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7/29/2019 Radical Polymerization - Wikipedia, The Free Encyclopedia
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Radical polymerizationFrom Wikipedia, the free encyclopedia
Free radical polymerization is a method of polymerization by which a polymer forms by the successive
addition of free radical building blocks. Free radicals can be formed via a number of different mechanisms
usually involving separate initiator molecules. Following its generation, the initiating free radical adds (nonradical)
monomer units, thereby growing the polymer chain.
Free radical polymerization is a key synthesis route for obtaining a wide variety of different polymers and
material composites. The relatively non-specific nature of free radical chemical interactions makes this one of the
most versatile forms of polymerization available and allows facile reactions of polymeric free radical chain ends
and other chemicals orsubstrates. In 2001, 40 billion of the 110 billion pounds of polymers produced in the
United States were produced by free radical polymerization.[1]
Free radical polymerization is a type of chain growth polymerization, along with anionic, cationic and
coordination polymerization.
Contents
1 Initiation
1.1 Types of initiation and the initiators
1.2 Initiator Efficiency
2 Propagation
3 Termination
3.1 Chain transfer4 Methods of radical polymerization
5 Controlled Radical Polymerization (CRP)
6 Kinetics
7 Thermodynamics
8 Stereochemistry of polymerization
9 Reactivity
10 Applications
11 Related Wiki Articles
12 External links
13 References
Initiation
Initiation is the first step of the polymerization process. During initiation, an active center is created from which a
polymer chain is generated. Not all monomers are susceptible to all types of initiators. Radical initiation works
best on the carbon-carbon double bond of vinyl monomers and the carbon-oxygen double bond in aldehydes
and ketones.[1]
Initiation has two steps. In the first step, one or two radicals are created from the initiatingmolecules. In the second step, radicals are transferred from the initiator molecules to the monomer units present.
Several choices are available for these initiators.
Types of initiation and the initiators
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1. Thermal decomposition: The initiator is heated until a bond is homolytically cleaved, producing two
radicals (Figure 1). This method is used most often with organic peroxides or azo compounds.[2]
Figure 1: Thermal decomposition of dicumyl
peroxide.
2. Photolysis: Radiation cleaves a bond homolytically, producing two radicals (Figure 2). This method is
used most often with metal iodides, metal alkyls, and azo compounds.[2][3]
Figure 2: Photolysis of azoisobutylnitrile (AIBN).
Photoinitiation can also occur by bi-molecular H-abstraction when the radical is in its lowest tripletexcited state.[4] An acceptable photoinitiator system should fulfill the following requirements:[4]
High absorptivity in the 300-400 nm range.
Efficient generation of radicals capable of attacking the olefinic double bond of vinyl monomers.
Adequate solubility in the binder system (prepolymer + monomer).
Should not impart yellowing or unpleasant odors to the cured material.
The photoinitiator and any byproducts resulting from its use should be non-toxic.
3. Redox reactions: Reduction of hydrogen peroxide or an alkyl hydrogen peroxide by iron (Figure 3).[2]
Other reductants such as Cr2+, V2+, Ti3+, Co2+, and Cu+ can be employed in place of ferrous ion in
many instances.[1]
Figure 3: Redox reaction of hydrogen peroxide and
iron.
4. Persulfates: The dissociation of a persulfate in the aqueous phase (Figure 4). This method is useful in
emulsion polymerizations in which the radical diffuses into a hydrophobic monomer-containing droplet.[2]
Figure 4: Thermal degradation of a
persulfate.
5. Ionizing radiation: -, -, -, or x-rays cause ejection of an electron from the initiating species, followed
by dissociation and electron capture to produce a radical (Figure 5).[2]
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Figure 5: The three steps
involved in ionizing
radiation: ejection,
dissociation, andelectron-capture.
6. Electrochemical: Electrolysis of a solution containing both monomer and electrolyte. A monomer
molecule will receive an electron at the cathode to become a radical anion, and a monomer molecule will
give up an electron at the anode to form a radical cation (Figure 6). The radical ions then initiate free
radical (and/or ionic) polymerization. This type of initiation of especially useful for coating metal surfaces
with polymer films.[5]
Figure 6: (Top) Formation of
radical anion at the cathode;
(bottom) formation of radical
cation at the anode.
