Editing Copolymer (section)

==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.