View source for Copolymer

{{Short description|Polymer derived from more than one species of monomer}}
{{TopicTOC-Polymer}}
[[Image:Copolymers.svg|right|thumb|350px|Different types of polymers: 1) homopolymer 2) alternating copolymer 3) random copolymer 4) block copolymer 5) graft copolymer.]]

In [[polymer chemistry]], a '''copolymer''' is a [[polymer]] derived from more than one species of [[monomer]]. The [[polymerization]] of monomers into copolymers is called '''copolymerization'''. Copolymers obtained from the copolymerization of two monomer species are sometimes called ''bipolymers''. {{anchor|terpolymer}} Those obtained from three and four monomers are called '''''terpolymers''''' <!--bold because it is the target of a redirect--> and ''quaterpolymers'', respectively.<ref name=goldbook1996>
{{cite journal
 |doi = 10.1351/goldbook.C01335
 |title = Glossary of basic terms in polymer science (IUPAC Recommendations 1996)
 |last1 = McNaught |first1 = A. D. |last2 = Wilkinson, A.
 |journal = [[Pure and Applied Chemistry]] |volume=68 |year=1996 |pages=2287–2311
|isbn = 978-0-9678550-9-7
 |doi-access = free}}</ref> Copolymers can be characterized by a variety of techniques such as [[Nuclear magnetic resonance spectroscopy|NMR spectroscopy]] and [[size-exclusion chromatography]] to determine the molecular size, weight, properties, and composition of the material.<ref name=":0" />

Commercial copolymers include [[acrylonitrile butadiene styrene]] (ABS), [[styrene/butadiene co-polymer]] (SBR), [[nitrile rubber]], [[styrene-acrylonitrile]], styrene-isoprene-styrene (SIS) and [[ethylene-vinyl acetate]], all of which are formed by [[chain-growth polymerization]]. Another production mechanism is [[step-growth polymerization]], which is used to produce the nylon-12/6/66 copolymer<ref>{{cite web | title=Nylon-12/6/66 Copolymer | website=Cosmetics Info | url=http://www.cosmeticsinfo.org/ingredient/nylon-12666-copolymer | access-date=12 April 2021 | archive-date=11 April 2021 | archive-url=https://web.archive.org/web/20210411080810/https://www.cosmeticsinfo.org/ingredient/nylon-12666-copolymer | url-status=dead }}</ref> of [[nylon 12]], [[nylon 6]] and [[nylon 66]], as well as the [[copolyester]] family. Copolymers can be used to develop commercial goods or drug delivery vehicles.

 {{Quote box|width = 35%
 |title = [[International Union of Pure and Applied Chemistry|IUPAC]] definition
 |quote = '''copolymer''': A [https://doi.org/10.1351/goldbook.P04735 polymer] derived from more than one species of [https://doi.org/10.1351/goldbook.M04017 monomer]. (See Gold Book entry for note.)
<ref name='Gold Book "copolymer"'>{{cite web |title=copolymer |url=https://goldbook.iupac.org/terms/view/C01335 |website=Gold Book |publisher=IUPAC |access-date=1 April 2024 |ref=Gold Book C01335 |doi=10.1351/goldbook.C01335}}</ref>
}}
Since a copolymer consists of at least two types of constituent units (also [[structural unit]]s), copolymers can be classified based on how these units are arranged along the [[Catenation|chain]].<ref name="Jenkins"/>  ''Linear copolymers'' consist of a single [[Backbone chain|main chain]] and include [[alternating copolymer]]s, [[statistical copolymer]]s, and [[block copolymer]]s. ''[[Branching (polymer chemistry)|Branched]] copolymers'' consist of a single main chain with one or more polymeric [[side chain]]s, and can be [[Graft polymer|grafted]], star shaped, or have other architectures.

==Reactivity ratios==
The ''reactivity ratio'' of a growing copolymer chain terminating in a given monomer is the ratio of the [[reaction rate constant]] for addition of the same monomer and the rate constant for addition of the other monomer. That is, <math>r_1 = \frac{k_{11}}{k_{12}}</math> and <math>r_2 = \frac{k_{22}}{k_{21}}</math>, where for example <math>k_{12}</math> is the rate constant for propagation of a polymer chain ending in monomer 1 (or A) by addition of monomer 2 (or B).<ref name=Cowie/>

The composition and structural type of the copolymer depend on these reactivity ratios r<sub>1</sub> and r<sub>2</sub> according to the [[Mayo–Lewis equation]], also called the '''copolymerization equation''' or '''copolymer equation''',<ref>{{cite journal | last1 = Mayo | first1 = Frank R. | author-link = Frank R. Mayo | author-link2 = Frederick M. Lewis | last2 = Lewis | first2 = Frederick M. | year = 1944 | title = Copolymerization. I. A Basis for Comparing the Behavior of Monomers in Copolymerization; The Copolymerization of Styrene and Methyl Methacrylate | journal = [[J. Am. Chem. Soc.]] | volume = 66 | issue = 9| pages = 1594–1601 | doi = 10.1021/ja01237a052 }}</ref><ref name=Cowie/> for the relative instantaneous rates of incorporation of the two monomers.

