C(O)OH 106
However! F 35-45!
Fluorine is smaller than Cl!
74
d. Relative Size of Pendant Side Groups Larger
side groups tend to produce a higher Tg.
CH2-CH R
R Tg (oC)
H -120 CH3 - 10 C6H5 100 C6H4CH3(ortho)
119 C12H7 135 C6H4CH3(meta) 72
Poly(a-vinyl naphthalene)
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e. Branching of Pendant Side Groups Bulkier
side groups tend to produce a higher Tg.
CH2-CH R
R Tg (oC)
CH3 - 5 n-C3H7 -40 -CH(CH3)2
50 n-C4H9 -50 -CH2CH(CH3)2 29 -C(CH3)3 64 n-
C5H11 -31 -CH2CH2CH(CH3)2 14 -CH2C(CH3)3 59
76

• Copolymerization
• a. Isomorphous Systems The component mono-
• mers occupy similar volumes and are capable of
• replacing each other in the crystal system.
• Tg V1Tg 1 V2Tg 2 V Volume Fraction
• b. Non-isomorphous Systems
• 1/Tg W1/Tg 1 W2/Tg 2 W Weight
  Fraction
• This equation is for alternating or random
  copolymers that have monomers with non-similar
  specific volumes but are homogeneous.

77
6) Crosslinking and Branching

• Crosslinking The process of crosslinking links
• separate molecules together with primary bonds.
• This necessarily reduces chain mobility and,
• thus, tends to increase Tg.
• Branching This process increases the separa-
• tion between polymer chains, thus, increasing
• free volume and lowering the Tg

HDPE LDPE
Tg -25 oC -120 oC
78
Mw Mn
? 1
Mn
Number Average Molecular Mass
Mw
Weight Average Molecular Mass
Polymer Molecules
Polydispersity Index
Molecular Mass
79
x x x x x x x x
xxxxxxx
x x x x x
x x x x x
Molecules
x x x
x x
x
50 60 70 80 90 100 110 120
Molar Mass x 103 u
A. Number Avg. Molecular Weight - Mn

1. Numerical Averages 12, 6, 8, 10, 18, 12, 11, 7

77/8 9.6
80
29 g
2. Mass Averages
32 g
30 g
27 g
31 g
25 g
22 g
27 g
30 g
Number Avg. Mass 253 g/9 balls 28.1 g/ball

1. Number Average Molecular Weight

2(60) 5(70) 7(80) 8(90) 5(100) 3(110)
1(120)
2 5 7 8 5 3 1
2700 000 g/31 mol 87 100 g/mol
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4. Weight Average Molecular Weight
2(60)2 5(70)2 7(80)2 8(90)2 5(100)2
3(110)2 1(120)2
2(60) 5(70) 7(80) 8(90) 5(100) 3(110)
1(120)
242 000 000 000/2700 000 89 600 g/mol
5. Polydispersity Index
89 600 g/mol
d
1.03
87 100 g/mol
82
Bimodal Molecular Mass Distribution
Polymer Molecules
Molecular Mass
83
Step-Growth Polymerization Joining Hands in
Molecular Partnerships

• Important Terms and Definitions
• Functional Group A reactive moiety within a
• molecule that is capable of undergoing reactions
• with other appropriate functional groups.
• Examples R-OH Alcohol
• R-COOH Acid
• R-NH2 Amine
• R-NCO Isocyanate
• R-CHCH2 Vinyl
• R-CH-(CO)-CHCH2 Acrylate

84
Step-Growth Polymerization
2. Functionality The number of reactive
functional groups within a single molecule.
Examples CH3CH2-OH Monofunctional HO-CH2CH2
-OH Difunctional HO-C-CH2CH2-OH Bifunctional
O H2N-CH2CHCH2-NH2 Trifunctiona
l NH2
85
Step-Growth Polymerization

• Step-Growth Polymers Polymers that are formed
  by a series of reactions between functional
  groups of adjacent multifunctional molecules,
  often with the loss of some small molecule such
  as H2O or CH3OH.
• Linear Step-Growth Polymers Made from
  difunctional monomers of the type X-R-Y
  (bifunctional monomer) or X-R-X Y-R-Y where
  X and Y are the functional groups. X and Y must
  be capable of condensing with one another.

