Chemorheological studies on a dicyanate resin modified with polyethersulfone

The chemorheology of a dicyanate resin modified with a polyethersulfone (PES) was investigated. The rheological and dielectrical property changes during curing of the dicyanate resin system catalyzed by an organic metal salt were monitored by a rheometer and dielectric analyzer, respectively, and used to investigate the curing behavior and chemorheology of the resin system. The curing rate of the dicyanate resin system decreased as the PES content was increased. A function that can describe the viscosity change of the dicyanate resin system during curing was determined by a nonlinear regression method using the rheometer data. The gelation time of the dicyanate resin system decreased with increasing isothermal curing temperature and with decreasing PES content. The curing behavior of the dicyanate resin system monitored by the dielectric analyzer coincided fairly well with that measured by the rheometer Copyright © 2004 Society of Chemical Industry     

Synthesis, cure kinetics and thermal properties of the 2,7-dihydroxynaphthalene dicyanate

The novel dicyanate ester resin containing the naphthalene ring (DNCY) was synthesized from 2,7-dihydroxynaphthalene and cyanogen bromide by two-step method. The monomer of DNCY was characterized by FT-IR, ¹H NMR, ¹³C NMR and elemental analyses (EA). The cure behavior of DNCY was studied by means of nonisothermal DSC, and the kinetics parameters were determined by the Kissinger method. The thermal properties of DNCY resin were studied by thermal degradation analysis at a heating rate of 10 °C min⁻¹ both in N₂ (thermal stability) and in air (thermal-oxidative stability). The DNCY resin showed excellent thermal stability, compared with that of bisphenol A dicyanate (BACY) resin, which could be demonstrated by the extensional onset temperature (435.8 °C), the temperature of maximum weight loss rate (450.3 °C) and the percentage char yields at 700 °C (60.5%) in N₂, and thermal-oxidative stability, which could be demonstrated by the extensional onset temperature (435.4 °C), the first temperature of maximum weight loss rate (450.7 °C), the second temperature of maximum weight loss rate (580.0 °C) and the temperature of complete degradation (704.4 °C) in air. The DNCY resin exhibited higher T_g and thermal degradation temperature than BACY resin.     

Determination of thermal cure kinetics of thin films of photocatalysed dicyanate ester by FTIR emission spectroscopy

Emission Fourier transform infrared (FTIR) spectroscopy has been found to be a suitable technique for monitoring the thermal cure of thin films of photocatalysed dicyanate ester resins. The kinetics of the polymerization of a commercial cyanate ester resin (AroCy RTX‐366) catalysed by an organometallic compound, tricarbonyl cyclopentadienyl manganese (CpMn(CO)₃), have been determined using this technique and the results compared with those obtained from transmission FTIR. The trimerization reaction rate of the resin is found to have a first order dependence upon both the cyanate fraction and the active catalyst concentration until diffusion control occurs. To elucidate the mechanism, a system with premade catalyst, which was the photoreaction product of the resin and the organometallic compound, has also been studied. The activation energy for this system is 91 ± 10 kJ mol⁻¹ compared to 72 ± 8 kJ mol⁻¹ for the directly irradiated system. This may arise from different distributions of three photoproducts identified as complexes between manganese and the cyanate ester. © 2000 Society of Chemical Industry     

Polymerization kinetics and thermal properties of dicyanate/clay nanocomposites

The polymerization kinetics and thermal properties of dicyanate/clay nanocomposites were investigated. A type of organically modified clay was used as nanometer‐size fillers for the thermosetting dicyanate resin. Differential scanning calorimetry (DSC) was used to study the curing behavior of the dicyanate/clay nanocomposite systems. The polymerization rate of the nanocomposite systems increased with increasing clay content. An autocatalytic reaction mechanism could adequately describe the polymerization kinetics of the dicyanate/clay nanocomposite systems. The polymerization kinetic parameters were determined by fitting the DSC conversion data to the proposed kinetic equation. The glass‐transition temperature of the dicyanate/clay nanocomposites increased with increasing clay content. The thermal decomposition behavior of the dicyanate/clay nanocomposites was investigated by thermogravimetric analysis. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1955–1960, 2004     