7. Plasma: A gaseous monomer is placed in an electric discharge at low pressures under conditions where aplasma (ionized gaseous molecules) is created. In some cases, the system is heated and/or placed in a
radiofrequency field to assist in creating the plasma.[1]
8. Sonication: High-intensity ultrasound at frequencies beyond the range of human hearing (16 kHz) can be
applied to a monomer. Initiation results from the effects of cavitation (the formation and collapse of
cavities in the liquid). The collapse of the cavities generates very high local temperatures and pressures.
This results in the formation of excited electronic states which in turn lead to bond breakage and radical
formation.[1]
9. Ternary Initiators: A ternary initiator is the combination of several types of initiators into one initiating
system. The types of initiators are chosen based on the properties they are known to induce in thepolymers they produce. For example, poly(methyl methacrylate) has been synthesized by the ternary
system benzoyl peroxide-3,6-bis(o-carboxybenzoyl)-N-isopropylcarbazole-di-5-indenylzicronium
dichloride (Figure 7).[6][7]
Figure 7: benzoyl peroxide-3,6-bis(o-carboxybenzoyl)-N-isopropylcarbazole-di-5-
indenylzicronium dichloride
This type of initiating system contains a metallocene, an initiator, and a heteroaromatic diketo carboxylic
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acid. Metallocenes in combination with initiators accelerate polymerization of poly(methyl methacrylate)
and produce a polymer with a narrower molecular weight distribution. The example shown here consists
of indenylzirconium (a metallocene) and benzoyl peroxide (an initiator). Also, initiating systems containing
heteroaromatic diketo carboxylic acids, such as 3,6-bis(o-carboxybenzoyl)-N-isopropylcarbazole in this
example, are known to catalyze the decomposition of benzoyl peroxide. Initiating systems with this
particular heteroaromatic diket carboxylic acid are also known to have effects on the microstructure of
the polymer. The combination of all of these componentsa metallocene, an initiator, and a
heteroaromatic diketo carboxylic acidyields a ternary initiating system that was shown to accelerate thepolymerization and produce polymers with enhanced heat resistance and regular microstructure.[6][7]
Initiator Efficiency
Due to side reactions and inefficient synthesis of the radical species, chain initiation is not 100%. The efficiency
factor,f, is used to describe the effective radical concentration. The maximum value offis 1.0, but values
typically range from 0.3-0.8. The following is a list of reactions that decrease the efficiency of the initiator.
Primary recombination: Two radicals re-combine before initiating a chain (Figure 8). This occurs within
the solvent cage, meaning that no solvent has yet come between the new radicals.[2]
Figure 8: Primary recombination of BPO; brackets
indicate that the reaction is happening within the
solvent cage.
Other recombination pathways: Two radical initiators re-combine before initiating a chain but not in the
solvent cage (Figure 9).[2]
Figure 9: Recombination of phenyl radicals
from the initiation of BPO outside the
solvent cage.
Side reactions: One radical is produced instead of the three radicals that could be produced (Figure
10).[2]
Figure 10: Reaction of polymer chain, R, with other
species in reaction.
Propagation
During polymerization, a polymer spends most of its time in increasing its chain length, or propagating. After the
radical initiator is formed, it attacks a monomer (Figure 11).[8] In an ethene monomer, one electron pair is held
securely between the two carbons in a sigma bond. The other is more loosely held in a pi bond. The free radical
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uses one electron from the pi bond to form a more stable bond with the carbon atom. The other electron returns
to the second carbon atom, turning the whole molecule into another radical. This begins the polymer chain.
Figure 12 shows how the orbitals of an ethylene monomer interact with a radical initiator. [9]
Figure 11: Phenyl initiator from benzoylperoxide (BPO) attacks a styrene molecule
to start the polymer chain.
Figure 12: An orbital drawing of the initiator attack on ethylene molecule, producing
the start of the polyethylene chain.
