BASIC TYPES OF POLYMERIZATIONS Flashcards
a process through
which a large number of monomer
molecules react together to form a
polymer
Polymerization
The macromolecules
produced from a polymerization may
have a _______________ structure.
linear or a branched
In _______, W. H. Carothers suggested a
classification of polymers into two
groups
1929
condensation (step-growth)
and addition (chain-growth) polymers
a process by which monomer
units are attached one at a time in chainlike
fashion to form a linear molecule
Chain-growth polymerization or addition
polymerization
In chain-growth polymerization or addition
polymerization, the composition
of the resultant product molecule is __________ of that of the original reactant monomer.
an exact
multiple
growth of a polymer chain proceeds exclusively by
reaction(s) between **monomer(s) and reactive
site(s) **on the polymer chain with regeneration of
the reactive site(s) at the end of each growth step
chain reaction
Chain-growth polymerization involves the addition of __________ to a rapidly growing chain
unsaturated
molecules
The most common unsaturated compounds that undergo chain-growth polymerization are
olefins
chain growth olefins, vinyl monomer example
image5
Chain-growth polymerization is a polymerization
technique where unsaturated monomer molecules
add onto the ________on a growing polymer chain ____________.
active site , one at a time
There are a ________ number of these
active sites at any moment during the polymerization which gives this method its key characteristics
limited
The growing polymer in chain-growth polymerization is a __________, and polymerization proceeds via ___________
free radical, chain
mechanism.
It is induced by the addition of ________________ or by ionic initiators.
-freeradical-forming reagents
It involves three fundamental steps
initiation,
propagation, and termination.
Growth centers can either be _____________________ in nature—
depending on the kind of initiator
system used.
ionic
(cationic or anionic), free radical,
or coordinational
Based on the nature of the growth centers, chaingrowth polymerization is further
classified as
- Free-Radical polymerization
- Cationic polymerization
- Anionic polymerization
- Coordination or stereoregular
polymerization
A chain
polymerization in which the
kinetic
-chain carriers are
radicals.
Free Radical
Polymerization
a method of
polymerization by which a
polymer forms by the successive
addition of free
-radical building
blocks (repeat units).
➢ Free
-radical polymerization
can be formed by
a number of different
mechanisms, usually involving
separate initiator molecules
Free radicals
1st step in free-radical polymerization wherein there is an active monomer
❑ Initiation
2ndstep in free-radical polymerization wherein there is a growth of the active
(free-radical) chain by sequential
addition of monomers
❑ Propagation
3rd step in free-radical polymerization wherein active chain give
the final polymer product.
❑ Termination
involves the acquisition of an
active site by the monomer
Initiation
This may occur spontaneously by the** absorption of
heat, light (ultraviolet and visible), redox
reagents, electricity, high-energy
radiation, etc. that is any process that
creates the essential free radicals.**
Initiation
initiation of free-radical
polymerization is brought about by the
addition of small quantities of
compounds called
initiators
Typical initiators include
peroxides, azo
compounds, Lewis acids, and organometallic
reagents
usually a **weak organic compound **
that can be decomposed thermally or by
irradiation to produce free radicals, which are
molecules containing atoms with unpaired
electrons.
initiator
example of organic
compounds that can be decomposed thermally
to produce free radicals.
Dialkyl peroxides (ROOR)
diacylperoxides (RCO-O-O-CO-R)
hydroperoxides (ROOH)
azo compound (RN>NR)
example of commonly used free-radical
initiator
Benzoyl peroxide azobisisobutyronitrile
dit-butylperoxide
Initiation in a free-radical polymerization consists of two steps
- dissociation of the initiator to form two radical species
- addition of a single monomer molecule to the initiating radical (the association step).
On heating, benzoyl peroxide decomposes to give
two free
radicals
(image 11)
(image 11)
what is the active site
the electrons in the oxygen–oxygen bond are unpaired and become the
active site.
R representing a generalized ____________, the free radical can
be written R
organic chemical group
initiation step usually includes the addition of the ___________________
first monomer molecule
In this initiation reaction the free radical attacks the monomer and adds to it. The double bond is
__________, and the _________ reappears at the far end
broken open , free radical
Chain initiation involves the __________ of a radical initiator molecule (I) which is
easily dissociated by heat or light into two free radicals (2 R°).
