Preparation and properties of cyanate ester/polyorganosiloxane blends with lower dielectric loss and improved toughness

Novel modified cyanate ester resins (EPMPS‐n/BADCy), with significantly decreased dielectric loss and improved toughness, were developed by copolymerizing the cyanate ester resin, 2, 2′‐bis (4‐cyanatophenyl) isopropylidene resin) (BADCy), with an epoxidized methyl phenyl silicone resin (EPMPS). The curing behavior of EPMPS‐n/BADCy and the typical properties of the corresponding cured EPMPS‐n/BADCy were systematically investigated. The results show that the addition of EPMPS into BADCy can not only accelerate the curing reaction of BADCy, but also decrease dielectric loss and enhance the impact strength as well as water resistance. For example, in the case of the modified BADCy resin with 15 wt%EPMPS, its impact strength is 17.8 kJ/m², about 3 times of that of pure BADCy resin and its water absorption is only 0.25%, about one‐half of that of pure BADCy resin. In addition, while the dielectric loss is only 79% of that of pure BADCy resin, while its dielectric constant remains constant over the frequency range of 1KHz‐1 MHz. The above results suggest that EPMPS‐n/BADCy have great potential to be used as the matrix or adhesive for advanced composites. Copyright © 2009 John Wiley & Sons, Ltd.     

Dielectric properties of self‐catalytic interpenetrating polymer network based on modified bismaleimide and cyanate ester resins

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     

PREPARATION AND PROPERTIES OF FUMED SILICA/CYANATE ESTER NANOCOMPOSITES

Fumed silica/bisphenol A dicyanate ester（BADCy）nanocomposites were prepared by introducing different contents of nano-sized fumed SiO₂ into the BADCy matrix.Two different average primary particle diameters of 12 and 40 nm were chosen.Dibutyltindilaurate（DBTDL）catalyst was chosen to catalyze the cyanate ester group into triazine group via cyclotrimerization reaction.The SEM micrographs indicated that the fumed SiO₂ particles were homogeneously dispersed in the poly（bisphenol A dicyanate）matrix by means of ultrasonic treatment and the addition of a coupling agent. The FTIR spectroscopy shows that,not only DBTDL catalyzes the polymerization reaction but also-OH groups of the SiO₂ particles surface help the catalyst for the complete polymerization of BADCy monomer.The thermal stability of the cured BADCy can be improved by adequate addition of fumed SiO₂.A slight increase in the dielectric constant and dielectric loss values were identified by testing the dielectric properties of the prepared nanocomposite samples.By increasing the SiO₂ content,there was a slight increasing in the thermal conductivity values of the tested samples.The obtained results proved that the fumed silica/BADCy nanocomposites had good thermal and dielectrical properties and can be used in many applications such as in the thermal insulation field.     

Thermoplastic modification of monomeric and partially polymerized Bisphenol A dicyanate ester

Bisphenol A dicyanate ester (BADCy) was modified with different amounts of an engineering thermoplastic, polysulfone (PS) to improve impact strength of the parent resin. Differential scanning calorimetry of the blends suggested that addition of PS widens the curing exotherm of the BADCy considerably. FTIR of cured neat resins indicated total conversion of cyanate functional groups into triazine rings by cyclotrimerization. The cured neat resins showed phase separated morphology with cyanate ester as the continuous phase. The modified resins were shown to have better thermal, hygrothermal and impact strength properties. However, when glass fiber reinforced composites were made using partially polymerized BADCy and PS, very little or no phase separation in the resin was noticed. Flexural and impact strength measurement of composites showed that PS modification has compromised the flexural properties and only retained the impact strength of the parent resin containing composite. This study thus suggests that improvements realized in thermoplastic modification of monomeric BADCy are not directly transferable to composites using a partially prepolymerized BADCy.     

