Radical Polymerization - Wikipedia, The Free Encyclopedia

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/Polystyrene


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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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Radical Polymerization - Wikipedia, The Free Encyclopedia

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