Synthesis and characterization of imide ring and siloxane-containing cycloaliphatic epoxy resins

A novel imide ring and siloxane-containing cycloaliphatic epoxy compound 1,3-bis[3-(4,5-epoxy-1,2,3,6-tetrahydrophthalimido)propyl]tetramethyldisiloxane (BISE) was synthesized from 1,3-bis(3-aminopropyl)tetramethyldisiloxane and tetrahydrophthalic anhydride by a two-step procedure, which was then thermally cured with alicyclic anhydrides hexahydro-4-methylphthalic anhydride (HMPA) and hexahydrophthalic anhydride (HHPA), respectively. As comparison, a commercial available cycloaliphatic epoxy 3,4-epoxycyclohexylmethyl-3′,4′-epoxycyclohexane carboxylate (ERL-4221) cured with the same curing agents was also investigated. The experimental results indicated that the BISE gave the exothermic starting temperature higher than ERL-4221 no mater what kind of curing agents applied, implying the reactivity of the former is lower than the latter. The fully cured BISE epoxy resins have good thermal stability with thermal decomposition temperature at 5% weight loss of 346–348 °C in nitrogen, although they gave the relatively low glass transition temperatures due to the presence of flexible propyl and siloxane segments in the epoxy backbone. The BISE epoxy resins exhibited good mechanical and dielectric properties as well as low water absorption. The improved dielectric properties and the reduced water absorption of BISE epoxy resins are attributed to the low polarity as well as the hydrophobic nature of siloxane segment in the epoxy backbone.