SYNTHETIC ORGANIC
POLYMERS
Convenor: Dr. Fawaz Aldabbagh
Polymers are large molecules made up of repeating units called Monomers
The synthetic process is Polymerization.
E.g.
Polymerization
H2C CH2
CH2 CH2
Monomer
Polymer
O
Monomer
n
Polymerization
CH2 CH2 O
n
Polymer
Note – define repeating unit in terms of monomer structure
Degree of Polymerization is the number of monomer units in a Polymer
However, for synthetic polymers it is more accurate to state average degree of
polymerization (DP
¯)
A polymer prepared from a single monomer is a homopolymer
If two or more monomers are employed, the product is a copolymer
Linear polymer has no branching
Graft copolymer is an example of a branched network
Two main classifications of Polymerization
Addition reaction or Chain growth
Molecular weight increases by successively adding monomers to a reactive polymer
chain end resulting in high molecular weights at low conversions.
STEP reaction or growth
Polymers are formed by linking monomer molecules to form dimers, trimers and
higher species in a step-wise fashion. The most abundant species react, and thus
high molecular weight formed only beyond 99% conversion.
Polymerization Conversion (p)
P =
M0 - Mt
M0
M0 = initial number of monomer molecules
Mt = Number of monomer molecules at time t
Ionic Chain (addition)-Growth Polymerization
The choice of ionic procedure depends greatly on the electronic
nature of the monomers to be polymerized
Vinyl monomers with electron-withdrawing groups
CN
CN
CO2R
CO2R
CO2R
Anionic Polymerization
Vinyl monomers with electron-donating groups
N
OR
SR
Cationic Polymerization
Monomers and reagents should be scrupulously purified; water and oxygen
should be removed.
Polymerizations carried out at very low temperatures
Anionic Polymerizations
Initiators include alkyl lithiums and sodium amide
Cationic Polymerization
-- the formed carbocation must be quite stable
+
Stable tertiary carbocation
H+
OR
H+
+
OR
stable oxonium ion
E.g. proton initiates polymerization of isobutane (2-methylpropene)
BF3/H2O
n
Adhesive, sealant, insulating oil, lubricating oil
Reactions of water with reactive carbanions and carbocations
H
_
CN
CN
O
H
H
acid
CN
CN
CN
CN
n
+
_
OH
Note – viable substrates for anionic polymerizations do not have -protons
H
H
O
H
base
H
+
OMe
OMe
OMe
OMe
OMe
n
+
H3O+
OMe
n
n
Chain Reaction: Free Radical Polymerization
RO
Initiation
2 RO
OR
RO
+
RO
Ph
Propagation
Ph
RO
RO
Ph
n
Ph
Random Termination
n
Ph
Ph
Dead chains
Conventional Radical Polymerization
Advantages –
1/wide range of vinyl monomers polymerizable
2/can be carried out in bulk, water, organic solvents and other solvents
3/no rigorous purification or drying of reagents required
Conditions: Usually heat required for initiation
Initiator decomposition time should be considered
- Amount of initiator, reaction temperature and initiator half-life (slow decomposition)
Initiation Rate = Termination Rate - “steady state” kinetics apply
Overall,
[radical concentration] = low
Since termination (disproportionation and coupling mechanism) is random, a broad
MWD results. This polymer is dead (cannot initiate new monomer additions).
