Objective: The objective of this work is to investigate a number of chemical cationic initiation systems for a mixture of SilMix® (3M ESPE), 50:50 bis[2-(3{7-oxabicyclo[4.1.0]heptyl})-ethyl]methylphenyl silane and 2,4,6,8-tetrakis(2-(7-oxabicyclo[4.1.0]heptan-3-yl)ethyl)-2,4,6,8-tetramethyl-1,3,5,7,2,4,6,8-tetraoxatetrasilocane.
Methods: The general procedure was as follows. Approximately, SilMix (1 g) and the acid catalyst were combined in a planetary mixer and mixed for 5 minutes. After which, the material was placed on a microscope slide and tested for hardness after 15 minutes using a Gillmore needle (one pound for pass/fail). Tests were continued for 30 minutes, 1 hour, 24 hours, and 48 hours.
Results: A total of fourteen acids were used at varying concentrations. Hydrochloric (2, 5, 10, 14, and 18 wt%), sulfuric (8 wt%), pentafluoropropionic (4, 15, and 18 wt %), acetic (5 wt %), triflic (2 and 4 wt%), p-toluenesulfonic (11.5 wt%), hydroiodic (6 wt%), trichloroacetic (9 wt%), hydrobromic (7.5 wt%), and trifluoroacetic (7 wt%) acid failed in all cases. Typical Lewis acids such as aluminum chloride (13 wt%) and tin (IV) chloride (7.4 wt%) also failed even after 48 hours. The only acid that passed the Gillmore needle test at all listed concentrations was hexafluorophosphoric acid (2.5, 4, 4.6, and 5 wt%). The amount of acid increased the rate of reaction (i.e., fifteen minutes for 4.6 and 5 wt%; thirty minutes for 2.5 and 4 wt%). The consistency of the polymerized material varied depending on the wt % of hexafluorophosphoric acid catalyst.
Conclusion: It was found that SilMix was able to be chemically-cured.
This work was supported in part by NIH/NIDCR Grant R21 DE018336, NIH/NIDCR T32 (DE07294), and Missouri Life Science Research Board Grant (#13234-2007).