Effect of lewis acids on cure kinetics and mechanical properties of hydroxyterminated polybutadiene polymers

The effect of two Lewis acids, viz. BF₃ and AlCl₃ on the cure reaction of hydroxy-terminated polybutadiene: toluene diisocyanate systems has been studied in order to evaluate them as possible pot-life extenders in solid propellant formulations. The enthalpy of the cure exotherm, evaluated from DSC curves, did not show any dependence on the concentration of the two acids. The kinetic parameters for the cure reaction showed an increase in both cases indicating the effectiveness of the acids as reaction retardants. However, BF₃ is not a suitable candidate for pot-life extension, because of its adverse effect on the elongation at break of the cured HTPB samples. The coefficient of thermal expansion is unaffected by the two additives, probably because of their negligible influence on the cross-link density of the cured network.     

Effect of surface area of nanosilica particles on the cure kinetics parameters of an epoxy resin system

Knowing of thermoset curing kinetics is essential for process development, quality control, and achieving desirable products. Hence, in this article, cure kinetics of an EPON 828 epoxy resin/dicyandiamide curing agent/diuron accelerator system is investigated. This resin system is usually used for the production of epoxy/glass fiber prepregs used in wind turbine blades. For this, differential scanning calorimetry analysis is used and the effect of temperature, weight percentage, and size of nanosilica is studied by conducting isothermal tests at several temperatures for samples with and without nanoparticles. An autocatalytic curing model is applied to describe the cure kinetic of system and then the variations in model parameters calculated by curve fitting using the MATLAB software. The results show that the increase in temperature, weight percentage of nanosilica from 0 to 6%, and surface area of nanosilica particles lead to the increase in curing rate, whereas the increase in the percentage and surface area of nanosilica particles significantly decreases total heat of reaction. At the end, the relation between each of model parameters and the total surface area of nanosilica particles, calculated by mathematical equations, is obtained. The allowable maximum surface area of nanosilica used in the mathematical equations is 12 m² g⁻¹. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47958.     

In situ FT‐IR and DSC investigation on the cure reaction of the dicyanate/diepoxide/diamine system

Cure reactions of a liquid aromatic dicyanate ester (1,1′‐bis(4‐cyanatophenyl)ethane, BEDCy) with a liquid bisphenol A epoxide (2,2‐bis(4‐glycidyloxyphenyl)propane, BADGE) and 4,4′‐diaminodiphenyl sulfone (DDS) were studied through correlation of the in situ FT‐IR spectroscopy and DSC in dynamic scanning mode. Before this system was examined, cure reactions of precursory systems of BADGE/DDS, BEDCy/BADGE and BEDCy/DDS were investigated separately. Cure reaction paths for each system are proposed. Some reactions in the precursory systems, such as polycyclotrimerization of dicyanate to form sym‐triazine and formation of alkyl isocyanurate, were not observed in the combined curing system BEDCy/BADGE/DDS. Four principal reaction paths are proposed for this curing system: (1) formation of oxazoline from the reaction between the epoxide and cyanate group; (2) reaction of epoxide with primary amine to form a hydroxyl group; (3) reaction of epoxide with the hydroxyl group to form an ether linkage; and (4) rearrangement of oxazoline to form oxazolidinone. Two distinct, but somewhat overlapping, exothermic peaks were observed on the DSC thermogram. The lower temperature peak on the DSC thermogram was primarily contributed by the first reaction path, whereas the higher temperature peak can mainly be attributed to the reaction paths 2, 3 and 4. © 2001 Society of Chemical Industry     

氰酸酯/苯乙烯体系的反应性及固化树脂的性能研究

用傅里叶变换红外光谱(FT-IR)研究了氰酸酯单体的等温固化反应。获得了有机锡催化氰酸酯和苯乙烯体系在不同固化温度下的转化率和动力学参数。氰酸酯的转化率随着温度的升高和催化剂的使用而提高。不含催化剂时苯乙烯对氰酸酯的影响较小,而有机锡和苯乙烯同时存在时对氰酸酯有很强的催化作用。在所有的体系中,催化反应速率常数对氰酸酯单体浓度在动力学控制阶段表现为一级反应。改性体系的冲击强度和弯曲强度比未改性氰酸酯最高分别提高了45．3%和18．7%。     

