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.     

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.     

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.     

超支化聚硅氧烷改性双马来酰亚胺树脂的研究

将共聚改性与端氨基超支化聚硅氧烷(HBPSi(N))的合成一步完成,建立了一步法制备改性双马来酰亚胺树脂(记为B/D/H(N))的方法.以N,N′-4,4′-二苯甲烷双马来酰亚胺(BMI)、二烯丙基双酚A(DBA)组成的体系(记为B/D)为对比,探讨了HBPSi(N)含量对B/D/H(N)树脂性能的影响.研究结果表明,HBPSi(N)含量对B/D/H(N)树脂的性能有重要影响.少量HBPSi(N)的加入不仅可以显著提高固化物的韧性,而且能有效加快树脂的凝胶时间,同时大幅度提高固化树脂的耐热性、介电性能和耐湿性.这些性能的改善主要缘于HBPSi(N)的加入改变了交联网络的分子结构.B/D/H(N)体系优异的综合性能使之在制备先进树脂基复合材料、胶黏剂方面显示出很大的应用潜力.     

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 and properties of hollow silica tubes/bismaleimide/diallylbisphenol A composites with improved toughness,dielectric properties,and flame retardancy

New high performance insulating composites based on hollow silica tubes (mHST) and bismaleimide/diallylbisphenol A (BDM/DBA) resin, which exhibit improved toughness, dielectric properties, and flame retardancy, were successfully developed. The effect of the amount of mHST on the properties of composites was systematically studied. Results show that the impact strength of the composite with 0.5 wt% mHST is about 2.2 times that of BDM/DBA resin. In addition, compared with BDM/DBA resin, the composites show lower and stable dielectric constant, better frequency stability of dielectric loss, significantly improved flame retardancy, and similarly outstanding thermal resistance. The reasons behind these attractive integrated properties are discussed from the view of structure–property relationship. Copyright © 2011 John Wiley & Sons, Ltd.     

Flame retardancy and heat resistance of phenol-biphenylene-type epoxy resin compound modified with benzoguanamine

The flame retardancy and heat resistance of a phenol-biphenylene-type epoxy resin compound, which forms a self-extinguishing network structure, were increased by the inclusion of a benzoguanamine-modified phenol biphenylene resin. The benzoguanamine-modified phenol biphenylene resin contains a benzoguanamine unit to release non-flammable nitrogen substances during ignition and to increase the resin's reactivity toward epoxy resins, and biphenylene units to keep the resin's thermal degradation and water resistance. The addition of the benzoguanamine-modified phenol biphenylene resin in the epoxy resin compound improved the epoxy resin compound's flame retardancy and heat resistance, and also increased its glass transition temperature while maintaining its water resistance and mechanical properties. Copyright © 2003 John Wiley & Sons, Ltd.     

Flame retardant epoxy resins based on diglycidyloxymethylphenylsilane

Silicon‐containing epoxy resins were prepared from diglycidyloxymethylphenyl silane (DGMPS) and diglycidylether of bisphenol A (DGEBA) by crosslinking with 4,4′‐diaminodiphenylmethane (DDM). Several DGMPS/DGEBA molar ratios were used to obtain materials with different silicon contents. Their thermal, dynamomechanical, and flame‐retardant properties were evaluated and related to the silicon content. The weight loss rate of the silicon‐containing resins is lower than that of the silicon free resin. Char yields under nitrogen and air atmospheres increase with the silicon content. The LOI (limited oxygen index) values increased from 24 for a standard commercial resin to 36 for silicon‐containing resins, demonstrating improved flame retardancy. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5580–5587, 2006     

Evaluation of physico-chemical properties and antimicrobial synergic effect of ceftazidime-modified chitosan

