Thermoplastic polymers
processed by a heat-form-cool cycle
John Summerscales
Summary of lecture
• basic chemical names
• addition polymers
configuration/conformation
o stereoregularity/tacticity
o crystalline or amorphous
o transition temperatures
o
• condensation polymers
• ring-opening polymers
Naming basic chemicals
Number
C atoms
1
2
3
4
5
6
7
8
9
10
Prefix
single
bond
double
bond
triple
bond
MethEthPropButPentHexHeptOctNonDec-
-ane
-ane
-ane
-ane
-ane
-ane
-ane
-ane
-ane
-ane
-ene
-ene
-ene
-ene
-ene
-ene
-ene
-ene
-ene
-yne
-yne
-yne
-yne
-yne
-yne
-yne
-yne
-yne
Basic chemicals
C atoms
1
2
3
Name
Methane
Ethane
Propane
Formula CnH2n+2
CH4
C2H6
C3H8
Boiling point
-164°C (gas)
-89°C (gas)
-42°C (gas)
4
5
6
Butane
Pentane
Hexane
C4H10
C5H12
C6H14
-0.5°C (gas)
36°C (liquid)
69°C (liquid)
7
8
9
10
Heptane
Octane
Nonane
Decane
C7H16
C8H18
C9H20
C10H22
98°C (liquid)
125°C (liquid)
151°C (liquid)
174°C (liquid)
Paraffins/waxes
1000+
Polyethylene
C20H42 melts at 37 °C
H[CH2]nH
quasi-solid
solid
Transition temperature data from http://www.elmhurst.edu/~chm/vchembook/501hcboilingpts.html
Bond rotation
• Movie of rotation about a single bond
o
file taken from
http://plc.cwru.edu/tutorial/enhanced/files/polymers/struct/bond.mov
• Movie of rotation with different side groups
o
file taken from
http://plc.cwru.edu/tutorial/enhanced/files/polymers/struct/conform.swf
Geometric isomers
• cis:
• trans:
Chemical Groups (reactants)
• Acid
O
C
O
H
• Alcohol
HO
• Amine
H
H
N
• NB: nitrogen in amine has a free p-orbital
which can become part of a π-bond
Chemical Groups (products)
• Ester
O
C
O
• Amide
O
C
H
• Ether
O
N
Polymers
• Polymers are class of materials
where many small molecules (monomers)
are linked together by covalent bonds
to form long chains or networks
• an alternative name for polymers is
macromolecules
• a homopolymer has only 1 repeating unit
• a copolymer has 2 different repeating units
• a terpolymer has 3 different repeating units.
Polymers
• Thermoplastic - usually long straight chains
sometimes with short branches
o
copolymers AB (and terpolymers ABC) can be
alternating
---ABABABABAB-- block
---AAABBAAABB-- graft (type B branches on type A backbone)
 random
---AABABBBAAB--
• Thermoset - usually 3-dimensional networks
• Elastomers - 3-D networks with sparse
interlinks between chains (e.g. rubber)
Addition polymers
• reaction by opening double bonds
• all atoms from reactants end up in the product
• n CH2=CHX reacts to become [- CH2-CHX-]n
o
o
o
o
o
o
if X = H, the polymer is polyethylene
if X = CH3, the polymer is polypropylene
if X = Cl, the polymer is polyvinylchloride
if X = C6H5, the polymer is polystyrene
... this list is not exhaustive
if monomer is CF2=CF2,
the polymer is polytetrafluoroethylene
Configuration/Conformation
• Configuration
the arrangements of atoms on the polymer chain
o fixed relative positions of atoms
o
• Conformation
the arrangement of the atoms in space
o regular linear chains can crystallise
o branched/bulky side-groups or irregular copolymers
have longer repeat units
and are thus less likely to crystallise
but more likely to be amorphous
o
Stereoregularity -> tacticity
• Isotactic
o
characteristic groups
all on the same side
of the polymer chain
• Syndiotactic
o
characteristic groups
on alternate sides
along polymer chain
• Atactic - characteristic groups located at
random along the polymer chain
o
images from
http://plc.cwru.edu/tutorial/enhanced/files/polymers/struct/Struct.htm
Crystalline vs amorphous
• Crystalline polymers
o
molecules pack more closely leading to:
higher density
 better mechanical properties (more bonds/m3)
 better resistance to environmental degradation

o
NB: common polymers are partially crystalline

crystallites distributed in an amorphous matrix
• Amorphous polymers
o
random configuration
reduced properties re. crystalline materials
 transparent to white light (e.g. PS, PC, PMMA)

