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SYNTHETIC ORGANIC POLYMERS

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Title: SYNTHETIC ORGANIC POLYMERS


1
SYNTHETIC ORGANIC POLYMERS
Convenor Dr. Fawaz Aldabbagh
2
Polymers are large molecules made up of repeating
units called Monomers The synthetic process is
Polymerization. E.g.
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
3
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
4
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)
5
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
Anionic Polymerization
Vinyl monomers with electron-donating groups
Cationic Polymerization
Monomers and reagents should be scrupulously
purified water and oxygen should be
removed. Polymerizations carried out at very low
temperatures
6
Anionic Polymerizations
Initiators include alkyl lithiums and sodium amide
7
Cationic Polymerization
-- the formed carbocation must be quite stable
Stable tertiary carbocation
stable oxonium ion
E.g. proton initiates polymerization of isobutane
(2-methylpropene)
Adhesive, sealant, insulating oil, lubricating oil
8
Reactions of water with reactive carbanions and
carbocations
Note viable substrates for anionic
polymerizations do not have ?-protons
9
Chain Reaction Free Radical Polymerization
Initiation
Propagation
Random Termination
Dead chains
10
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).
11
Examples of Polymers Prepared by Radical
Polymerization
Monomer
Polymer
n
Poly(styrene)
n
Poly(acrylonitrile)
n
Poly(methylacrylate)
n
Poly(vinylacetate)
12
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)
Ion-exchange resins, smart polymers
13
Radical Polarity
Polar Effects are important in radical
polymerizations, and can give alternating
copolymers
14
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

Chain polymerization without termination
e.g. nitroxide-mediated radical
polymerization (NMP)
Living
Initiator decomposes quickly, and polymer chains
have long life times
15
Nitroxide-mediated Controlled/living Radical
Polymerization (NMP)
?
propagation
T? Nitroxide P? Propagating radical
T? is sterically congested
  • Features
  • Molecular weight increases linearly with
    conversion
  • Narrow molecular weight distributions obtained
  • Polymer chains contain living ends enabling chain
    extension or block copolymer synthesis

Block copolymer synthesis
16
Conventional Radical Polymerization
Broad MWD
Dead Polymer
Controlled Radical Polymerization
Narrow MWD 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
17
Example of Block Copolymer Formation
Please correct block copolymer structure in
questions
Reversible trapping added to propagation to
prevent irreversible termination
First living poly(styrene) block heated in the
presence of methyl acrylate to give diblock D
18
n
AIBN
Poly(methyl methacrylate)
perspex
MMA
Nitroxides cannot control MMA Polymerizations
McHale, Aldabbagh, Zetterlund, J. Polym. Sci.
Part A Polym. Chem. 2007, 45, 2194-2203
19
Alternating, Block and Graft Copolymers are made
by radical copolymerization
Graft Copolymer Formation
20
Recent Example of a Graft Copolymer Synthesis

Copolymerization
macromonomer
monomer
Graft copolymer
Poly(AA)
NIPAM

N-Isopropylacrylamide NIPAM monomer (excess)
Poly(acrylic acid) macromonomer
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
21
Copolymerization of Poly(AA) Macromonomer with
NIPAM in ethanol at 60 ºC
macromonomer
4
63
40
19
Shift to higher MW
22
Dual-Responsive Smart Graft Copolymer
Copolymerization

macromonomer
Monomer
Graft copolymer
Poly(AA)
NIPAM
Graft copolymer in NaOH solution (40ºC)
Poly(NIPAM) in water (40ºC)
Insoluble in water
Soluble in NaOH (aq)
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
23
Ziegler-Natta Chain (Addition) Polymerization
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
Few monomers polymerized by Z/N
24
Ziegler-Natta Addition Polymerization
Isotactic polymerization
s-complex
p-complex
25
Stereochemistry and Polymers
Many useful polymers, such as poly(styrene),
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. 
26
Step-growth Polymerization
Step-polymers are made by allowing difunctional
monomers with complementary functional groups to
react with one another
Condensation between two molecules
Poly(ethylene terephthalate)
terephthalic acid
ethylene glycol
PET
This is an example of a poly(ester) The reaction
is a transesterification
Recyclable plastic bottles and textile fabrics
Using a condensation reaction
27
These are poly(amides) bristles of
toothbrishes, stockings, rope, tires, carpet fibre
Step-growth Polymerization
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
First patented by BASF
Also opened by cations anions
High temp. to drive off water
Nylon 6 is made by heating caprolactam to about
250 ºC with about 5-10 water
28
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)

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
29
Step-growth Polymerization
30
Step-addition no by-products
Insulation foam, HP adhesives, sealants, carpet
underlay
Bayer-patented
180 C
Poly(urethane)
Lower Temp. than condensation reactions
rt
bisdiene
benzoquinone
Cyclic diene held cis is very reactive e.g.
dicyclopentadiene
Chain-growth condensation
BF3
CH2N2 CH2
N2
n
Impurity found in diazomethane
31
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
32
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.
33
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
34
Recycling of plastic containers and wrapping
Chemical Recycling by Eastman Kodak
methanolysis
H
PET
These monomers are purified by distillation or
recrystallization and used as feedstocks for
further PET film manufacture.
35
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.
4. Draw structures of the polymers obtained from
the following reactions
5. Give one example of an isotatic polymer and
block and alternating copolymer. Provide
reactions (with conditions) and mechanisms for
their synthesis.
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