Thermal and mechanical evaluation of cyanate ester resin modified with bismaleimide and diallyl phthalate

Cyanate ester resins have excellent dielectric, mechanical, and thermal properties; however, their major drawback is their brittleness. A high performance matrix blend was developed using bisphenol A dicyanate (BADCy), bismaleimide (BMI) and diallyl phthalate (DAP), and Cobalt (III) acetylacetonate dissolved in nonyl phenol (NP) as a complex catalyst system for BADCy. The properties of the BADCy/BMI/DAP blends, such as thermal and mechanical properties, were investigated in detail by dynamic mechanical analysis (DMA), thermogravimetric analysis (TGA), and mechanical measurement. The results show that the addition of the appropriate amount of DAP and BMI can improve the impact strength and the flexural strength and this possibly comes from forming an interpenetrating polymer network in the systems. However, the thermal stability of the blends was found to be lower than that of the unmodified BADCy resin. Copyright © 2009 John Wiley & Sons, Ltd.     

High performance toughened cyanate ester resin with low injection temperature for RTM process

A high‐performance modified cyanate resin system with low injection temperature for fabricating advanced composites via resin transfer molding (RTM) was developed, which was made of bisphenol A dicyanate ester (BADCy) and diallyl phthalate (DAP). The processing characteristics, mechanical, and thermal properties of the resin were studied, and the effect of the content of DAP on the processing and performance parameters was discussed. The results show that the processing properties of the modified cyanate system are dependent on the content of DAP. All the formulations studied in this paper have good processing characteristics; their injection temperatures are between 30 and 40°C and the pot life is about 20 hr at 50°C. The cured resins exhibited good thermal stability, excellent toughness, and good hot–wet resistance, suggesting that the toughened cyanate resin is a potential high‐performance RTM matrix for advanced composites. Copyright © 2008 John Wiley & Sons, Ltd.     

Novel fiber reinforced bismaleimide/diallyl bisphenol A/microcapsules composites

Three kinds of poly(urea‐formaldehyde) (PUF) microcapsules filled with epoxy resins (MCEs) were applied to bismaleimide (BMI)/O,O′‐diallyl bisphenol A (BA) system to develop novel fiber reinforced BMI/BA/MECs composites. The effects of MCEs on the mechanical properties, the hot‐wet resistance, and the dynamic mechanical properties of fiber reinforced BMI/BA composites were investigated. The morphologies of fiber reinforced BMI/BA/MCEs composites were characterized by scanning electron microscope (SEM) and optical microscope (OM). Results indicate that the appropriate contents of MCEs can significantly improve the mechanical properties and the hot‐wet resistance of fiber reinforced BMI/BA composites. In this study, MCEs may decrease the storage modulus of fiber reinforced BMI/BA composite but they have no significant influence on the glass transition temperature (T_g) of the composite. Copyright © 2010 John Wiley & Sons, Ltd.     

耐高温可溶性聚酰亚胺树脂及其复合材料

制备了2种耐高温可溶型聚酰亚胺树脂(PI-1, PI-2)及其复合材料, 系统研究了树脂的工艺性, 纯树脂固化物的热性能及其复合材料的界面形貌、 介电性能和力学性能. 研究结果表明, 树脂低聚物在极性非质子溶剂中具有良好的溶解性, 且熔体黏度较低, 表明其具有优异的加工性能. 两种树脂固化物在空气中的5%热失重温度均高于550 ℃, PI-1树脂的玻璃化转变温度(T_g)为430 ℃, PI-2树脂的T_g为380 ℃. 石英纤维/PI-1和石英纤维/PI-2复合材料具有较低的介电常数和介电损耗. 碳纤维/PI-1复合材料在420 ℃下的弯曲强度保持率可达62%, 层间剪切强度保持率可达48%, 具有较优异的高温力学性能. 采用普通模压工艺制备了厚度高达45 mm的复合材料制件, 进一步证明这2种树脂具有优异的工艺性.     

Thermal and water absorption properties of cyanate ester resins modified by fluoride‐containing and silicone‐containing components

In order to enhance the moisture resistance of cyanate ester resins, modifiers containing silicon or fluorine moieties were introduced. The curing behaviors of the obtained resins, as well as thermal, water absorption, and dielectric properties of all cured polymers, were investigated in detail. Results show that properties of fillers in polymer have great influence on the thermal property and of polymer. In all cases, modifier exhibited percolation threshold at 5 wt%. Compared with pristine cyanate ester resins (CE), when the methyl phenyl silicone resin B filler was added, the cured polymer exhibited water absorption as low as 0.39% and excellent thermal oxygen stability at 300°C. The introduction of silicon H improved thermal oxidative stability at 400°C without significant compromise in processability or mechanical properties.     

