1. Chapter 4
Structures
of Polymers

2. Structures of Solid Materials
general
Structures of Solid Materials
Crystalline materials
Materials which have crystal structure.
dense, ordered packing.
atoms pack in periodic, 3D long range atomic order.
tend to have higher (max.) bond energies.
Occurs for: normal solidification conditions.
Typical of: metals, many ceramics & certain polymers.
Energy r
typical neighbor bond length
typical neighbor bond energy
typical neighbor
bond length
bond energy
crystal structure
amorphous structure
crystalline SiO2
noncrystalline SiO2
metals
ceramics
polymers
SC, BCC, FCC, HCP crystal structures
Others: silicate, glass, carbon ceramics.
AX, AX2 & ABX3 type crystal structures,
Linear, branched, cross-linked, network structures (as molecular chains)
(refer to atomic arrangement in crystalline materials)
Noncrystalline materials
Materials which have amorphous structure.
non dense, random packing.
atoms have no periodic short range order.
tend to have lower (min.) bond energies.
Occurs for: complex rapid cooling.
Typical of: polymers, some ceramics & metals.
(refer to atomic arrangement in noncrystalline materials)

3. Structures of Solid Materials
Characteristics of polymer molecules
metals
ceramics
polymers
Chemistry (repeat unit composition)
Size (molecular weight)
Shape (chain, twisting, entanglement, etc)
Structure (as polymer molecular chains)
In general
All polymer are made from organic
materials.
natural polymers – plants & animals
(organic materials), such as: wood,
rubber, cotton, wool, leather, silk etc.
synthetic polymers – R&D from organic
materials, such as: polyethylene,
polypropylene, polystyrene, Kevlar,
nylon etc.
Most polymeric materials are…
hydrocarbons (made up of H & C)
– organic materials.
composed of very large molecular
chains (in 2D array) with organics
group (methyl, ethyl, side
group of various atoms (O, Cl, etc).
2 classifications:
Thermoplastic polymers.
Thermosetting polymers.
SC, BCC, FCC, HCP crystal structures
Others: silicate, glass, carbon ceramics.
AX, AX2 & ABX3 type crystal structures,
Linear, branched, cross-linked, network structures (as molecular chains)
Linear, branched, cross-linked, network
Linear
Cross-linked
Branched
Network
Isomeric states
Stereo isomers
Geometrical isomers
cis
trans
Isotactic
Syndiotactic
Atactic

4. Structures of Solid Materials
repeat
unit
repeat
unit
Structures of Solid Materials C H
Polyethylene (PE) H
Polypropylene (PP) C
CH3
Polymers
ceramics
Metals
repeat
unit
Repeat units:
Smaller structural entities that are repeated along the molecular chain. Cl C H
Poly(vinyl chloride) (PVC)
Chemistry of polymer molecules
Polymer molecules (composition & structure)
polymer is defined as many repeat unit (in terms of
molecular chains).
these macromolecules are composed of repeat units.
2 types of bond exist:
intramolecular bonds: covalent (between C – C).
intermolecular bonds: hydrogen & van der Waals
(between C – H @ C – other atoms (O, Cl etc)).
ex: ethane, C2H6
Adapted from Fig. 4.2, Callister & Rethwisch 3e.
General terms
C2H6
composition (chemical formula)
Intramolecules Covalent bond (strong)
structure
Intermolecules Hydrogen & van der Waals bonds (weak)

