Journal of Dental Research, Vol 70, 67-71, Copyright © 1991 by International & American Associations for Dental Research Online Journals
The effect of catalyst structure on the synthesis of a dental restorative monomer
M. Farahani, A. D. Johnston and R. L. Bowen
Paffenbarger Research Center, National Institute of Standards and Technology, Gaithersburg, Maryland 20899.
The addition product of 2-hydroxyethyl methacrylate (HEMA) and pyromellitic
dianhydride (PMDA), known as PMDM, is a mixture of two structural isomers.
The para PMDM isomer--currently used in mediating adhesive bonding of
restorative materials to hard tooth tissues--is a crystalline solid. The
meta isomer is a liquid. In the synthesis of PMDM, the para isomer, which
can be purified by crystallization, is usually present to the extent of
only 50% of the product mixture. The effect of the amine catalyst structure
was studied relative to its role in increasing the yield of the para
isomer, either by a reduction in the amount of the meta isomer or by an
increase in the extent of overall reaction. The chemical structure of the
amine catalyst had an important role in the synthesis of PMDM and
influenced the ratio of the isomers. Among aliphatic amines, especially
noteworthy as catalysts that gave excellent yields of the para isomer in
high purity were N,N-di-isopropyl-ethylamine and hexamethylenetetramine.