<math>\frac{\mathrm{d} \left[ \mathrm{M}_1 \right]}{\mathrm{d} \left[ \mathrm{M}_2 \right]} = \frac{\left[ \mathrm{M}_1 \right] \left( r_1 \left[ \mathrm{M}_1 \right] + \left[ \mathrm{M}_2 \right] \right)}{\left[ \mathrm{M}_2 \right] \left( \left[ \mathrm{M}_1 \right] + r_2 \left[ \mathrm{M}_2 \right] \right)}</math>

==Linear copolymers==

===Block copolymers===

Block copolymers comprise two or more [[Polymer#Monomers and repeat units|homopolymer]] subunits linked by covalent bonds. The union of the homopolymer subunits may require an intermediate non-repeating subunit, known as a '''junction block'''. '''Diblock copolymers''' have two distinct blocks; '''triblock copolymers''' have three. Technically, a block is a portion of a macromolecule, comprising many units, that has at least one feature which is not present in the adjacent portions.<ref name=goldbook1996/> A possible sequence of repeat units A and B in a triblock copolymer might be ~A-A-A-A-A-A-A-B-B-B-B-B-B-B-A-A-A-A-A~.<ref>Cowie, p.4</ref>

 {{Quote box|width = 35%
 |title = [[International Union of Pure and Applied Chemistry|IUPAC]] definition
 |quote = '''block copolymer''': A [https://doi.org/10.1351/goldbook.C01335 copolymer] that is a [https://doi.org/10.1351/goldbook.B00685 block polymer]. In the [https://doi.org/10.1351/goldbook.C01281 constituent] macromolecules of a [https://doi.org/10.1351/goldbook.B00682 block] [https://doi.org/10.1351/goldbook.C01335 copolymer], adjacent blocks are constitutionally different, i.e. adjacent blocks comprise [https://doi.org/10.1351/goldbook.C01288 constitutional unit] derived from different species of [https://doi.org/10.1351/goldbook.M04017 monomer] or from the same species of [https://doi.org/10.1351/goldbook.M04017 monomer] but with a different composition or [https://doi.org/10.1351/goldbook.ST06775 sequence] distribution of constitutional units. 
<ref name='Gold Book "block copolymer"'>{{cite web |title=block copolymer |url=https://goldbook.iupac.org/terms/view/B00683 |website=Gold Book |publisher=IUPAC |access-date=1 April 2024 |ref=Gold Book B00683 |doi=10.1351/goldbook.B00683}}</ref>
}}

Block copolymers are made up of blocks of different [[polymerized]] [[monomers]]. For example, polystyrene-b-poly(methyl methacrylate) or PS-b-PMMA (where b = block) is usually made by first polymerizing [[styrene]], and then subsequently polymerizing [[methyl methacrylate]] (MMA) from the reactive end of the polystyrene chains. This polymer is a "diblock copolymer" because it contains two different chemical blocks. Triblocks, tetrablocks, multiblocks, etc. can also be made. Diblock copolymers are made using [[living polymerization]] techniques, such as atom transfer free radical polymerization ([[ATRP (chemistry)|ATRP]]), reversible addition fragmentation chain transfer ([[RAFT (chemistry)|RAFT]]), [[ring-opening metathesis polymerization]] (ROMP), and living cationic or living anionic [[living polymerization|polymerization]]s.<ref>Hadjichristidis N., Pispas S., Floudas G. Block copolymers: synthetic strategies, physical properties, and applications – Wiley, 2003.</ref> An emerging technique is [[chain shuttling polymerization]].

The synthesis of block copolymers requires that both reactivity ratios are much larger than unity (r<sub>1</sub> >> 1, r<sub>2</sub> >> 1) under the reaction conditions, so that the terminal monomer unit of a growing chain tends to add a similar unit most of the time.<ref name=Fried>{{cite book |last=Fried |first=Joel R. |date=2003 |edition=2nd |title=Polymer Science and Technology |publisher=Prentice Hall |pages=41–43 |isbn=978-0-13-018168-8}}</ref>

The "'''blockiness'''" of a copolymer is a measure of the adjacency of comonomers vs their statistical distribution.  Many or even most synthetic polymers are in fact copolymers, containing about 1-20% of a minority monomer.  In such cases, blockiness is undesirable.<ref name=Chum>{{cite journal | last1 = Chum | first1 = P. S. | last2 = Swogger | first2 = K. W. | year = 2008 | title = Olefin Polymer Technologies-History and Recent Progress at the Dow Chemical Company | journal = Progress in Polymer Science | volume = 33 | issue = 8 | pages = 797–819 | doi = 10.1016/j.progpolymsci.2008.05.003 }}</ref> A ''block index'' has been proposed as a quantitative measure of blockiness or deviation from random monomer composition.<ref>{{cite journal |last1=Shan |first1=Colin Li Pi |last2=Hazlitt |first2=Lonnie G. |date=2007 |title=Block Index for Characterizing Olefin Block Copolymers |journal=Macromol. Symp. |volume=257 |pages=80–93 |citeseerx=10.1.1.424.4699 |doi=10.1002/masy.200751107 }}</ref>