Each radical R°
then adds a first monomer molecule (M) to start a chain which terminates with a
monomer activated by the presence of an ____________ (RM1°).
I → 2 R°
R° + M → RM1°
dissociation , unpaired electron
Involves the linear
growth of the polymer chain by
the sequential addition of
monomer units to this active
growing chain molecule
Propagation
On the addition of each monomer,
the free radical moves to the
end
of the chain.
Chain growth is relatively rapid;
the period required to grow a
molecule consisting of say , __________
repeat units in on the order of ____________ s.
1000 , 10-2
to 10-3
a reaction of an active center on the
growing polymer molecule, which
adds one monomer molecule to
form a new polymer molecule
(RM1°) one repeat unit longer.
Propagation
RM1° + M → RM2°
RMn° + M → RMn+1°
Propagation
**active center **remains an atom with
an unpaired electron.
The addition of the second monomer and a
typical later addition step
radical polymerization
due to annihilation of the radical center of the propagating chain.
Termination
The termination step involves the reaction of any two free radicals with each other, either by
combination or disproportionation.
Two propagating chains are terminated when two radicals combine to form an electron-pair (covalent) bond
combination (or coupling)
reaction of the unpaired electrons of two chains to
form a covalent bond between them
Combination
product is a single polymer
molecule with the combined length of
the two reactant chains:
RMn° + RMm°→ Pn+m
Combination
A pair of radicals can form two new molecules
disproportionation
a disproportionation termination step involves two growing molecules that react to from
two
“dead chains”
complicated step in which two growing polymer
chains are rendered inactive.
a disproportionation
transfer of a hydrogen atom from one chain to the
other, so that the two product chain
molecules are **unchanged in length **but
are no longer free radicals
RMn° + RMm° → Pn + Pm
Disproportionation
a growing polymer chain is deactivated or terminated
by transferring its growth activity to a previously inactive species
Chain Transfer
additional step usually involved in a free-radical polymerization
Chain Transfer
a step in which the growing polymer chain RMn°
takes an atom X from an inactive molecule XY, terminating the growth of the polymer chain
RMn° + XY → RMnX + Y°.
Chain transfer
RMn° + XY → RMnX + Y°.
The Y fragment ls a __________ which adds more monomer M
to form a new growing chain YMn°
new active center
can be categorized according to the nature
of the growing polymer centers, which yields the classifications
cationic polymerization and anionic polymerization.
Ionic polymerization
involve chain carriers or reactive centers that
are organic ions or charged organic groups
Ionic polymerization
an
ionic polymerization in which the kinetic-chain
carriers are cations.
Cationic polymerization
___________ is a type of chain growth
polymerization in which a cationic initiator transfers
charge to a monomer, which then becomes _______________. This reactive monomer goes on to react similarly with other monomers to form a polymer.
Cationic polymerization , reactive
The types of monomers necessary for cationic
polymerization are limited to __________ with ________________
alkenes , electrondonating substituents and heterocycles.
The growth center in this class of ionic
polymerizations is cationic in nature.
Cationic
Polymerization
polymer cation adds on the monomer
molecules to it sequentially, just as the
polymer radical adds on the monomer in
radical polymerization.
Cationic
Polymerization
a true
catalyst that is restored at the end of the
polymerization and does not become
incorporated into the terminated polymer
chain
Cationic
Polymerization
The initiation of the polymerization is accomplished by catalysts that are _________________.
proton donors (e.g.,protonic acids such as H2SO4)
Typical catalysts that are effective for cationic
polymerization include
AlCl3
AlBr3
BF3
TiCl4
SnCl4
sometimes H2SO4
exception of H2SO4,
these compounds are all _________________.
Lewis acids with strong
electron-acceptor capability
To be effective, H2SO4 (lewis acids) catalysts generally require the presence of a Lewis base such as water, alcohol, or acetic acid as a __________
cocatalyst.
The monomer molecules act like _____________ and react with the catalyst, giving rise to polymer ions.
electron donors
The successive addition of the monomer to the polymer ion is the
propagation reaction
Monomers that polymerize readily with these catalysts include
isobutylene
styrene
α-methylstyrene
vinyl alkyl ethers.
Cationic polymerizations proceed at _______________
.
high rates at low temperatures.
