Atom transfer radical polymerization (ATRP) is an example of a living polymerization or a controlled/living radical polymerization (CRP). Like its counterpart, ATRA or atom transfer radical addition, it is a means of forming a carbon-carbon bond through a transition metalcatalyst. As the name implies, the atom transfer step is the key step in the reaction responsible for uniform polymer chain growth. ATRP (or transition metal-mediated living radical polymerization) was independently discovered by Mitsuo Sawamoto et al.[1] and by Krzysztof Matyjaszewski in 1995.[2] This is a typical ATRP reaction:
General ATRP Reaction. A. Initiation. B. Equilibrium with dormant species. C.Propagation
IUPAC definition
Controlled reversible-deactivation radical polymerization in which the deactivation
of the radicals involves reversible atom transfer or reversible group transfer catalyzed usually,
though not exclusively, by transition-metal complexes.[3]
The uniformed polymer chain growth, which leads to low dispersity, stems from the transition metal based catalyst. This catalyst provides an equilibrium between active, and therefore propagating, polymer and an inactive form of the polymer; known as the dormant form. Since the dormant state of the polymer is vastly preferred in this equilibrium, only a few (theoretically one) monomer unit is added at a time. This slow rate of propagation is responsible for the low polydispersity due to the fact that the chains polymerized are of a uniform length, as well as the fact that termination is avoided until almost 100 percent conversion.
This equilibrium in turn lowers the concentration of propagating radicals, therefore suppressing unintentional termination and controlling molecular weights.
ATRP reactions are very robust in that they are tolerant of many functional groups like allyl, amino, epoxy, hydroxy and vinyl groups present in either the monomer or the initiator.[4] ATRP methods are also advantageous due to the ease of preparation, commercially available and inexpensive catalysts (copper complexes), pyridine based ligands and initiators (alkyl halides).[5]
The ATRP with styrene. If all the styrene is reacted (the conversion is 100%) the polymer will have 100 units of styrene built into it. PMDETA stands for N,N,N',N,N pentamethyldiethylenetriamine.
There are five important variable components of Atom Transfer Radical Polymerizations. They are the monomer, initiator, catalyst, solvent and temperature. The following section breaks down the contributions of each component to the overall polymerization.
Monomers that are typically used in ATRP are molecules with substituents that can stabilize the propagating radicals; for example, styrenes, (meth)acrylates, (meth)acrylamides, and acrylonitrile.[6] ATRP are successful at leading to polymers of high number average molecular weight and a narrow polydispersity index when the concentration of the propagating radical balances the rate of radical termination. Yet, the propagating rate is unique to each individual monomer. Therefore, it is important that the other components of the polymerization (initiator, catalysts, ligands and solvents) are optimized in order for the concentration of the dormant species to be greater than the concentration of the propagating radical and yet not too great to slow down or halt the reaction.[7][8]
The number of growing polymer chains is determined by the initiator. The faster the initiation, the fewer terminations and transfers, the more consistent the number of propagating chains leading to narrow molecular weight distributions.[8] Organic halides that are similar in the organic framework as the propagating radical are often chosen as initiators.[7] Most initiators for ATRP are alkyl halides.[9] Alkyl halides such as alkyl bromides are more reactive than alkyl chlorides and both have good molecular weight control.[7][8] The shape or structure of your initiator can determine the architecture of your polymer. For example, initiators with multiple alkyl halide groups on a single core can lead to a star-like polymer shape.[10]
The catalyst is the most important component of ATRP because it determines the equilibrium constant between the active and dormant species. This equilibrium determines the polymerization rate and an equilibrium constant too small may inhibit or slow the polymerization while an equilibrium constant too large leads to a high distribution of chain lengths.[8]
There are several requirements for the metal catalyst:
there needs to be two accessible oxidation states that are separated by one electron
the metal center needs to have a reasonable affinity for halogens
the coordination sphere of the metal needs to be expandable when its oxidized so to be able to accommodate the halogen
The most studied catalysts are those that polymerizations involving copper, which has shown the most versatility, showing successful polymerizations regardless of the monomer.
