Living polymerization
Encyclopedia
In polymer chemistry
, living polymerization is a form of addition polymerization
where the ability of a growing polymer chain to terminate
has been removed. This can be accomplished in a variety of ways. Chain termination
and chain transfer reactions are absent and the rate of chain initiation is also much larger than the rate of chain propagation
. The result is that the polymer chains grow at a more constant rate
than seen in traditional chain polymerization
and their lengths remain very similar (i.e. they have a very low polydispersity index
). Living polymerization is a popular method for synthesizing block copolymers since the polymer can be synthesized in stages, each stage containing a different monomer
. Additional advantages are predetermined molar mass
and control over end-group
s.
Living polymerization in the literature is often called "living" polymerization or controlled polymerization. Living polymerization was demonstrated by Michael Szwarc
in 1956 in the anionic polymerization of styrene with an alkali metal
/ naphthalene
system in tetrahydrofuran
(THF
). He found that after addition of monomer to the initiator system that the increase in viscosity
would eventually cease but that after addition of a new amount of monomer after some time the viscosity would start to increase again.
The main living polymerization techniques are:
proposed that anionic polymerization of styrene and butadiene by consecutive addition of monomer to an alkyl lithium initiator occurred without chain transfer or termination. Twenty years later, living polymerization was demonstrated by Szwarc through the anionic polymerization
of styrene in THF
using sodium naphthalenide
as celerator.
, styrene, and N-vinylcarbazole. The initiators are binary systems consisting of a electrophile and a Lewis acid. The method was developed around 1980 with contributions from Higashimura, Sawamoto and Kennedy.
in 1986 based on norbornene
and Tebbe's reagent
and in 1978 Grubbs together with Richard R. Schrock
describing living polymerization with a tungsten
carbene complex.
chemistry. These techniques involved catalytic chain transfer
polymerization, iniferter mediated polymerization, stable free radical mediated polymerization (SFRP), atom transfer radical polymerization (ATRP), reversible addition-fragmentation chain transfer (RAFT
) polymerization, and iodine-transfer polymerization.
monomers and the initiator is a silyl ketene acetal. New monomer adds to the initiator and to the active growing chain in a Michael reaction
. With each addition of a monomer group the trimethylsilyl group is transferred to the end of the chain. The active chain-end is not ionic as in anionic or cationic polymeriation but is covalent. The reaction can be catalysed by bifluorides and bioxyanions such as tris(dialkylamino)sulfonium bifluoride or tetrabutyl ammonium bibenzoate. The method was discovered in 1983 by O.W. Webster
and the name first suggested by Barry Trost
.
) is an alpha-olefin and the active site contains an alkyl to metal bond. Chain growth is based on the Cossee-Arlman mechanism
. An early method (Doi, 1979) describes propene polymerization in toluene
at -50°C using diethylaluminium chloride and a vanadium
catalyst for example V(acac
)3 to syndiotactic polypropylene
with a polydispersity index
of 1.05 to 1.4. Another living system as described by McConville in 1996 is based on titanium using 1-hexene
, [RN(CH2)3NR]TiMe2 and tris(pentafluorophenyl)boron
Polymer chemistry
Polymer chemistry or macromolecular chemistry is a multidisciplinary science that deals with the chemical synthesis and chemical properties of polymers or macromolecules. According to IUPAC recommendations, macromolecules refer to the individual molecular chains and are the domain of chemistry...
, living polymerization is a form of addition polymerization
Addition polymerization
Chain growth polymerization is a polymerization technique where unsaturated monomer molecules add on to a growing polymer chain one at a time...
where the ability of a growing polymer chain to terminate
Chain termination
Chain termination is any chemical reaction that ceases the formation of reactive intermediates in a chain propagation step in the course of a polymerization, effectively bringing it to a halt.- Mechanisms of Termination :...
has been removed. This can be accomplished in a variety of ways. Chain termination
Chain termination
Chain termination is any chemical reaction that ceases the formation of reactive intermediates in a chain propagation step in the course of a polymerization, effectively bringing it to a halt.- Mechanisms of Termination :...
and chain transfer reactions are absent and the rate of chain initiation is also much larger than the rate of chain propagation
Chain propagation
Chain propagation is a process in which a reactive intermediate is continuously regenerated during the course of a chemical reaction. In polymerization reaction, the reactive end-groups of a polymer chain react in each propagation step with a new monomer molecule transferring the reactive group to...
