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Chem 471 Part 4. Industrial Polymers · 4.1 Polymer Terminology Polymer a large molecule composed...
Transcript of Chem 471 Part 4. Industrial Polymers · 4.1 Polymer Terminology Polymer a large molecule composed...
Chem 471 Part 4. Industrial Polymers
4.1 Polymer Terminology
4.2 The Big Six Industrial Polymers
4.3 Step- and Chain-Growth Polymerization
4.4 Co-Polymers
4.5 Thermoset Polymers
4.1 Polymer Terminology
Polymer a large molecule composed of many repeating units called
monomers (from poly meaning many and meros meaning unit)
Monomer a subunit making up a polymer
Oligomer a polymer with a small number of repeating units
Thermoplastic a polymer that softens or melts when heated and
dissolves in suitable solvents
Thermosets polymers with elaborately cross-linked three-dimensional
structures which are set or hardened by undergoing a chemical
process during the manufacturing of the final product,
decompose on heating, insoluble in any solvent
length of the chain (number of monomer units)
three-dimensional arrangement of polymer chains in the solid
chain branching
chemical composition of the monomer units
bonding between chains (cross linking)
orientation of monomer units within the chain
for copolymers, the ordering of different monomer units in the chains
( ABABABABA, AAABBAAABBAAABB, etc.)
endless possibilities for manufacturing different kinds of polymers
Factors influencing polymer properties
4.2 Industrial Polymers: The Big Six
1
2
3
4
5
6
HOOC COOH HOOH
terephthalic acid ethylene glycol
Symbol Monomer(s) Polymer Properties
H
HH
H
ethylene
H
HH
H
ethylene
vinyl chloride
H
ClH
H
H
CH3H
H
propylene
H
PhH
H
styrene
Name
polyethylene terephthalate (PET or PETE)
polyethylene (HDPE)
polyvinyl chloride (PVC)
polyethylene (LDPE)
polypropylene (PP)
polystyrene (PS)
transparent, high impact strength,
impervious to acid and air, not subject to
stretching, most costly of the six
similar to LDPE (low density polyethylene), more
opaque, denser, tougher, more crystalline and rigid
rigid thermoplastic, impervious to oils and most
organic materials, transparent, high impact strength
opaque, white, soft, flexible, impermeable to water
vapor, unreactive toward acids and bases, absorbs oils
and softens, melts at 100 to 125 oC, does not become
brittle until –100 oC, oxidizes on exposure to sunlight.
opaque, high melting point (160 to 170 oC), high
tensile strength and rigidity, lowest density commercial
plastic, impermeable to liquids and gases, smooth
surface with high luster
glassy, sparkling clarity, rigid, brittle, easily fabricated,
upper temperature use 90oC, soluble in many organic
materials
Industrial Polymers (“Plastics”)
Big Six production / millions of tonnes per year
polyethylene 100
polypropylene 60
polyethyleneterephthalate 60
polyvinylchloride 40
polystyrene 15
Other common polymers polyurethanes polyesters
polymethylmethacrylate (acrylic) polycarbonates
polyacrylonitrilebutadienestyrene (ABS) polyamides (e.g., nylons)
polystyrenebutadiene (synthetic rubber) poylisoprene (rubber)
Uses of industrial polymers about 1/3 for construction (insulation, pipes, siding, flooring, framing, etc.)
about 1/3 for packaging (bottles, pails, bags, wraps, etc.)
other consumer products (textiles, automotive, electronics, etc.)
Importance of industrial polymers
100 kg of plastics produced per person per year (much higher in “developed” countries)
Ever considered a world without plastics? Clothing only from cotton, wool,
leather, fur? Other items only from wood, metal, stone, glass or ceramics?
