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Plastic fantastic

Dear Reader,

In recent times I have shown how a lad can have fun with the unit cells of inorganic solids, but now it is time to move onto something with carbon in it. I choose to look at the solid state structure of a polymer which is a high temperature engineering polymer.

LIMMUP in the crystallographic database is Poly((4,4′-diphenylene)pyromellitimide) which was described by Y. Obata, K. Okuyama, S. Kurihara, Y. Kitano and T. Jinda in Macromolecules, 1995, 28, 1547. This is a solid which is an endless chain of atoms covalently linked to the next. Here is a picture of the unit cell.

Unit cell of the polymer

While here is a picture of five of the polymer chains.

Polymer chains

While looking for examples of the polymer chains I noticed something else, this brings me onto another subject. I hold the view that one of the first steps to maturity is the point at which a person truly accepts that things which they are not interested in, involved in or have experience in can be truly worthwhile and valid. I have to add the warning that there is some work out there which is not worthwhile and is frankly close to worthless, but I do not want to point the finger by naming names well at least not today.

I have spent much of my life working on trying to get molecules to selectively recognise metals; I used to share an office with a man (Zhixue Zhu) who worked for Howard Colquhoun on a project where he was trying to get molecules to recognise short parts of polymer chains. While it might not have been quite the sort of thing that I have done in life, I still hold the view that the work is good work which is worthwhile.

Here what Dr Zhu did was to use a pair of pyrene groups to recognise part of a short chain model of kapton (poly(4,4′-oxydiphenylene-pyromellitimide)); his tweezers recognized the pyromellitimide part of the chain. Here is a picture of the solid which he published in Chemical Communications, 2004 page 2650 together with H.M. Colquhoun, C.J. Cardin and Yu Gan.

Dr Zhu's mini tongs which grip the polymer chain

I suspect that Christine Cardin found this solid interesting as her group have done a lot of work in the past on how things like acridines bond onto DNA through pi-pi effects.


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