Examples of Polymers Prepared by Radical Polymerization
Monomer
H
H
n
Polymer
CH2CH
n
Poly(styrene)
H
n
H
H
CH2CH
CN
H
H
H
n
CH2CH
H
Poly(acrylonitrile)
n
CN
C
O
MeO
n
O
Poly(methylacrylate)
OMe
H
H
n
H
O
Me
CH2CH
n
O
O
C
Me
O
Poly(vinylacetate)
Advantages of Radical Polymerization
1. Wide variety of vinyl monomers can be polymerized (electron rich and
deficient DBs)
2. Can be carried out in bulk and in a wide variety of solvents, which include
water and organic solvents
3. No rigorous purification of reagents or drying of solvents required
4. Rapid formation of high molecular weight polymer after small conversions of
monomer to polymer ( chain (addition) polymerization)
5. Living/controlled polymerizations enable easy formation of block copolymers
and sophisticated architectures
75% of commercial polymers are made by radical polymerizations
Some monomers can only be polymerized by radical means, e.g. acrylic acid (AA)
H
H
H
H
C
C
AIBN
C
C
H
C
O
OH
H
n
COOH
Ion-exchange resins, smart polymers
Radical Polarity
Polar Effects are important in radical polymerizations, and can give
alternating copolymers
CN
R

R

Ph
Ph
Ph
CN
R
n
Ph
CN
Ph
CN
Chain Reaction – initiation, propagation, termination
Chain polymerization with termination
e.g. conventional radical polymerization
Life time of polymer radical chain is about 1 second
Initiator added so to slowly decompose throughout
polymerization time
Typically, rate of initiation = rate of termination
Therefore, [propagating radical] remains constant
Steady State
DP
100
50
conversion
Chain polymerization without termination
e.g. nitroxide-mediated radical polymerization
(NMP)
DP =
DP
“Living”
[monomer]
[Initiator]
Initiator decomposes quickly, and polymer chains have long life times
100
50
conversion
Nitroxide-mediated Controlled/living Radical Polymerization (NMP)
∆
P
T
+
P
T
propagation
T● = Nitroxide
P● = Propagating radical
T● is sterically congested
Features:
1. Molecular weight increases linearly with conversion
2. Narrow molecular weight distributions obtained
3. Polymer chains contain living ends enabling chain extension or block
copolymer synthesis
Block copolymer synthesis
AAAA
n
A
T
AAAA
n
A
+
T
propagation
Bn
AAAA
n
A
BBBB
B
n
T
Conventional Radical Polymerization
Broad MWD
Dead Polymer
Controlled Radical Polymerization
T
T
T
T
T
Narrow MWD
T
Living Polymer
Life time of radicals extended from 1 second to hours, as the radicals
do not get involved in irreversible bimolecular termination reactions,
since radicals are trapped by nitroxide reversibly
Initiator must decompose quickly to insure narrow MWD
Example of Block Copolymer Formation
n-1
Ph
Ph
m
O
OMe
D : n = 60
: m = 20
AIBN, heat
SG1
Ph
n
n = 60
Ph
First living poly(styrene) block
heated in the presence of methyl
acrylate to give diblock D
P
O
O OEt
n-1
Ph
Please correct block copolymer structure in questions
Reversible trapping added to
propagation
to
prevent
irreversible termination
OEt
N
heat
Ph
n-1
Ph
+
N
O
OEt
P
OEt
O
SG1
propagation
OMe
m = 20
m
O
n-1
Ph
Ph
O N
m
O
OMe
D : n = 60
: m = 20
O
P
O
O
Me
H
C
C
H
C
Me
n
O
CH2 C
C
AIBN
MeO
n
O
Poly(methyl methacrylate)
OMe
“perspex”
MMA
Nitroxides cannot control MMA Polymerizations
H
CH3
C
+
C
CO2Me
H
PMMA
N
O
OEt
P
OEt
O
SG1
H
disproportionation
C
CH2
C
H
PMMA=
+
CO2Me
OEt
N
P
OEt
OH O
SG1-H
McHale, Aldabbagh, Zetterlund, J. Polym. Sci. Part A: Polym. Chem. 2007, 45, 2194-2203
Alternating, Block and Graft Copolymers are made by radical copolymerization
AIBN, heat
excess small
monomer
macromonomer
Graft Copolymer
Graft Copolymer Formation
Recent Example of a Graft Copolymer Synthesis
Copolymerization
+
macromonomer
monomer
Poly(AA)
Graft copolymer
NIPAM
H
Br
H
H
CH2 C
CH2 C
O
C
OH
O
C
CH C
n 2
C
C
OH
H2C
H
+
OCH2CH3
O
Poly(acrylic acid) macromonomer
CH
H3C
C
O
CH N
H3C
H
N-Isopropylacrylamide
NIPAM monomer (excess)
Insoluble in water above the lower critical solution temperature (LCST)
McHale, Aldabbagh, Carroll, Yamada, J. Polym. Sci. Part A: Polym. Chem. 2007, 45, 4394-4400
Copolymerization of Poly(AA) Macromonomer with NIPAM in ethanol at 60 ºC
0.6
W (log M )
0.5
macromonomer
4%
0.4
0.3
63%
40%
19%
0.2
0.1
0.0
2
3
4
5
6
7
log M
Shift to higher MW
8
Dual-Responsive “Smart” Graft Copolymer
Copolymerization
+
macromonomer
Poly(AA)
Insoluble in water
Monomer
Graft copolymer
NIPAM
Soluble in NaOH (aq)
Poly(NIPAM)
in water
(40ºC)
Graft copolymer
in NaOH solution
(40ºC)
Graft copolymer
in NaOH (50ºC)
McHale, Aldabbagh, Carroll, Yamada, J. Polym. Sci. Part A: Polym. Chem. 2007, 45, 4394-4400