. The result is that the polymer chains grow at a more constant rate
Reaction rate
The reaction rate or speed of reaction for a reactant or product in a particular reaction is intuitively defined as how fast or slow a reaction takes place...
than seen in traditional chain polymerization
Polymerization
In polymer chemistry, polymerization is a process of reacting monomer molecules together in a chemical reaction to form three-dimensional networks or polymer chains...
and their lengths remain very similar (i.e. they have a very low polydispersity index
Polydispersity index
In physical and organic chemistry, the polydispersity index , is a measure of the distribution of molecular mass in a given polymer sample. The PDI calculated is the weight average molecular weight divided by the number average molecular weight. It indicates the distribution of individual...
). Living polymerization is a popular method for synthesizing block copolymers since the polymer can be synthesized in stages, each stage containing a different monomer
Monomer
A monomer is an atom or a small molecule that may bind chemically to other monomers to form a polymer; the term "monomeric protein" may also be used to describe one of the proteins making up a multiprotein complex...
. Additional advantages are predetermined molar mass
Molar mass
Molar mass, symbol M, is a physical property of a given substance , namely its mass per amount of substance. The base SI unit for mass is the kilogram and that for amount of substance is the mole. Thus, the derived unit for molar mass is kg/mol...
and control over end-group
End-group
An end-group in polymer chemistry is a constitutional unit that is an extremity of a macromolecule or oligomer molecule. For example the end-group of a PET polyester may be an alcohol group or a carboxylic acid group...
s.
Living polymerization in the literature is often called "living" polymerization or controlled polymerization. Living polymerization was demonstrated by Michael Szwarc
Michael Szwarc
Michael Szwarc was a British and American polymer chemist who discovered and studied ionic living polymerization.- Biography :...
in 1956 in the anionic polymerization of styrene with an alkali metal
Alkali metal
The alkali metals are a series of chemical elements in the periodic table. In the modern IUPAC nomenclature, the alkali metals comprise the group 1 elements, along with hydrogen. The alkali metals are lithium , sodium , potassium , rubidium , caesium , and francium...
/ naphthalene
Naphthalene
Naphthalene is an organic compound with formula . It is a white crystalline solid with a characteristic odor that is detectable at concentrations as low as 0.08 ppm by mass. As an aromatic hydrocarbon, naphthalene's structure consists of a fused pair of benzene rings...
system in tetrahydrofuran
Tetrahydrofuran
Tetrahydrofuran is a colorless, water-miscible organic liquid with low viscosity at standard temperature and pressure. This heterocyclic compound has the chemical formula 4O. As one of the most polar ethers with a wide liquid range, it is a useful solvent. Its main use, however, is as a precursor...
(THF
ThF
Follicular B helper T cells , are antigen-experienced CD4+ T cells found in the B cell follicles of secondary lymphoid organs such as lymph nodes, spleens and Peyer's patches, and are identified by their constitutive expression of the B cell follicle homing receptor CXCR5...
). He found that after addition of monomer to the initiator system that the increase in viscosity
Viscosity
Viscosity is a measure of the resistance of a fluid which is being deformed by either shear or tensile stress. In everyday terms , viscosity is "thickness" or "internal friction". Thus, water is "thin", having a lower viscosity, while honey is "thick", having a higher viscosity...
would eventually cease but that after addition of a new amount of monomer after some time the viscosity would start to increase again.
The main living polymerization techniques are:
- Living anionic polymerizationLiving anionic polymerizationLiving anionic polymerization is living polymerization technique involving an anionic propagating species.Living anionic polymerization was demonstrated by Szwarc and co workers in 1956. Their initial work was based on the polymerization of styrene and dienes....
- Living cationic polymerizationLiving cationic polymerizationLiving cationic polymerization is a living polymerization technique involving cationic propagating species. It enables the synthesis of very well defined polymers and of polymers with unusual architecture such as star polymers and block copolymers and living cationic polymerization is therefore as...
- Ring opening metathesis polymerization
- Living free radical polymerizationLiving free radical polymerizationLiving free radical polymerization is a type of living polymerization where the active polymer chain end is a free radical. Several methods exist...