For example, the polymerization at –100°C of isobutylene with BF3 or
AlCl3 as catalysts yields, within a few seconds, a polymer with _______________________
molecular weight as high as 10^6
polymerization of isobutylene with BF3 as the
catalyst procedure
(image 28 & 29)
- Boron Triflouride (catalyst) react with Water (cocatalyst) to produce Catalystcocatalyst
complex - Catalystcocatalyst complex react with isobutylene
- Isobutylene carbonium ion produced with gegen ion (Catalystcocatalyst complex without H+ outside)
Termination occurs either by ______________ to yield a polymer molecule with an unsaturated terminal unit and the original complex or through __________.
rearrangement of the ion pair
transfer to a monomer
in
which the kinetic
-chain carriers are anion
An ionic polymerization
a form of chain-growth polymerization or addition
polymerization that involves the
polymerization of monomers initiated with
anions.
An ionic polymerization
Anionic polymerizations are chain
-growth
processes in which the active center to which
successive monomers are added is a __________ that is associated with a ________________
negative ion
positive counterion
The _________________ between the
macromolecular anion and its counterion
depends on the nature of the respective ions and the medium in which the polymerization is proceeding
degree of interaction
While initiators for anionic polymerization are all _________ of varying base strengths, the initiator type required for a particular polymerization depends on the ease with which an anion can be formed from the monomer
electron donors
The initiator in an anionic polymerization may be any ____________, including Grignard reagents and other ________________ like n-butyl (n-C4H4) lithium
strong nucleophile
organometallic compounds
In general, the strength of the base required to initiate polymerization ______________ with increasing electronegativity of the
substituent on the monomer
decreases
commonly used initiator systems
for anionic polymerization
- Alkali metals and alkali metal complexes (Na, K, Li, and their stable complexes with
aromatic compounds, liquid ammonia, or
ethers - Organometallic compounds (butyl lithium,
boron alkyl, tetraethyl lead, Grignard reagent) - Lewis bases (ammonia, triphenyl methane,
xanthene, aniline) - High-energy radiation
initiate polymerization by transfer of
an electron to the double bond
of the monomer
Alkali metals and alkali metal
complexes
Initiation by** direct attack **on the
alkali metal involves transfer of
the ____________ from
a Group IA metal atom to the
monomer. A radical ion (i.e., a
species having both ionic and
radical centers) is formed
loosely helds electron
The radical ion may dimerize to give a dianion
Initiation in Anionic Polymerization
The initiation process making dianion results in a _____________ capable of propagating at both of its ends
bifunctional dicarbanion
species
Initiation by organometallic compounds
and Lewis bases occurs by a _____________
of these compounds on the double bond
of the monomer molecule.
direct attack
Before the Lewis base can attack the
monomer, it must _________, and only then can
a carbanion be formed.
ionize
Anionic propagation is generally much ________
than free-radical reactions
faster
Propagation in anionic addition polymerization
results in the __________________ of
monomer.
complete consumption
If the starting reagents are pure and if the
polymerization reactor is **purged of all oxygen **and traces of water, propagation can
proceed indefinitely or until all monomer are consumed.
anionic polymerization proceed indefinitely or until all monomer are consumed
“living” polymerization.
most important group of initiators in Coordination Polymerization
Ziegler-Natta catalysts
In polymerizations of this type, each monomer is inserted between the growing macromolecule and the initiator.
Coordination Polymerization
Complexing of the monomer to the initiator frequently precedes the **insertion process **and this polymerization
coordination polymerization.
The field of coordination polymerization
originated in the __________ with the
pioneering works of ______________________
mid-1950s ,
Karl Ziegler in
Germany and Giulio Natta in Italy
Karl Ziegler discovered in the early 1950s that a combination of aluminum alkyls with certain ______________________ such as TiCl4 or VCl4
generated complexes that would polymerize
_______________ at low temperatures and pressures,
producing ______________ with an essentially linear
structure, now referred to as ________________________
transition metal compounds
ethylene
polyethylene
high-density polyethylene (HDPE)
Giulio Natta’s work led to the
recognition that the catalytic complexes described
by Ziegler were capable of polymerizing _____________
(commonly known as ___________ in the chemical
industry) to yield stereoregular polymers.
