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.     

Nanostructures and thermal‐mechanical properties of cyanate ester/epoxy thermosets modified with poly(ethylene oxide)‐poly(propylene oxide)‐poly(ethylene oxide) triblock copolymer

Phase structures and mechanical properties of epoxy/acryl triblock copolymer alloys using several curing agents were studied. The nanostructured thermosets were obtained at the compositions investigated for every blends studied. The dependence of the morphological structures on block copolymer content and dicyanate ester, 2,2′‐bis(4‐cyanatophenyl) isopropylidene (BCE)/epoxy (EP) ratio for thermosetting blends was interpreted on the basis of the difference in hydrogen bonding interactions and reaction resulting from the cross‐linked network structures of matrixes. Moreover, the effect of F68 (poly(ethylene oxide)‐co‐poly(propylene oxide)‐co‐poly(ethylene oxide) block copolymer) on the curing characteristics and performance of BCE/EP resin was discussed. Results show that the incorporation of F68 cannot only effectively promote the curing reaction of BCE/EP but can also significantly improve the toughness of the cured BCE/EP resin. In addition, the toughening effect of F68/EP is greater than single EP resin. For example, the notched impact strength of systems with BE‐80/20 (B and E being the overall contents of BCE and EP, respectively) modified with 10 wt% F68 showed 55% increase compared with neat BCE/EP resin and even is more than three times of that value for pure BCE resin, 5.9 kJ/cm². Copyright © 2015 John Wiley & Sons, Ltd.     

Preparation and properties of new high performance maleimide‐triazine resins for resin transfer molding

High performance matrix is the key base for preparing advanced composites via resin transfer molding (RTM). A novel high performance modified maleimide‐triazine (BT) resin system (coded as MBT) for RTM was developed, which is made of 4,4′‐bismaleimidodi‐ phenylmethane, o,o'‐diallylbisphenol A, 2,2′‐bis (4‐cyanatophenyl) isopropylidene, and hyperbranched polysiloxane (HBPSi). The effects of HBPSi on the processing and performance parameters of MBT system are evaluated. Results show that the processing characteristics of the MBT system are greatly dependent on the content of HBPSi in the system, while three MBT resins developed in this paper have significantly better integrated properties than BT resin. For example, compared to original BT resin, MBT resins have enlarged pot life (>8 hr) and good reactivity; more interestingly, cured MBT resins exhibit better dielectric properties and moisture resistance; in addition, MBT resins with suitable content of HBPSi have improved flexural and impact strengths as well as outstanding thermal property, suggesting that MBT system is the right kind of matrices with great potentiality for fabricating advanced structural and functional composites via RTM technique. Copyright © 2010 John Wiley & Sons, Ltd.     

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.     

Modified cyanate ester resins with lower dielectric loss,improved thermal stability,and flame retardancy

Novel modified cyanate ester (CE) resins with decreased dielectric loss, improved thermal stability, and flame retardancy were developed by copolymerizing CE with hyperbranched phenyl polysiloxane (HBPPSi). HBPPSi was synthesized through the hydrolysis of phenyltrimethoxysilane, and its structure was characterized by ¹H‐NMR, ²⁹Si‐NMR, and Fourier transform infrared spectra. The effect of the incorporation of HBPPSi into CE resin on the curing behavior, chemical structure of cured networks, and typical performance of HBPPSi/CE resins were systemically evaluated. It is found that the incorporation of HBPPSi into CE network obviously not only catalyzes the curing of CE, but also changes the chemical structure of resultant networks, and thus results in significantly decreased dielectric loss, improved thermal stability, and flame retardancy as well as water absorption resistance. For example, in the case of the modified CE resin with 10 wt% HBPPSi, its limited oxygen index is about 36.0, about 1.3 times of that of neat CE resin, its char yield at 800°C increases from 31.6 to 35.4 wt%; in addition, its dielectric loss is only about 61% of that of neat CE resin at 1 kHz. All these changes of properties are discussed from the view of the structure–property relationship. The significantly improved integrated properties of CE resin provide a great potential to be used as structural and functional materials for many cutting‐edges fields. Copyright © 2011 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     

Free volume hole size of Cyanate ester resin/Epoxy resin interpenetrating networks and its correlations with physical properties

Cyanate ester (CE) resin was blended with epoxy resin (EP) at different mass ratios (CE/EP: 100/0, 90/10, 70/30, 50/50, 30/70, 10/90, and 0/100). The curing process of the blend system was characterized by Fourier transform infrared spectrometry (FTIR) and differential scanning calorimetry (DSC). Examination of the mechanical properties, thermal stability, and morphology of the blend systems showed that addition of epoxy resin resulted in improved toughness but a little sacrifice in thermal stability when compared with neat CE. The free volume size of the blend system determined by positron annihilation lifetime spectroscopy (PALS) decreased with the epoxy resin content, which is consistent with the chemical structure changes for the copolymerization between CE and EP. The crosslinking units of curing products (oxazoline, oxazolidinone, and polyether network) of the blends are all smaller in size than those of triazine ring structure from neat CE. Therefore, the free volume size of the blends decreases with increase of EP content. The correlations between the free volume properties and other physical properties (thermal stability and mechanical properties) have also been discussed.     