Once a chain has been initiated, the chain propagates (Figure 13) until there is no more monomer (living
polymerization) or until termination occurs. There may be anywhere from a few to thousands of propagation
steps depending on several factors such as radical and chain reactivity, the solvent, and temperature.[10][11] The
mechanism of chain propagation is as follows:
Figure 13: Propagation of polystyrene with a phenyl radical initiator.
Termination
Chain termination will occur unless the reaction is completely free of contaminants. In this case, the
polymerization is considered to be a living polymerization because propagation can continue if more monomer is
added to the reaction. Living polymerizations are most common in ionic polymerization, however, due to the
high reactivity of radicals. Termination can occur by several different mechanisms. If longer chains are desired,
the initiator concentration should be kept low; otherwise, many shorter chains will result.[2]
1. Combination of two active chain ends: one or both of the following processes may occur.
Combination: two chain ends simply couple together to form one long chain (Figure 14). One can
determine if this mode of termination is occurring by monitoring the molecular weight of the
propagating species: combination will result in doubling of molecular weight. Also, combination will
result in a polymer that is C2 symmetric about the point of the combination.[3][9]
Figure 14: Termination by the combination of two poly(vinyl
chloride) (PVC) polymers.
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Radical disproportionation: a hydrogen atom from one chain end is abstracted to another,
producing a polymer with a terminal unsaturated group and a polymer with a terminal saturated
group (Figure 15).[5]
Figure 15: Termination by disproportionation of poly(methyl methacrylate).
2. Combination of an active chain end with an initiator radical (Figure 16).[2]
Figure 16: Termination of PVC by reaction with
radical initiator.
3. Interaction with impurities or inhibitors. Oxygen is the common inhibitor. The growing chain will react with
molecular oxygen, producing an oxygen radical, which is much less reactive (Figure 17). This significantly
slows down the rate of propagation.
Figure 17: Inhibition of polystyrene propagation due
to reaction of polymer with molecular oxygen.
Nitrobenzene, butylated hydroxyl toluene, and diphenyl picryl hydrazyl (DPPH, Figure 18) are a few
other inhibitors. The latter is an especially effective inhibitor because of the resonance stabilization of the
radical.[2]
Figure 18: Inhibition of polymer chain, R, by
DPPH.
Chain transfer
Contrary to the other modes of termination, chain transfer results in the destruction of only one radical, but also
the creation of another radical. Often, however, this newly created radical is not capable of further propagation.
Similar to disproportionation, all chain transfer mechanisms also involve the abstraction of a hydrogen atom.
There are several types of chain transfer mechanisms.[2][12]
1. To solvent: a hydrogen atom is abstracted from a solvent molecule, resulting in the formation of radicalon the solvent molecules, which will not propagate further (Figure 19).
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Figure 19: Chain transfer from polystyrene to solvent.
The effectiveness of chain transfer involving solvent molecules depends on the amount of solvent present
(more solvent leads to greater probability of transfer), the strength of the bond involved in the abstraction
step (weaker bond leads to greater probability of transfer), and the stability of the solvent radical that is
formed (greater stability leads to greater probability of transfer). Halogens, except fluorine, are easily
transferred.[2]
2. To monomer: a hydrogen atom is abstracted from a monomer. While this does create a radical on the
affected monomer, resonance stabilization of this radical discourages further propagation (Figure 20).[2]
Figure 20: Chain transfer from polypropylene to monomer.
3. To initiator: a polymer chain reacts with an initiator, which terminates that polymer chain, but creates anew radical initiator (Figure 21). This initiator can then begin new polymer chains. Therefore, contrary to
the other forms of chain transfer, chain transfer to the initiator does allow for further propagation.
Peroxide initiators are especially sensitive to chain transfer.[2]
Figure 21: Chain transfer from polypropylene to di-t-butyl peroxide initiator.
4. To polymer: the radical of a polymer chain abstracts a hydrogen atom from somewhere on anotherpolymer chain (Figure 22). This terminates one of the polymer chains, but allows the other to branch.