Gibbons, Carroll, Aldabbagh, Yamada, J. Polym. Sci. Part A: Polym. Chem. 2006, 44, 6410-6418
Ziegler-Natta Chain (Addition) Polymerization
H
H
C
C
H
H
TiCl4/AlEt3
1-4 atm, rt
n
Milder conditions than radical polymerization
HDPE (high density poly(ethylene) is 3-10 times stronger than LDPE
Less cross-linking, as terminal DBs less reactive than substituted DBs of radical
polymerization
Termination reaction
H
H
Cl3Ti
Few monomers polymerized by Z/N
+
Cl
H Ti Cl
Cl
Ziegler-Natta Addition Polymerization
Isotactic polymerization
TiCl4 / AlR3
R
1-4 atm, rt
n
R
Cl3Ti
TiCl4 + AlR3
Cl3Ti
AlR2
R + Cl
scomplex
AlR2
Cl
R
Cl3Ti
Cl3Ti
R
Cl3Ti
pcomplex
Cl3Ti
R
Cl3Ti
R
Cl3Ti
R
Cl3Ti
n
R
R
Stereochemistry and Polymers
M any useful pol ym e r s, suc h as pol y( st yr e ne ),
poly(acrylonitrile) and poly(vinyl chloride) are atactic as
normally prepared. Customized catalysts that effect
stereoregular polymerization of poly(propylene) and
some other monomers have been developed, and the
improved properties associated with the increased
crystallinity of these products has made this an
important field of investigation.
Amorphous polymer – melts to
a hard rubbery, glassy state
The properties of a given polymer will vary considerably with its tacticity. Atactic poly(propylene)
is useless as a solid construction material, and is employed mainly as a component of adhesives
or as a soft matrix for composite materials. In contrast, isotactic polypropylene is a high-melting
solid (ca. 170 ºC) which can be molded or machined into structural components.
Because poly(propylene) rope is so light, it is the only rope that floats. For
this reason, it is very popular among ropes for pool makers and water
sports. Also when wet it is flexible and does not shrink.
Step-growth Polymerization
Step-polymers are made by allowing difunctional monomers with
c o m p l e m e n t a r y f u n c t i o n a l g r o u p s t o r e a c t w i th o n e an o t h e r
Condensation between two molecules
O
HO
O
+
MeO
OMe
terephthalic acid
O
O
C
C OCH2CH2O
n
OH
ethylene glycol
Poly(ethylene terephthalate)
This is an example of a poly(ester)
The reaction is a transesterification
Using a condensation reaction
PET
Recyclable plastic
bottles and textile
fabrics
Step-growth Polymerization
These are poly(amides) – bristles of toothbrishes,
stockings, rope, tires, carpet fibre
Molten nylon spun
into fibres
- H2O
260-280 °C
250 psi
First patented by Dupont
MW = 10,000, m.pt. 250 °C, fibres stretched (to increase strength) to 4 times their length
Self-Condensation or Ring-Opening Polymerization
Also opened by
cations & anions
First patented by BASF
High temp. to drive off water
Nylon 6 is made by heating caprolactam to about 250 ºC with about 5-10% water
Step-growth Polymerization
1. Polymers retain their functionality as end groups at the
end of the polymerization
2. Only a single reaction is responsible for polymer formation
3. Molecular weight increases slowly even at high
conversion. This is given by the Carothers equation,
where conversion is (p)
DP =
1
1-p
At 98% conversion, the degree of polymerization is only 50%
Larger chains react only at very high conversion
4. Exact stoichiometric balance and very pure monomers
are required to achieve high molecular weights
5. Equilibrium reactions – necessary to remove by-product
Step-growth Polymerization
Step-addition – “no by-products”
O
C
N
N
180 °C
O
Insulation foam, HP adhesives, sealants,
carpet underlay
C
O
+
Bayer-patented
HO
OH
O
N
N
H
H
O
O
n
Poly(urethane)
Lower Temp. than condensation reactions
O
CH2
O
rt
+
CH2
6
6
n
O
bisdiene
O
benzoquinone
Cyclic diene held cis is very reactive
e.g. dicyclopentadiene
Chain-growth condensation
CH2N2
BF3
[ CH2 ]n
+
N2
Impurity found in diazomethane
Time for litter to biodegrade
Product
Time to biodegrade
Paper
2-5 months
Wool socks
1 to 5 years
Plastic coated paper milk cartons
5 years
Plastic bags
10 to 20 years
Nylon fabric
30 to 40 years
Aluminum cans
80 to 100 years
Plastic 6-pack holder rings
450 years
Glass bottles
1 million years
Plastic bottles
Forever
Plastic resin identification codes (1)
Codes
Descriptions
Recycled products
Polyethylene terephthalate (PET, PETE) is clear, tough, and
has good gas and moisture barrier properties. Commonly
used in soft drink bottles and many injection molded. Other
applications include strapping and both food and non-food
containers. Cleaned recycled PET flakes and pellets are in
great demand for spinning fiber for carpet yarns, producing
fiberfill and geo-textiles.