4.3 Chain- and Step-Growth Polymerization Chain Growth Polymerization
intermediates in the process are transient free radicals, ions or metal complexes
and cannot be isolated
once the chain is initiated, the monomer units add on very quickly and the
molecular weight builds up in a fraction of a second
the monomer concentration decreases steadily throughout the reaction
long reaction times have little effect on the molecular weight, but do affect the yield
at any time the reaction mixture contains monomer and fully grown polymer, but a
low concentration of growing chains
the monomers frequently contain carbon-carbon double bonds, but can contain
cyclic ethers and aldehydes
there is no net loss of atoms in the polymerization reaction
examples:
n
CH2 OCH2=Onorn
nO
XO
X
orn
n
X
X
occurs between molecules containing different functional groups
can be stopped at any time and low molecular weight oligomers can be isolated
the concentration of monomer does not decrease steadily in the reaction, but
disappears early because of oligomer formation
long reaction times gradually build up the molecular weight
after the early stages, there is neither much reactant nor much fully grown product
but a wide distribution of slowly growing oligomers
a small molecule such as water is frequently lost in the reaction
E.g.
hexamethylene diamine
adipic acid
Nylon 66n
NNH
O
O
H
-H2O
H2NNH2
HOOH
O
O
Types of polymerization Step Growth Polymerization
Chain Growth Polymerization Free radical Initiation
General mechanism:
chain transfer
disproportionation
coupling
branching
R'
n
R'RO
R' H
RO
R'
R'
R' R'n
++
n
RO
R'
R'
R' R'
R'RO
R'n
or
++R'
OR
R'Hnn
R'RO
R'n
R'OR
R'
R'RO
R'
H
n
ornnn
RO
R'
RO
R' R' R'
2R'
RO
R'
etc.
Termination
R'RO
R'
+ R'R'RO
Propagation
Initiation
R'RO
+ R'RO
RO2RO OR
Other types of chain transfer
intramolecular chain transfer
addition of a chain transfer agent
n
R'RO
R'
+ CCl4
R'RO
R' Cln
CCl3+
CCl3 R'+R'
Cl3Cetc.
R'
1)
2)
Mercaptans (RSH) and phenols (PhOH) also work as chain transfer agents.
CH2=CH2
HH
Chain Growth Polymerization
Common mono-olefin polymers
n n
Cl
F F
F F
nn
CN
polyethylene poly(vinyl chloride)
polyacrylonitrile(Orlon)
polytetrafluoroethylene(Teflon)
poly(methyl methacrylate)(Lucite, Plexiglass)
polystyrene
n n
H3C CO2CH3
Chain Growth Polymerization
Free radical polymerization of dienes
Conjugated dienes polymerize readily by a free radical mechanism:
n
n
polybutadiene
1,3-butadiene
ROOR 2 RO
Initiation
RO
Propagation
+ RO
RO+ RO
etc.
Termination(as before)
polybutadiene
n
S
heat
S
S
n
nVulcanization
polyisoprene
polychloroprene(Neoprene, Duprene)
CH3
n
nCl
Chain Growth Polymerization
Ionic Initiation
Olefins with an electron withdrawing group on the double bond can undergo ionic
polymerization by an anionic initiation mechanism:
Ionic polymerization can also occur with cationic initiation using a protic acid or a
Lewis acid:
H+
n
etc.
