Amine-Containing Phthalonitrile Catalyst for Cyanate Esters with High Catalytic Activity and Low Side Effects

The curing reaction of cyanate ester (CE) resin is characterized by high temperature and long time, which makes its preparation process complicated, time-consuming, and energy-consuming. To reduce their curing temperature and time, a nonmetallic catalyst, 4-(4-aminophenoxy) phthalonitrile (PN-NH2), was applied to accelerate the curing of bisphenol E cyanate ester (BECE). The effects of PN-NH2 contents on the curing behavior, thermal, mechanical, and dielectric properties of PN-NH2/BECE were investigated. The characteristic curing temperatures of PN-NH2/BECE, compared to that of pure BECE, were significantly decreased by the incorporation of PN-NH2 and so was the activation energy. For instance, when the content of PN-NH2 ≥ 7 wt %, the mixtures would gel at room temperature and the activation energy was decreased by 42.4% for Ozawa–Flynn–Wall method and 45.2% for Kissiger–Akahira–Sunose method; compared with pure BECE, the maximum reduction of onset, peak, and endset temperatures for catalyzed resins are decreased by 198.6, 93.5, and 61.9 °C, respectively. In addition, unlike the traditional catalysts, PN-NH2 was chemically bounded to the cross-linked network of CE, thus avoiding stress concentration, migration, precipitation, and plasticizing effects of residual catalysts in the cured resins. Consequently, the superior properties of BECE, such as mechanical (flexural strength >163 MPa and tensile strength >107 MPa) and dielectric properties (dielectric constant of 2.94 to 3.17), were retained whilst the curing temperatures were greatly reduced. The improved processability could broaden the application of cyanate esters.