In reverse ATRP, the catalyst is added in its higher oxidation state. Chains are activated by conventional radical initiators (e.g. AIBN) and deactivated by the transition metal. The source of transferrable halogen is the copper salt, so this must be present in concentrations comparable to the transition metal. A mixture of radical initiator and active (lower oxidation state) catalyst allows for the creation of block copolymers (contaminated with homopolymer) which is impossible using standard reverse ATRP. This is called SR&NI (simultaneous reverse and normal initiation ATRP).
Activators generated by electron transfer uses a reducing agent unable to initiate new chains (instead of organic radicals) as regenerator for the low-valent metal. Examples are metallic Cu, tin(II), ascorbic acid, or triethylamine. It allows for lower concentrations of transition metals, and may also be possible in aqueous or dispersed medium.
This technique uses a variety of different metals/oxidation states, possibly on solid supports, to act as activators/deactivators, possibly with reduced toxicity or sensitivity.[11][12] Iron salts can, for example, efficiently activate alkyl halides but requires an efficient Cu(II) deactivator which can be present in much lower concentrations (3–5 mol%)
Initiators for continuous activator regeneration is a technique that uses large excesses of initiator to continuously regenerate the activator, lowering its required concentration from thousands of ppm to around 1 ppm; making it an industrially relevant technique. Styrene is especially interesting because it generates radicals when sufficiently heated.
Activators regenerated by electron transfer can be used to make block copolymers using a method similar to AGET but requiring strongly reduced amounts of metal, since the activator is regenerated from the deactivator by a large excess of reducing agent (e.g. hydrazine, phenoles, sugars, ascorbic acid, etc...) It differs from AGET ATRP in that AGET uses reducing agents to generate the active catalyst (in quasi stoichiometric amounts) while in ARGET a large excess is used to continuously regenerate the activator allowing transition metal concentrations to drop to ~1 ppm without loss of control.
Jump up ^Kato, M; Kamigaito, M; Sawamoto, M; Higashimura, T (1995). "Polymerization of Methyl Methacrylate with the Carbon Tetrachloride/Dichlorotris-(triphenylphosphine)ruthenium(II)/Methylaluminum Bis(2,6-di-tert-butylphenoxide) Initiating System: Possibility of Living Radical Polymerization". Macromolecules28: 1721–1723. Bibcode:1995MaMol..28.1721K. doi:10.1021/ma00109a056.
Jump up ^Wang, J; Matyjaszewski, K (1995). "Controlled/"living" radical polymerization. Atom transfer radical polymerization in the presence of transition-metal complexes". J. Am. Chem. Soc.117: 5614–5615. doi:10.1021/ja00125a035.
Jump up ^Cowie, J. M. G.; Arrighi, V. In Polymers: Chemistry and Physics of Modern Materials; CRC Press Taylor and Francis Group: Boca Raton, Fl, 2008; 3rd Ed., pp. 82–84 ISBN 0849398134
^ Jump up to: abcdOdian, G. In Radical Chain Polymerization; Principles of Polymerization; Wiley-Interscience: Staten Island, New York, 2004; Vol. , pp 316–321.
Jump up ^Matyjaszewski, Krzysztof; Nicolay V. Tsarevsky (2009). "Nanostructured functional materials prepared by atom transfer radical polymerization". Nature Chemistry1 (4): 276–288. Bibcode:2009NatCh...1..276M. doi:10.1038/NCHEM.257.
Jump up ^Xiong, De'an; He, Zhenping (15). "Modulating the catalytic activity of Au/micelles by tunable hydrophilic channels". JOURNAL OF COLLOID AND INTERFACE SCIENCE341 (2): 273–279. doi:10.1016/j.jcis.2009.09.045.Cite uses deprecated parameters (help);Check date values in: |date= (help)
Jump up ^chen, xi; He, Zhenping, etc (05). "Core-shell-corona Au-micelle composites with a tunable smart hybrid shell". Langmuir24 (15): 8198–8204. doi:10.1021/la800244g.Cite uses deprecated parameters (help);Check date values in: |date= (help)
Pervasive GRE detected the following words on this page:
affinity
feeling of kinship; similarity; Ex. strong affinity for her; Ex. many affinities between two languages>
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cite
quote; commend; Ex. cited for bravery in an official
record>
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catalyst
agent which brings about a chemical change while it
remains unaffected and unchanged; CF. catalysis>
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Like its counterpart, ATRA or atom transfer radical addition, it is a means of forming a carbon-carbon bond through a transition metal catalyst.