===Alternating copolymers===
 {{Quote box|width = 35%
 |title = [[International Union of Pure and Applied Chemistry|IUPAC]] definition
 |quote = '''alternating copolymer''': A [https://doi.org/10.1351/goldbook.C01335 copolymer] consisting of [https://doi.org/10.1351/goldbook.M03667 macromolecule] comprising two species of [https://doi.org/10.1351/goldbook.M04018 monomeric unit] in alternating [https://doi.org/10.1351/goldbook.ST06775 sequence]. (See Gold Book entry for note.)
<ref name='Gold Book "alternating copolymer"'>{{cite web |title=alternating copolymer |url=https://goldbook.iupac.org/terms/view/A00250 |website=Gold Book |publisher=IUPAC |access-date=1 April 2024 |ref=Gold Book A00250 |doi=10.1351/goldbook.A00250}}</ref>
}}
An alternating copolymer has regular alternating A and B units, and is often described by the formula: -A-B-A-B-A-B-A-B-A-B-, or -(-A-B-)<sub>n</sub>-. The molar ratio of each monomer in the polymer is normally close to one, which happens when the reactivity ratios r<sub>1</sub> and r<sub>2</sub> are close to zero, as can be seen from the Mayo–Lewis equation. For example, in the free-radical copolymerization of [[styrene maleic anhydride]] copolymer, r<sub>1</sub> = 0.097 and r<sub>2</sub> = 0.001,<ref name=Fried/> so that most chains ending in styrene add a maleic anhydride unit, and almost all chains ending in maleic anhydride add a styrene unit. This leads to a predominantly alternating structure.

A step-growth copolymer -(-A-A-B-B-)<sub>n</sub>- formed by the [[condensation reaction|condensation]] of two [[bifunctional]] monomers A–A and B–B is in principle a perfectly alternating copolymer of these two monomers, but is usually considered as a [[Polymer#Monomers and repeat units|homopolymer]] of the dimeric repeat unit A-A-B-B.<ref name=Cowie>{{cite book |last=Cowie |first=J.M.G. |date=1991 |edition=2nd |title=Polymers: Chemistry and Physics of Modern Materials |publisher=Blackie (USA: Chapman and Hall) |pages=[https://archive.org/details/polymerschemistr0000cowi/page/104 104–106] |isbn=978-0-216-92980-7 |url=https://archive.org/details/polymerschemistr0000cowi/page/104 }}</ref> An example is [[nylon 66]] with repeat unit -OC-( CH<sub>2</sub>)<sub>4</sub>-CO-NH-(CH<sub>2</sub>)<sub>6</sub>-NH-, formed from a [[dicarboxylic acid]] monomer and a [[diamine]] monomer.

===Periodic copolymers===

Periodic copolymers have units arranged in a repeating sequence. For two monomers A and B, for example, they might form the repeated pattern (A-B-A-B-B-A-A-A-A-B-B-B)<sub>n</sub>.

===Statistical copolymers===
 {{Quote box|width = 35%
 |title = [[International Union of Pure and Applied Chemistry|IUPAC]] definition
 |quote = '''statistical copolymer''': A [https://doi.org/10.1351/goldbook.C01335 copolymer] consisting of [https://doi.org/10.1351/goldbook.M03667 macromolecule] in which the sequential distribution of the [https://doi.org/10.1351/goldbook.M04018 monomeric unit] obeys known statistical laws. (See Gold Book entry for note.)
<ref name='Gold Book "statistical copolymer"'>{{cite web |title=statistical copolymer |url=https://goldbook.iupac.org/terms/view/S05955 |website=Gold Book |publisher=IUPAC |access-date=1 April 2024 |ref=Gold Book S05955 |doi=10.1351/goldbook.S05955}}</ref>
}}
In statistical copolymers the sequence of monomer residues follows a statistical rule. If the probability of finding a given type monomer residue at a particular point in the chain is equal to the mole fraction of that monomer residue in the chain, then the polymer may be referred to as a truly '''random copolymer'''<ref name="PC14">Painter P. C. and Coleman M. M., ''Fundamentals of Polymer Science'', CRC Press, 1997, p 14.</ref> (structure 3).