1-alkenes
alpha olefins
Many polymers are now manufactured on a commercial scale using Ziegler-Natta catalysts, the most prominent among them being ________________ of high molecular weight.
stereoregular (isotactic)
polypropylene
Since the Ziegler-Natta catalyst systems appear to
function via formation of a **coordination complex ** between the catalyst, growing chain, and incoming monomer, the process is also referred to as
________________ and the catalysts as __________________
coordination addition polymerization
coordination catalysts
arises because of order in the
spatial structures of polymer chains.
Stereoregularity
Ziegler–Natta catalyst systems consist of a mixture of the following two classes of compounds:
- Compounds (normally halides) of transition elements of **groups IV to VIII **called catalyst ( TiCl3, TiCl4, VCl4, e, ZrCl4)
- Compounds (hydrides, alkyls, or aryls) of elements of groups I to IV, called cocatalysts (Al(C2H5)3, Al(i-C4H9)3)
Coordination Polymerization ordered spatial structures are determined by two
phenomena.
- During the polymerization step the monomer
units are** joined together in a regular sequence ** determined by the catalyst used and by the polymerization conditions. Regularity of this type cannot be altered or changed during subsequent physical treatment of the polymer. - Subsequently these regularly constructed
polymer chains spontaneously arrange
themselves into helical structures
Coordination
Polymerization -
Mechanism 3 types
(image 43)
isotactic
syndiotactic
atactic
Each polymer molecule __________ in size at a rapid
rate once its growth has been started. When the
macromolecule stops growing it ____________ generally
react with more monomers
increases , cannot
Growth of polymer molecules is caused by a _____________________
kinetic
chain of reactions.
Chain-growth polymerization involves the reaction
of _________________ that may be free
radicals, ions, or polymer-catalyst bonds
monomers with active centers
In ______________ polymerizations the mechanisms
and rates of the reactions that initiate, continue, and terminate polymer growth are _____________
chain-growth , different.
Chain-growth polymerization is usually
initiated by some _______________ and
the reaction is allowed to proceed under
conditions in which monomers ____________ react
with each other without the intervention of
an active center.
external source (energy,
highly reactive compound, or catalyst)
cannot
Polymers made by chain-growth reactions
are often ____________ by Carothers’s
definition. The most common polymers
made by these processes have only ____________ in their backbones.
addition polymers
carboncarbon links
refers to a type of polymerization mechanism in
which bi-functional or multifunctional
monomers react to form first dimers, then
trimers, longer oligomers and eventually
long chain polymers.
Step-growth polymerization
Many naturally-occurring and some
synthetic polymers are produced by
Step-growth polymerization
polyesters,
polyamides, polyurethanes, etc.example of
Step-growth polymerization
its** interlinking capacity**, or the
number of sites it has available for
**bonding with other molecules **under the
specific polymerization conditions.
functionality
A molecule may be classified as
______________________ depending on whether it
has one, two, or greater than two sites
available for linking with other
molecules.
monofunctional, bifunctional, or
polyfunctional
In step-growth polymerization, the **stepwise
reaction **occurs between pairs of _____________________ on the reacting
molecules.
chemically
reactive or functional groups
There is usually a **low-molecular-weight **byproduct such as water that is eliminated (or
condensed)
STEP-GROWTH
POLYMERIZATION
No reactant species has the chemical formula of the repeat unit, and the intermolecular reaction occurs every time a repeat unit is formed.
STEP-GROWTH
POLYMERIZATION
Each step may consist of a combination of two
polymers having a different or the same length to form a longer-length molecule.
STEP-GROWTH
POLYMERIZATION
In a step-growth polymerization, the molecular weight of the polymer chain builds
up ____________ and there is __________reaction mechanism for the formation of polymer
slowly , only one
The polymerization reaction proceeds by individual reactions of the functional
groups on the monomers.
STEP-GROWTH POLYMERIZATION
two monomers react to form a dimer
Monomer + Monomer = Dimer +H2O
STEP-GROWTH POLYMERIZATION
(1st step)
The dimer may now react with another dimer to produce a tetramer, or the dimer
may react with more monomer to form a trimer
Monomer + Dimer = Trimer +H2O
Dimer + Dimer = Tetramer + H2O
STEP-GROWTH POLYMERIZATION (2nd step so on)
Any two species in the reaction mixture can react with
each other.