Crystallinity
• Two model structures have been proposed
• Images from
http://chem.chem.rochester.edu/~chem421/cryst.htm
http://www.pslc.ws/mactest/crystal.htm respectively
Fringed micelle
Folded lamella
Transition temperatures
• Tg = Glass transition temperature
segmental motion is frozen out
o brittle elastic below Tg
o tough/viscoelastic above Tg
o
• Tm = Crystalline melting point
o
only occurs in crystallites
• both temperatures may be a range
rather than a specific temperature
Transition temperatures
Rubbery
Specific volume
Amorphous/
glassy
Liquid
Crystalline solid
Tg
Tm
Temperature
Condensation polymers
• XOH + HY  XY + H2O
• HOXOH + HYH  HOXYH + H2O
o
further reactions with HOXOH and HYH
will produce a linear molecule
Condensation polymers
• Acid + base  salt + water
o
HCl + NaOH  NaCl + H2O
• Acid + alcohol  ester + water
o
R.C=O.OH + HO.R’  R.C=O.O.R’ + H2O
• Acid + amine  amide + water
o
R.C=O.OH + H2N.R’  R.C=O.HN.R’ + H2O
• If two reactive sites on each molecule,
then a polymer chain will result
Ring-opening polymers
• HOXOH + HYH  HOXYH +H2O
o
further reactions with HOXOH and HYH
will produce a linear molecule
• HOXH + HOXH  HOXXH +H2O
i.e. both reactants might be on one molecule
o but such a system could react with itself
to form a cyclic molecule if X > 4C atoms
o such a cyclic molecule can polymerise
without loss of water
(H2O already removed in cyclisation reaction)
o
Ring-opening polymers
• Ring-opening polymerisation
during composite manufacture has potential
to produce thermoplastic matrix composites
from RTM/RIFT
caprolactam to produce polyamide 6
(e.g. DSM Fiber Intermediates APA-6),
o laurolactam to produce polyamide 12
(e.g. EMS-Grivory APLC12), and
o cyclic butylene terephthalate oligomers to
produce PBT polyester (e.g. Cyclics Corporation).
o
Voluntary Plastic Container
Coding System
n
abc
• proposed by Society for the Plastics Industry
(SPI) in the United States of America
• remember Tm = Tg + 200°C (±~50°C)
so some common thermoplastics are.....
Polymer Acronym
Coding
Tg (ºC)
Tm (ºC)
Morphlgy
Low-density
polyethylene
LDPE
4
-130
+105
crystalline
High-density
polyethylene
HDPE
2
-125
+135
crystalline
Polypropylene
PP
5
-27 .. -10
+165 .. +170
crystalline
Polyamide
(nylon) 6,6
PA6,6
7
+55
+255
crystalline
Poly
vinylchloride
PVC (V)
3
+75 .. +80
--
amorphous
Polystyrene
PS
6
+90 .. +100
--
amorphous
Polyethylene
terephthalate
PET
1
+67 .. +80
265
crystalline
Polycarbonate
PC
7
+145 .. +150
--
amorphous
Polyoxymethylene
POM
7
< -150
+180
crystalline
Polyurethane
PU
7
+140
--
amorphous
Poly ether
ether ketone
PEEK
7
+144
367
crystalline
(acetal)
(PETE)
Periodic Table of Thermoplastics
(Tangram Technology)
http://polymer.w9of.com/wp-content/uploads/2011/01/Polymer-Periodic-Table.pdf
Summary of
thermoplastics lecture
• basic chemical names
• addition polymers
configuration/conformation
o stereoregularity/tacticity
o crystalline or amorphous
o transition temperatures
o
• condensation polymers
• ring-opening polymers