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.     

High efficiency synthesis of octavinylsilsesquioxanes and its high performance hybrids based on bismaleimide‐triazine resin

An improved method is developed to synthesize octavinylsilsesquioxanes (VPOSS) with shorter time and higher yield, and then VPOSS is used to prepare new hybrids based on bismaleimide‐triazine (BD/CE) resin, coded as VPOSS/BD/CE. The effect of the content of VPOSS on the key properties including curing behavior, thermal, mechanical, and dielectric properties as well as water resistance of VPOSS/BD/CE hybrids were systematically discussed. Compared with BD/CE resin, hybrids show similar curing behavior but different chemical structures and thus macro‐performance. These key properties of hybrids are dependent on the content of VPOSS, all hybrids show significantly improved dielectric properties, water resistance, and dimensional stability; moreover, the hybrids with suitable content of VPOSS have bigger impact strengths. Specifically, with the addition of 7 wt% VPOSS to BD/CE resin, the dielectric constant decreases from 3.7 to 3.2, the dielectric loss decreases 55%, and the coefficient of thermal expansion reduces 23%; moreover, the glass transition temperature and initial decomposition temperature increase about 15°C. The attractive integrated properties suggest that VPOSS/BD/CE hybrids have great potential to be used as structural and functional materials for many cutting‐edge fields. Copyright © 2011 John Wiley & Sons, Ltd.     

Synthesis of mesoporous silica and its modification of bismaleimide/cyanate ester resin with improved thermal and dielectric properties

A novel method is proposed to synthesize new mesoporous silica containing amine groups (MPSA), and it was further employed to modify bismaleimide‐dialllyl bisphenol (BD)/cyanate ester (CE) resin to form novel MPSA/BD/CE hybrids; in addition, the typical properties of MPSA/BD/CE were systematically investigated. Results show that these hybrids have very low dielectric constant and loss as well as good thermal properties. Compared with BD/CE resin, all hybrids have not only decreased dielectric constant and loss but also similar dependence of dielectric properties on frequency over the whole frequency from 10 to 10⁶ Hz. Specifically, with the addition of MPSA to BD/CE resin, the dielectric constant reduces from 3.5 to 3.0, and the dielectric loss is only 85% of that of BD/CE resin. Note that all hybrids show better thermal resistance (reflected by higher glass transition temperature, decreased maximum degradation rate, and higher char yield at 800°C) than BD/CE resin. All these differences in macro‐properties are attributed to the different structure between MPSA/BD/CE hybrids and BD/CE resin. Copyright © 2011 John Wiley & Sons, Ltd.     

Poly(phenylene oxide) modified cyanate resin for self‐healing

Self‐healing cyanate ester resins (CE) were developed by adding low molecular weight poly(phenylene oxide) (PPO) resin, yielding a high performance CE/PPO system via a low‐temperature process. The addition of PPO improved the flexural strength and fracture toughness of the CE matrix without sacrificing thermal properties. CE/PPO formulations with 5, 10, and 15 wt.% PPO showed 43%, 65%, and 105% increase in fracture toughness due to a combination of crack deflection, crack pinning, and matrix cavitation around second‐phase particles. When PPO was introduced into the CE, dielectric properties were either unchanged or declined. During thermal treatment to heal damaged CE, liquid PPO flowed into cracks, and during subsequent cooling, solidified to bond the crack surfaces. The self‐healing efficiency for CE with 15 wt.% PPO after heating to 220°C for 1 h exhibited a recovery of 73% in toughness and 81% in microtensile strength. Copyright © 2014 John Wiley & Sons, Ltd.     

Curing of dicyanate ester/epoxy copolymers modified with polysiloxane and butadiene-acrylonitrile rubbers

The cyanate ester (CE) and epoxy (EP) resins were cured together at various mass compositions. The curing behavior of CE and CE/EP systems was studied by means of differential scanning calorimetry (DSC) in non-isothermal conditions. The DSC measurements indicated that the curing reactions were dependent on the stoichiometric ratio of the mixtures and showed the dilution effect of the EP resin in the cyclotrimerization of the catalyzed CE resin. The CE and CE/EP (70/30) systems were modified using reactive liquid butadiene-acrylonitrile copolymer (ETBN) and polysiloxane core?Cshell (PS) elastomer. The influence of ETBN and PS on the curing process and glass transition temperature (T _g) of CE/EP systems was determined. The impact resistance characteristics of the completely cured systems indicated the influence of the modifiers and the EP content in the mixtures on its impact resistance.     

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.     