When this occurs, the average molar mass remains relatively unaffected.[3]
Figure 22: Chain transfer from polypropylene to backbone of another polypropylene.
Effects of chain transfer: The most obvious effect of chain transfer is a decrease in the polymer chain length. If
the rate of termination is much larger than the rate of propagation, then very small polymers are formed with
chain lengths of 2-5 repeating units (telomerization). The Mayo-Lewis equation estimates the influence of chain
transfer on chain length (xn): . Where ktris the rate constant for chain
transfer and kp is the rate constant for propagation. The Mayo-Lewis equation assumes that transfer to solvent
is the major termination pathway.[2]
Methods of radical polymerization
There are four industrial methods of radical polymerization[2]:
1. Bulk polymerization: reaction mixture contains only initiator and monomer, no solvent.
2. Solution polymerization: reaction mixture contains solvent, initiator, and monomer.
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3. Suspension polymerization: reaction mixture contains an aqueous phase, water-insoluble monomer, and
initiator soluble in the monomer droplets (both the monomer and the initiator are hydrophobic).
4. Emulsion polymerization: similar to suspension polymerization except that the initiator is soluble in the
aqueous phase rather than in the monomer droplets (the monomer is hydrophobic, and the initiator is
hydrophilic). An emulsifying agent is also needed.
Other methods of radical polymerization include the following:
1. Template polymerization: In this process, polymer chains are allowed to grow along template
macromolecules for the greater part of their lifetime. A well-chosen template can affect the rate of
polymerization as well as the molar mass and microstructure of the daughter polymer. The molar mass of
a daughter polymer can be up to 70 times greater than those of polymers produced in the absence of the
template and can be higher in molar mass than the templates themselves. This is because of retardation of
the termination for template-associated radicals and by hopping of a radical to the neighboring template
after reaching the end of a template polymer.[13]
2. Plasma polymerization: The polymerization is initiated with plasma. A variety of organic molecules
including alkenes, alkynes, and alkanes undergo polymerization to high molecular weight products under
these conditions. The propagation mechanisms appear to involve both ionic and radical species. Plasma
polymerization offers a potentially unique method of forming thin polymer films for uses such as thin-film
capacitors, antireflection coatings, and various types of thin membranes.[1]
3. Sonication: The polymerization is initiated by high-intensity ultrasound. Polymerization to high molecular
weight polymer is observed but the conversions are low (
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Figure 23: Reaction scheme for SFRP.
Figure 24:
TEMPO
molecule used
to functionalize
the chain ends.
Because the chain end is functionalized with the TEMPO molecule (Figure 24), premature termination by
coupling is reduced. As with all living polymerizations, the polymer chain grows until all of the monomer is
consumed.[14]
Kinetics
In typical chain growth polymerization, the reaction rate for initiation, propagation and termination can be
described as follows.
wherefis the efficiency of the initiator and kd, kp, and kt are the constants for initiator dissociation, chain
propagation and termination, respectively. [I], [M] and [M\cdot] is the concentration of the initiator, monomer
and the active growing chain.
Under the steady state approximation, the concentration of the active growing chains remains constant, i.e. the
rate of initiation and termination is the same. The concentration of active chain can be derived and expressed in
terms of the other known species in the system.
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In this case, the rate of chain propagation can be further described using a function of the initiator and monomer
concentration
The kinetic chain length v is a measure of the average number of monomer units reacting with an active center
during its lifetime and is related to the molecular weight through the mechanism of the termination. Without chain
transfer, the dynamic chain length is only the function of propagation rate and initiation rate.
Assuming no chain transfer effect occurs in the reaction, the number average degree of polymerization P n can be
correlated with the kinetic chain length. In the case of termination by disproportionation, one polymer molecule
is produced per every kinetic chain:
Termination by combination leads to one polymer molecule per two kinetic chains:
Any mixture of these both mechanisms can be described by using the value , and the contribution ofdisproportionation to the overall termination process:
If chain transfer is considered, then there are other pathways to terminate the growing chain. The equation for
dynamic chain length will be modified as the following.
