Abstract
The capabilities of imidazoles-intercalated α-zirconium phosphate (α-ZrP·imidazole): imidazol (α-ZrP·Im), 2-methylimidazole (α-ZrP·2MIm), and 2-ethyl-4-methylimidazole (α-ZrP·2E4MIm) as latent thermal initiators were examined by the copolymerization of glycidyl phenyl ether (GPE) and hexahydro-4-methylphthalic anhydride (MHHPA) with the imidazoles-intercalated α-zirconium phosphate at varying temperatures for one-hour periods. Polymerization was not observed until the reactants were heated to 100 °C or above. Increasing the temperature, polymerization in the presence of α-ZrP·Im, α-ZrP·2MIm, or α-ZrP·2E4MIm proceeded at 140 °C for 1 h with over 90% conversion. The thermal stabilities of α-ZrP·Im, α-ZrP·2MIm, and α-ZrP·2E4MIm in the reaction at 40 °C for 264 h were tested. With α-ZrP·2MIm, the conversion was less than 15% up to 96 h. In the cases of α-ZrP·Im and α-ZrP·2E4MIm, the conversion reached less than 15% at 264 h. The thermal stabilities of α-ZrP·Im, α-ZrP·2MIm, and α-ZrP·2E4MIm at 40 °C were superior to those of the commercially available thermal latent initiators: HX-3088 and HX-3722.
Highlights
There has been considerable interest in the development of latent polymerization catalysts that are inert in the monomer or prepolymer under storage conditions
Corresponded to the amount deintercalated imidazoles. > α-zirconium phosphate (α-ZrP)·2E4MIm > αZrP·Im, which corresponded to the amount of the deintercalated imidazoles
The activities of α-ZrP·Im, α-ZrP·2MIm, and α-ZrP·2E4MIm in the copolymerization of glycidyl phenyl ether (GPE) and MHHPA as latent thermal initiators were examined in this study
Summary
There has been considerable interest in the development of latent polymerization catalysts that are inert in the monomer or prepolymer under storage conditions. These catalysts can initiate polymerization under external impetus such as thermal or photo irradiation. We have previously reported that primary alkylamines intercalated with α-zirconium phosphate (α-ZrP) can serve as latent thermal initiators in the reaction of glycidyl phenyl ether (GPE) [10] and that intercalation compounds of 1,4-diazabicyclo(2,2,2)octane (DABCO) and 1,8-diazabicyclo(5,4,0)undec-7-ene (DBU) with α-ZrP: Catalysts 2017, 7, 172; doi:10.3390/catal7060172 www.mdpi.com/journal/catalysts. Catalysts 2017, 7, 172 α-ZrP·DABCO and α-ZrP·DBU show good performance as latent thermal catalysts in the reaction of GPE with hexahydro-4-methylphthalic anhydride (MHHPA) [11]. Romanchick prepared 1,3-dialkylimidazolium salts in the curing of epoxy resin [14]
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