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For polymerization in DNA, see DNA polymerase.
monomer unit's double bond reforms as a single bond with another styrene monomer and forms
polystyrene.In
polymer chemistry,
polymerization is a process of
chemical bond monomers, or "single units" together through a variety of reaction mechanisms to form longer chains named
polymers. Polymers exist as a variety of 3-dimensional shapesInternational Union of Pure and Applied Chemistry, et al. (2000) "Gold Book", each with specific individual properties relevant to the monomers or reaction mechanisms they are formed from.
Introduction
{| align="right" class="infobox" style="text-align:center;"|Single-monomer formed polymers
A + A + A... \rightarrow AAA ...
Co-polymers
A + B + A... \rightarrow ABA ...
|}In chemical compounds, polymerization occurs via a variety of reaction mechanisms which vary in complexity due to
functional groups present in reacting compoundsClayden, J., Greeves, N. et al (2000), p1450-1466 and their inherent steric effects explained by
VSEPR Theory. In more straightforward polymerization, alkenes, which are a relatively stable due to \sigma chemical bonding between carbon atoms form polymers through relatively simple radical reactions; conversely, more complex reactions such as those that involve substitution at the carbonyl atom require more complex synthesis due to the way in which reacting molecules polymerise.
As alkenes can be formed in somewhat straightforward reaction mechanisms, they form useful compounds such as polyethene and polyvinyl chloride (PVC) when undergoing radical reactions, which are produced in high tonnages each year due to their usefulness in manufacturing processes of commercial products, such as piping, insulation and packaging. Polymers such as PVC are generally referred to as "
singular" polymers as they consist of repeated long chains or structures of the same monomer unit, whereas polymers that consist of more than one molecule are referred to as "
co-polymers".
Other monomer units, such as formaldehyde hydrates or simple aldehydes, are able to polymerize themselves at quite low temperatures (>-80oC) to form trimers; molecules consisting of 3 monomer units which can cyclize to form ring cyclic structures, or undergo further reactions to form
tetramers, or 4 monomer-unit compounds. Further compounds either being referred to as oligomers in smaller molecules. Generally, because formaldehyde is an exceptionally reactive electrophile it allows nucleophile addition of hemiacetal intermediates, which are generally short lived and relatively unstable "mid stage" compounds which react with other molecules present to form more stable polymeric compounds.
Polymerization that is not sufficiently moderated and proceeds at an undesirably fast rate can be very hazardous. This phenomenon is known as
Hazardous polymerization and can cause fires and explosions.
Chain-Growth Polymerization
Addition polymerization involves the linking together of molecules incorporating double or triple
chemical bonds. These unsaturated
monomers (the identical molecules which make up the polymers) have extra internal bonds which are able to break and link up with other monomers to form the repeating chain. Addition polymerization is involved in the manufacture of polymers such as polyethene, polypropylene and polyvinyl chloride (PVC). A special case of addition polymerization leads to living polymerization.
Condensation polymerization occurs when monomers bond together through
condensation reactions. Typically these reactions can be achieved through reacting molecules incorporating
alcohol, amine or
carboxylic acid (or other carboxyl derivative) functional groups. When an amine reacts with a carboxylic acid an
amide or peptide bond is formed, with the release of water (hence
condensation polymerization.) This is the process through which amino acids link up to form proteins, as well as how
kevlar is formed.
The chain growth-step growth system categorizes polymers based on their mechanism. While most polymers will fall into their similar category from the addition-condensation method of categorization, there are a few exceptions.
Chain growth polymers are defined as polymers formed by the reaction of monomer with a reactive center. These polymers grow to high molecular weight at a very fast rate. It is important to note that the overall conversion rates between chain and step growth polymers are similar, but that high molecular weight polymers are formed in addition reactions much more quickly than with step polymerizations.
Addition polymerization involves the breaking of double or triple bonds, which are used to link monomers into chains. In the polymerization of ethene (fig. 1), its pi bond is broken and these two electrons rearrange to create a new propagating center like the one that attacked it. The form this propagating center takes depends on the specific type of addition mechanism. There are several mechanisms through which this can be initiated. The
free radical mechanism was one of the first methods to be used. Free radicals are very reactive atoms or molecules which have unpaired electrons. Taking the polymerization of ethene as an example, the free radical mechanism can be divided in to three stages: initiation, propagation and termination.