Thermal and mechanical properties of epoxy resin toughened with epoxidized soybean oil

A series of new modified epoxy resin (EP) cured products were prepared from epoxidized soybean oil and commercial epoxy resin, with methyl nadic anhydride as curing agent and 1-methylimidazole as promoting agent. The thermal properties of the resins were characterized by DMA and TG; DSC was used to determine the curing process. Fourier transform infrared spectroscopy was utilized to investigate their molecular structures and scanning electron microscopy was used to observe the micro morphology of their impact fracture surfaces. Tensile and impact testing was employed to characterize the mechanical properties of the cured products. The combination of commercial EP with 20 wt% ESO resulted in a bioresin with the optimum set of properties: 130.5 °C T _g, 396.9 °C T _50 %, 74.89 MPa tensile strength, and 48.86 kJ m^?2 impact resistance.     

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.     

Synthesis and performance of flexible epoxy resin with long alkyl side chains via click reaction

Epoxy resin is a thermosetting polymer with excellent performance and wide application. However, it suffers from low toughness and high brittleness because of its high crosslink density. To overcome these disadvantages, this study synthesizes a toughened, flexible, and hydrophobic epoxy resin (DGEBDBP) by introducing a flexible segment into the polymer network via a thiol-ene click reaction. The cured flexible epoxy resin is obtained by mixing E44, DGEBDBP, and polyamide curing agents of varying contents. The long alkyl side chains significantly improve the mechanical properties and hydrophobicity of the cured epoxy resin. The sample containing 75% DGEBDBP and 25% E44 achieve the highest breaking elongation that was nine times that of pure E44, the highest compressive strength of 112.8 MPa, and the highest contact angle of 101.4°. The introduction of side chains through the thiol-ene click reaction can provide a simple and effective method for designing and preparing multifunctional epoxy resins.     

Synthesis and application of phenolic resin internally toughened by chain extension polymer of epoxidized soybean oil

A novel epoxidized soybean oil (ESO) internally toughened phenolic resin(ESO-IT-PR) with both good toughness and excellent thermal stability was prepared as the matrix resin of copper clad laminate (CCL). FTIR was adopted to investigate the molecular structure of modified phenolic resins and SEM was used to observe the micro morphology of their impacted intersections. The properties of CCLs prepared with these modified phenolic resins were studied to determine the optimal process and investigate the toughening mechanism. The main modifying mechanism is the etherification reaction between phenol hydroxyl and ESO catalyzed by triethanolamine and the chain extension polymerization between ESO and multi-amine gives the long-chain ESO epoxy grafting on the phenolic resin prepolymer. when the ESO content is 30% and the curing agent content is 7%, the ESO toughened phenolic resin possesses optimal performance. The flexible ESO epoxy shows significant toughening effect and it crosslinks with the phenolic resin to form an internally toughened network, which is the key factor for improving the solderleaching resistance of CCL prepared with this modified phenolic resin. __________ Translated from Journal of South China University of Technology (Natural Science Edition), 2007, 35(7): 99–104 [译自: 华南理工大学学报(自然科学版)]     

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.     

Benzoxazine modified diglycidyl ether of bisphenol-a/silicon/siliconized epoxy hybrid polymer matrices: Mechanical,thermal, electrical and morphological properties

Benzoxazines modified epoxy hybrid polymer matrices were developed using benzoxazines (CB_DDM and BMPB_DDM) and epoxy resins (DGEBA, SE and EP-HTPDMS) to make them suitable for high performance applications. The benzoxazine-epoxy hybrid polymer matrices were prepared via in-situ polymerization and were investigated for their thermal, thermo-mechanical, mechanical, electrical and morphological properties. Two types of skeletal modified benzoxazines namely 1,1-bis(3-methyl-4-hydroxyphenyl)cyclohexane benzoxazine (CB_DDM) and bis(4-maleimidophenyl) benzoxazine (BMPB_DDM) were synthesized by reacting paraformaldehyde and 4,4′-diaminodiphenylmethane with 1,1-bis (3-methyl-4-hydroxyphenyl)cyclohexane and N-(4-hydroxyphenyl)maleimide respectively. Epoxy resins viz., diglycidyl ether of bisphenol-A (DGEBA), silicon incorporated epoxy (SE) and siliconized epoxy resin (EP-HTPDMS) were modified with 5, 10 and 15 wt% of benzoxazines using 4,4′-diaminodiphenylmethane as a curing agent at appropriate conditions. The chemical reaction of benzoxazines with the epoxy resin was carried out thermally and the resulting product was analyzed by FT-IR spectra. The glass transition temperature, curing behavior, thermal stability, char yield and flame resistance of the hybrid polymers were analysed by means of DSC, TGA and DMA. Mechanical properties were studied as per ASTM standards. The benzoxazines modified epoxy resin systems exhibited lower values of dielectric constant and dielectric loss with an enhanced values of of arc resistance, glass transition temperatures, degradation temperatures, thermal stability, char yield, storage modulus, tensile strength, flexural strength and impact strength.     

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.