Statistical copolymers are dictated by the reaction kinetics of the two chemically distinct monomer reactants, and are commonly referred to interchangeably as "random" in the polymer literature.<ref name="Chanda">Chanda, M. ''Introduction to Polymer Science and Chemistry''. Second Edition. CRC Press, 2013.</ref> As with other types of copolymers, random copolymers can have interesting and commercially desirable properties that blend those of the individual homopolymers. Examples of commercially relevant random copolymers include [[rubber]]s made from styrene-butadiene copolymers and resins from styrene-acrylic or [[methacrylic acid]] derivatives.<ref>Overberger, C. ″Copolymerization: 1. General Remarks; 2: Selective Examples of Copolymerizations″. ''Journal of Polymer Science: Polymer Symposium'' 72, 67-69 (1985).</ref>  Copolymerization is particularly useful in tuning the [[glass transition]] temperature, which is important in the operating conditions of polymers; it is assumed that each monomer occupies the same amount of free volume whether it is in a copolymer or homopolymer, so the [[glass transition]] temperature (T<sub>g</sub>) falls between the values for each homopolymer and is dictated by the mole or mass fraction of each component.<ref name="Chanda" />

A number of parameters are relevant in the composition of the polymer product; namely, one must consider the reactivity ratio of each component. Reactivity ratios describe whether the monomer reacts preferentially with a segment of the same type or of the other type. For example, a reactivity ratio that is less than one for component 1 indicates that this component reacts with the other type of monomer more readily. Given this information, which is available for a multitude of monomer combinations in the "Wiley Database of Polymer Properties",<ref>Greenley, Robert. ″Free Radical Copolymerization Reactivity Ratios″. ''The Wiley Database of Polymer Properties''. 2003. {{doi|10.1002/0471532053.bra007}}</ref> the [[Mayo-Lewis equation]] can be used to predict the composition of the polymer product for all initial mole fractions of monomer. This equation is derived using the [[Markov model]], which only considers the last segment added as affecting the kinetics of the next addition; the Penultimate Model considers the second-to-last segment as well, but is more complicated than is required for most systems.<ref>{{Cite journal | doi = 10.1021/ma971043b| pmid = 9680398| title = Ethene−Norbornene Copolymerization with Homogeneous Metallocene and Half-Sandwich Catalysts: Kinetics and Relationships between Catalyst Structure and Polymer Structure. 3. Copolymerization Parameters and Copolymerization Diagrams| journal = Macromolecules| volume = 31| issue = 15| pages = 4681–3| year = 1998| last1 = Ruchatz| first1 = Dieter| last2 = Fink| first2 = Gerhard| bibcode = 1998MaMol..31.4681R}}</ref> When both reactivity ratios are less than one, there is an azeotropic point in the Mayo-Lewis plot. At this point, the mole fraction of monomer equals the composition of the component in the polymer.<ref name="Chanda" />

There are several ways to synthesize random copolymers. The most common synthesis method is [[free radical polymerization]]; this is especially useful when the desired properties rely on the composition of the copolymer rather than the molecular weight, since free radical polymerization produces relatively disperse polymer chains. Free radical polymerization is less expensive than other methods, and produces high-molecular weight polymer quickly.<ref>Cao, Ti and Stephen E. Webber. ″Free-Radical Copolymerization of Fullerenes with Styrene″. ''Macromolecules'', 1996, 28, pp 3741-3743.</ref>  Several methods offer better control over [[dispersity]]. [[Anionic polymerization]] can be used to create random copolymers, but with several caveats: if [[carbanion]]s of the two components do not have the same stability, only one of the species will add to the other. Additionally, anionic polymerization is expensive and requires very clean reaction conditions, and is therefore difficult to implement on a large scale.<ref name="Chanda" /> Less disperse random copolymers are also synthesized by ″living″ [[controlled radical polymerization]] methods, such as [[atom-transfer radical-polymerization]] (ATRP), [[nitroxide mediated radical polymerization]] (NMP), or [[reversible addition−fragmentation chain-transfer polymerization]] (RAFT). These methods are favored over anionic polymerization because they can be performed in conditions similar to free radical polymerization. The reactions require longer experimentation periods than free radical polymerization, but still achieve reasonable reaction rates.<ref>{{Cite journal | doi = 10.1016/S1359-0286(96)80101-X| title = Controlled radical polymerization| journal = Current Opinion in Solid State and Materials Science| volume = 1| issue = 6| pages = 769–776| year = 1996| last1 = Matyjaszewski| first1 = Krzysztof| bibcode = 1996COSSM...1..769M}}</ref>

===Stereoblock copolymers===

[[File:Stereobl.png|thumb|right|A stereoblock vinyl copolymer]]

In stereoblock copolymers the blocks or units differ only in the [[tacticity]] of the monomers.

===Gradient copolymers===

In gradient copolymers the monomer composition changes gradually along the chain.

==Branched copolymers==

There are a variety of architectures possible for nonlinear copolymers. Beyond grafted and star polymers discussed below, other common types of branched copolymers include '''brush copolymers''' and '''comb copolymers'''.

