Bismaleimide (BMI) resins with good thermal stability, fire resistance, low water absorption, and good retention of mechanical properties at elevated temperatures, especially in hot/wet environments, have attracted more attention in the electronic and aerospace industries. However, their relatively high dielectric constant limits their application in the aforementioned fields. In this work, a new promising approach is presented that consists of the formation of a self‐catalytic thermoset/thermoset interpenetrating polymer network. Interpenetrating polymer networks (IPNs) based on modified BMI resin (BMI/DBA) and cyanate ester (b10) were synthesized via prepolymerization followed by thermal curing. The self‐catalytic curing mechanism of BMI/DBA‐CE IPN resin systems was examined by differential scanning calorimetry. The dielectric properties of the cured BMI/DBA‐CE IPN resin systems were evaluated by a dielectric analyzer and shown in dielectric properties‐temperature‐log frequency three‐dimensional plots. The effect of temperature and frequency on the dielectric constant of the cured BMI/DBA‐CE IPN resin systems is discussed. The composition effect on the dielectric constant of the cured IPN resin systems was analyzed on the basis of Maxwell's equation and rule of mixture. The obtained BMI/DBA‐CE IPN resin systems have the combined advantages of low dielectric constant and loss, high‐temperature resistance, and good processability, which have many applications in the microelectronic and aerospace industries. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1123–1134, 2003
In searching for high performance polymer resins that have a combination of low dielectric constant and loss, high temperature resistance, ease of being processed, and other desirable properties, an interpenetrating polymer network (IPN) based on cyanate ester (CE) and 2,2Ј-diallylbisphenol A (DBA) modified bismaleimide resin (BMI) was prepared via prepolymerization followed by thermal curing. This work discusses the use of multiple waveform rheological technique to investigate the crosslinking and gelation behavior of this resin system at various temperatures. The gel point can be accurately determined from a single experiment using this technique. At the point of gelation, both the storage modulus (GЈ) and loss modulus (GЉ) of the IPN follow a similar power law equation with oscillation frequency used in the rheological measurement. Both the relaxation exponent n, a viscoelastic parameter related to the cluster size of the gel, and gel strength S, related to the mobility of the crosslinked chain segments, were determined via a curve fitting method. Both n and S were found to be temperature dependent in this BMI/ DBA-CE IPN system. The apparent activation energy of gelation or curing reaction was found to be approximately 47.6 kJ/mol.
ABSTRACT:Interpenetrating polymer networks (IPNs) based on different ratios of modified bismaleimide (BMI) resin [BMI/2,2Ј-diallylbisphenol A (DBA)] and cyanate ester (CE) (b10) have been synthesized via prepolymerization followed by thermal curing. A systematic study of both static and dynamic mechanical properties of the cured BMI/ DBA-CE IPN resin systems was conducted through flexural, impact testing, and dynamic mechanical analysis (DMA). The static mechanical investigation shows that the flexural strength, flexural strain at break, and impact strength of the cured BMI/DBA-CE IPN resin systems are relatively lower than that calculated by rule of mixture of two individuals: BMI/DBA and b10. However, the flexural moduli of the IPN resin systems have more consistent features compared to that calculated by rule of mixture. Single damping peaks are detected for the cured BMI/DBA-CE IPN resin systems, which suggests a substantial degree of interpenetration between two networks. The damping peaks of the cured BMI/ DBA-CE IPN resin systems do tend to become broader with increasing concentration of BMI/DBA, whereas the intensity of damping peaks of the IPN resin systems decreases. The obtained results not only provide insight information about the characteristic structures of these BMI/DBA--CE IPN resin systems, but also give guidelines for their applications.
Interpenetrating polymer networks (IPNs) based on different ratios of a modified bismaleimide resin (BMI/DBA) and cyanate ester (b10) have been synthesized via prepolymerization followed by thermal curing. A systematic thermal degradation study of these new BMI/DBA‐CE IPN resin systems was conducted by thermogravimetric analysis at different heating rates both in N2 (thermal stability) and in air (thermal‐oxidative stability). The cured BMI/DBA‐CE IPN resin systems show excellent thermal stability, which could be demonstrated by 5% weight loss temperature (T5%) ranging between 409 and 423 °C, maximum decomposition rate temperature (Tmax) ranging between 423 and 451 °C, and the char yields at 800 °C ranging from 37% to 41% in nitrogen at a heating rate of 10 °C min−1. The apparent activation energy associated with the main degradation stage of the cured BMI/DBA‐CE IPN resin systems was determined using the Kissinger method. The obtained results provide useful information in drawing correlation between thermal properties and structure.© 2003 Society of Chemical Industry
Cyanate esters with inherently low relative permittivity and loss are well known as good resin materials used in the electronics industry. However, very high temperatures (>300°C) are usually required for crosslinking by cyclotrimerisation of cyanate ester groups in uncatalysed systems. It has been reported that phenolic hydroxy groups could have a catalytic effect on cyclotrimerisation of cyanate esters. In this study, 2,2∞-diallylbisphenol A (DBA), with two phenolic hydroxy groups, has been used as a catalyst for the crosslinking of a cyanate ester (b10). The double bonds on DBA can readily copolymerise with added bismaleimide to form interpenetrating polymer networks (IPN). High performance IPNs based on different ratios of cyanate ester (b10) and DBA with added bismaleimide have been synthesised. In these self-catalytic IPN resin systems, cyanate ester and DBA/bismaleimide are believed to crosslink via different reactions to form two interpenetrating polymer networks in the cured resin structure. Such a unique combination thus enables cyanate esters to be cured at a lower temperature while largely maintaining their superior dielectric properties. The catalytic effect of hydroxy phenolic groups and the reactivity of new CE-DBA/bismaleimide IPN resin systems were investigated by differential scanning calorimetry. The glass transition temperature and mechanical properties were evaluated by dynamic mechanical analysis and flexural and impact testing. The dielectric properties of the cured resins are also discussed. The IPN resin systems obtained have potential applications in the aerospace and microelectronics industries.
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