Initiation is the creation of free radicals necessary for propagation. The radicals can be created from radical initiators, such as organic peroxide molecules, molecules containing an O-O single bond, by reacting
oxygen with
ethene. The products formed are unstable and easily break down into two radicals. 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 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 in to another radical.
Propagation is the rapid reaction of this radicalised ethene molecule with another ethene monomer, and the subsequent repetition to create the repeating chain.
Termination occurs when a radical reacts in a way that prevents further propagation. The most common method of termination is by coupling where two radical species react with each other forming a single molecule. Another, less common method of termination is disproportionation where two radicals meet, but instead of coupling, they exchange a proton, which gives two terminated chains, one saturated and the other with a terminal double bond.
Free radical addition polymerization of ethylene must take place at high temperatures and pressures, approximately 300°C and 2000 At. While most other free radical polymerizations do not require such extreme temperatures and pressures, they do tend to lack control. One effect of this lack of control is a high degree of branching. Also, as termination occurs randomly, when two chains collide, it is impossible to control the length of individual chains.A newer method of polymerization similar to free radical, but allowing more control involves the Ziegler-Natta catalyst especially with respect to
branched polymer.
Other forms of addition polymerization include cationic addition polymerization and anionic addition polymerization. While not used to a large extent in industry yet due to stringent reaction conditions such as lack of water and oxygen, these methods provide ways to polymerize some monomers that cannot be polymerized by free radical methods such as polypropylene. Cationic and anionic mechanisms are also more ideally suited for
living polymerizations, although free radical living polymerizations have also been developed.
Step-Growth Polymerization
Step growth polymers are defined as polymers formed by the stepwise reaction between functional groups of monomers. Most step growth polymers are also classified as condensation polymers, but not all step growth polymers (like
polyurethanes formed from
isocyanate and alcohol bifunctional monomers) release condensates. Sean Step growth polymers increase in molecular weight at a very slow rate at lower conversions and only reach moderately high molecular weights at very high conversion (i.e. >95%).
To alleviate inconsistencies in these naming methods, adjusted definitions for condensation and addition polymers have been developed. A condensation polymer is defined as a polymer that involves
elimination reaction of small molecules during its synthesis, or contains functional groups as part of its backbone chain, or its
repeat unit does not contain all the atoms present in the hypothetical monomer to which it can be degraded.
See also
Notes
References
International Union of Pure and Applied Chemistry, et al. (2000) "IUPAC Gold Book" Retrieved on 11th May 2007 from "IUPAC Gold Book" on http://goldbook.iupac.org/
Clayden, J., Greeves, N. et al (2000). "Organic chemistry" Oxford
ca:Polimeritzaciócs:Polymerizace
de:Polymerisationes:Polimerizaciónfr:Polymérisation
gl:Polimerizaciónhe:פלמור
id:Polimerisasimk:Полимеризација
nl:Polymerisatieja:重合反応pl:Polimeryzacjapt:Polimerização
ru:Полимеризацияsr:Полимеризацијаsu:Polimérisasifi:Polymerointi
sv:Polymerisationuk:Полімеризаціяzh:聚合
For polymerization in DNA, see DNA polymerase.
monomer unit's double bond reforms as a single bond with another styrene monomer and forms
polystyrene.In polymer chemistry,
polymerization is a process of
chemical bond monomers, or "single units" together through a variety of reaction mechanisms to form longer chains named polymers. Polymers exist as a variety of 3-dimensional shapesInternational Union of Pure and Applied Chemistry, et al. (2000) "Gold Book", each with specific individual properties relevant to the monomers or reaction mechanisms they are formed from.
Introduction
{| align="right" class="infobox" style="text-align:center;"|Single-monomer formed polymers
A + A + A... \rightarrow AAA ...
