Editing Polyimide (section)

==Synthesis==
Several methods are possible to prepare polyimides, among them:
* The reaction between a di[[Acid anhydride|anhydride]] and a [[diamine]] (the most used method).
* The reaction between a dianhydride and a di[[isocyanate]].

The polymerization of a diamine and a dianhydride can be carried out by a two-step method in which a [[poly(amidocarboxylic acid)]] is prepared first, or directly by a one-step method. The two-step method is the most widely used procedure for polyimide synthesis. First a soluble poly(amidocarboxylic acid) ('''2''') is prepared which is cyclized after further processing in a second step to the polyimide ('''3'''). A two-step process is necessary because the final polyimides are in most cases infusible and insoluble due to their aromatic structure.

[[File:Polyimide Formation (schematic) V1.png|center|500px]]

Dianhydrides used as precursors to these materials include pyromellitic dianhydride, [[benzoquinonetetracarboxylic dianhydride]] and [[naphthalene tetracarboxylic dianhydride]]. Common diamine building blocks include [[4,4'-diaminodiphenyl ether]] (DAPE), [[meta-phenylenediamine]] (MDA) and 3,3'-diaminodiphenylmethane.<ref name=Ullmann/> Hundreds of diamines and dianhydrides have been examined to tune the physical and especially the processing properties of these materials.  These materials tend to be insoluble and have high softening temperatures, arising from charge-transfer interactions between the planar subunits.<ref>{{cite journal|doi=10.1016/j.progpolymsci.2012.02.005|title=Advanced polyimide materials: Syntheses, physical properties and applications|journal=Progress in Polymer Science|volume=37|issue=7|pages=907–974|year=2012|last1=Liaw|first1=Der-Jang|last2=Wang|first2=Kung-Li|last3=Huang|first3=Ying-Chi|last4=Lee|first4=Kueir-Rarn|last5=Lai|first5=Juin-Yih|last6=Ha|first6=Chang-Sik}}</ref>

===Analysis===
The imidization reaction can be followed via [[Infrared spectroscopy|IR spectroscopy]]. The IR spectrum is characterized during the reaction by the disappearance of absorption bands of the poly(amic acid) at 3400 to 2700&nbsp;cm<sup>−1</sup> (OH stretch), ~1720 and 1660 (amide C=O) and ~1535&nbsp;cm<sup>−1</sup> (C-N stretch). At the same time, the appearance of the characteristic imide bands can be observed, at ~1780 (C=O asymm), ~1720 (C=O symm), ~1360 (C-N stretch) and ~1160 and 745&nbsp;cm<sup>−1</sup> (imide ring deformation).<ref>K. Faghihi, J. Appl. Polym. Sci., 2006, 102, 5062–5071. Y. Kung and S. Hsiao, J. Mater. Chem., 2011, 1746–1754. L. Burakowski, M. Leali and M. Angelo, Mater. Res., 2010, 13, 245–252.</ref>⁠　Detailed analyses of polyimide<ref>{{Cite journal |last1=Kato |first1=Tomofumi |last2=Yamada |first2=Yasuhiro |last3=Nishikawa |first3=Yasushi |last4=Ishikawa |first4=Hiroki |last5=Sato |first5=Satoshi |date=2021-06-30 |title=Carbonization mechanisms of polyimide: Methodology to analyze carbon materials with nitrogen, oxygen, pentagons, and heptagons |url=https://www.sciencedirect.com/science/article/pii/S0008622321002839 |journal=Carbon |language=en |volume=178 |pages=58–80 |doi=10.1016/j.carbon.2021.02.090 |s2cid=233539984 |issn=0008-6223|url-access=subscription }}</ref> and carbonized polyimide<ref>{{Cite journal |last1=Kato |first1=Tomofumi |last2=Yamada |first2=Yasuhiro |last3=Nishikawa |first3=Yasushi |last4=Ishikawa |first4=Hiroki |last5=Sato |first5=Satoshi |date=2021-06-30 |title=Carbonization mechanisms of polyimide: Methodology to analyze carbon materials with nitrogen, oxygen, pentagons, and heptagons |url=https://www.sciencedirect.com/science/article/pii/S0008622321002839 |journal=Carbon |language=en |volume=178 |pages=58–80 |doi=10.1016/j.carbon.2021.02.090 |s2cid=233539984 |issn=0008-6223|url-access=subscription }}</ref> and graphitized polyimide<ref>{{Cite journal |last1=Kato |first1=Tomofumi |last2=Yamada |first2=Yasuhiro |last3=Nishikawa |first3=Yasushi |last4=Otomo |first4=Toshiya |last5=Sato |first5=Hayato |last6=Sato |first6=Satoshi |date=2021-10-01 |title=Origins of peaks of graphitic and pyrrolic nitrogen in N1s X-ray photoelectron spectra of carbon materials: quaternary nitrogen, tertiary amine, or secondary amine? |journal=Journal of Materials Science |language=en |volume=56 |issue=28 |pages=15798–15811 |doi=10.1007/s10853-021-06283-5 |bibcode=2021JMatS..5615798K |s2cid=235793266 |issn=1573-4803|doi-access=free }}</ref> have been reported.