=== Graft copolymers ===
[[File:Graft Copolymer.png|thumb|225px|The graft copolymer consists of a main polymer chain or backbone (A) covalently bonded to one or more side chains (B)]]

[[Graft polymer|Graft copolymers]] are a special type of branched copolymer wherein the side chains are structurally distinct from the main chain. Typically, the main chain is formed from one type of monomer (A) and branches are formed from another monomer (B), or the side-chains have constitutional or configurational features that differ from those in the main chain.<ref name="Jenkins">{{cite journal|title=Glossary of basic terms in polymer science (IUPAC Recommendations 1996)|journal=[[Pure and Applied Chemistry]]|year=1996|volume=68|issue=12|pages=2287–2311|doi=10.1351/pac199668122287|last1=Jenkins|first1=A. D|last2=Kratochvíl|first2=P|last3=Stepto|first3=R. F. T|last4=Suter|first4=U. W|doi-access=free}}</ref>

The individual chains of a graft copolymer may be homopolymers or copolymers. Note that different copolymer sequencing is sufficient to define a structural difference, thus an A-B diblock copolymer with A-B alternating copolymer side chains is properly called a graft copolymer.

For example, [[polystyrene]] chains may be grafted onto [[polybutadiene]], a [[synthetic rubber]] which retains one reactive C=C [[double bond]] per [[repeat unit]]. The polybutadiene is dissolved in styrene, which is then subjected to [[free-radical polymerization]]. The growing chains can add across the double bonds of rubber molecules forming polystyrene branches. The graft copolymer is formed in a mixture with ungrafted polystyrene chains and rubber molecules.<ref>{{cite book |last=Rudin |first=Alfred |date=1982 |title=The Elements of Polymer Science and Engineering |publisher=Academic Press |page=[https://archive.org/details/elementsofpolyme0000rudi/page/19 19] |isbn=978-0-12-601680-2 |edition=1st |url=https://archive.org/details/elementsofpolyme0000rudi/page/19 }}</ref>

As with block copolymers, the quasi-[[composite material|composite]] product has properties of both "components." In the example cited, the rubbery chains absorb energy when the substance is hit, so it is much less brittle than ordinary polystyrene. The product is called [[Polystyrene#Co-polymers|high-impact polystyrene]], or HIPS.

===Star copolymers===

[[File:Star Shaped Polymers.png|thumb|200px|Star shaped polymers or copolymers]]

[[Star-shaped polymer|Star copolymers]] have several polymer chains connected to a central core.

==Microphase separation==<!-- [[Microphase separation]] redirects here -->

[[File:Sbs block copolymer.jpg|thumb|right|SBS block copolymer in [[Transmission electron microscopy|TEM]]]]

Block copolymers can "microphase separate" to form periodic [[nanostructures]],<ref>Hamley, I.W. "The Physics of Block Copolymers" – Oxford University Press, 1998.</ref><ref>Hamley, I.W. "Developments in Block Copolymer Science and Technology" – Wiley, 2004.</ref> such as styrene-butadiene-styrene block copolymer. The polymer is known as [[Kraton (polymer)|Kraton]] and is used for shoe soles and [[adhesive]]s. Owing to the microfine structure, transmission electron microscope or [[Transmission electron microscopy|TEM]] was used to examine the structure. The butadiene matrix was stained with [[osmium tetroxide]] to provide contrast in the image. The material was made by [[living polymerization]] so that the blocks are almost [[monodisperse]] to create a regular microstructure. The [[molecular weight]] of the polystyrene blocks in the main picture is 102,000; the inset picture has a molecular weight of 91,000, producing slightly smaller domains.

[[Image:SBSstructure.svg|thumb|right|SBS block copolymer schematic microstructure]]