If chain transfer is considered, the kinetic chain length is not affected by the transfer process because the
growing free-radical center generated by the initiation step stays alive after any chain transfer event, although
multiple polymer chains are produced. However, the number average degree of polymerization decreases as the
chain transfers, since the growing chains are terminated by the chain transfer events. Taking into account the
chain transfer reaction towards solvent S, initiatorI, polymerP, and added chain transfer agent T. The equation
of Pn can be expanded:
It is usual to define chain transfer constants C for the different molecules
, , , ,
Thermodynamics
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In chain growth polymerization, the position of the equilibrium between polymer and monomers can be
determined by the thermodynamics of the polymerization. The Gibbs free energy (Gp) of the polymerization is
commonly used to quantify the tendency of a polymeric reaction. The polymerization will be favored if Gp < 0;
if Gp > 0, the polymer will undergo depolymerization. According to the thermodynamic equation G = H -
TS, a negative enthalpy and an increasing entropy will shift the equilibrium towards polymerization.
In general, the polymerization is an exothermic process, i.e. negative enthalpy change, since addition of a
monomer to the growing polymer chain involves the conversion of bonds into bonds or an ring openingreaction that releases the ring tension in a cyclic monomer. Meanwhile, during polymerization, a large amount of
small molecules are associated, losing rotation and translational degrees of freedom. As a result, the entropy
decreases in the system, Sp < 0 for nearly all polymerization processes. Since depolymerization is almost
always entropically favored, the Hp must then be sufficiently negative to composite for the unfavorable entropic
term. Only then will polymerization be thermodynamically favored by the resulting negative Gp.
In practice, polymerization is favored at low temperatures: TSp is small. Depolymerization is favored at high
temperatures: TSp is large. As the temperature increases, Gp become less negative. At certain temperature,
the polymerization reaches equilibrium (rate of polymerization = rate of depolymerization). This temperature is
called the ceiling temperature (Tc). Gp = 0
Stereochemistry of polymerization
The stereochemistry of polymerization is concerned with the difference in atom connectivity and spatial
orientation in polymers that has the same chemical composition. Staudinger studied the stereoisomerism in chain
polymerization of vinyl monomers in late 1920s, and it took another two decades for people to fully appreciate
the idea that each of the propagation steps in the polymer growth could give rise to stereoisomerism. The major
milestone in the stereochemistry was established by Ziegler and Natta and their coworkers in 1950s, as they
developed metal based catalyst to synthesize stereoregular polymers. The reason why the stereochemistry of thepolymer is of particular interest is because the physical behavior of a polymer depends not only on the general
chemical composition but also on the more subtle differences in microstructure.[15] Atactic polymers consist of a
random arrangement of stereochemistry and are amorphous (noncrystalline), soft materials with lower physical
strength. The corresponding isotactic (like substituents all on the same side) and syndiotactic (like substituents of
alternate repeating units on the same side) polymers are usually obtained as highly crystalline materials. It is
easier for the stereoregular polymers to pack into a crystal lattice since they are more ordered and the resulting
crystallinity leads to higher physical strength and increased solvent and chemical resistance as well as differences
in other properties that depend on crystallinity. The prime example of the industrial utility of stereoregular
polymers is polypropene. Isotactic polypropene is a high-melting (165 C), strong, crystalline polymer, which isused as both a plastic and fiber. Atactic polypropene is an amorphous material with an oily to waxy soft
appearance that finds use in asphalt blends and formulations for lubricants, sealants, and adhesives, but the
volumes are minuscule compared to that of isotactic polypropene.[16]
When a monomer adds to a radical chain end, there are two factors to consider regarding its stereochemistry: 1)
the interaction between the terminal chain carbon and the approaching monomer molecule and 2) the
configuration of the penultimate repeating unit in the polymer chain.[5] The terminal carbon atom hassp2
hybridization and is planar. Consider the polymerization of the monomer CH2=CXY. There are two ways that a
monomer molecule can approach the terminal carbon: the mirror approach (with like substituents on the same
side) or the non-mirror approach (like substituents on opposite sides). If free rotation does not occur before thenext monomer adds, the mirror approach will always lead to an isotactic polymer and the non-mirror approach
will always lead to a syndiotactic polymer (Figure 25).[5]
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Figure 25: (Top) formation of isotactic polymer;
(bottom) formation of syndiotactic polymer.