n
termination
(- H+
)
H2O
+ Li+
+ OH-
CNBu
CN H
nn
CNBu
CN
CNBu
CNCN
Li+
CNBu
CN+Bu
-Li
+
Chain Growth Polymerization
Metal Complex Initiation (Ziegler-Natta Catalysis)
catalysts discovered by Karl Ziegler and Giulio Natta in 1950 (Nobel Prize)
polymerize olefins and dienes with stereoregularity to give an isotactic polymer
for example, polypropylene:
isotactic atacticsyndiotactic
The mechanism is somewhat understood:
R
Ti
Cl
Cl Cl
Cl+
R
Ti
Cl
Cl Cl
ClTi
Cl
Cl Cl
Cl
R
Ti
Cl
Cl Cl
Cl
R
=Ti
Cl
Cl Cl
Cl
R
Ti
Cl
Cl Cl
Cl
R n n
Chain Growth Polymerization
Polyamides (Nylons) work began on synthetic polyamides in 1929 by Carothers (Dupont)
interested in replacing silk ( a natural polyamide)
first industrially prepared polyamide was Nylon 66
Nylons are usually prepared condensing a dicarboxylic acid with a diamine
the first number in a nylon’s name is the number of carbon atoms in the amine, the
second is the number in the carboxylic acid
other methods for making polyamides use amino acids or ring-opening lactams
n
N
O H
NH
O
H2NOH
O
-H2O
Nylon 6caprolactam
6-aminohexanoic acid
-H2O
Nylon 66 (MW = 10,000 - 25,000, n= 40 - 100)
n
NHN
O
O
hexamethylenediamineadipic acid
+H2N
NH2
HOOH
O
O
H
Step Growth Polymerization
block copolymers are another type of copolymers
a low molecular weight polymer is extended by reaction with a new monomer
using a “living polymer”
imagine we have a styrene polymer and then add some butadiene and polymerized
it further
we would end up with a number of styrene units bundled together and a number of
butadiene units also together
S S S S S B B B S S S B B S S S S
graft copolymers result when a polymer chain of one monomer is grafted onto an
existing polymer backbone by creating a free radical site along the
backbone which initiates growth of a polymer chain
e.g., styrene chains can be grafted onto a butadiene rubber backbone
4.4 Copolymerization
4.5 Thermoset Polymers Phenol-Formaldehyde Polymers (Phenolic Resins)
discovered in 1910 by Leo Baekland
given the tradename Bakelite
first fully synthetic polymer
the first step in the synthesis is to prepare an initial resin under basic conditions:
OH
OH-
O-
+ H2O
CH2=O
OH
CH2 O-
O-
CH2OH
OHOH
CH2OH
+ di and tri-substituted derivatives
under acidic conditions these compounds can be cross-linked:
H+OH
CH2
OH
OH
CH2
H
OH
OH
OH
CH2
OH
CH2OH2H
+
OH
CH2OH
Phenolic Resins the final product is highly branched
most linkages between aromatic rings are CH2 groups, but some CH2OCH2
linkages exist OH
OH HOOH OHA phenolic or Bakelite resin
a second method uses an acid catalyst to give a linear polymer
these compounds have no free hydroxymethyl groups for cross-linking
OH
CH2
OH OH
HO
HOH
OH H+
OH
OH2
OH
OHOH
OH
HOH
OH
higher molecular weightpolymers and crosslinkedthermosets
Urea Formaldehyde Resins urea gives cross-linked resins with formaldehyde
urea reacts with formaldehyde under basic conditions to produce a “methylolurea”
prolonged heating under acidic conditions results in a complex thermoset of
poorly defined structure which includes ring formation
reaction of this compound (these compounds) under acidic conditions gives a
fairly linear low molecular weight polymer
O
NHH2N OH
H+
-H2O
O
NHH2N
O
NHH2N OH
O
NHN OHNH2N
HH
OH
O
NHN OHNH2N
HH
OO
NHN OHNN
HH
O
Hn
O
NHH2N OH
O
NHH2N O-
H2COH2O+
O
NH-
H2N-OH+
O
NH2H2NH2O
+ HO-
Melamine-Formaldehyde Resins
N N
N NH2
NH2
H2N
+ H2CHON N
N NH
NH2
H2N CH2OH
N N
N NH2
NH2
H2N
N N
N NH
NH2
H2N
N N
N NH2
NH2
HN
N N
N N
N
N
N N
N N
N
N
N N
NN
N N
NN
N
N N
N
a melamine orFormica resin
melamine has three amino groups and six labile hydrogens and will form
thermoset resins with formaldehyde
the chemistry is similar to that for the urea resins
Polyurethane Foams
the important reaction here is the formation of a urethane linkage from an isocyanate and an alcohol
most useful polyurethanes are cross-linked
those commonly used in foams start with a diisocyanate like toluene diisocyanate (TDI) and a low molecular weight polyether
one way of ensuring crosslinking is to use a triol in the polymerization mixture
water is added to the mixture to produce a foam by reaction with some of the isocyanate
+RNCO H2O RNH2 + CO2
n
n
CH3
N
NH
O
O
O
O
CH3
NCO
NCOn
HOO O
OHx.s.+O
HOOH
H