Microphase separation is a situation similar to that of [[oil]] and [[water]]. Oil and water are immiscible (i.e., they can phase separate). Due to the incompatibility between the blocks, block copolymers undergo a similar phase separation. Since the blocks are covalently bonded to each other, they cannot demix macroscopically like water and oil. In "microphase separation," the blocks form [[nanometer]]-sized structures. Depending on the relative lengths of each block, several morphologies can be obtained. In diblock copolymers, sufficiently different block lengths lead to nanometer-sized spheres of one block in a matrix of the second (e.g., [[Polymethyl methacrylate|PMMA]] in polystyrene). Using less different block lengths, a "hexagonally packed cylinder" geometry can be obtained. Blocks of similar length form layers (often called [[lamella (materials)|lamellae]] in the technical literature). Between the cylindrical and lamellar phase is the [[gyroid]] phase. The nanoscale structures created from block copolymers can potentially be used to create devices for computer [[memory]], nanoscale-templating, and nanoscale separations.<ref>{{cite journal | last1 = Gazit | first1 = Oz | last2 = Khalfin | first2 = Rafail | last3 = Cohen | first3 = Yachin | last4 = Tannenbaum | first4 = Rina | author4-link = Rina Tannenbaum | year = 2009 | title = Self-assembled diblock copolymer "nanoreactors" as catalysts for metal nanoparticle synthesis | journal = Journal of Physical Chemistry C | volume = 113 | issue = 2| pages = 576–583 | doi = 10.1021/jp807668h }}</ref> Block copolymers are sometimes used as a replacement for phospholipids in [[model lipid bilayer]]s and [[liposome]]s for their superior stability and tunability.<ref>{{cite journal | last1=Meier | first1=Wolfgang | last2=Nardin | first2=Corinne | last3=Winterhalter | first3=Mathias | title=Reconstitution of Channel Proteins in (Polymerized) ABA Triblock Copolymer Membranes | journal=Angewandte Chemie International Edition | publisher=Wiley | volume=39 | issue=24 | date=2000-12-15 | issn=1433-7851 | doi=10.1002/1521-3773(20001215)39:24<4599::aid-anie4599>3.0.co;2-y | pages=4599–4602| pmid=11169683 }}</ref><ref>{{cite journal | last1=Zhang | first1=Xiaoyan | last2=Tanner | first2=Pascal | last3=Graff | first3=Alexandra | last4=Palivan | first4=Cornelia G. | last5=Meier | first5=Wolfgang | title=Mimicking the cell membrane with block copolymer membranes | journal=Journal of Polymer Science Part A: Polymer Chemistry | publisher=Wiley | volume=50 | issue=12 | date=2012-03-11 | issn=0887-624X | doi=10.1002/pola.26000 | pages=2293–2318| bibcode=2012JPoSA..50.2293Z | doi-access=free }}</ref>

Polymer scientists use [[thermodynamics]] to describe how the different blocks interact.<ref>{{cite journal|author-link1=Frank S. Bates |author-link2=Glenn H. Fredrickson | last1 = Bates | first1 = Frank S.  | last2 = Fredrickson | first2 = Glenn H. | year = 2014 | title = Block Copolymer Thermodynamics: Theory and Experiment | journal = Annual Review of Physical Chemistry | volume = 41 | pages = 525–557 | doi = 10.1146/annurev.pc.41.100190.002521| bibcode = 1990ARPC...41..525B | pmid = 20462355}}</ref><ref>{{cite journal | last1 = Chremos | first1 = Alexandros | last2 = Nikoubashman | first2 = Arash | last3 = Panagiotopoulos | first3 = Athanassios | year = 2014 | title = Flory-Huggins parameter χ, from binary mixtures of Lennard-Jones particles to block copolymer melts | journal = J. Chem. Phys. | volume = 140 | issue = 5| pages = 054909 | doi = 10.1063/1.4863331 | pmid = 24511981 | bibcode = 2014JChPh.140e4909C }}</ref> The product of the degree of polymerization, ''n'', and the Flory-Huggins [[interaction parameter]], <math>\chi</math>, gives an indication of how incompatible the two blocks are and whether they will microphase separate. For example, a diblock copolymer of symmetric composition will microphase separate if the product <math>\chi N</math> is greater than 10.5. If <math>\chi N</math> is less than 10.5, the blocks will mix and microphase separation is not observed. The incompatibility between the blocks also affects the solution behavior of these copolymers and their adsorption behavior on various surfaces.<ref>{{cite journal | last1 = Hershkovitz | first1 = Eli | last2 = Tannenbaum | first2 = Allen | author2-link = Allen Tannenbaum | last3 = Tannenbaum | first3 = Rina | author3-link = Rina Tannenbaum | year = 2008 | title = Adsorption of block co-polymers from selective solvents on curved surfaces | journal = Macromolecules | volume = 41 | issue = 9| pages = 3190–3198 | doi = 10.1021/ma702706p | pmid = 20976029 | bibcode = 2008MaMol..41.3190H | pmc=2957843}}</ref>

Block copolymers are able to self-assemble in selective solvents to form micelles among other structures.<ref>Hamley, I.W. "Block Copolymers in Solution" – Wiley, 2005.</ref>

In thin films, block copolymers are of great interest as masks in the lithographic patterning of semiconductor materials for applications in high density data storage. A key challenge is to minimise the feature size and much research is in progress on this.<ref>{{cite journal | last1 = Hamley | first1 = IW | year = 2009 | title = Ordering in Thin Films of Block Copolymers: Fundamentals to Potential Applications | journal = Progress in Polymer Science | volume = 34 | issue = 11| pages = 1161–1210 | doi = 10.1016/j.progpolymsci.2009.06.003 }}</ref>

== Characterization ==
[[Characterization (materials science)|Characterization]] techniques for copolymers are similar to those for other polymeric materials. These techniques can be used to determine the average [[Molecular mass|molecular weight]], molecular size, chemical composition, molecular [[Homogeneity and heterogeneity|homogeneity]], and physiochemical properties of the material.<ref name=":0" /> However, given that copolymers are made of base polymer components with heterogeneous properties, this may require multiple characterization techniques to accurately characterize these copolymers.<ref>{{Cite journal |last1=Rowland |first1=Steven M. |last2=Striegel |first2=André M. |date=2012-06-05 |title=Characterization of Copolymers and Blends by Quintuple-Detector Size-Exclusion Chromatography |url=https://pubs.acs.org/doi/abs/10.1021/ac3003775 |journal=Analytical Chemistry |language=en |volume=84 |issue=11 |pages=4812–4820 |doi=10.1021/ac3003775 |pmid=22591263 |issn=0003-2700}}</ref>

