Dicyanate Ester Research Articles

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

AbstractA 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.

Thermal and physical properties of flame-retardant epoxy resins containing 2-(6-oxido-6 H-dibenz〈 c, e〉〈1,2〉oxaphosphorin-6-yl)-1,4-naphthalenediol and cured with dicyanate ester

2-(6-oxido-6 H-dibenz( c, e)(1,2)oxaphosphorin-6-yl)-1,4-naphthalenediol (DOPONQ) was prepared by the addition reaction of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) with 1,4-naphthoquinone. The phosphorus-containing diol (DOPONQ) was used as a reactive flame retardant by an advancement reaction with the diglycidyl ether of bisphenol-A epoxy (DGEBA) resin at various stoichiometric ratios. DOPONQ-containing advanced epoxy was separately cured with various dicyanate esters to form flame-retardant epoxy/cyanate ester systems. The effect of the phosphorus content and dicyanate ester structure on the curing characteristic, glass transition temperature, dimensional stability, thermal stability, flame retardancy, and dielectric property was studied and compared with that of the control advanced bisphenol-A epoxy system. The DOPONQ-containing epoxy/cyanate ester systems exhibited higher glass transition temperatures as well as better thermal dimensional and thermal degradation stabilities. The flame retardancy of the phosphorus-containing epoxy/dicyanate ester system increased with the phosphorus content, and a UL-94 V-0 rating could be achieved with a phosphorus content as low as 2.1%.

Porous thermosets via hydrolytic degradation of poly(ε-caprolactone) fragments in cyanurate-based hybrid networks

New nanoporous film thermosets were developed from polycyanurates (PCNs) obtained by polycyclotrimerization of dicyanate ester of bisphenol E in the presence of hydrolytically labile poly(ε-caprolactone) (PCL). During the synthesis of PCL-modified PCN networks, it was established that PCL was partially incorporated into the PCN structure. Porous frameworks were then derived from such PCN/PCL-based hybrid networks by selective hydrolysis of a significant part of PCL sub-chains under mild conditions. The structure and properties of the precursory networks as investigated by FTIR, solid-state 13C NMR, DSC, TGA, and pycnometry were compared to those of the resulting porous materials. Thermogravimetric analyses showed that the porous hybrid systems were characterized by thermal and thermal oxidative stabilities higher than those of their non-hydrolyzed homologues. The porosity of the resulting hydrolyzed networks was examined by SEM and DSC-thermoporometry: pore sizes ranging from 10 to 150 nm – at most – were thus determined.

Synthesis, cure kinetics, and thermal properties of the Bis(3‐allyl‐2‐cyanatophenyl)sulphoxide/BMI blends

AbstractA novel allyl functionalized dicyanate ester resin bearing sulfoxide linkage was synthesized. The monomer was characterized by Fourier Transform Infrared (FT‐IR) Spectroscopy, 1H‐, and 13C Nuclear Magnetic Resonance (NMR) spectroscopy and elemental analysis. The monomer was blended with bismaleimide (BMI) at various ratios in the absence of catalyst. The cure kinetics of one of the blends was studied using differential scanning calorimetry [nonisothermal] and the kinetic parameters like activation energy (E), pre‐exponential factor (A), and the order of the reaction (n) were calculated by Coats‐Redfern method and compared with those calculated using the experimental Borchardt‐Daniels method. The thermal stability of the cured dicyanate, BMI, and the blends was studied using thermogravimetric analyzer. The initial weight loss temperature of dicyanate ester is above 380°C with char yield of about 54% at 800°C. Thermal degradation of BMI starts above 463°C with the char yield of about 68%. Inclusion of BMI in cyanate ester increases the thermal stability from 419 to 441°C. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Synthesis and Characterization of Novel Betti Type Cyanate Esters

Several aromatic diols bearing amino benzyl linkage in the main chain have been synthesized through high yield Betti reaction, which involves the reaction of an aldehyde with p-amino phenol and 8-hydroxy quinoline. Five different aldehydes have been used to prepare five new bisphenols. These bisphenols were converted to their corresponding cyanate esters by the treatment of cyanogen bromide in the presence of triethyl amine. The structures of the diols and dicyanate esters were confirmed by FT-IR, 1H-NMR, 13C-NMR spectral studies and elemental analysis. The cyclotrimerization reactions of cyanate esters have been studied by differential scanning calorimetry (DSC). The maximum curing temperatures of these cyanate esters are in the range of 186-201oC. Tgvalues of the polycyanurate networks are above 270oC. Thermogravimetric analysis (TGA) shows that the 10% weight loss of all the cured cyanate esters is above 400oC in N2 atmosphere. The char yield is in the range of 66-73%. The flame retardancy of the cyanate ester resins have been studied using Limiting Oxygen Index (LOI) value which is in the range of 43.9-46.7% at 700oC.