磺化聚醚砜提高聚醚砜膜亲水性和血液相容性研究

Polyethersulfone (PES) is widely used as biomaterials due to its thermal stability, mechanical strength, and chemical inertness. Nevertheless, their blood compatibility is still not adequate for hemodialysis and blood pu-rification. In this study, the sulfonated polyethersulfone (SPES) was synthesized through an electrophilic substitu-tion reaction, and PES/SPES blending membranes were prepared. The characterization of the SPES was studied by FTIR. The water adsorption and water contact angle experiments show that the hydrophilicity of PES/SPES blend membrane was improved as for the sulfonate group existing in the SPES. Moreover, PES/SPES blend membrane could effectively reduce bovine serum albumin adsorption and prolong the blood coagulation time compared with the PES membrane, thereby improving blood compatibility.     

Preparation,cure kinetics,and thermal properties of novel acetylene terminated silazanes

A new kind of acetylene terminated silazanes, N‐(3‐acetylenephenyl)‐diorganosilazanes (abbreviated as APSZs) with three kind of substituents, were synthesized by the aminolysis of dichlorosilane with 3‐aminophenylacetylene (3‐APA). Structure of APSZs was confirmed by Fourier transform infrared spectroscopy (FT‐IR) and nuclear magnetic resonance (NMR). Thermal behavior of the cured silazanes was determined by thermogravimetry analysis (TGA), revealing that cured silazanes exhibited high temperature resistance. The ceramic yields of APSZ‐Me₂, APSZ‐MeVi, and APSZ‐Ph₂ at 1000°C under nitrogen were 77.6, 81.9, and 68.7%, respectively. The peak separation of derivative thermogravimetric data was employed to evaluate the three major regions of the thermolysis, and the kinetic parameters of thermolysis were calculated by the method of Kissinger from dynamic thermogravimetric measurement in nitrogen atmosphere at several different heating rates. Influence of substituents on the thermal behavior of cured silazanes in each separated region was discussed. The results showed that the vinyl derivative exhibit higher thermal stability than methyl and phenyl derivatives due to the high decomposition activation energy and small pendant group. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

硫化温度对硅橡胶发泡硫化动力学及性能的影响

采用动力学方程自催化模型Sestak-Berggren以及Arrhenius方程研究了模压过程中交联以及发泡的活化能,并结合扫描电镜(SEM)照片研究了不同硫化温度条件下发泡试样的力学性能及静压缩条件下的载荷保持率。实验结果表明,硫化过程的活化能大于发泡过程,即温度对硫化过程的影响程度较为明显。硫化温度对发泡材料的泡孔结构有很大的影响,温度越高,发泡倍率越大,其泡孔也越加均匀紧密。静态压缩条件下,硫化温度越高,试样内部的载荷保持率下降速度越快,强度也越低。     

Catalyst effect on cure reactions in the blend of aromatic dicyanate ester and bismaleimide

Catalyst effects on cure reactions of a bismaleimide [4,4′‐bismaleimidodiphenylmethane (BMI)] associated with a liquid aromatic dicyanate ester [1,1′‐bis(4‐cyanatophenyl)ethane (BEDCy)] and with a powder type of aromatic dicyanate ester [bisphenol A dicyanate (BADCy)] were thoroughly investigated by in situ FTIR and DSC dynamic scanning. In noncatalyzed blend systems, coreactions between the dicyanate ester and bismaleimide always occur, and thus the formation of the pyrimidine and/or pyridine structures occurs. The pyrimidine structure always predominates. The use of a dicyanate‐sensitive catalyst facilitates the formation of a sequential interpenetrating network (IPN). The extent of the sequential IPN depends on the level of catalyst and the type of matrix materials, and thus the extent of coreactions. Probable reaction paths were also proposed for various formulations of hybrid blends. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 345–354, 2004     

The effects of spinning temperature on morphologies and properties of polyethersulfone hollow fiber membranes

