Journal of Dental Research, Vol 62, 121-125, Copyright © 1983 by International & American Associations for Dental Research Online Journals
Extent of polymerization of dental resins by differential scanning calorimetry
J. M. Antonucci and E. E. Toth
The traditional infrared spectroscopic methods for assessing the degree of
polymerization of dental monomers are often hampered by the difficulties of
sample preparation and, in the case of composites, by interference from the
filler component. These difficulties may be circumvented by the use of
another technique, differential scanning calorimetry (DSC). In this
preliminary investigation, DSC was used to ascertain the degree of vinyl
polymerization of an experimental monomer system consisting of seven parts
BIS-GMA and three parts TEGDMA (triethylene glycol dimethacrylate).
Thermally-activated polymerizations of this monomer system were studied
using benzoyl peroxide (BP) as the initiator. Both the heating rate and the
concentration of BP affected the percent of reacted vinyl groups. For a BP
concentration of 0.39% and heating rates of 10 degrees/min and 2.5
degrees/min, conversions were 73 and 38%, respectively.
Chemically-activated polymerizations using BP and fast-acting amine
accelerators (e.g., p-t-butyl-N,N-dimethylaniline) gave approximately the
same results (e.g., 50% conversion) as those obtained with slower-acting
promoters (e.g., ascorbyl palmitate). Experimental difficulties are
encountered in observing an exotherm with the very reactive accelerators
unless the other parameters (e.g., BP or inhibitor content) involved in the
reaction are adjusted accordingly. As a method for evaluating the
performance of various dental monomers, initiator systems, and inhibitors,
DSC has great potential utility.