The aim of this work was to study the effect of tris(3-nitrophenyl) phosphine (NPPh3), which showed a good thermal stability and carbon-forming ability, on the flame retardancy and thermal degradation mechanism of epoxy resins. A series of diglycidyl ether of bisphenol A (DGEBA) loaded with tris(3-nitrophenyl) phosphine (NPPh3) were prepared. It was found that NPPh3 can effectively improve the flame retardancy and thermal stability of the composites. When the loading amount of NPPh3 was 14%, the LOI value of the DGEBA composites was 29.2% (about 1.53 times the corresponding value of the original DGEBA resin). Thermal stability was studied by thermogravimetric analysis, and the results showed that the addition of NPPh3 can improve char formation of this system both in nitrogen and in air atmosphere. Specifically, its combustion residue at 800 °C in nitrogen atmosphere was about 4.26 times of the original resin. Differential scanning calorimetry indicated that NPPh3 slightly decreased the glass transition temperature of epoxy resins. Additionally, the gaseous degradation products were analyzed by thermogravimetric analysis/infrared spectrometry, providing insight into the thermal degradation mechanism. Scanning electron microscopy and Fourier transform infrared were brought together to evaluate the morphology and structure of the residual char obtained after combustion.     

Fire Retardancy of Aluminum Hydroxide Reinforced Flame Retardant Modified Epoxy Resin Composite

A novel phosphorous containing flame retardant epoxy resin is synthesized by modifying the epoxy resin initially with phosphoric acid and further with aluminum hydroxide (ATH) to enhance the fire retardancy of the modified epoxy resin. The several phosphorous modified epoxy resin to ATH mass ratios were used to study the effect of ATH addition on epoxy. Thermal and mechanical properties. The structure of the modified flame retardant epoxy resin was characterized using Fourier-transform infrared spectroscopy (FTIR) while thermal degradation behavior and flame retardant properties were examined using thermo-gravimetric analysis (TGA) and UL-94 testing. Furthermore, ultimate tensile strength and young modulus were analyzed to study the effect of ATH addition on mechanical properties. The findings indicated that fire retardancy of ATH reinforced modified ep oxy resin is higher than virgin and phosphorous modified epoxy resin and depicted eminent flame retardant properties with suitable mechanical properties.

     

Synergistic effect of combined dimethyl methylphosphonate with aluminum hydroxide or ammonium polyphosphate retardant systems on the flame retardancy and thermal properties of unsaturated polyester resin

A series of flame-retardant unsaturated polyester resin (UPR) were prepared by the addition of dimethyl methylphosphonate (DMMP) with various amounts of aluminum hydroxide (ATH) or ammonium polyphosphate (APP) as the flame retardants. The combustion resistance effects of ATH/DMMP and APP/DMMP systems were evaluated by limiting oxygen index test and vertical burning test (UL-94). The thermal properties of UPR were investigated by thermogravimetric analysis. The structure of char was observed by scanning electron microscopy. DMMP incorporated with ATH or APP improved the flame retardancy and thermal properties of UPR. However, the fire-retardant mechanism of these two systems were different: The ATH/DMMP system provided synergistic effect in charring property of the UPR, produced great amount of residual char, and thus revealed the excellent flame retardancy. The APP/DMMP system further improved the flame retardancy of the UPR due to the change in the residual char structure rather than the increase in the production of char.     

Synthesis and properties of phosphorus-containing bio-based epoxy resin from itaconic acid

A phosphorus-containing bio-based epoxy resin (EADI) was synthesized from itaconic acid (IA) and 9,10-dihydro-9-oxa-10-phosphaphenanthrene 10-oxide (DOPO). As a matrix, its cured epoxy network with methyl hexahydrophthalic anhydride (MHHPA) as the curing agent showed comparable glass-transition temperature and mechanical properties to diglycidyl ether in a bisphenol A (DGEBA) system as well as good flame retardancy with UL94 V-0 grade during a vertical burning test. As a reactive flame retardant, its flame-resistant effect on DGEBA/MHHPA system as well as its influence on the curing behavior and the thermal and mechanical properties of the modified epoxy resin were investigated. Results showed that after the introduction of EADI, not only were the flame retardancy determined by vertical burning test, LOI measurement, and thermogravimetric analysis significantly improved, but also the curing reactivity, glass transition temperature (T _g), initial degradation temperature for 5% weight loss (T _d(5%)), and flexural modulus of the cured system improved as well. EADI has great potential to be used as a green flame retardant in epoxy resin systems.     