Polyethersulfone (PES) hollow fiber membranes were prepared by traditional dry‐wet spinning technique. Scanning electronic microscopy (SEM) was used to characterize membrane morphologies, and the membrane properties were evaluated via bubble point measurements and ultrafiltration experiments. The effects of spinning temperature on the morphologies and properties of PES fibers were investigated in detail. At a high spinning temperature, the obtained membrane structure consisting of a thin skin‐layer and loose sponge‐like sublayer endows PES membrane with not only good permeability, but also high solute rejection. Based on the determination of ternary phase diagrams and light transmittance curves, the relationship of membrane morphologies with thermodynamics and precipitation kinetics of membrane‐forming system was discussed. It was concluded that the morphologies and properties of PES hollow fiber membrane could be conveniently tuned by the adjustment of the spinning temperature and air gap. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

双酚A二氰酸酯/环氧树脂固化共混物结构的红外光谱研究

通过熔融共混制备了双酚A二氰酸酯/双酚A二缩水甘油醚环氧树脂、双酚A二氰酸酯/酚醛环氧树脂两种共混物。用红外光谱研究了组分比对两类共混物各种基团相对含量的影响。结果表明,随着共混物中环氧量的增加,芳醚的吸收会由于共聚产物的增加而出现蓝移,酚醛环氧树脂中的酚羟基能影响共聚产物的生成;环氧量较大的氰酸酯/酚醛环氧村脂共混物生成了相当含量的酚-氰酸酯加成物,这使得共聚产物相对含量的计算变得困难。     

Study on the cure behavior of 2,7‐dihydroxynaphthalene dicyanate

The cure behavior of 2,7‐dihydroxynaphthalene dicyanate (DNCY) was studied by means of nonisothermal DSC, isothermal DSC, and FTIR. In nonisothermal DSC, the cure kinetics parameters of DNCY were calculated by the Coats–Redfern method and compared with those of biphenol A dicyanate (BACY). It was revealed that the activation energy of DNCY was enhanced compared with that of BACY because of the presence of naphthalene, and the gelation of DNCY occurred within the conversion range 50–55%, which is lower than that of BACY. In isothermal DSC, a good time–temperature superposition of the conversion profiles of DNCY was obtained during conversions below about 50%. These results were consistent with those obtained by nonisothermal DSC. For the catalyzed system, the autocatalytic behavior prevailed at conversions below 30%, whereas the catalytic behavior occurred only at conversions above 30%. In situ FTIR spectra revealed that a triazine network was formed by cyclotrimerization of the OCN functional group during the cure process for systems with and without catalysts. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 3927–3939, 2004     

Effect of polyaniline surface modification of carbon nanofibers on cure kinetics of epoxy resin

Polyaniline (PANI) “nanograss” was grown on carbon nanofibers (CNFs). The cure behavior of an epoxy resin with and without unmodified CNFs or PANI modified CNFs was studied by means of non‐isothermal and isothermal differential scanning calorimetry (DSC). CNFs accelerated the reaction of epoxy and diamine. PANI surface modification further increased the reaction rate and the extent of reaction. An autocatalytic cure kinetic model was used to fit the reaction curves. It was found that activation energies of the epoxy reaction decreased in the presence of CNFs and PANI modified CNFs. The observed catalytic effect of CNF and PANI surface coating can be very useful for low temperature cure of large epoxy composite products. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Studies on the cure kinetics and networks properties of neat and polydimethylsioxane modified tetrafunctional epoxy resins

The cure kinetics of tetrafunctional epoxy resins with three different backbone structures and their modification by polydimethylsioxane (PDMS) were studied by means of differential scanning calorimetry with dynamic approach. The development of epoxy networks was characterized by dynamic viscoelastic measurements. Results showed that all the epoxy resins obeyed the autocatalytic reaction mechanism with a reaction order of about 3. Epoxy resin with softer aliphatic backbone demonstrated a higher cure reactivity and stronger tendency towards autocatalysis, as well as lower crosslinking density. The PDMS‐modified epoxy resins showed higher early cure reactivity and a lower crosslinking density due to the plasticization and restriction effect of the dispersed PDMS phase, respectively. Based on cure kinetics and dynamic viscoelastic results, the α_m was found to be an effective precursor for describing the developing of epoxy networks during the course of cure. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Application of surface modifying macromolecules in polyethersulfone membranes: Influence on PES surface chemistry and physical properties