However, if interactions between the substituents of the penultimate repeating unit and the terminal carbon atom
are significant, then conformational factors could cause the monomer to add to the polymer in a way that
minimizes steric or electrostatic interaction (Figure 26).[5]
Figure 26: Penultimate unit interactions cause
monomer to add in a way that minimizes steric
hindrance between substituent groups. (P
represents polymer chain.)
Reactivity
Traditionally, the reactivity of monomers and radicals are assessed by the means of copolymerization data. Q-e
scheme, the most widely used tools for the semiquantitative prediction of monomer reactivity ratios, was first
proposed by Alfrey and Price in 1940s. The scheme takes into account the intrinsic thermodynamic stability and
polar effects in the transition state. A given radical and a monomer is considered to have an intrinsic reactivity of
Q1 and Q2, respectively. The polar effects in the transition state, the supposed permanent electric charge carriedby that entity (radical or molecule), is quantified by the factore, which is a constant for a given monomer, and
has the same value for the radical derived from that specific monomer. For reaction between a radical (species
1) and a monomer (species 2), the rate constant, k12, was postulated to be related to the four relevant reactivity
parameters by
The monomer reactivity ratios for the copolymerization of monomers 1 and 2 can be given by
Applications
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Free radical polymerization has found myriad applications including, but not limited to, the manufacture of
polystyrene, thermoplastic block copolymer elastomers[17] (which may be used for a wide variety of
applications including adhesives, footwear, and toys), cardiovascular stents,[18] chemical surfactants,[19] and
lubricants.
Free radical polymerization has many uses in research as well. One novel and particularly interesting application,
one that exemplifies the power of the technique, is its use in the functionalization of carbon nanotubes.[20]
Carbon nanotubes, due to their intrinsic electronic properties, tend to form large aggregates in solution,precluding their use for useful applications. Adding small chemical groups to the walls of nanotubes can eliminate
this propensity toward aggregation and can be used to tune the response of a nanotube to its surrounding
environment; the use of polymers instead of smaller molecules can be used to drastically modify nanotube
properties (and conversely, nanotubes can be used to modify polymer mechanical and electronic properties).[17]
For example, Lou et al.[21] were able to demonstrate the coating of carbon nanotubes by polystyrene by first
polymerizing polystyrene via chain radical polymerization and subsequently mixing it at 130 C with carbon
nanotubes to generate polystyrene radicals and graft them onto the walls of carbon nanotubes (Figure 27). The
advantage of this approach lies in the order of chemical reaction rather than growing a polymer off of a carbon
nanotube (the grafting from approach), chain growth polymerization is used to first synthesize a polymer with
predetermined properties. Purification of the polymer can be used to obtain a more uniform length distributionbefore grafting onto the nanotubes. Conversely, the grafting from approach, performed with radical
polymerization techniques such as atom transfer radical polymerization (ATRP) or nitroxide-mediated
polymerization (NMP) allows rapid growth of high molecular weight polymers (as opposed to the
aforementioned grafting to approach where large, bulky polymers prohibitively slow the ability for free radical
chain ends to find and couple with the nanotubes).
Figure 27: Grafting of a polystyrene free radical onto a single-walled carbon nanotube.
