ADDITION POLYMERS

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ADDITION POLYMERS
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ADDITION POLYMERS
A
A
A
A
A
A
A
A
monomers
polymer
linear
ethylene (ethene)
polyethylene
branched
propylene (propene)
polypropylene
many (n) monomers
n A
(A)n
polymer
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PREPARATION OF ADDITION POLYMERS
CATIONIC MECHANISM
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POLYMERIZATION
concentrated,
smaller amount,
not cold
Polymerization
polymer
A cationic polymerization catalyst (Ziegler
Catalyst) can be used instead of H2SO4.
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CATIONIC MECHANISM
could be as simple as a proton from sulfuric acid
styrene

Catalyst
resonance stabilized
(Markovnikoff)
H2SO4 or
()
()
cationic catalyst
()
etc.
Polystyrene
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POLYSTYRENE
n
repeating unit
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COPOLYMERS
Polymers which are formed by combining two
different monomers in alternating fashion are
called copolymers.
A
B
A
B
A
B
A
B



butadiene
styrene
styrene-butadiene rubber (SBR)
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THERMOPLASTICS
Thermoplastics can be softened or melted by
heat and reformed (molded) into another shape.
Most addition polymers are thermoplastics.
The polymer chains are held together by
weak interactions (noncovalent bonds) such as
van der Waals forces, London dispersion
forces and Dipole-dipole attractions. These
interactions are disrupted by heating,
allowing the chains to become independent of each
other.
Heating and reforming can be repeated
indefinitely (if degradation doesnt occur). This
allows recycling.
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PLASTICIZERS
Most polymers of high molecular weight are quite
rigid.
These polymers can be softened and made flexible
by adding plasticizers, usually dialkyl
phthalate esters, such as dibutyl phthalate, a
high boiling liquid.
dibutyl phthalate
The plasticizer separates the individual polymer
chains from one another. It acts as a lubricant
which reduces the attractions between the polymer
chains.
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THERMOSET PLASTICS
Thermoset plastics melt initially, but on
further heating they become permanently hardened.
Once formed, thermoset plastics cannot be
remolded, and they cannot be recycled.
On heating, thermoset plastics become
cross-linked (covalent bonds form between the
chains). The cross-linked chains form a rigid
network
heat
cross-linked
linear
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HIGH-DENSITY POLYMERS
Linear polymers with chains that can pack
closely together. These polymers are often quite
rigid.
LOW-DENSITY POLYMERS
Branched-chain polymers that cannot pack
together as closely. There is often a degree of
cross-linking. These polymers are often more
flexible than high- density polymers.
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SOME COMMON ADDITION POLYMERS
uses
monomer
polymer
example
most common polymer bags, wire insulation, squeeze
bottles
polyethylene
polypropylene
fibers, bottles, indoor-outdoor carpet
polystyrene
styrofoam, inexpensive molded objects household
items, toys
synthetic leather, clear bottles, floor
coverings, water pipe
polyvinyl chloride
(PVC)
non-stick surfaces, chemically resistant items
Teflon
polyacrylonitrile
fiber used in sweaters, blankets, carpets
(Orlon, Acrilan)
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COMMON ADDITION POLYMERS (cont)
uses
monomer
polymer
example
poly(methyl methacrylate)
unbreakable glass, latex paint
(Lucite, Plexiglass)
adhesives, latex paints, textile coatings chewing
gum
poly(vinyl acetate)
(PVA)
natural rubber
the polymer is cross- linked with sulfur
(vulcanization)
neoprene rubber
cross-linked with ZnO, resistant to gasoline
and oil
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PREPARATION OF ADDITION POLYMERS CATIONIC
AND FREE-RADICAL PROCEDURES
MECHANISMS
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CATIONIC MECHANISM
could be as simple as a proton from sulfuric acid
styrene

Catalyst
resonance stabilized
(Markovnikoff)
H2SO4 or
()
()
cationic catalyst
()
etc.
Polystyrene
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RADICAL MECHANISM
styrene
.
.
Catalyst
resonance stabilized
(.)
(.)
Catalyst
(.)
.
.
etc.
Polystyrene
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ZIEGLER-NATTA CATALYSTS POLYMERIZATION
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Ziegler-Natta Catalysts
Cationic, anionic or radical processes are not
involved and the polymerization is often
stereoselective (next slide).

potential coordination site fo alkene
insertion
etc.
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STEREOISOMERIC POLYPROPYLENE POLYMERS
stereoregular polymers
ISOTACTIC all methyl groups on the same side
SYNDIOTACTIC methyl groups alternate sides
not regular
ATACTIC methyl groups randomly oreinted
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CONDENSATION POLYMERS
A DIFFERENT TYPE OF POLYMER
NOT AN ADDITION POLYMER !
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CONDENSATION POLYMERS
Condensation polymers are copolymers made from
more than one type of monomer.
Many functional groups are used (instead of
alkenes) and each type of monomer has a
different functional group.
When condensation polymers are formed, a small
molecule (usually H2O) is often eliminated as
each bond forms.
Ethylene glycol
Terephthalic acid
Dacron polymer
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SOME COMMON CONDENSATION POLYMERS
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RECYCLING CODES
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CODE SYSTEM FOR PLASTIC MATERIALS
These codes allow consumers to separate plastics
for recycling.
polyethylene terephthalate
soft drink bottles
1
PETE
milk and beverage containers, products in squeeze
bottles
high-density polyethylene
HDPE
2
polyvinyl chloride
bottles with cleaning agents in them,
some shampoo bottles
3
V
thin plastic bags, plastic wrap
low-density polyethylene
LDPE
4
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PLASTIC MATERIALS CODE SYSTEM (cont)
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PP
polypropylene
heavy-duty, microwavable containers used in the
kitchen
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PS
polystyrene
foam beverage cups, envelope windows
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Other
All other resins, multilayered materials, containe
rs made of other materials
ketchup bottles, snack containers, mixtures
where the top differs from the bottom
The codes are frequently stamped on the bottom of
containers.