This catalyst provides an equilibrium between active, and therefore propagating, polymer and an inactive form of the polymer; known as the dormant form.
The uniformed polymer chain growth, which leads to low dispersity, stems from the transition metal based catalyst.
They are the monomer, initiator, catalyst, solvent and temperature.
The catalyst is the most important component of ATRP because it determines the equilibrium constant between the active and dormant species.
A mixture of radical initiator and active (lower oxidation state) catalyst allows for the creation of block copolymers (contaminated with homopolymer) which is impossible using standard reverse ATRP.
In reverse ATRP, the catalyst is added in its higher oxidation state.
hydrazine, phenoles, sugars, ascorbic acid, etc...) It differs from AGET ATRP in that AGET uses reducing agents to generate the active catalyst (in quasi stoichiometric amounts) while in ARGET a large excess is used to continuously regenerate the activator allowing transition metal concentrations to drop to ~1 ppm without loss of control.
absolute
complete; totally unlimited; having complete power; certain; not relative; Ex. absolute honesty/ruler; CF. absolutism>
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bulk
size or volume (esp. when very large); main part; Ex.
The bulk of the work has already been done; ADJ. bulky:
having great size>
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accommodate
oblige or help someone; adjust or bring into harmony; adapt; make enough space for; ADJ. accommodative; CF. accomodating: helpful and obliging>
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accessible
easy to approach; obtainable>
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conventional
ordinary; typical; not nuclear; Ex. conventional weapons>
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Chains are activated by conventional radical initiators (e.
counterpart
thing that completes another; things very much alike;
thing that has the same purpose in a different system>
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Like its counterpart, ATRA or atom transfer radical addition, it is a means of forming a carbon-carbon bond through a transition metal catalyst.
component
element; ingredient>
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The following section breaks down the contributions of each component to the overall polymerization.
There are five important variable components of Atom Transfer Radical Polymerizations.
The catalyst is the most important component of ATRP because it determines the equilibrium constant between the active and dormant species.
initiate
begin; originate; receive into a group; introduce to
a new field or activity; Ex. initiate someone into the
mysteries of a secret religion; N: one who has been initiated>
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Activators generated by electron transfer uses a reducing agent unable to initiate new chains (instead of organic radicals) as regenerator for the low-valent metal.
solvent
substance that dissolves another; ADJ: capable of dissolving
another substance>
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They are the monomer, initiator, catalyst, solvent and temperature.
Since the dormant state of the polymer is vastly preferred in this equilibrium, only a few (theoretically one) monomer unit is added at a time.
This catalyst provides an equilibrium between active, and therefore propagating, polymer and an inactive form of the polymer; known as the dormant form.
Therefore, it is important that the other components of the polymerization (initiator, catalysts, ligands and solvents) are optimized in order for the concentration of the dormant species to be greater than the concentration of the propagating radical and yet not too great to slow down or halt the reaction.
The catalyst is the most important component of ATRP because it determines the equilibrium constant between the active and dormant species.
inhibit
restrain; prohibit; retard or prevent; N. inhibition>
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This equilibrium determines the polymerization rate and an equilibrium constant too small may inhibit or slow the polymerization while an equilibrium constant too large leads to a high distribution of chain lengths.
equilibrium
balance of opposing forces; balance of the mind; equanimity>
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Since the dormant state of the polymer is vastly preferred in this equilibrium, only a few (theoretically one) monomer unit is added at a time.
This catalyst provides an equilibrium between active, and therefore propagating, polymer and an inactive form of the polymer; known as the dormant form.
This equilibrium in turn lowers the concentration of propagating radicals, therefore suppressing unintentional termination and controlling molecular weights.
This equilibrium determines the polymerization rate and an equilibrium constant too small may inhibit or slow the polymerization while an equilibrium constant too large leads to a high distribution of chain lengths.
The catalyst is the most important component of ATRP because it determines the equilibrium constant between the active and dormant species.
hybrid
mongrel; mixed breed; V. hybridize>
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"Core-shell-corona Au-micelle composites with a tunable smart hybrid shell".
low
moo; make the sound of a cow>
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This slow rate of propagation is responsible for the low polydispersity due to the fact that the chains polymerized are of a uniform length, as well as the fact that termination is avoided until almost 100 percent conversion.
