Characterization of Mechanical, Electrical and Thermal Properties of Bismaleimide Resins Based on Different Branched Structures

Bismaleimide (BMI) resin is an excellent performance resin, mainly due to its resistance to the effect of heat and its insulating properties. However, its lack of toughness as a cured product hampers its application in printed circuit boards (PCBs). Herein, a branched structure via Michael addition was introduced to a BMI system to reinforce its toughness. Compared with a pure BMI sample, the flexural strength of the modified BMI was enhanced, and its maximum value of 189 MPa increased by 216%. The flexural modulus of the cured sample reached 5.2 GPa. Using a scanning electron microscope, the fracture surfaces of BMI samples and a transition from brittle fracture to ductile fracture were observed. Furthermore, both the dielectric constant and the dielectric loss of the cured resin decreased. The breakdown field strength was raised to 37.8 kV/mm and the volume resistivity was improved to varying degrees. Consequently, the resulting modified BMI resin has the potential for wide application in high-frequency and low-dielectric resin substrates, and the modified BMI resin with a structure including three different diamines can meet the needs of various applications.

Preparation and characterization of a novel benzoxazines/bismaleimide/2,2′-diallylbisphenol A blend with multiphase structures

Novel benzoxazine (BOZ)/bismaleimide (BMI)/2,2′-diallylbisphenol A (BA), with a multiphase structure, was successfully prepared under the catalysis of methyl p-toluenesulfonate (PTSM) through reaction-induced phase separation. The curing reaction of BOZ with BMI and ring-opening polymerization of BOZ under the catalysis of PTSM were studied by Fourier transform-infrared spectroscopy and differential scanning calorimetry analyses, respectively. Mechanical measurements, thermogravimetric analysis, and microanalyses were conducted to assess the toughness and morphology of the composite. The reaction between BOZ and 4,4′-bismaleimidodiphenyl methane (BDM) occurs at a relatively high temperature. The ring-opening reaction of BOZ starts at a low temperature of 100°C because of the catalysis of PTSM. The BOZ/BDM/BA system with an appropriate amount of BOZ significantly improves the impact strength and flexural strength compared with those of the BA/BDM resin. The BOZ/BDM/BA system with PTSM also features high impact strength and flexural strength. Scanning electron microscopy images and energy-dispersive spectroscopy results show that BOZ-rich phase is dispersed in BDM-rich phase in the BOZ/BDM/BA system with PTSM. Thermogravimetric data show that the BOZ/BDM/BA blend with a multiphase structure exhibits superior thermal resistance to those of the BOZ/BDM/BA and BA/BDM resins. The formation mechanism of the ternary system under the catalysis of PTSM is elucidated with Gibbs free energy theory.