聚苯乙炔基苯基硅氧硼烷树脂及其复合材料的性能

将双(N-间乙炔基苯基邻苯二甲酰亚胺)醚(DAIE)和双酚A型氰酸酯(CE)分别加到聚苯乙炔基苯基硅氧硼烷(PSOB)和三苯乙炔基苯基硅烷(PTPES)混合体系中进行改性,制得两种纤维增强复合材料PSOB-PTPES-DAIE和PSOB-PTPES-CE.研究了固化后树脂的热稳定性能、力学性能、介电性能和耐水性能.结果...     

Flame retardancy and flame retarding mechanism of high performance hyperbranched polysiloxane modified bismaleimide/cyanate ester resin

A novel kind of modified bismaleimide/cyanate ester (BCE) resins by copolymerizing with hyperbranched polysiloxane including high content of phenyl (HBPSi) was first reported. The effect of HBPSi on the curing mechanism, and that on the dielectric properties and flame retardancy of cured networks were systemically investigated. Results show that compared with BCE resin, HBPSi/BCE resin has obviously different cross-linked structure, and thus leading to simultaneously improved dielectric properties and flame retardancy. The reactions between HBPSi and the decomposition structure of BCE resin change the thermo-oxidative degradation mechanism of the first step in the thermo-oxidative degradation; in addition, the presence of HBPSi in BCE resin also significantly reduces the mass loss rate (MLR) and increases char yield at 800 °C under an air atmosphere. Therefore, the positive effect of HBPSi on improving the flame retardancy is attributed to the condensed phase mechanism. On the other hand, HBPSi/BCE resins exhibit improved dielectric properties (including decreased dielectric constant and loss) with increasing the content of HBPSi. More importantly, this investigation demonstrates that designing new polysiloxane with suitable chemical structure is important to develop high performance resins with attractive flame retardancy and dielectric properties.     

Study on properties of flame‐retardant cyanate esters modified with DOPO and triazine compounds

Ternary flame‐retardant modified cyanate ester blends (CEPG and CEPA) are formed by combining triazine compounds (TGIC or TAIC) and 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene‐10‐oxide with cyanate ester resin. The curing behaviors, thermal and mechanical properties, and the flame‐retardant properties are investigated. The results show that the CEPG and CEPA blends result in lower curing temperatures and glass transition temperatures than those of neat CE. Both of CEPG and CEPA blends significantly improve the flame‐retardant properties of CE resins, and UL‐94V‐0 rate is achieved for CEPG‐1.0 and CEPA‐0.5. The dielectric constant and loss of CEPA blends are lower than those of CEPG blend with the same phosphors content, and both of them are lower than those of neat CE. Therefore, the ternary flame‐retardant modified cyanate ester blends provide 2 ways for composites of producing printed circuit board with high flame‐retardant property and low dielectric constant and loss.     

Cyanate Ester/Functionalized Silica Nanocomposite: Synthesis,Characterization and Properties

In this paper silica nanoparticles with covalently grafted polymer chains were incorporated into bisphenol A dicyanate ester (BADCy) to prepare composites which resulted in improvements in the mechanical and thermal properties. Fourier‐transform infrared (FT‐IR) spectroscopy transmission electron microscopy (TEM) and thermogravimetric analysis (TGA) were employed to examine the surface functionalization of silica nanoparticles. The effects of functionalized SiO₂ (F‐SiO₂) on the curing reactivity mechanical and thermal properties of BADCy resin were investigated systematically. The curing reaction of the system was facilitated with the addition of F‐SiO₂. Meanwhile compared with the neat resin the incorporation of appropriate content of modified F‐SiO₂ can enhance the mechanical properties including impact flexural strengths and fracture toughness K_IC of BADCy resin. In addition the thermal stability of BADCy/F‐SiO₂ nanocomposites is also superior to that of pure BADCy resin.     