The power of free radical polymerization in polymerization from surfaces has also been exemplified in the
synthesis of nanocomposite hydrogels.[22] These gels are made of water-swellable nano-scale clay (especially
those classed as smectites) enveloped by some network polymer and are often biocompatible and havemechanical properties (such as flexibility and strength) that make them promising candidates for applications
such as synthetic tissue. Synthesis of these materials is currently possible only by the use of free radical
polymerization. The general synthesis procedure is depicted in Figure 28. The clay is first dispersed in water
where it forms very small, porous plates. Subsequent addition of the organic monomer, generally an acrylamide
or acrylamide derivative, is immediately proceeded by addition of the initiator and a catalyst. The initiator is
chosen to have stronger interaction with the clay than the organic monomer, so it preferentially adsorbs to the
surface of the clay. The entire mixture of clay, organic monomer, initiator, catalyst, and water solvent is heated
to initiate polymerization. Polymers grow off of the initiators which are in turn bound to the clay. Due to
recombination and disproportionation reactions, growing polymer chains bind to one another, forming a strong,
cross-linked network polymer, with clay particles acting as branching points for multiple polymer chain
segments.[23] Free radical polymerization used in this context allows the synthesis of polymers from a wide
http://en.wikipedia.org/wiki/Radical_polymerization#cite_note-ht2002-23http://en.wikipedia.org/wiki/Cross-linkhttp://en.wikipedia.org/wiki/Adsorbshttp://en.wikipedia.org/wiki/Acrylamidehttp://en.wikipedia.org/wiki/Network_polymerhttp://en.wikipedia.org/wiki/Smectitehttp://en.wikipedia.org/wiki/Clayhttp://en.wikipedia.org/wiki/Radical_polymerization#cite_note-h2008-22http://en.wikipedia.org/wiki/Hydrogelshttp://en.wikipedia.org/wiki/Nanocompositehttp://en.wikipedia.org/wiki/File:Nanotube_grafting_1.jpghttp://en.wikipedia.org/wiki/Atom_transfer_radical_polymerizationhttp://en.wikipedia.org/wiki/Radical_polymerization#cite_note-ldspj2004-21http://en.wikipedia.org/wiki/Radical_polymerization#cite_note-bm2007-17http://en.wikipedia.org/wiki/Radical_polymerization#cite_note-hla2007-20http://en.wikipedia.org/wiki/Carbon_nanotubeshttp://en.wikipedia.org/wiki/Radical_polymerization#cite_note-pcptcmv2000-19http://en.wikipedia.org/wiki/Surfactantshttp://en.wikipedia.org/wiki/Radical_polymerization#cite_note-rsrcms2005-18http://en.wikipedia.org/wiki/Stentshttp://en.wikipedia.org/wiki/Radical_polymerization#cite_note-bm2007-17http://en.wikipedia.org/wiki/Thermoplastichttp://en.wikipedia.org/wiki/Polystyrene7/29/2019 Radical Polymerization - Wikipedia, The Free Encyclopedia
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variety of chemical substrates (the chemistries of suitable clays are quite varied), and the termination reactions
unique to chain growth polymerization are taken advantage of for the actualization of a material with flexibility,
mechanical strength, and biocompatibility.
Figure 28: General synthesis procedure for a nanocomposite hydrogel.
Related Wiki Articles
Anionic Addition Polymerization
Chain Growth Polymerization
Chain Transfer
Living Polymerization
Polymer
Polymerization
Step-Growth Polymerization
External linksAddition Polymerization (http://www.materialsworldmodules.org/resources/polimarization/3-
addition.html)
Addition Polymerization (video) (http://www.youtube.com/watch?v=hbu71zsAdDU)
Free Radical Polymerization - Chain Transfer (http://chem.chem.rochester.edu/~chem421/ct1.htm)
Free Radical Vinyl Polymerization (http://www.pslc.ws/mactest/radical.htm)
The Polymerization of Alkenes (http://www.chemguide.co.uk/organicprops/alkenes/polymerisation.html)
Polymer Synthesis (http://plc.cwru.edu/tutorial/enhanced/files/Polymers/synth/Synth.htm)
Radical Reaction Chemistry (http://www.meta-synthesis.com/webbook/14_radical/radical.html)
Stable Free Radical Polymerization (http://www.xeroxtechnology.com/sfrp)
References
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with extraordinary mechanical, optical, and swelling/de-swelling properties". Advanced Materials14 (16):
11201123. doi:10.1002/1521-4095(20020816)14:163.0.CO;2-9
(http://dx.doi.org/10.1002%2F1521-4095%2820020816%2914%3A16%3C1120%3A%3AAID-
ADMA1120%3E3.0.CO%3B2-9) .
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Categories: Reaction mechanisms Polymerization reactions
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