5. Structures of Solid Materials
Other organic groups:
Methyl, CH3
Ethyl, C2H5
Phenyl, C6H5
Alcohols (methyl alcohol), R – OH
Ethers (dimethyl ether), R – OH – R
Acids (acetic acid), CH3O2H
Aldehydes (formaldehyde)
Aromatic hydrocarbons (phenol)
Structure of phenyl group
free radical, R from organic groups
Polymers
ceramics
Metals
Chemistry of polymer molecules
Polymer molecules (composition & structure)
composed of hydrocarbons molecules.
saturated & unsaturated hydrocarbons.
Unsaturated hydrocarbons
double & triple bonds between 2
carbon atoms.
- unstable & can form new bonds.
ex: ethylene or ethene, C2H4
Saturated hydrocarbons
also known as paraffin molecules/compounds.
each carbon singly bonded to 4 other atoms.
ex: ethane, C2H6
double bond
ex: acetylene or ethyne, C2H2
others: methane, CH4, propane, C3H8,
butane, C4H10, pentane, C5H10 &
hexane, C6H14
triple bond

6. Structures of Solid Materials
Isomerism
hydrocarbon molecules (compounds) with same composition (chemical
formula) can have quite different structures (atomic arrangement).
ex: C8H18
Polymers
ceramics
Metals
Octane (normal) 
2,4-dimethylhexane
Chemistry of polymer molecules
Polymer molecules
Polymerization
2 steps of polymerization:
reaction between R (catalyst species/free radical) & monomer (from unsaturated hydrocarbon) to form solid polymer materials.
Monomer:
Small molecule from which polymer is synthesized.

7. Structures of Solid Materials
A listing of 10 common polymeric materials
Polymeric materials Structure repeat unit
Polymers
ceramics
Metals
Chemistry of polymer molecules
Polymer molecules

8. Structures of Solid Materials
A listing of 10 common polymeric materials
Polymeric materials Structure repeat unit
Polymers
ceramics
Metals
Chemistry of polymer molecules
Polymer molecules

9. Structures of Solid Materials
Molecular size
- not all chains in a polymer are of the same length.
i.e., there is a distribution of molecular weights.
short molecule chains
Polymers
ceramics
Metals
Low M
long molecule chains
high M
- molecular weight, M: Mass of a mole of chains.
Size of polymer molecules
Molecular weight distribution
Mi = mean (middle) molecular weight of size range i
xi = number fraction of chains in size range i
wi = weight fraction of chains in size range i

10. Structures of Solid Materials
Molecular size
Student
Weight
mass (lb) 1
104 2
116 3
140 4
143 5
180 6
182 7
191 8
220 9
225 10
380
Molecule weight calculation
ex: average mass of a class
Polymers
ceramics
Metals
What is the average weight of the students in
this class:
Based on the number fraction of students in each mass range?
Based on the weight fraction of students in each mass range?
answer:
The first step is to sort the students into weight ranges. Using 40 lb ranges gives the following table:
Size of polymer molecules
Calculate the number and weight fraction of students in each weight range as follows:
total number
total weight

11. Structures of Solid Materials
chain
Polymers
ceramics
Metals
Shape of polymer molecules
Molecular shape
Twisting
also known as conformation.
chain bending and twisting are possible by
rotation of carbon atoms around their chain
bonds.
note: not necessary to break chain bonds to
alter molecular shape.
Entanglement

12. Structures of Solid Materials
(1) Linear structures
(2) Branched structures
polymers are synthesized in which…
repeat units are joined together
end to end in single chains.
flexible & spaghetti like.
common polymers:
Polyethylene
Poly(vinyl chloride)
Polystyrene
Poly(methyl methacrylate)
Nylon
Fluorocarbons
polymers are synthesized in which…
side-branch chains are connected to
the main chains.
the branches may…
result from side reactions that
occur during synthesis.
reduced the packing efficiency &
lowered the polymer density.
- common polymers:
high-density polyethylene (HDPE)
low-density polyethylene (LDPE)
Polymers
ceramics
Metals
Structure of polymer molecules
Molecular chains structures
(3) Cross-linked structures
(4) Network structures
polymers are synthesized in which…
adjacent linear chains are joined one
to another at various positions by
covalent bonds.
accomplished by additive atoms that
are covalently bonded to the chains.
common polymers:
rubber elastic materials.
polymers are synthesized in which…
multifunctional monomers forming 3
@ more active covalent bonds make
3D networks.
polymer that is highly cross-linked
may also be classified as a network
polymer.
these polymers have distinctive
mechanical & thermal properties.
common polymers:
epoxies
polyurethanes
phenol-formaldehyde
shows the structure
of the molecular
chains.
all structures contain
van der Waals &
hydrogen bonding
between the chains. B
ranched
Cross-Linked
Network
Linear
secondary
bonding