Preparation of Low-dielectric Permittivity Polyimide Resins with High Surface Activity from Chemically Bonded Hyperbranched Polysiloxane

Thermosetting resin matrix is the key component of advanced wave-transparent composites,where low dielectric constant,excellent processability,high thermal stability,as well as good bonding ability are required for resins.Herein,we prepared a series of phenylethynyl terminated polyimide(PI)resins by grafting amine-functionalized hyperbranched polysiloxane(HBPSi)to PI chains during the in situ polymerization.The effects of HBPSi on the processability of oligomers,molecular packing,thermal stability,dielectric property and bonding ability to reinforce Kevlar fibers of the cured PI/HBPSi composite resins have been examined in detail.The dielectric constants of the cured composite resins were greatly reduced from 3.29 to 2.19 without compromising its processability and thermal stability.Meanwhile,the 10 wt％HBPSi-containing PI resin demonstrated better bonding ability to reinforce fibers with the interfacial shear strength(IFSS)of 37.64 MPa,compared with that of neat PI-6 matrix(27.34 MPa),and better adhesion to metal with the lap shear strength of 10.48 MPa,50％higher than that of neat resin PI-6(6.98 MPa).These resultant PI/HBPSi composite resins exhibit excellent comprehensive properties,indicating their great potential as low-dielectric constant resin matrix in radar radome.     

Low Dielectric Thermoset from Redistributed Poly(phenylene oxide)

A curable low-molecular-weight poly(phenylene oxide) (PPO) was prepared by the redistribution of regular PPO with bisphenol-A (BPA) followed by etherification of the redistributed-PPO (BPA-PPO) with N,N-diallyl-2-chloroacetamide. The redistributed-PPO with allyl group (AL-PPO) was characterized by proton nuclear magnetic resonance, and Fourier transform infrared spectroscopy. The AL-PPO oligomers with reactive double bounds were cured with triallylisocyanurate (TAIC) and/or phosphorus-containing allyl-functionalized monomer (allyl-DOPO). The glass transition temperatures were measured by dynamic mechanical analysis (DMA). Electrical properties of cured resins were studied using dielectric analyzer (DEA). The flame retardancy was determined by a UL-94 vertical test. The effects of curing accelerator, amount of TAIC and allyl-DOPO incorporated into the network on the glass transition temperatures, dielectric properties, and flame retardancy of the resulting systems were investigated. The results indicated that AL-PPO cured with TAIC exhibited high glass-transition temperature (162–198°C), low dielectric constants (2.36–2.57 at 1 GHz) and dissipation factors (0.0039–0.0043 at 1 GHz). The AL-PPO/TAIC copolymerized with allyl-DOPO could achieve a flame retardancy rating of UL-94 V-0 at about 1.35% phosphorus content. The AL-PPO/TAIC resins have potential applications in the fabrication of printed circuit board.     

Novel toughened cyanate ester resin with good dielectric properties and thermal stability by copolymerizing with hyperbranched polysiloxane and epoxy resin

A novel toughened cyanate ester (CE) resin with good dielectric properties and thermal stability was developed by copolymerizing 2,2′‐bis(4‐cyanatophenyl)iso‐propylidene (BCE) with a combined modifier (HBPSiEP) made up of hyperbranched polysiloxane (HBPSi) and epoxy (EP) resin. HBPSi was synthesized through the hydrolysis of 3‐(trimethoxysilyl)propyl methacrylate. The effect of differing stoichiometries of HBPSiEP on the curing characteristics and performance of BCE resin is discussed. Results show that the incorporation of HBPSiEP can not only effectively promote the curing reaction of BCE, but can also significantly improve the toughness of the cured BCE resin. In addition, the toughening effect of HBPSiEP is greater than single EP resin. For example, the impact strength of modified BCE resin with 30 wt% of HBPSiEP is 23.3 KJ/m², which is more than 2.5 times of that of pure BCE resin, while the maximum impact strength of EP/BCE resin is about 2 times of pure BCE resin. It is worthy to note that HBPSiEP/BCE resins also exhibit improved thermal stability, dielectric properties, and flame retardancy, suggesting that the novel toughened CE resins have great potentiality to be used as a matrix for advanced functional composites or electronic packing resins. Copyright © 2009 John Wiley & Sons, Ltd.     