86
Step-Growth Polymerization
HOOC-CH2CH2CH2CH2-COOH Adipic
Acid H2N-CH2CH2CH2CH2CH2CH2-NH2
1,6-Hexamethylenediamine
C(CH2)4C-NH-(CH2)6-NHn 2n H2O
O O
Nylon 6,6 a linear polyamide
87
Step-Growth Polymerization
Branched and/or Crosslinked Step-Growth Polymers
Made from multifunctional monomers, at least one
of which must be tri- or higher functionality.
HOOC-R-COOH HO-R-OH OH
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Step-Growth Polymerization

• Monomers that Undergo Step-Growth Polymer-
• ization
• Glycols HO-CH2CH2-OH (EG)
• Isocyanates H3C-(C6H3)-(NCO)2 (TDI)
• Acids HOOC-(CH2)4COOH (Adipic Acid)
• Amines H2N-(CH2)6-NH2 (1,6- HMDA)
• Epoxies See Board (DGEBA)
• Silanols HO-Si(CH3)2-OH (Dimethylsilanediol)
  
• Phenol-aldehydes See Board (Phenolic
  Resins)
• Urea-aldehydes See Board (UF Resins)
• Others

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Step-Growth Polymerization

• 5. Types of Step-Growth Polymers
• Polyesters -R-O-(CO)-R-(CO)-O-
• Polyamides -R-NH-(CO)-R-(CO)-NH-
• Polyurethanes -R-O-(CO)-NH-R-NH-(CO)-O-
• Polyureas -R-NH-(CO)-NH-R-NH-(CO)
• Polyepoxies See Board
• Phenolics See Board

90
Step-Growth Polymerization

• Polyurethanes Polymers containing multiple
  urethane linkages in the backbone.
• OCN-R-NCO HO-R-OH

Versatility!
(CO)-NH-R-NH-(CO)-O-R-O
R R can be polyether, polyester,
polysiloxane, hydrocarbon, aliphatic, aromatic,
etc., etc.
91
Step-Growth Polymerization

• Kinetics Review of General Characteristics
• A. Linear polymers are synthesized either from
• monomers of the A-B type or from a
  combin- ation of A-A and B-B type difunctional
  mono- mers.
• B. Network polymers are formed from monomers
  having a functionality greater than two.
• C. Polymers retain their functionality as end
  groups at the completion of polymerization.

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Step-Growth Polymerization
D. A single type of reaction (or reaction
sequence) is responsible for all steps involved
in step- growth polymer formation. E.
Molecular weight increases slowly even at high
levels of conversion. F. High yield reactions
and an exact stoichio- metric balance are
necessary to obtain high molecular weight linear
polymers.
93
Step-Growth Polymerization

• Kinetics Kinetic Considerations
• A. Simplifying Assumptions
• 1) The rate constant for a reaction is
  independent of the polymer chain length.
• 2) The mechanism of the reaction remains
  constant throughout the polymerization.
• 3) The rate of diffusion is usually much
  higher than the rate of functional group
  reaction. Thus, the reaction rate is NOT
  diffusion controlled.

94
Step-Growth Polymerization
B. Catalyzed Linear Polymerization 1) First
order with respect to A and B - dA
dt
kAB
2) For exact stoichiometry
- dA dt
kA2
95
Step-Growth Polymerization
3) Rearrange and Integrate A
t ? - dA/A2 ? kdt
A0 0 A t - ?
A-2 dA k? dt A0
0 1 1 A A0
- kt
96
Step-Growth Polymerization
1/A kt 1/A0 (y mx b)
4) Extent of reaction, P, is the fraction of
functional groups that has reacted at time,
t . So the fraction NOT reacted 1-P
At/A0. At A0 (1-P) 5)
Substitute these into the integrated rate
expression, getting everything in terms of
A0 1 1 A0(1-P) A0
- kt
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Step-Growth Polymerization
6) Average Degree of Polymerization DP
A0/At DP 1/(1-P) (Carothers
Equation) DP 1 A0
A0 ? DP A0kt 1
- kt