Dielectric properties of toughened polybenzoxazine based composites in the microwave frequency region

Abstract

Polybenzoxazine based/BST composites were proposed as new dielectric materials operated at microwave frequency. To alleviate the brittleness of usual monomeric benzoxazines, the toughness of polybenzoxazine was improved via two approaches. The first method is by alloying with flexible urethane and another strategy is by synthesizing high molecular weight benzoxazine precursors. It was found that for alloying system. at 90/10 vol. % of poly(benzoxazine/urethane), (PBA-a/PU) yielded good dielectric and thermal properties. For the synthesis route, those properties of methylenedianiline-based (BA-mda) polybenzoxazine were superior to hexamethylenediamine (BA-hda). Thus at 90/10 vol.%o of PBA-aPU and poly(BA-mda) were used as matrices for composite fabrication. The dielectric constant of all the polymer based composites was increased in relation to the amount of BST. The better filler distribution was obtained in PBA-a/PU than BA-mda matrix when using 3-aminopropyl-trimethoxysilane and polymer based as surface modifiers on BST. 'The loss tangent and especially the dielectric constant of prepared composites had a weak dependence on frequency (300 MHz to 1 GHz) and temperature (-50 ºC to 150 ºC), indicating low relaxation behaviors when compared with general polymers. According to the study, at 90/10 vol.% of PBA-a/PU composed of silane coupling agent modified BST exhibited the prominent dielectric characteristics at various BST loadings. This type of composite, at 60 wt.% of BST content provided the highest dielectric constant (13.9) with low dissipation factor (0.0095), demonstrating high-performance as a candidate material for microwave frequency applications.