Polycyanurate–Organically Modified Montmorillonite Nanocomposites: Structure–Dynamics–Properties Relationships

Polycyanurate‐modified montmorrilonite (PCN‐MMT) nanocomposites were synthesized by polymerization of dicyanate ester of bisphenol A in the presence of MMT dispersed by ultrasound. Techniques of IR spectroscopy, WAXD, and TEM were applied to study polymerization kinetics and structure of the nanocomposites prepared, whereas their dynamics and thermal/mechanical properties over the −30 to 420°C range were studied by using DSC, laser‐interferometric creep rate spectroscopy (CRS), and dielectric relaxation spectroscopy (DRS) techniques. It was shown that a small amount of MMT additive acts as a catalyst of polymerization and results in the formation of complicated intercalated/exfoliated structures, as well as strongly modifies the dynamics in the PCN network. Pronounced dynamic heterogeneity was observed for PCN/MMT nanocomposites. Along with the main PCN glass transition, two new glass transitions, at much higher and much lower temperatures, were revealed as a consequence of constrained dynamics in matrix interfacial nanolayers and due to incomplete local cross‐linking in the PCN matrix, respectively. In addition, increased sub‐T g mobility was observed in these nanocomposites. A two‐fold rise of modulus of elasticity as well as increasing thermal stability and arising microplasticity at low temperatures, promoting, obviously, improved crack resistance in a brittle PCN network, were found for the PCN‐MMT nanocomposites.

Curing of Bisphenol M Dicyanate Ester under Nanoscale Constraint

Nanoscale constraint is known to have a significant impact on the thermal properties of materials. Although thermosetting resins have been cured in the presence of nanoparticles and nanotubes, cure of thermosetting resins under the well-defined nanoscale constraints imposed by controlled pore glass (CPG) or similar matrices has not been previously documented. In this work, we investigate the isothermal curing under nanoscale constraint of a thermosetting resin, bisphenol M dicyanate ester (BMDC), which trimerizes to form a polycyanurate network material. Differential scanning calorimetry is used to monitor the evolution of the glass transition temperature (Tg) and the conversion during cure as a function of the diameter of the silanized control pore glass matrix which is used for confinement. A Tg depression is observed for both the bisphenol M dicyanate ester monomer and the polycyanurate networks; the depression is only a few degrees for the monomer, whereas a 56 K depression is observed for the “fully cured” network in 11.5 nm pores. The nanoscale constraint is also found to strongly increase the rate of cure of bisphenol M dicyanate ester, but it does not affect the normalized Tg vs conversion relationship. The appearance of a secondary Tg above the primary Tg in the smaller pores and the associated length scale are discussed.

Synthesis and characterization of polycyanurate networks modified by oligo(ϵ-caprolactone) as precursors of porous thermosets

Oligo(ϵ-caprolactone)-modified polycyanurate networks were synthesized by thermal polycyclotrimerization of dicyanate ester of bisphenol E in the presence of a dihydroxy-telechelic poly(ϵ-caprolactone) (PCL) oligomer with varying compositions. Using FTIR, gel fraction content and density measurements, it has been proved that the main part of the reactive modifier was chemically incorporated into the PCN network structure. According to the thermal behavior of the polymer networks as investigated by TGA, they can be divided into two groups. The first group of systems with low modifier content (i.e., up to 20 wt %) is characterized by one stage of decomposition under nitrogen, and two stages under oxygen. A second group of systems with higher modifier content is generally characterized by two stages of decomposition in nitrogen and three stages in oxygen. DSC and DMTA investigations have shown the occurrence of at least a two-phase structure in all the samples. The PCN/PCL-based hybrid networks can be effectively used as precursors for the generation of porous PCN thermosets, as evidenced by FTIR and SEM. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007

Determining the Quantum Efficiency for Activation of an Organometallic Photoinitiator for Cationic Polymerization