- Group transfer polymerization
- living Ziegler-Natta polymerization
Living anionic polymerization
As early as 1936, Karl ZieglerKarl Ziegler
Karl Waldemar Ziegler was a German chemist who won the Nobel Prize in Chemistry in 1963, with Giulio Natta, for work on polymers. The Nobel Committee recognized his "excellent work on organometallic compounds [which]...led to new polymerization reactions and ... paved the way for new and highly...
proposed that anionic polymerization of styrene and butadiene by consecutive addition of monomer to an alkyl lithium initiator occurred without chain transfer or termination. Twenty years later, living polymerization was demonstrated by Szwarc through the anionic polymerization
Anionic addition polymerization
Anionic addition polymerization is a form of chain-growth polymerization or addition polymerization that involves the polymerization of vinyl monomers with strong electronegative groups. This polymerization is carried out through a carbanion active species. Like all addition polymerizations, it...
of styrene in THF
ThF
Follicular B helper T cells , are antigen-experienced CD4+ T cells found in the B cell follicles of secondary lymphoid organs such as lymph nodes, spleens and Peyer's patches, and are identified by their constitutive expression of the B cell follicle homing receptor CXCR5...
using sodium naphthalenide
Sodium naphthalenide
Sodium naphthalenide, also known as sodium naphthalide, is a soluble one-electron reductant employed in organic, organometallic, and inorganic chemistry. It is prepared by stirring sodium metal with naphthalene in a polar solvent such as tetrahydrofuran or dimethoxyethane, resulting in the...
as celerator.
Living cationic polymerization
Monomers for living cationic polymerization are electron-rich alkenes such as vinyl ethers, isobutyleneIsobutylene
Isobutylene is a hydrocarbon of significant industrial importance. It is a four-carbon branched alkene , one of the four isomers of butylene. At standard temperature and pressure it is a colorless flammable gas.-Uses:...
, styrene, and N-vinylcarbazole. The initiators are binary systems consisting of a electrophile and a Lewis acid. The method was developed around 1980 with contributions from Higashimura, Sawamoto and Kennedy.
Living ring-opening metathesis polymerization
Given the right reaction conditions ring-opening metathesis polymerization (ROMP) can be rendered living. The first such systems were described by Robert H. GrubbsRobert H. Grubbs
Robert Howard Grubbs is an American chemist and Nobel laureate.As he noted in his official Nobel Prize autobiography, "In some places, my birthplace is listed as Calvert City and in others Possum Trot [NB: both in Marshall County]...
in 1986 based on norbornene
Norbornene
Norbornene or norbornylene or norcamphene is a bridged cyclic hydrocarbon. It is a white solid with a pungent sour odor. The molecule consists of a cyclohexene ring bridged with a methylene group in the para position...
and Tebbe's reagent
Tebbe's reagent
The Tebbe reagent is the organometallic compound with the formula 2TiCH2ClAl2. It used in the methylenation of carbonyl compounds, that is it converts organic compounds containing the R2C=O group into the related R2C=CH2 derivative...
and in 1978 Grubbs together with Richard R. Schrock
Richard R. Schrock
Richard Royce Schrock is an American chemist and Nobel laureate recognized for his contributions to the metathesis reaction used in organic chemistry.-Biography:...
describing living polymerization with a tungsten
Tungsten
Tungsten , also known as wolfram , is a chemical element with the chemical symbol W and atomic number 74.A hard, rare metal under standard conditions when uncombined, tungsten is found naturally on Earth only in chemical compounds. It was identified as a new element in 1781, and first isolated as...
carbene complex.
Living free radical polymerization
Starting in the 1970s several new methods were discovered which allowed the development of living polymerization using free radicalRadical (chemistry)
Radicals are atoms, molecules, or ions with unpaired electrons on an open shell configuration. Free radicals may have positive, negative, or zero charge...
chemistry. These techniques involved catalytic chain transfer
Catalytic Chain Transfer
Catalytic chain transfer is a process that can be incorporated into radical polymerization to obtain greater control over the resulting products.-Introduction:...
polymerization, iniferter mediated polymerization, stable free radical mediated polymerization (SFRP), atom transfer radical polymerization (ATRP), reversible addition-fragmentation chain transfer (RAFT
RAFT (chemistry)
Reversible Addition-Fragmentation chain Transfer or RAFT polymerization is one kind of controlled radical polymerization. Discovered at the Commonwealth Scientific and Industrial Research Organisation in 1998, RAFT polymerization is a relatively new method for the synthesis of living radical...
) polymerization, and iodine-transfer polymerization.
