Low Dielectric Polymers with High Thermostability Derived from Biobased Vanillin

Abstract

Vanillin has recently been prepared on a large scale from lignin, which becomes the second largest renewable resource. Because it has a naturally aromatic ring and an easily modified functional group, vanillin is considered as one of the ideal feedstocks for the synthesis of high-performance polymers. Based on this, there are a few investigations on low dielectric polymers derived from vanillin, and we have designed and synthesized a monomer containing cross-linkable vinyl and benzocyclobutene units starting from vanillin. This monomer can be easily thermally polymerized into a cross-linked network, which displays good thermostability with a 5% weight loss temperature (T5d) of up to 436 °C and a coefficient of thermal expansion (CTE) of 60.9 ppm/°C. Moreover, no obvious glass-transition temperature (Tg) of the cross-linked network is observed from room temperature to 400 °C during the dynamic mechanical analysis (DMA). In addition, the DMA test indicates that the cross-linked network exhibits good mechanical properties with a storage modulus of up to 3.89 GPa at room temperature. Furthermore, the cross-linked network displays good dielectric properties with a dielectric constant (Dk) of less than 2.84 and a dissipation factor (Df) of below 4.9 × 10–3 for frequencies ranging from 0.15 to 20 MHz. At a high frequency of 5 GHz, the cross-linked network exhibits a Dk of 2.81 and a Df of 6.79 × 10–3, respectively. When the cross-linked polymer is immersed in water at room temperature for 96 h, it shows a low water uptake of 0.44%. These results indicate that the new biobased thermosetting resin has potential applications as a matrix resin or an encapsulation material in the microelectronic industry.