Novel surface modifying macromolecules (SMMs) were developed for incorporation into polyethersulfone (PES) membranes, intended for pervaporation applications. These materials were synthesized with a diisocyanate, polypropylene oxide (PPO), and a fluoro-alcohol, and characterized for elemental analysis, molecular weight, and glass transition temperatures. PES/SMM blends with eight types of SMMs were characterized for surface and physical properties and compared with PES. Water droplet contact angle measurements and X-ray photoelectron spectroscopy data showed that the SMMs migrated to the surface and rendered the PES material more hydrophobic. While advancing contact angle data were equivalent to those of pure Teflon™, the highest average values of receding angles of these systems were less than those of commercial Teflon™. The opaqueness of PES/SMMs films and data from differential scanning calorimetry experiments showed that the SMMs were either immiscible or only partially miscible with PES. It was also observed, for a fixed PES concentration of 25 wt %, that increases in the molecular weight of the SMMs and the weight fraction of PPO in the SMMs led to phase separation in the ternary PES/SMMs/dimethylacetamide (i.e., membrane casting solution) system. On the other hand, in the binary PES/SMMs system (i.e., cast membrane film), an increasing weight fraction of fluorine in the SMMs contributed to an increase in the phase separation. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 1363–1378, 1999     

New aspects of unsaturated polyester resin synthesis. Part 2. Reactant sequence distribution and its effect on cure kinetics

The distribution of unsaturations in the prepolymer of a typical unsaturated polyester (UP) resin (maleic anhydride, phthalic anhydride and 1,2‐propylene glycol) has been shown to influence the kinetics of the cure process with styrene monomer. Segments containing double bonds in close proximity appear to lower the reactivity of the resin due to steric hindrance, as indicated by the fact that the rate of cure and the final degree of cure, measured by differential scanning calorimetry (DSC), increase as the average sequence length (SL) of maleic units decreases. This implies that the reactivity of UP resins may be improved by synthesis of prepolymers with certain reactant sequence‐length distributions. The copolymer formed by the melt condensation process of maleic anhydride, phthalic anhydride and 1,2‐propylene glycol in the absence of a transesterification catalyst has a non‐random structure with a tendency towards blockiness. This was established using ¹H NMR analysis in tandem with deterministic and Monte Carlo modelling techniques. Copyright © 2003 Society of Chemical Industry     

Reactive blends of epoxy resin (DGEBA) crosslinked by anionically polymerized polycaprolactam: Process of epoxy cure and kinetics of decomposition

The curing reactions, kinetics, morphology, and thermal stability of the reactive blends of diglycidyl ether of bisphenol‐A (DGEBA) and polycaprolactam were studied by differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and thermogravimetric analysis. DSC studies showed that the heat of reaction (ΔH) increased when the DGEBA content was increased from 50 to 80 wt % and increased drastically above 70 wt % DGEBA content because of an increase in the extent of crosslinking. The activation energy and pre‐exponential factor of cure reactions increased drastically with an increase in the DGEBA content above 70 wt % because of a drastic increase in crosslink density. The extent of curing reaction of polycaprolactam with DGEBA is dependent on the blend composition. The nucleophilic attack on oxirane ring by amide nitrogen of polycaprolactam is a dominant curing reaction in low DGEBA compositions, and another type of curing reaction with relatively large activation energy and pre‐exponential factor also occurred, which becomes dominant when the DGEBA content reaches above 70 wt %. FTIR studies also revealed that two types of reactions do exist during the curing of polycaprolactam with DGEBA. It was observed during SEM studies that the reactive blends show multiphase system and on increasing the DGEBA content from 50 to 80 wt %, the mixing of the two phases increased. The reactive blend Ep₈₀Ca₂₀ with 80 wt % DGEBA content exhibits a single‐phase system because of better mixing of the two phases. The results of thermogravimetric analysis also indicate that the initial degradation temperature (T_i), activation energy (E), and pre‐exponential factor (Z) increased with increasing DGEBA content from 50 to 80 wt % in the reactive blends and increased drastically above 70 wt % DGEBA content due to the higher crosslink density. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 687–697, 2004