The uniformed polymer chain growth, which leads to low dispersity, stems from the transition metal based catalyst.
smart
intelligent; quick and energetic; fashionable; Ex.
smart pace/restaurant; V: cause or feel a sharp pain;
N: smarting pain>
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"Core-shell-corona Au-micelle composites with a tunable smart hybrid shell".
hide
skin of an animal>
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robust
strong; vigorous>
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ATRP reactions are very robust in that they are tolerant of many functional groups like allyl, amino, epoxy, hydroxy and vinyl groups present in either the monomer or the initiator.
functional
made for practical use only (without decoration); functioning;
Ex. functional modern furniture; CF. functionalism>
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"Nanostructured functional materials prepared by atom transfer radical polymerization".
medium
element that is a creature's natural environment; nutrient
setting in which microorganisms are cultivated; appropriate
occupation or means of expression; channel of communication;
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substan>
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It allows for lower concentrations of transition metals, and may also be possible in aqueous or dispersed medium.
regeneration
spiritual rebirth; Ex. regeneration of the prisoners;
V. regenerate: give or obtain new life; reform spiritually>
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Initiators for continuous activator regeneration is a technique that uses large excesses of initiator to continuously regenerate the activator, lowering its required concentration from thousands of ppm to around 1 ppm; making it an industrially relevant technique.
relevant
having importance; pertinent; referring to the case
in hand; N. relevance, relevancy>
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Initiators for continuous activator regeneration is a technique that uses large excesses of initiator to continuously regenerate the activator, lowering its required concentration from thousands of ppm to around 1 ppm; making it an industrially relevant technique.
generate
cause; produce; create>
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hydrazine, phenoles, sugars, ascorbic acid, etc...) It differs from AGET ATRP in that AGET uses reducing agents to generate the active catalyst (in quasi stoichiometric amounts) while in ARGET a large excess is used to continuously regenerate the activator allowing transition metal concentrations to drop to ~1 ppm without loss of control.
Activators regenerated by electron transfer can be used to make block copolymers using a method similar to AGET but requiring strongly reduced amounts of metal, since the activator is regenerated from the deactivator by a large excess of reducing agent (e.
start
move suddenly or involuntarily; Ex. start at the sight
of a snake>
The most studied catalysts are those that polymerizations involving copper, which has shown the most versatility, showing successful polymerizations regardless of the monomer.
termination
end; V. terminate>
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This slow rate of propagation is responsible for the low polydispersity due to the fact that the chains polymerized are of a uniform length, as well as the fact that termination is avoided until almost 100 percent conversion.
This equilibrium in turn lowers the concentration of propagating radicals, therefore suppressing unintentional termination and controlling molecular weights.
ATRP are successful at leading to polymers of high number average molecular weight and a narrow polydispersity index when the concentration of the propagating radical balances the rate of radical termination.
title
name (of a book, film, etc.); mark of rank; formal
appellation as of rank or office (such as Lord or General);
right or claim to possession; championship; Ex. title
as head of the family; Ex. title to the estate>
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transition
going from one state of action to another>
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ATRP (or transition metal-mediated living radical polymerization) was independently discovered by Mitsuo Sawamoto et al.
Like its counterpart, ATRA or atom transfer radical addition, it is a means of forming a carbon-carbon bond through a transition metal catalyst.
The uniformed polymer chain growth, which leads to low dispersity, stems from the transition metal based catalyst.
The source of transferrable halogen is the copper salt, so this must be present in concentrations comparable to the transition metal.
AIBN) and deactivated by the transition metal.
It allows for lower concentrations of transition metals, and may also be possible in aqueous or dispersed medium.
hydrazine, phenoles, sugars, ascorbic acid, etc...) It differs from AGET ATRP in that AGET uses reducing agents to generate the active catalyst (in quasi stoichiometric amounts) while in ARGET a large excess is used to continuously regenerate the activator allowing transition metal concentrations to drop to ~1 ppm without loss of control.
unique
without an equal; single in kind>
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Yet, the propagating rate is unique to each individual monomer.