Synthesis and properties of a phosphorus-containing flame retardant epoxy resin based on bis-phenoxy (3-hydroxy) phenyl phosphine oxide

A reactive phosphorus-containing compound, bis-phenoxy (3-hydroxy) phenyl phosphine oxide (BPHPPO) was first successfully synthesized to produce the phosphorus-containing flame retardant epoxy resin (BPHPPO-EP). The chemical structures were characterized from FTIR, MS, NMR spectra and elemental analyses. Thermal degradation behaviors and flame retardant properties of the cured epoxy resins were investigated from the thermogravimetric analysis (TGA) and the limiting oxygen index (LOI) test using 4,4′-diaminodiphenylsulfone (DDS) as curing agent. The high char yields and the high limiting oxygen index values were found to certify the great flame retardancy of this phosphorus-containing epoxy resin.     

Flame retardancy of fibre-reinforced epoxy resin composites for aerospace applications

The applicability of phosphorus-containing reactive amine, which can be used in epoxy resins both as crosslinking agent and as flame retardant, was compared in an aliphatic and an aromatic epoxy resin system. In order to fulfil the strong requirements on mechanical properties of the aircraft and aerospace applications, where they are mostly supposed to be applied, carbon fibre-reinforced composites were prepared. The flame retardant performance was characterized by relevant tests and mass loss type cone calorimeter. Besides the flame retardancy, the tensile and bending characteristics and interlaminar shear strength were evaluated. The intumescence-hindering effect of the fibre reinforcement was overcome by forming a multilayer composite, consisting of reference composite core and intumescent epoxy resin coating layer, which proved to provide simultaneous amelioration of flame retardancy and mechanical properties of epoxy resins.     

Flame‐retardant epoxy resins with high glass‐transition temperatures from a novel trifunctional curing agent: Dopotriol

A novel phosphorus‐containing trifunctional novolac (dopotriol) was synthesized through the addition reaction of 9,10‐dihydro‐9‐oxa‐10‐phosphaphenanthrene 10‐oxide and rosolic acid. The structure of dopotriol was confirmed with NMR spectroscopy and elemental analyses. The dopotriol was blended with phenol novolac in the ratios of 10/0, 8/2, 6/4, 4/6, 2/8, and 0/10 to serve as a curing agent for diglycidyl ether of bisphenol A. Thermal properties, such as the glass‐transition temperature, thermal decomposition temperature, and flame retardancy, moisture absorption, and dielectric properties of the cured epoxy resins were evaluated. The activity and activation energy of curing were studied with the methods of Kissinger and Ozawa by dynamic differential scanning calorimetry scans. The glass‐transition temperatures of the cured epoxy resins were 138–159 °C, increasing with the phosphorus content. This is rarely seen in the literature after the addition of a flame‐retardant element. The flame retardancy increased with the phosphorus content, and a UL‐94 V‐0 grade was achieved with a phosphorus content of 1.87%. Similar dielectric properties and moisture absorption were observed for these phosphorus‐containing epoxy resins, and this implied that the addition of phosphorus to epoxy did not affect the dielectric properties and moisture absorption. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2862–2873, 2005     

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.     

Studies of fluorine-containing bismaleimide resins. Part I: Synthesis and characteristics of model compounds

A series of fluorine-containing bismaleimide (FBMI) monomers are synthesized by a 2-step reaction for using as the applications of low-k materials. The synthesized FBMI monomers are characterized by the ¹H, ¹³C, ¹⁹F nuclear magnetic resonance (NMR) spectroscopy and element analysis. These FBMI monomers react with free radical initiator or self-cure to prepare FBMI-polymers. All the self-curing FBMI resins have the glass transition temperatures T _g in the range of 130–141°C and show the 5% weight loss temperatures T _5% of 280–322°C in nitrogen atmosphere. The higher heat resistance of self-curing FBMI resin relative to FBMI-homopolymer is due to its higher cross-linking density. The FBMI resins exhibit improved dielectric properties as compared with commercial bismaleimide (BMI) resins with the dielectric constants ? lower than 2.44 which is related to the low polarizability of the C-F bond and the large free volume of CF₃ groups in the polymers. Besides, the flame retardancy of all these FBMI resins could be enhanced via the introduction of Br-atom.     