Co-polymers
A + B + A... \rightarrow ABA ...
|}In chemical compounds, polymerization occurs via a variety of reaction mechanisms which vary in complexity due to
functional groups present in reacting compoundsClayden, J., Greeves, N. et al (2000), p1450-1466 and their inherent
steric effects explained by
VSEPR Theory. In more straightforward polymerization,
alkenes, which are a relatively stable due to \sigma chemical bonding between carbon atoms form polymers through relatively simple radical reactions; conversely, more complex reactions such as those that involve substitution at the carbonyl atom require more complex synthesis due to the way in which reacting molecules polymerise.
As alkenes can be formed in somewhat straightforward reaction mechanisms, they form useful compounds such as polyethene and polyvinyl chloride (PVC) when undergoing radical reactions, which are produced in high tonnages each year due to their usefulness in manufacturing processes of commercial products, such as piping, insulation and packaging. Polymers such as PVC are generally referred to as "
singular" polymers as they consist of repeated long chains or structures of the same monomer unit, whereas polymers that consist of more than one molecule are referred to as "
co-polymers".
Other monomer units, such as formaldehyde hydrates or simple aldehydes, are able to polymerize themselves at quite low temperatures (>-80oC) to form trimers; molecules consisting of 3 monomer units which can cyclize to form ring cyclic structures, or undergo further reactions to form
tetramers, or 4 monomer-unit compounds. Further compounds either being referred to as
oligomers in smaller molecules. Generally, because formaldehyde is an exceptionally reactive electrophile it allows
nucleophile addition of hemiacetal intermediates, which are generally short lived and relatively unstable "mid stage" compounds which react with other molecules present to form more stable polymeric compounds.
Polymerization that is not sufficiently moderated and proceeds at an undesirably fast rate can be very hazardous. This phenomenon is known as
Hazardous polymerization and can cause fires and explosions.
Chain-Growth Polymerization
Addition polymerization involves the linking together of molecules incorporating double or triple
chemical bonds. These unsaturated
monomers (the identical molecules which make up the polymers) have extra internal bonds which are able to break and link up with other monomers to form the repeating chain. Addition polymerization is involved in the manufacture of polymers such as polyethene,
polypropylene and polyvinyl chloride (PVC). A special case of addition polymerization leads to
living polymerization.
Condensation polymerization occurs when monomers bond together through
condensation reactions. Typically these reactions can be achieved through reacting molecules incorporating alcohol,
amine or
carboxylic acid (or other carboxyl derivative) functional groups. When an amine reacts with a carboxylic acid an amide or
peptide bond is formed, with the release of water (hence
condensation polymerization.) This is the process through which
amino acids link up to form proteins, as well as how
kevlar is formed.
The chain growth-step growth system categorizes polymers based on their mechanism. While most polymers will fall into their similar category from the addition-condensation method of categorization, there are a few exceptions.
Chain growth polymers are defined as polymers formed by the reaction of
monomer with a reactive center. These polymers grow to high molecular weight at a very fast rate. It is important to note that the overall conversion rates between chain and step growth polymers are similar, but that high molecular weight polymers are formed in addition reactions much more quickly than with step polymerizations.
Addition polymerization involves the breaking of double or triple bonds, which are used to link monomers into chains. In the polymerization of ethene (fig. 1), its pi bond is broken and these two electrons rearrange to create a new propagating center like the one that attacked it. The form this propagating center takes depends on the specific type of addition mechanism. There are several mechanisms through which this can be initiated. The
free radical mechanism was one of the first methods to be used. Free radicals are very reactive atoms or molecules which have unpaired electrons. Taking the polymerization of ethene as an example, the free radical mechanism can be divided in to three stages: initiation, propagation and termination.
Initiation is the creation of free radicals necessary for propagation. The radicals can be created from
radical initiators, such as organic peroxide molecules, molecules containing an O-O single bond, by reacting
oxygen with
ethene. The products formed are unstable and easily break down into two radicals. 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 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 in to another radical.
Propagation is the rapid reaction of this radicalised ethene molecule with another ethene monomer, and the subsequent repetition to create the repeating chain.
Termination occurs when a radical reacts in a way that prevents further propagation. The most common method of termination is by coupling where two radical species react with each other forming a single molecule. Another, less common method of termination is disproportionation where two radicals meet, but instead of coupling, they exchange a proton, which gives two terminated chains, one saturated and the other with a terminal double bond.