Spectroscopic techniques, such as [[nuclear magnetic resonance spectroscopy]], [[infrared spectroscopy]], and [[Ultraviolet–visible spectroscopy|UV spectroscopy]], are often used to identify the molecular structure and chemical composition of copolymers. In particular, NMR can indicate the [[tacticity]] and configuration of polymeric chains while IR can identify functional groups attached to the copolymer.

Scattering techniques, such as [[static light scattering]], [[dynamic light scattering]], and [[small-angle neutron scattering]], can determine the molecular size and weight of the synthesized copolymer. Static light scattering and dynamic light scattering use light to determine the average molecular weight and behavior of the copolymer in solution whereas small-angle neutron scattering uses neutrons to determine the molecular weight and chain length. Additionally, x-ray scattering techniques, such as [[small-angle X-ray scattering]] (SAXS) can help determine the nanometer morphology and characteristic feature size of a microphase-separated block-copolymer or suspended micelles. <ref>{{Cite journal |last1=Hu |first1=Hanqiong |last2=Gopinadhan|first2=Manesh|last3=Osuji|first3=Chinedum O.  |date=2014-03-21 |title=Directed self-assembly of block copolymers: a tutorial review of strategies for enabling nanotechnology with soft matter|url=https://pubs.rsc.org/en/content/articlelanding/2014/sm/c3sm52607k |journal=Soft Matter |language=en |volume=22 |issue=10 |pages=3867-3889 |doi=10.1039/C3SM52607K}}</ref>

[[Differential scanning calorimetry]] is a thermoanalytical technique used to determine the thermal events of the copolymer as a function of temperature.<ref>{{Cite book |last=Skoog |first=Douglas A. |url=https://www.worldcat.org/oclc/37866092 |title=Principles of instrumental analysis |date=1998 |publisher=Saunders College Pub. |others=F. James Holler, Timothy A. Nieman |isbn=0-03-002078-6 |edition=5th |location=Philadelphia |oclc=37866092}}</ref> It can indicate when the copolymer is undergoing a [[phase transition]], such as crystallization or melting, by measuring the heat flow required to maintain the material and a reference at a constantly increasing temperature.

[[Thermogravimetric analysis]] is another thermoanalytical technique used to access the thermal stability of the copolymer as a function of temperature. This provides information on any changes to the physicochemical properties, such as phase transitions, thermal decompositions, and redox reactions.<ref>{{Cite journal |last1=Coats |first1=A. W. |last2=Redfern |first2=J. P. |date=1963-01-01 |title=Thermogravimetric analysis. A review |url=https://pubs.rsc.org/en/content/articlelanding/1963/an/an9638800906 |journal=Analyst |language=en |volume=88 |issue=1053 |pages=906–924 |doi=10.1039/AN9638800906 |bibcode=1963Ana....88..906C |issn=1364-5528}}</ref>

[[Size-exclusion chromatography]] can separate copolymers with different molecular weights based on their hydrodynamic volume.<ref>{{Cite book |last=Yamakawa |first=Hiromi |url=https://www.worldcat.org/oclc/159244 |title=Modern theory of polymer solutions. |date=1971 |publisher=Harper & Row |isbn=0-06-047309-6 |location=New York |oclc=159244}}</ref> From there, the molecular weight can be determined by deriving the relationship from its hydrodynamic volume. Larger copolymers tend to elute first as they do not interact with the column as much. The collected material is commonly detected by light scattering methods, a refractometer, or a viscometer to determine the concentration of the eluted copolymer.  

== Applications ==

=== Block copolymers ===
A common application of block copolymers is to develop [[thermoplastic elastomer]]s (TPEs).<ref name=":0">{{Cite book |last1=Hadjichristidis |first1=Nikos |url=http://doi.wiley.com/10.1002/0471269808 |title=Block Copolymers |last2=Pispas |first2=Stergios |last3=Floudas |first3=George |date=2002-11-15 |publisher=John Wiley & Sons, Inc. |isbn=978-0-471-39436-5 |location=Hoboken, USA |language=en |doi=10.1002/0471269808}}</ref> Early commercial TPEs were developed from [[Polyurethane|polyurethranes]] (TPUs), consisting of alternating soft segments and hard segments, and are used in automotive bumpers and snowmobile treads.<ref name=":0" /> Styrenic TPEs entered the market later, and are used in footwear, bitumen modification, thermoplastic blending, adhesives, and cable insulation and gaskets.<ref name=":0" /> Modifying the linkages between the blocks resulted in newer TPEs based on [[polyester]]s (TPES) and [[polyamide]]s (TPAs), used in hose tubing, sport goods, and automotive components.<ref name=":0" />