13. Structures of Solid Materials
Stereo isomers
Stereoisomers are mirror images – can’t
superimpose without breaking a bond.
ex: E B A D C
mirror plane
Polymers
ceramics
Metals
- Tacticity – stereoregularity or spatial arrangement of R units along chain.
- It can be isotactic, syndiotactic & atactic.
Isotactic configuration
Structure of polymer molecules
- all R groups on same side of chain.
Molecular chains structures – isomeric states
shows the molecular configurations for polymers.
to change configurations, it must break bonds.
Syndiotactic configuration
- R groups alternate sides.
Geometrical isomers
- either trans isomerism.
cis
trans
H atom and CH3 group on same side of chain.
- H atom and CH3 group on opposite sides of chain.
Atactic configuration
- R groups randomly positioned.
ex: cis-isoprene
ex: trans-isoprene

14. Structures of Solid Materials
Thermoplastic polymers
soften when heated (eventually liquefy) &
harden when cooled.
processes that are reversible & repeated.
structures: most linear polymers & some
branched polymers with flexible chains.
properties: soft & less dimensional stability.
common polymers:
polyethylene.
poly(vinyl chloride).
polystyrene.
poly(ethylene terephthalate).
Polymers
ceramics
Metals
Classification of polymeric materials
Polymers classification
Copolymers
random
block
graft
alternating
- more monomers polymerized
together.
- 4 types:
random – A and B randomly positioned along chain.
alternating – A and B alternate in polymer chain.
block – large blocks of A units alternate with large blocks of B units.
graft – chains of B units grafted onto A backbone.
A – B –
Thermosetting polymers
permanently hard during their formation
& do not soften when heated.
processes that are not reversible &
repeated.
structures: most network polymers &
cross-linked polymers.
properties: hard, strong & high
dimensional stability.
common polymers:
epoxies.
phenolics.
polyester resins.

15. Structures of Solid Materials
Polymer crystallinity
ordered atomic arrangements involving
molecular chains.
crystal structures in terms of unit cells.
ex: thin platelets with chain folds at
faces.
polyethylene unit cell.
Polymers
ceramics
Metals
10 nm
Adapted from Fig. 4.12, Callister & Rethwisch 3e.
Polymer crystallinity
chain folded structure
polyethylene unit cell
crystalline
region
amorphous
- polymers rarely 100% crystalline.
difficult for all regions of all chains
to become aligned.
degree of crystallinity expressed as
% crystallinity.
some physical properties depend
on % crystallinity.
heat treating causes crystalline
regions to grow & % crystallinity to
increase.
Adapted from Fig , Callister 6e.
(Fig is from H.W. Hayden, W.G. Moffatt,
and J. Wulff, The Structure and Properties of Materials, Vol. III, Mechanical Behavior, John Wiley and Sons, Inc., 1965.)

16. Structures of Solid Materials
Polymer single crystal
single crystals – only for slow and
carefully controlled growth rates.
electron micrograph – multilayered
single crystals (chain-folded layers) of
polyethylene.
Polymers
ceramics
Metals
Polymer crystallinity
Polymer semi crystal
some semicrystalline polymers form
spherulite structures.
alternating chain-folder crystallites and
amorphous regions.
spherulite structure for relatively rapid
growth rates.
Cross-polarized light used - a maltese cross appears in each spherulite
Photomicrograph – Spherulites in polyethylene

17. End of Chapter 4