Editing Copolymer (section)

===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>