Retention of propanal and diacetyl in experimental resins.

The degree of evaporation from experimental resins containing 0.40 mol% propanal or diacetyl was determined over a 6-month period at 60 degrees C. From the results the maximum evaporation possible, M infinity was calculated for each resin and was found to vary between 0.28% and 7.51% by weight. At low contents of propanal or diacetyl, M infinity 1 remained unchanged as compared with the control resins without additive. At higher contents of additive, M infinity increased significantly. In resins based on BisGMA and TEGDMA, propanal was retained to a lesser extent than diacetyl. In resins based on UEDMA and HEMA, propanal was retained to a greater extent than diacetyl. This study confirms that propanal and diacetyl become bound in the polymer structure, and theories as to the reaction mechanisms are presented.