Preparation of phthalonitrile resins containing siloxane linkages with improved processability

To improve the processability of biphenyl phthalonitrile resin, a flexible siloxane structure was introduced into the phthalonitrile monomer through molecular design, which was then blended with a biphenyl monomer to prepare phthalonitrile alloy resins. When the ratio of phthalonitrile monomer containing flexible siloxane to biphenyl phthalonitrile monomer was 1:1, the processing window widened from 58 to 110°C, as compared to that of biphenyl phthalonitrile. Due to the introduction of the biphenyl structure into the phthalonitrile alloy resins, the initial decomposition temperature of the silicon-containing phthalonitrile resin increased from 385 to 516°C. More importantly, the phthalonitrile alloy resin exhibited a high bending strength (66 MPa) and bending modulus (3762 MPa), indicating that it could be potentially applied as high temperature structural composite matrices. Furthermore, it provides a new strategy for processing phthalonitrile resins with a high melting point and narrow processing window.

Fast-Processable Non-Flammable Phthalonitrile-Modified Novolac/Carbon and Glass Fiber Composites

Phthalonitrile resins (PN) are known for their incredible heat resistance and at the same time poor processability. Common curing cycle of the PN includes dozens hours of heating at temperatures up to 375 °C. This work was aimed at reducing processing time of phthalonitrile resin, and with this purpose, a novolac oligomer with hydroxyl groups fully substituted by phthalonitrile moieties was synthesized with a quantitative yield. Formation of the reaction byproducts was investigated depending on the synthesis conditions. The product was characterized by ¹H NMR and FT-IR. Curing of the resins with the addition of different amounts of novolac phenolic as curing agent (25, 50 and 75 wt.%) was studied by rheological and DSC experiments. Based on these data, a curing program was developed for the further thermosets' investigation: hot-pressing at 220 °C and 1.7 MPa for 20 min. TGA showed the highest thermal stability of the resin with 25 wt.% of novolac (T_5% = 430 °C). The post-curing program was developed by the use of DMA with different heating rates and holding for various times at 280 or 300 °C (heating rate 0.5 °C/min). Carbon and glass fiber plastic laminates were fabricated via hot-pressing of prepregs with T_g's above 300 °C. Microcracks were formed in the CFRP, but void-free GFRP were fabricated and demonstrated superior mechanical properties (ILSS up to 86 MPa; compressive strength up to 620 MPa; flexural strength up to 946 MPa). Finally, flammability tests showed that the composite was extinguished in less than 5 s after the flame source was removed, so the material can be classified as V-0 according to the UL94 ratings. For the first time, fast-curing phthalonitrile prepregs were presented. The hot-pressing cycle of 20 min with 150 min free-standing post-curing yielded composites with the unique properties. The combination of mechanical properties, scale-up suitable fast-processing and inflammability makes the presented materials prospective for applications in the electric vehicle industries, fast train construction and the aerospace industry.

Design and Evaluation of a Cyanate Ester Containing Oxaspirocyclic Structure for Electronic Packaging

A type of pentaerythritol cinnamaldehyde bisphenol dicyanate ester (PCBDCy) containing oxaspirocyclic structure is well designed and synthesized in three steps from cinnamaldehyde, pentaerythritol, phenol, and cyanogen bromide. The products in each step are characterized by elemental analysis, Fourier transform infrared (FT-IR) spectroscopy, and 1H NMR spectroscopy. The mechanical properties, dielectric properties, thermostability, and water absorption of PCBDCy are investigated in detail. The results show that compared with bisphenol A dicyanate (BADCy), the PCBDCy possesses more excellent comprehensive properties. The bending strength and flexural strength are increased by 10.71% and 47.62%, respectively. The fracture toughness $K_{\text{IC}}$ and $G_{\text{IC}}$ are 1.5 times and 2 times of BADCy, respectively, indicating that its mechanical properties have been considerably improved. The dynamic mechanical curves indicates that the degree of phase separation is significantly reduced, the tan (δ) value representing the flexible phase is obviously shifted to the high temperature region, and the initial decomposition temperature was 12°C higher than that of BADCy, indicating that the material has excellent thermal stability. In addition, the dielectric constant and loss tangent are almost as same as those of BADCy, maintaining good dielectric properties. The water absorption rate has increased to $1.03\pm 0.03\%$ . Compared with BADCy, its comprehensive performance is more suitable for the field of microelectronic packaging.