Living group-transfer polymerization
Group-transfer polymerization also has characteristics of living polymerization. It is applied to alkylated methacrylateMethacrylate
Methacrylates are the salts or esters of methacrylic acid.Methacrylates contain methyl-vinyl groups, that is, two carbon atoms double bonded to each other, directly attached to the carbonyl carbon, and wherein the vinyl group is substituted with a non-terminal methyl group.Methacrylates are common...
monomers and the initiator is a silyl ketene acetal. New monomer adds to the initiator and to the active growing chain in a Michael reaction
Michael reaction
The Michael reaction or Michael addition is the nucleophilic addition of a carbanion or another nucleophile to an alpha, beta unsaturated carbonyl compound. It belongs to the larger class of conjugate additions. This is one of the most useful methods for the mild formation of C-C bonds...
. With each addition of a monomer group the trimethylsilyl group is transferred to the end of the chain. The active chain-end is not ionic as in anionic or cationic polymeriation but is covalent. The reaction can be catalysed by bifluorides and bioxyanions such as tris(dialkylamino)sulfonium bifluoride or tetrabutyl ammonium bibenzoate. The method was discovered in 1983 by O.W. Webster
Owen Webster
Owen W. Webster is a distinguished member of the organic and polymer chemistry communities. His polymerization technique for making block copolymer dispersing agents is used by DuPont to make ink-jet printer inks....
and the name first suggested by Barry Trost
Barry Trost
Barry M. Trost is an American chemist, Tamaki Professor of Humanities and Sciences at Stanford University....
.
Living Ziegler-Natta polymerization
Several reported methods exist that introduce livingness in Ziegler-Natta polymerization. The monomer in this type of polymerization (a subset of coordination polymerizationCoordination polymerization
Coordination polymerization is a form of addition polymerization in which monomer adds to a growing macromolecule through an organometallic active center...
) is an alpha-olefin and the active site contains an alkyl to metal bond. Chain growth is based on the Cossee-Arlman mechanism
Cossee-Arlman mechanism
The Cossee-Arlman mechanism in polymer chemistry is the main pathway for the formation of C-C bonds in the polymerization of alkenes. The mechanism features an intermediate coordination complex that contains both the growing polymer chain and the monomer...
. An early method (Doi, 1979) describes propene polymerization in toluene
Toluene
Toluene, formerly known as toluol, is a clear, water-insoluble liquid with the typical smell of paint thinners. It is a mono-substituted benzene derivative, i.e., one in which a single hydrogen atom from the benzene molecule has been replaced by a univalent group, in this case CH3.It is an aromatic...
at -50°C using diethylaluminium chloride and a vanadium
Vanadium
Vanadium is a chemical element with the symbol V and atomic number 23. It is a hard, silvery gray, ductile and malleable transition metal. The formation of an oxide layer stabilizes the metal against oxidation. The element is found only in chemically combined form in nature...
catalyst for example V(acac
Acac
ACAC may refer to:* American Council for Accredited Certification, a private, non-profit certifying body* Atlanta Contemporary Art Center, a contemporary art museum in Atlanta* ACAC consortium, a subsidiary of China Aviation Industry Corporation...
)3 to syndiotactic polypropylene
Polypropylene
Polypropylene , also known as polypropene, is a thermoplastic polymer used in a wide variety of applications including packaging, textiles , stationery, plastic parts and reusable containers of various types, laboratory equipment, loudspeakers, automotive components, and polymer banknotes...
with a polydispersity index
Polydispersity index
In physical and organic chemistry, the polydispersity index , is a measure of the distribution of molecular mass in a given polymer sample. The PDI calculated is the weight average molecular weight divided by the number average molecular weight. It indicates the distribution of individual...
of 1.05 to 1.4. Another living system as described by McConville in 1996 is based on titanium using 1-hexene
1-Hexene
1-Hexene is an organic compound with the formula CH2CHC4H9. It is an alkene that is classified in industry as higher olefin and an alpha-olefin, the latter term meaning that the double bond is located at the alpha position, endowing the compound with higher reactivity and thus useful chemical...
, [RN(CH2)3NR]TiMe2 and tris(pentafluorophenyl)boron
Tris(pentafluorophenyl)boron
Trisboron is the chemical compound 3B. The molecule consists of three pentafluorophenyl groups attached in a "paddle-wheel" manner to a central boron atom; the BC3 core is planar. It has been described as the “ideal Lewis acid” because of its versatility and the relative inertness of the B-C bonds...
External links
- IUPAC Gold BookGold BookThe Compendium of Chemical Terminology is a book published by the International Union of Pure and Applied Chemistry containing internationally accepted definitions for terms in chemistry...
Definition - precise definitions from the American Chemical Society
- Living Ziegler-Natta Polymerization Article
- Living polymers 50 years of evolution Article