[[Amphiphile|Amphiphilic]] block copolymers have the ability to form [[micelle]]s and [[nanoparticle]]s.<ref name=":1">{{Cite journal |last1=Cho |first1=Heui Kyoung |last2=Cheong |first2=In Woo |last3=Lee |first3=Jung Min |last4=Kim |first4=Jung Hyun |date=2010 |title=Polymeric nanoparticles, micelles and polymersomes from amphiphilic block copolymer |url=http://link.springer.com/10.1007/s11814-010-0216-5 |journal=Korean Journal of Chemical Engineering |language=en |volume=27 |issue=3 |pages=731–740 |doi=10.1007/s11814-010-0216-5 |s2cid=95286455 |issn=0256-1115}}</ref> Due to this property, amphiphilic block copolymers have garnered much attention in research on vehicles for drug delivery.<ref name=":1" /><ref>{{Cite journal |last1=Rösler |first1=Annette |last2=Vandermeulen |first2=Guido W. M. |last3=Klok |first3=Harm-Anton |date=2012-12-01 |title=Advanced drug delivery devices via self-assembly of amphiphilic block copolymers |url=https://www.sciencedirect.com/science/article/pii/S0169409X12002864 |journal=Advanced Drug Delivery Reviews |series=MOST CITED PAPERS IN THE HISTORY OF ADVANCED DRUG DELIVERY REVIEWS: A TRIBUTE TO THE 25TH ANNIVERSARY OF THE JOURNAL |language=en |volume=64 |pages=270–279 |doi=10.1016/j.addr.2012.09.026 |issn=0169-409X}}</ref> Similarly, amphiphilic block copolymers can be used for the removal of organic contaminants from water either through micelle formation<ref name=":0" /> or film preparation.<ref name=":2">{{Cite journal |last1=Herrera-Morales |first1=Jairo |last2=Turley |first2=Taylor A. |last3=Betancourt-Ponce |first3=Miguel |last4=Nicolau |first4=Eduardo |date=2019 |title=Nanocellulose-Block Copolymer Films for the Removal of Emerging Organic Contaminants from Aqueous Solutions |journal=Materials |language=en |volume=12 |issue=2 |pages=230 |doi=10.3390/ma12020230 |issn=1996-1944 |pmc=6357086 |pmid=30641894|bibcode=2019Mate...12..230H |doi-access=free }}</ref>

=== Alternating copolymers ===
The styrene-maleic acid (SMA) alternating copolymer displays amphiphilicity depending on pH, allowing it to change conformations in different environments.<ref name=":3">{{Cite journal |last1=Huang |first1=Jing |last2=Turner |first2=S. Richard |date=2017-05-05 |title=Recent advances in alternating copolymers: The synthesis, modification, and applications of precision polymers |journal=Polymer |language=en |volume=116 |pages=572–586 |doi=10.1016/j.polymer.2017.01.020 |issn=0032-3861|doi-access=free }}</ref> Some conformations that SMA can take are random coil formation, compact globular formation, micelles, and nanodiscs.<ref name=":3" /> SMA has been used as a [[dispersing agent]] for dyes and inks, as drug delivery vehicles, and for membrane solubilization.<ref name=":3" />

=== Copolymer engineering ===
Copolymerization is used to modify the properties of manufactured plastics to meet specific needs, for example to reduce crystallinity, modify [[glass transition temperature]], control wetting properties  or to improve solubility.<ref>{{Cite journal | doi = 10.1002/ppap.201700053| title = Tunable wettability and pH-responsiveness of plasma copolymers of acrylic acid and octafluorocyclobutane| journal = Plasma Processes and Polymers| volume = 14| issue = 10| pages = 1700053| year = 2017| last1 = Muzammil| first1 = Iqbal| last2 = Li| first2 = Yupeng| last3 = Lei| first3 = Mingkai| s2cid = 104161308}}</ref> It is a way of improving mechanical properties, in a technique known as [[rubber toughening]]. Elastomeric phases within a rigid matrix act as crack arrestors, and so increase the energy absorption when the material is impacted for example. [[Acrylonitrile butadiene styrene]] is a common example.
 
==See also==
* [[Polymer#Monomer arrangement in copolymers|Copolymers section of Polymer article]]
* [[Thermoplastic elastomer]]
* [[Tholin]]

==References==
{{reflist|2}}

==External links==
{{Commons|Copolymers}}
* [https://web.archive.org/web/20060919043838/http://www.chem.rochester.edu/~chem421/copoly.htm  Introduction to Polymer Chemistry]
* [http://www.wiley.com/WileyCDA/WileyTitle/productCd-0470015578.html Block Copolymers in Solution: Fundamentals and Applications]

[[Category:Polymer chemistry]]
[[Category:Copolymers| ]]