Free radical addition polymerization of ethylene must take place at high temperatures and pressures, approximately 300°C and 2000 At. While most other free radical polymerizations do not require such extreme temperatures and pressures, they do tend to lack control. One effect of this lack of control is a high degree of branching. Also, as termination occurs randomly, when two chains collide, it is impossible to control the length of individual chains.A newer method of polymerization similar to free radical, but allowing more control involves the Ziegler-Natta catalyst especially with respect to branched polymer.
Other forms of addition polymerization include cationic addition polymerization and anionic addition polymerization. While not used to a large extent in industry yet due to stringent reaction conditions such as lack of water and oxygen, these methods provide ways to polymerize some monomers that cannot be polymerized by free radical methods such as polypropylene. Cationic and anionic mechanisms are also more ideally suited for
living polymerizations, although free radical living polymerizations have also been developed.
Step-Growth Polymerization
Step growth polymers are defined as polymers formed by the stepwise reaction between functional groups of monomers. Most step growth polymers are also classified as condensation polymers, but not all step growth polymers (like polyurethanes formed from
isocyanate and alcohol bifunctional monomers) release condensates. Sean Step growth polymers increase in molecular weight at a very slow rate at lower conversions and only reach moderately high molecular weights at very high conversion (i.e. >95%).
To alleviate inconsistencies in these naming methods, adjusted definitions for condensation and addition polymers have been developed. A condensation polymer is defined as a polymer that involves elimination reaction of small molecules during its synthesis, or contains functional groups as part of its
backbone chain, or its
repeat unit does not contain all the atoms present in the hypothetical monomer to which it can be degraded.
See also
- Plasma polymerization
- Ziegler-Natta catalyst
- Metallocene
Notes
References
International Union of Pure and Applied Chemistry, et al. (2000) "IUPAC Gold Book" Retrieved on 11th May 2007 from "IUPAC Gold Book" on http://goldbook.iupac.org/
Clayden, J., Greeves, N. et al (2000). "Organic chemistry" Oxford
ca:Polimeritzaciócs:Polymerizacede:Polymerisation
es:Polimerizaciónfr:Polymérisationgl:Polimerizaciónhe:פלמור
id:Polimerisasimk:Полимеризацијаnl:Polymerisatieja:重合反応
pl:Polimeryzacjapt:Polimerizaçãoru:Полимеризацияsr:Полимеризација
su:Polimérisasifi:Polymerointisv:Polymerisation
uk:Полімеризаціяzh:聚合
Polymerization - Wikipedia, the free encyclopedia
In polymer chemistry, polymerization is a process of reacting monomer molecules together in a chemical reaction to form three-dimensional networks or polymer chains [1] [2] [3].
Radical polymerization - Wikipedia, the free encyclopedia
Radical polymerization is a type of polymerization in which the reactive center of a polymer chain consists of a radical. The polymerization reaction is initiated by three classes ...
Definition: polymerization from Online Medical Dictionary
The Online Medical Dictionary is a searchable dictionary of definitions from medicine, science and technology.
polymerization - Hutchinson encyclopedia article about polymerization
Chemical union of two or more (usually small) molecules of the same kind to form a new compound. Addition polymerization produces simple multiples of the same compound ...
polymerization definition of polymerization in the Free Online ...
polymerization. Any process in which monomer s combine chemically to produce a polymer. The monomer molecules—which in the polymer usually number from at least 100 to many ...
Polymerization
Polymerization. Forming large molecules from small molecules - Polymerization. Just as a house can be constructed from building blocks, so too large molecules can be constructed ...
Polymerization - Yu-Gi-Oh!
Related Communities. Entertainment TV shows, movies, cartoons and comics. Gaming Get your game on with Wikia's video game wikis. Science Fiction Explore the world of the future ...
Category:Polymerization - Wikimedia Commons
Media in category "Polymerization" The following 20 files are in this category, out of 20 total.
addition polymerization
Polymerization reaction in which a single monomer gives rise to a single polymer, with no other reaction products. Addition polymerization occurs in alkenes, hydrocarbons ...
polymerization -- Britannica Online Encyclopedia
Britannica online encyclopedia article on polymerization: any process in which relatively small molecules, called monomers, combine chemically to produce a very large chainlike or ...