Synergetic effect of thermal conductivity and flame retardancy of cyanate ester composites containing DOPO and BN with great dielectric properties

DOPO and boron nitride (BN) fillers with different particle sizes and several loadings were employed to improve the properties of cyanate ester (CE) resin. The effects of BN content and particle size on the thermal conductivity of the BN‐DOPO/CE ternary composites were discussed. The influence of enhancing the thermal conductivity of the ternary composites on their flame retardancy was studied. The consequences showed that increasing the thermal conductivity of BN‐DOPO/CE composites had an active impact on their flame retardancy. Approving flame retardancy of the ternary composites was certified by the high limiting oxygen index (LOI), UL‐94 rating of V‐0, and low heat release rate (HRR) and total heat release (THR). For instance, in contrast with pure CE matrix, peak of HRR (pk‐HRR), average of HRR (av‐HRR), THR, and average of effective heat of combustion (av‐EHC) of CEP/BN_{0.5 μm}/10 composite were decreased by 51.7%, 33.8%, 18.7%, and 18.9%, respectively. Thermal gravimetry analysis (TGA) showed that the addition of BN fillers improves the thermal stability of the composites. Moreover, the ternary composites possess good dielectric properties. Their dielectric constants (ε) are less than 3, and dielectric loss tangent (tgδ) values are lower than neat CE resin.     

Alkoxysilane functionalized polycaprolactone/polysiloxane modified epoxy resin through sol-gel process

Incorporating elastic polysiloxane and/or an inorganic silica network in epoxy resin could result in the enhancement of physico-chemical properties due to the existence of Si-O bonds. To improve the compatibility between polysiloxane and epoxy matrices and intensively strengthen the properties of the modified system, here polysiloxane was introduced into epoxy resin through compatibilizing epoxy-immiscible polysiloxane with epoxy-miscible polycaprolactone segments via a sol-gel process. To fulfill the process, a blend containing alkoxysilane-functionalized polycaprolactone/polydimethylsiloxane (PCS-2Si) was firstly synthesized using direct nucleophilic addition between -OH groups of polydiol and -NCO of a silane. And then a series of modified epoxy resins were prepared in different epoxy/PCS-2Si weight ratios. All the modified composites were characterized by conventional methods, and their morphological, thermal degradation and surface properties were studied. The results showed that increasing the PCS-2Si content caused the changes of miscibility between epoxy and polysiloxane. Also, the thermal stability of the modified composites was greatly improved. As for the temperature value at 5% weight loss, it reached to 308.5 °C for the composite containing 50-60% (wt%) PCS-2Si, over 150 °C higher than that for neat amine-cured epoxy resin. Similarly, the modified composites showed good hydrophobicity. The improvement of these properties came from the improved interaction between PCS-2Si and epoxy, the forming of Si-O-Si network and the enrichment of siloxane chains on the surface of films. Therefore, it is believed that this modified epoxy appears promising as new high performance and highly functional materials.     

Phosphorus‐free boron nitride/cerium oxide hybrid: A synergistic flame retardant and smoke suppressant for thermally resistant cyanate ester resin

Establishing a phosphorus‐free strategy to fabricate high‐performance thermosetting resins owning outstanding thermal resistance, good flame retardancy, and smoke suppression is important for sustainable development. Herein, a unique phosphorus‐free hybrid (BN@CeO₂) was synthesized through chemically grafting cerium oxide (CeO₂) on surface of exfoliated boron nitride (BN) nanosheet with the aids of γ‐aminopropyltriethoxysilane and polydopamine coating, which was then embedded into bisphenol A cyanate ester (BCy) resin to fabricate new BN@CeO₂/BCy composites with high thermal resistance. Compared with BCy resin, the BN@CeO₂/BCy composite with 4 wt% BN@CeO₂ not only has delayed initial ignition time by 23 seconds but also severally shows 58.1%, 23.1%, and 44.4% lower smoke produce rate, total heat release, and peak heat release rate. The study on mechanism behind outstanding flame retardancy reveals that the improved heat resistance and flame retardancy of BN@CeO₂/BCy composite are attributed to multiply effects induced by BN@CeO₂ and its interaction with BCy resin; specifically, these effects come from BN (physical barrier) and CeO₂ (free radical trapping effect and catalytic char layer formation) as well as those from the synergistic effect of BN and CeO₂. These excellent comprehensive properties of BN@CeO₂/BCy composites demonstrate that BN@CeO₂ is an environment‐friendly and synergistic modifier for developing heat‐resisting thermosetting resins with outstanding flame retardancy and smoke suppression.