MadSci Network: Chemistry
Query:

Re: What are possible reactions between formic acid and PMMA?

Date: Sun Jul 3 20:29:50 2005
Posted By: John Christie, Faculty, Dept. of Chemistry,
Area of science: Chemistry
ID: 1120174516.Ch
Message:

Chris, I am fairly confident that what you are observing is a manifestation of a phenomenon known as 
contractility, and that you are observing a physical process, not a chemical process.

The PMMA in a film is in a highly crystalline state. The actual polymer chains are in an extended 
conformation. Where the formic acid drops, it will free up the motions of the molecular chains, which 
will then move from an extended crystalline to a random coil conformation. In doing so the material will 
contract away from the point of solvent contact into the bulk. The result will be pits and even holes 
where the solvent touched, and a slight wall thickening (that you will not notice unless you look really 
carefully) around the edges of the pits.

This sort of phenomenon is discussed in most standard Polymer science textbooks. You will find some 
discussion, for example, in Mandelkern 'An Introduction to Macromolecules', Springer, 1972., p. 89 and 
following.


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