We present a new laboratory experiment on the photochemistry of organometallic ?5,?6-mixed-sandwich compounds, which is suitable for both the physical chemistry and inorganic chemistry laboratory. Specifically, students use 1,10�phenanthroline to trap the intermediate formed when [CpFe(isopropylbenzene)]PF6 is photolyzed with 458 nm light from an argon�krypton laser. Using quantitative UV�vis spectroscopy students then determine the quantum yield of arene ring displacement from the mixed-sandwich complex. The photogenerated intermediate, [CpFe(solvent)3]+ is an efficient initiator for the polymerization of epoxides, dicyanate esters, pyrrole, styrene, dioxolenes, and acrylates. The efficiency with which the intermediate is photochemically formed is therefore an important property in determining its commercial utility. Although the experiment can easily be done in one 3�4 hour laboratory period, it readily lends itself to broadening into a multi-week research project. In this mode, students can examine how changing the nature of the solvent and the irradiation wavelength affect the quantum yield of reaction. Such information can be used to reveal the role of the solvent in the reaction and the electronic excited states from which reaction occurs. Furthermore, in the inorganic laboratory, students could be asked to synthesize [CpFe(isopropylbenzene]PF6 before looking at its photochemical behavior, thus gaining experience in working under air-free conditions.

Viscoelastic Shear Response and Network Structure in Polycyanurates

The shear response of polycyanurate networks with different cross-link densities, varied by changing the ratio of difunctional to monofunctional cyanate ester, is measured from shear stress relaxation and dynamic experiments. Master curves are constructed following the time−temperature superposition principle, and the temperature dependence of the shift factors is examined. The discrete relaxation time spectra are calculated from the viscoelastic responses and are found to be independent of cross-link density over the time/frequency range measured. The cross-link density, determined from the rubbery modulus, and the sol content, measured from sol extraction experiments, are modeled for the fully cured polycyanurate networks using the recursive method; a monomer cyclization reaction is assumed in the modeling based upon the chemical composition of the sol which was determined by mass spectroscopy. The effect of monomer cyclization on the conversion at gelation of dicyanate esters is discussed.

Structure and Dynamic/compositional Heterogeneity in Polycyanurate—poly(Tetramethylene Glycol) Hybrid Networks

Structure and dynamics over the range from −150 to 300°C were studied in a series of polycyanurate‐poly(tetramethylene glycol) (PCN‐PTMG) hybrid networks. Wide‐angle x‐ray diffraction (WAXD), small‐angle x‐ray scattering (SAXS), laser‐interferometric creep rate spectroscopy (CRS), differential scanning calorimetry (DSC), and thermally stimulated depolarization currents (TSDC) techniques were applied. The networks were synthesized from the dicyanate ester of bisphenol A (DCEBA) and hydroxyl‐terminated PTMG with M n =1000, 2000 or 5000 g/mol and weight fraction of 10, 20, 30, and 40%. The noncrystalline structure and the pronounced structural nanoheterogeneity, depending on PTMG chain length and PCN‐PTMG ratio in the hybrid systems, were evidenced. Combined CRS/DSC analysis revealed a complex dynamics in these networks, in particular a dispersion of glass transitions in a wide temperature range. On this basis, the presence of nanodomains with different degrees of rigid cross‐linking (X CN→PCN), i.e., compositional nanoheterogeneity in these hybrids was shown. The results obtained turned out to be of applied interest because of a substantial increase in tensile strength because of arising microplasticity at low temperatures, and retaining some creep resistance, at low stresses, up to temperatures much higher the basic T g . In Commemoration of the Contributions of Professor Valery P. Privalko to Polymer Science.

Dielectric and thermal properties of polymer network based on bismaleimide resin and cyanate ester containing dicyclopentadiene or dipentene. III

AbstractA series of bismaleimide‐triazine (BT) resins were prepared from commercial bismaleimide (DDMBMI) and 2,6‐dimethylphenol‐dicyclopentadiene dicyanate ester (DCPDCY) or 2,6‐dimethylphenol‐dipentene dicyanate ester (DPCY). The thermal properties of cured BT resins containing DCPD or DP were studied using a dielectric analyzer (DEA), dynamic mechanical analyzer (DMA), and thermal gravimetric analyzer (TGA). These data were compared with that of DDMBMI cured with bisphenol A dicyanate ester (BADCY). The cured DDMBMI/DCPDCY or DDMBMI/DPCY exhibits a lower dielectric constant, dissipation factor, and moisture absorption than those of DDMBMI/BADCY. The effects of blend composition on the glass transition temperatures and thermal stability are discussed. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1942–1951, 2007

