CR39^®

The plastic is made by the polymerization of the oxydi-2,1-ethanediyl di-2-propenyl ester of carbonic acid. The monomer is an allyl resin which means that it contains the following functional group:

[ CH₂ = CH – CH₂ –]

The monomer itself contains two of these functional groups and has the following structure:

Because of the presence of the two allyl functional groups, the monomer can not only polymerize but also cross-link —which results in a thermoset plastic and not a thermoplastic. "Thermosetting" polymer which form random three dimensional cross-linked structures are characterized by being infusible and insoluble in all solvents. A sample of thermosetting material can be considered to be a single molecule, since covalent bonds link every portion of the material with every other.

 

Further readings:

B.G. Cartwright and E.K. Shirk "A nuclear track recording polymer of unique sensityvity and resolution", Nucl. Inst. and Meth. 153 (1978) 457