Fiber, tote bags, clothing,
film and sheet, food and
beverage containers, carpet,
strapping, fleece wear,
luggage and bottles.
High Density Polyethylene (HDPE) is used to make bottles for
milk, juice, water and laundry products. Unpigmented bottles
are translucent, have good barrier properties and stiffness,
and are well suited to packaging products with a short shelf
life such as milk. Because HDPE has good chemical
resistance, it is used for packaging many household and
industrial chemicals.
Bottles; pipe, buckets,
crates, flower pots, garden
edging, film and sheet,
recycling bins, benches,
dog houses, plastic lumber,
floor tiles, picnic tables,
fencing.
Polyvinyl Chloride or PVC has excellent chemical resistance,
good weatherability, flow characteristics and stable electrical
properties. The vinyl products can be broadly divided into
rigid and flexible materials. Bottles and packaging sheet are
major rigid markets, but it is also widely used as pipes and
fittings, siding, carpet backing and windows. Flexible vinyl is
used in wire and cable insulation, film and sheet, floor
coverings synthetic leather products, coatings, blood bags,
medical tubing and many others.
Packaging, binders, decking,
paneling, gutters, mud flaps,
film and sheet, floor tiles
and resilient flooring, cables,
mats, cassette trays,
electrical traffic cones,
boxes, garden hose, mobile.
Plastic resin identification codes (2)
Codes
Descriptions
Recycled products
Low Density Polyethylene (LDPE) used predominately in film
applications due to its toughness, flexibility and relative
transparency, making it popular for use in applications where
heat sealing is necessary. LDPE is also used to manufacture
some flexible lids and bottles and it is used in wire and cable
applications.
Shipping envelopes,
garbage can liners, film
and sheet, furniture,
compost bins, paneling,
trash cans, landscape
timber, lumber
Polypropylene (PP) has good chemical resistance, is strong, and
has a high melting point making it good for hot-fill liquids. PP is
found in flexible and rigid packaging to fibers and large molded
parts for automotive and consumer products.
Automobile battery cases,
signal lights, battery
cables, brooms, brushes,
oil bins, funnels, bicycle
racks, trays pallets,
sheeting.
Polystyrene (PS) is a versatile plastic that can be rigid or foamed.
General purpose polystyrene is clear, hard and brittle. It has a
relatively low melting point. Typical applications include
protective packaging, containers, lids, cups, bottles and trays.
Light switch plates, vents,
thermal insulation, desk
trays, rulers, license plate
frames, foam packing,
foam plates, utensils
Other. Use of this code indicates that the package in question is
made with a resin other than the six listed above, or is made of
more than one resin listed above, and used in a multi-layer
combination.
Bottles, plastic lumber
Recycling of plastic containers and wrapping
Chemical Recycling by Eastman Kodak
methanolysis
O
O
C
C OCH2CH2O
CH3OH
H+
n
O
HO
O
C
MeO
C
+
OMe
PET
These monomers are purified by distillation or recrystallization and used
as feedstocks for further PET film manufacture.
OH
Representative Exam Questions
1. Using one appropriate monomer for each polymerization classification, discuss the mechanism and
kinetics;
(a) Step-growth, b) conventional (non-living) chain (addition), c) living chain (addition) polymerizations.
In your answer give details of reaction conditions and reagents required.
2. (a) Discuss the stability of nitroxide radicals, and there use in living radical polymerizations.
(b) Why is it not possible to control the radical polymerization of methyl methacrylate with nitroxides?
3. How would you prepare the following polymers? Give reaction conditions, reagents and detailed
mechanisms for each polymerization. Name polymers A-D.
n
n
n
C
B
n-1
Ph
Ph
m
O
OMe
D : n = 60
: m = 20
A
4. Draw structures of the polymers obtained from the following reactions;
CO2Me
+
MeO2C
O
HO
OH
H+
KOH
5. Give one example of an isotatic polymer and block and alternating copolymer. Provide reactions (with
conditions) and mechanisms for their synthesis.