Viscoelastic, Thermal and Mechanical Properties of Dicyclopentadiene Bisphenol Diyanate Ester / Epoxy Co-polymers

Dicyanate ester containing dicyclopentadiene cycles and epoxy co-polymers were prepared by copolymerization between epoxy and dicyclopentadiene bisphenol cyanate esters (DCPDCE). Viscoelastic properties of the co-polymers were characterized by the technique of dynamic mechanical analysis (DMA), which indicated that the introduction of E51 in the co-polymers would effectively improve the toughness of DCPDCE, while the thermal dimensional stability would be weakened. Results from thermogravimetric analysis (TGA) are in good accordance with the Tg values from DMA curves. Mechanical testing of the cured co-polymers shows that E51 can improve the mechanical properties of the co-polymers while its usage is controlled among 5% to 15%.

Preparation and characterization of organic–inorganic hybrid composites based on multiepoxy silsesquioxane and cyanate resin

AbstractA multiepoxy cubic silsesquioxane was prepared by the hydrolysis and polycondensation of trifunctional monomer (γ‐glycidoxypropyl)trimethoxysilane in a solvent mixture of methyl isobutyl ketone and anhydrous ethanol with a tetraethyl ammonium hydroxide aqueous solution acting as the catalyst, and it was successfully introduced into a cyanate resin and formed highly crosslinked organic–inorganic hybrid composites on a molecular level via a mutual cure reaction. The properties of the multiepoxy cubic silsesquioxane/bisphenol A dicyanate ester resin composites were investigated, and the results showed that introducing the cubic silsesquioxane unit into the cyanate resin successfully modified the local structure of the molecule, made the chain more rigid, restricted the chain mobility, and eventually improved the thermal stability and flame retardancy of the resin. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3652–3658, 2006

Study on cure reaction of the blends of bismaleimide and dicyanate ester

In this work, the cure reaction of the blends of bisphenol A dicyanate ester (BADCy) and 4,4′-bismaleimidodiphenylmethane (BMI) was investigated by using DSC, in situ FTIR, DMA and generalized 2D correlation analysis. The results clarified that there existed different kinds of cure mechanism in the blends of bismaleimide and dicyanate ester. In non-catalyzed blends, the dicyanate ester and bismaleimide cured independently and formed two kinds of network: polycyanurate and polybismaleimide. A cyanate curing catalyst accelerated the cure of dicyanate ester but did not change the independent cure mechanism of two components. Moreover a commercial ring closure catalyst, which was usually used in the synthesis of bismaleimide, resulted in the co-reaction between two components and formed a homogeneous network. Thus, the cure mechanism of the blends of dicyanate ester and bismaleimide was related to the catalyst presented in the blends systems.

Synthesis, characterization, and properties of novel epoxy resins and cyanate esters

AbstractWe synthesized a novel epoxy (dopotep) and cyanate ester (dopotcy) based on a phosphorus‐containing triphenol (dopotriol). The proposed structures were confirmed by IR, mass spectra, NMR spectra, and epoxy‐equivalent‐weight titration. The synthesized dopotep or dopotcy was copolymerized with diglycidyl ether of bisphenol A (DGEBA), 6′,6‐bis(3‐phenyl‐3,4‐dihydro‐2H‐1,3‐benzoxazineyl)methane (F‐a), or dicyanate ester of bisphenol A (BADCY). Thus, copolymers based on DGEBA/dopotep/diphenylmethane (ddm), F‐a/dopotep, BADCY/dopotcy, and DGEBA/dopotcy were developed. The thermal properties, dielectric properties, and flame retardancy of these copolymers were investigated. The curing kinetics of dopotep/ddm and dopotep/diamino diphenylsulfone were studied with differential scanning calorimetry. The microstructure of DGEBA/dopotcy was studied with IR. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3487–3502, 2006

Modification of bisphenol A dicyanate ester by carboxyl‐terminated liquid butadiene‐acrylonitrile and its composites