STEP-GROWTH POLYMERIZATION
expressed by n-mer +m-mer = (n+m)-mer
Step polymerization
(n and m from 1- large number)
reaction between dimethyl terephthalate and ethylene glycol to form a
linear poly(ethylene terephthalate) or
PET molecule with methyl alcohol as a by-product
Small molecule is eliminated at each step
Polycondensation
The structural unit in step-growth polymers is __________________ to the structure of the starting
monomer(s).
not
identical chemically
Step-growth polymers derive their names from
the __________________ involved in the polymerization process.
reactive type (characteristic interunit linkage)
In the reaction between the glycol and
dicarboxylic acid, the resulting
polymer is a ___________, in consonance with the
general name of reactions between ____________________
polyester
hydroxyl groups (–OH) and carboxylic cid groups (–COOH)
Monomers react without the elimination of a small molecule.
Polyaddition
______________ form a large class of
commercially important
polymers.
Polyesters
A typical polyester
is ______________________ the largest volume
synthetic fiber. It is also used
as ______________ and in bottle
applications.
poly(ethylene terephthalate)
(PETP)
film (mylar)
s are a special class of polyesters derived from carbonic acid (image 56)
Polycarbonates
second largest by volume engineering thermoplastics next
to polyamides.
Polycarbonates
Polycarbonates preparation involves the linking together of _______________ ,
by reacting them with a derivative of carbonic acid such as ____________________________
aromatic dihydroxy compounds (2,2-bis(4-hydroxyphenyl) propane or bisphenol A)
phosgene or diphenyl carbonate
characterized by the
presence of amide linkages (–CONH–) on the polymer main chain.
Polyamides, or nylons
a large number of polyamides can be synthesized based on four main synthetic routes
(1) condensation reaction between a dicarboxylic acid and a diamine,
(2) reaction between a diacid chloride and a diamine,
(3) dehydration–condensation reactions of amino acids
(4) ring-opening polymerization of
lactams.
nylons may be divided into two categories
based on synthetic routes (1) and (2)
based on routes (3) and (4).
are condensation polymers obtained from the reaction of dianhydrides with diamines.
Polyimides
synthesized generally from aromatic dianhydrides and** aliphatic diamines**
Polyimides
from the reaction of aromatic dianhydrides with aromatic diamines.
aromatic polyimides
families of synthetic heterocycles with a wide
range of applications due to their physical and
chemical properties
Polybenzimidazoles and
Polybenzoxazoles
These man-made molecules are commonly used in medicinal, agricultural, and environmental areas due to their **ability to form strong metallic complexes **and their unique thermal and electrical
properties.
Polybenzimidazoles and
Polybenzoxazoles
also known as ladder
polymers or linker polymers
Aromatic ladder polymers,
type of polymer that consists of repeating units connected by aromatic linkers, such as benzene rings.
Aromatic ladder polymers,
popular for their **versatility **and
can be used in a variety of applications, including
coatings, adhesives, and membranes.
Aromatic Ladder Polymers
Ladder polymers are designed to have ____________________ and _____________________,
which makes them resistant to heat and degradation.
high
molecular weights and high melting temperatures
employed in the production of aminoplasts and phenoplasts, which are two different but related classes of thermoset polymers.
Formaldehyde
aminoplasts and phenoplasts
thermoset polymers
are products of the condensation reaction between either urea (urea–formaldehyde or UF resins) or** melamine** (melamine–formaldehyde or MF resins) with formaldehyde.
Aminoplasts
are prepared from the condensation products of phenol or resorcinol and formaldehyde
Phenoplasts or phenolic (phenol–formaldehyde or PF)
are polymers consisting of monomers joined together by ether linkages (two carbon atoms bonded to an oxygen atom).
Polyethers
example of Polyethers
elastomers
The structures of the Polyethers compounds vary
significantly, yet they all preserve the ____________.
C—O—C
connection
Polyethers can be either _____________ polyethers.
aliphatic or
aromatic
closely related to polyethers in
structure and properties
Polysulfides
Polysulfides also known as
Aromatic polythioethers
A typical aromatic polysulfide is _____________ which is used as electrical insulators and structural parts in the building of engines and vehicles.
poly(phenylene sulfide)
(PPS),
is prepared by the condensation
reaction between p-dichlorobenzene and sodium sulfide
Poly(phenylene sulfide)
Another family of linear aromatic
polymers which are tough, high-temperature-resistant engineering thermoplastics.