活性酯固化环氧树脂物性的研究

主要对活性酯固化环氧树脂的吸水性、高耐湿性、电气特性等方面进行了研究,同时也对其树脂极性、交联结构、分子链运动等方面也进行了研究．     

Improved dielectric and mechanical properties of polystyrene-hybrid silica sphere composite induced through bifunctionalization at the interface

Hybrid silica spheres (HS) of size 270-350 nm with vinyl and aminopropyl surface groups were incorporated in polystyrene (PS), and its effect on dielectric properties, coefficient of thermal expansion (CTE), and strength of PS-HS composite was studied. Incorporation of HS in PS followed a decrease in the dielectric constant from 3.2 for PS to 2.6 for composite with 7.5 vol % HS. The decrease in the dielectric constant was attributed to (i) increased interfacial porosity, (ii) formation of anhydrous HS having low dielectric constant, during hot processing of the composites, and (iii) dispersion and preservation of the anhydrous HS in the hydrophobic matrix. The dielectric constant of the composites with HS content up to 7.5 vol % does not vary much with temperature in the range from -20 to 65 °C. These composites also exhibited reduced CTE and improved flexural strength/stiffness due to good interfacial bonding through HS vinyl groups and dispersion of the filler in the matrix. The dielectric loss increased with HS content, and the loss measured for 7.5 vol % PS-HS composite was 6 × 10(-3), as compared to 10(-4) for PS. At HS loading above 7.5 vol %, the tendency of HS to agglomerate and form percolated structure lead to an increase in the dielectric constant and decrease in the mechanical properties of the composites.     

Synthesis and properties of novel fluorinated epoxy resins based on 1,1-bis(4-glycidylesterphenyl)-1-(3′-trifluoromethylphenyl)-2,2,2-trifluoroethane

A novel fluorinated epoxy resin, 1,1-bis(4-glycidylesterphenyl)-1-(3′-trifluoromethylphenyl)-2,2,2-trifluoroethane (BGTF), was synthesized through a four-step procedure, which was then cured with hexahydro-4-methylphthalic anhydride (HMPA) and 4,4′-diaminodiphenyl-methane (DDM). As comparison, a commercial available epoxy resin, bisphenol A diglycidyl ether (BADGE), cured with the same curing agents was also investigated. We found that the BGTF gave the exothermic starting temperature lower than BADGE no mater what kind of curing agents applied, implying the reactivity of the former is higher than the latter. The fully cured fluorinated BGTF epoxy resins have good thermal stability with glass transition temperature of 170-175 °C and thermal decomposition temperature at 5% weight loss of 370-382 °C in nitrogen. The fluorinated BGTF epoxy resins also showed the mechanical properties as good as the commercial BADGE epoxy resins. The cured BGTF epoxy resins exhibited improved dielectric properties as compared with the BADGE epoxy resins with the dielectric constants and the dissipation factors lower than 3.3 and dissipation 2.8 × 10⁻³, respectively, which is related to the low polarizability of the C-F bond and the large free volume of CF₃ groups in the polymer. The BGTF epoxy resins also gave low water absorption because of the existence of hydrophobic fluorine atom.     

Synthesis and characterization of siloxane resins derived from silphenylene‐siloxane copolymers bearing benzocyclobutene pendant groups

Two bis(dimethylamimo)silanes with benzocyclobutene (BCB) groups, bis(dimethylamino)methyl(4′‐benzocyclobutenyl)silane ( 2 ) and bis(dimethylamino)methyl [2′‐(4′‐benzocyclobutenyl)vinyl]silane ( 4 ), were synthesized from different synthetic routes, which were then employed to prepare two novel silphenylene‐siloxane copolymers (SiBu and SiViBu) bearing latent reactive BCB groups by polycondensation procedure with 1,4‐bis(hydroxydimethylsilyl)benzene. At elevated temperatures these copolymers were readily converted to highly crosslinked films and molding disks with network structures by polymer chain crosslinking, which followed the first‐order kinetic reaction model. The final resins of SiBu and SiViBu demonstrated excellent thermal stability with high glass transition temperatures (218 and 256 °C) and high temperatures at 5% weight loss (553 and 526 °C in N₂, 530 and 508 °C in air). After aging at 300 °C in air for 100 h, the cured resins showed weight loss lower than 4%. The films of cured SiBu and SiViBu also exhibited relatively low dielectric constants of 2.66 and 2.64, low dissipation factors of 2.23 and 2.12 × 10^?3, low water absorptions (≤0.28%), and high transparence in the visible region with cutoff wavelengths of 321 and 314 nm. Moreover, the aged films exhibited good dielectric properties and low water absorptions. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7868–7881, 2008