AbstractCyanate esters with excellent high‐temperature properties and easy processing are well known as good resin materials used in aerospace and electrical industries, but the drawback of brittleness limits their usage. In this study, carboxyl‐terminated liquid butadiene‐acrylonitrile (CTBN) was introduced to improve the toughness of bisphenol A dicyanate resin (BADCy), a typical kind of the cyanate esters. Fourier transform infrared spectroscopy and differential scanning calorimetry were employed to investigate the effects of CTBN on the curing behavior of BADCy; the results indicate that the addition of CTBN has a great influence on the curing behavior of BADCy at lower temperatures, but little at higher temperatures. Data from the thermogravimetric analysis and heat deflection temperature analysis showed that the thermal properties of the modified systems were poorer than that of pristine BADCy resin. On the basis of the scanning electron micrographs of the modified systems, toughening mechanism of the systems was discussed. Mechanical and dielectric properties of the cured resins and glass fiber‐reinforced composites were also studied. Modified systems exhibit attractive properties for the future applications in aerospace industries. POLYM. ENG. SCI. 46:581–587, 2006. © 2006 Society of Plastics Engineers.

Dielectric and thermal properties of dicyclopentadiene containing bismaleimide and cyanate ester. Part IV

A novel bismaleimide (BMI), bis(4-maleimidophenoxy-3,5-dimethylphenyl)dicyclopentadiene (DCPDBMI), containing a large dicyclopentadiene (DCPD) and aryl ether linkage, was synthesized from bis(4-aminophenoxy-3,5-dimethylphenyl)dicyclopentadiene and maleic anhydride by the usual two-step procedure that included ring-opening addition to give bismaleamic acid, followed by cyclodehydration to bismaleimide. The monomers were characterized by Fourier transform infrared spectroscopy (FT-IR), proton nuclear magnetic resonance (NMR), elemental analyses (EA), and mass spectra (MS). A series of bismaleimide-triazine (BT) resins were prepared from synthesized bismaleimide (DCPDBMI) and then cured with 2,6-dimethyl phenol-dicyclopentadiene dicyanate ester (DCPDCY) at various molar ratios. Thermal properties of cured BT resins (DCPDBMI/DCPDCY) were studied using dielectric analyzer (DEA), dynamic mechanical analyzer (DMA) and thermalgravimetric analyzer (TGA). These data were compared with that of commercial bismaleimide (DDMBMI) cured with bisphenol A dicyanate ester (BADCY). The cured DCPDBMI/DCPDCY exhibits lower dielectric constant, dissipation factor and moisture absorption than those of DDMBMI/BADCY. The effects of blend composition on the glass transition temperatures and thermal stability are discussed.

Structural/compositional nanoheterogeneity and glass‐transition plurality in amorphous polycyanurate–poly(tetramethylene glycol) hybrid networks

AbstractThe nanostructure and dynamics over the temperature range of −140 to 300 °C were studied in a series of polycyanurate (PCN)–poly(tetramethylene glycol) (PTMG) hybrid networks by wide‐angle X‐ray diffraction and small‐angle X‐ray scattering, with a synchrotron radiation setup, and by differential scanning calorimetry (DSC) and laser‐interferometric creep rate spectroscopy (CRS) techniques, respectively. The networks were synthesized from the dicyanate ester of bisphenol A and hydroxyl‐terminated PTMG with a number‐average molecular weight of 1.000 g/mol; the PTMG content varied from 0 to 40 wt %, and the degree of its chemical incorporation into the PCN network changed from 78.8 to 97%. The noncrystalline structure and considerable structural nanoheterogeneity of the hybrid networks were shown. CRS/DSC analysis revealed a complicated dynamic behavior, that is, a wide dispersion of glass transitions in the hybrid networks due to the presence of nanodomains with different degrees of rigid crosslinking (i.e., compositional nanoheterogeneity). Besides the physical significance, the plurality of glass transitions found in the PCN–PTMG hybrid networks was also of practical interest because it resulted in increasing mechanical strength of the brittle PCN network due to microplasticity arising at room temperature and moderate temperatures and the retention of some rigidity and creep resistance at temperatures much higher than the basic glass‐transition temperature. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3261–3272, 2005

Evolution of the coefficient of thermal expansion of a thermosetting polymer during cure reaction

The evolution of the coefficient of thermal expansion (CTE) of a thermosetting polymer during cure reaction is an important parameter for industrial applications such as composite processing since it influences the development of internal stresses in the material. The CTE being almost impossible to measure on a reacting thermoset, we propose to use an indirect method based on the modelling of ionic conductivity by a modified WLF equation, allowing to calculate the evolution of CTE from dielectric spectroscopy measurements. This method is applied to a dicyanate ester thermosetting polymer, leading to encouraging results both qualitatively and quantitatively.