Polysulfones
Polysulfones may be synthesized by
the nucleophilic substitution of ________________ with activated ___________________.
alkali salts of biphenates
aromatic dihalides
A polysulfone from the reaction of disodium salt of
bisphenol A with dichlorodiphenyl sulfone
preparation
of bisphenol
In STEP-GROWTH, Monomers bearing _______________________ undergo step
polymerization.
functional groups such as
-OH, -COOH, -NH2, -NCO, etc.,
```
~~~
In chain growth, Monomers with ____________________
undergo polymerization when an active center
is formed.
carbon-carbon unsaturation
In step-growth , the growth of polymer molecules proceeds
by a ______________________________ , normally with the elimination of small molecules as by-products of condensation, such as H2O, HCl, NH3, etc., in each step.
stepwise intermolecular reaction (at a
relatively slow rate
The molecule never stops growing during polymerization.
STEP-GROWTH
Any two molecular species present can react.
STEP-GROWTH
In chain growth. each polymer molecule/chain ____________ once its growth has been
started by formation of an active center.
increases in size at a rapid rate
When the macromolecule stops growing (due to
termination reaction) it can generally not react
with more monomers (barring side reactions)
CHAIN-GROWTH
Only growth reaction adds repeating unit one
at a time of the chain.
CHAIN-GROWTH
In STEP-GROWTH, Monomer units _______react with each other or with polymers of any size.
can
Growth occurs in a _____________ and starts as the reactive species of a monomer or polymer encounters other species with which it can form a link.
series of fits
This can occur even in the absence of an added catalyst
STEP-GROWTH
In chain growth of a polymer molecule is caused by
a kinetic chain of reactions involving rapid
addition of monomer to an active center that
may be a _______________________
free radical, ion, or polymer-catalyst
bond.
The active center is produced by some
external source (energy, highly reactive
compound, or catalyst)
CHAIN-GROWTH
At any moment the reaction mixture essentially
consists of full-grown,** large polymer molecules,** unreacted monomer molecules, and a very low concentration (10-8- 10-3 mol L-1) of growing chains (i.e., possessing an active center) of intermediate sizes
CHAIN-GROWTH
In STEP-GROWTH, backbone of polymer chains contains
________________________ at **regular
intervals **due to condensed interunit links.
heteroatoms such as N, O, S, etc.,
In chain growth, usually the backbone of polymer chains consists
of_____________ and other kinds of
atoms such as O, N, S, etc., may appear in the
side groups
-C-C- linkages
A polymerization in which a cyclic monomer yields a monomeric unit which is acyclic or contains fewer cycles than the
monomer.
RING-OPENING POLYMERIZATION
Ring-opening polymerization (ROP) is a form of chain-growth polymerization in which the** terminus of a polymer chain attacks** ___________ to form a longer polymer. The reactive center can
be radical, anionic or cationic.
cyclic monomers
method where cylic monomers are
opened up to make extended chain
structures.
RING-OPENING POLYMERIZATION
The RING-OPENING POLYMERIZATION reaction is typically
driven by the release of
ring strain
example of ringopening of cyclic organic
compounds
epoxides
- ethylene
- propylene oxides
- epichlorohydrin
other cyclic ethers
- trioxane
- tetrahydrofuran.
Other important systems include
- cyclic esters (lactones)
- cyclic amides (lactams)
- cycloolefins
- siloxane.
Major applications of polymers
obtained from ring-opening
polymerization are in
coatings
fibers
elastomers
adhesives
thermoplastics
thermoset-based composite system
RING-OPENING
POLYMERIZATION
- initial ring-opening of the cyclic monomer
- polyaddition.
- resulting polymers are normally linear.
Their structural units usually have the same
composition as the monomer.
RING-OPENING
POLYMERIZATION
(image 73)
- type
- what is the X?
RING-OPENING
POLYMERIZATION
X may be a heteroatom such as O, S,
or a group like NH, –O–CO–, –NH–CO, or –C›
C–.
________________ is capable of ring-opening
polymerization to produce a linear chain of
degree of polymerization, n.
Cyclic structure
such that it** provides a mechanism** for a
catalyst or initiator to form the initiating
coordination intermediate with the cyclic
ring.
nature of X
