Preparation and characterization of novel film adhesives based on cyanate ester resin for bonding advanced radome

In this paper, the novel film adhesives based on phenolphthalein poly(ether sulfone) (PES-C) and epoxy (EP) modified cyanate ester resin (CE) were prepared for bonding an advanced radome. The film adhesives are convenient for applying to manufacture, possessing good adhesion strength, thermal durability and excellent dielectric property. The curing behaviors were confirmed by differential scanning calorimetry (DSC), showing that the main reaction pathways are not varied with adding PES-C but the reaction rates are evidently accelerated, and the film adhesives can be well cured at lower temperature of 177 °C. The adhesion strength was evaluated in lap shear strength and peel strength, indicating that the better adhesion strength is obtained with increasing in PES-C. The maximum value of lap shear strength is 33 MPa at room temperature. The thermal durability was determined by thermal aging tests of lap shear specimens, showing that the decrease in strength gets faster with adding PES-C, and the usability of film adhesives over 2000 h at 200 °C. The dielectric properties were measured by dielectric resonator methods, finding that the introduction of PES-C brings a positive effect on dielectric properties. The lowest value of determined dielectric loss is 0.0075 at 10 GHz.     

Phase separation behavior of cyanate ester resin/polysulfone blends

The composition of the blends and the curing temperature affect the morphology of the blends and the phase separation mechanism. The phase separation mechanism depends on the viscosity of medium at the initial stage of phase separation determined by the amount of thermoplastics and the curing temperature, and is closely related with the final morphology. When the homogeneous bisphenol A dicyanate (BADCy)/polysulfone (PSF) blends with low content of PSF (less than 10 wt %) were cured isothermally, the blends were phase separated by nucleation and growth (NG) mechanism to form the PSF particle structure. On the other hand, with more than 20 wt % of PSF content, the BADCy/PSF blends were phase separated by spinodal decomposition (SD) to form the BADCy particle structure. With about 15 wt % of PSF content, the blends were phase separated by SD and then NG to form a combined structure having both the PSF particle structure and the BADCy particle structure. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 33–45, 1999     

Liquid-liquid phase separation and crystallization behavior of poly(ethylene terephthalate)/poly(ether imide) blend

The liquid-liquid (L-L) phase separation and crystallization behavior of poly(ethylene terephthalate) (PET)/poly(ether imide) (PEI) blend were investigated with optical microscopy, light scattering, and small angle X-ray scattering (SAXS). The thermal analysis showed that the concentration fluctuation between separated phases was controllable by changing the time spent for demixing before crystallization. The L-L phase-separated specimens at 130 °C for various time periods were subjected to a temperature-jump of 180 °C for the isothermal crystallization and then effects of L-L phase separation on crystallization were investigated. The crystal growth rate decreased with increasing L-L phase-separated time (t_s). The slow crystallization for a long t_s implied that the growth path of crystals was highly distorted by the rearrangement of the spinodal domains associated with coarsening. The characteristic morphological parameters at the lamellar level were determined by the correlation function analysis on the SAXS data. The blend had a larger amorphous layer thickness than the pure PET, indicating that PEI molecules in the PET-rich phase were incorporated into the interlamellar regions during crystallization.     

The study on poly(ether sulfone) modified cyanate ester resin and epoxy resin cocuring blends

Poly(ether sulfone) terminated with phenolic hydroxyl groups modified cyanate ester resin and epoxy resin cocuring blends were investigated by differential scanning calorimetry, Fourier transform infrared spectroscopy, scanning electron microscopy, rheometry, and mechanical properties measurement. The results suggested that poly (ether sulfone) (PES) could accelerate the polycyclotrimerization reaction of cyanate ester and cocuring processes between cyanate ester and epoxy of modified blends because of the presence of phenolic hydroxyl groups at the end of the PES molecules. It was found that the evolution of the morphologies and complex viscosities of the modified blends sensitive to molecular weight and content of PES, the tensile strength and elongation at break of the modified blends were correlated with the morphologies of modified blends. Moreover, the evolution of complex viscosities of the modified blends also showed an exponential growth at the early stage of phase separation, which demonstrated experimentally that the coarsening processes of droplets of bisphenol‐A dicyanate and diglycidyl ether of bisphenol A and the final morphologies obtained in the blends modified with PES were affected by viscoelastic behavior. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Phase separation behavior of poly(ether imide)/N,N‐dimethyl acetamide/nonsolvent systems

The phase separation behavior of a poly(ether imide) (PEI)/N,N‐dimethyl acetamide (DMAc)/nonsolvent system was investigated. Three kinds of nonsolvents were used in the study: H₂O, ethanol, and acetic acid (AA). It was found that the three systems (PEI/DMAc/H₂O, PEI/DMAc/ethanol, and PEI/DMAc/AA) agree with the linearized cloud point (LCP) relation. The binodal lines of the three systems were calculated according to the LCP relation. The binodal line of the PEI/DMAc/(H₂O + DMAc) system was also calculated according to the LCP relation of the PEI/DMAc/H₂O system. The phase separation of the PEI/DMAc/(H₂O + AA) system was studied, and the results agree with the LCP relation. These results can offer useful information for the establishment of dope and coagulation media using for the fabrication of a PEI membrane. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 875–881, 2003     

端羟基聚丁二烯改性氰酸酯体系固化反应动力学

采用示差扫描量热法(DSC)研究了端羟基聚丁二烯(HTPB)改性双酚A型氰酸酯树脂(BADCy)体系的固化反应动力学,根据Arrhenius方程对固化过程动力学参数进行了求解,建立了固化反应动力学模型。结果表明,随着HTPB含量的增大,动态DSC固化反应放热峰向低温方向移动,说明HTPB可以催化固化反应并降低体系的反应温度。纯BADCy和BADCy/15%HTPB体系等温固化符合自催化反应模型。纯BADCy体系以及BADCy/15%HTPB体系的表观反应活化能分别为59.67 kJ/mol、56.91 kJ/mol。     

环氧树脂改性双马来酰亚胺/氰酸酯树脂固化工艺研究

采用差示扫描量热(DSC)法和红外光谱(FT-IR)法对缩水甘油胺型环氧树脂(AG-80)与脂环族缩水甘油酯型环氧树脂(TDE-85)共同改性双马来酰亚胺(BMI)/氰酸酯树脂(CE)的固化反应历程进行了研究,并按照Kissinger和Crane法计算出该改性树脂体系固化反应的动力学参数。结果表明:改性树脂体系的固化反应表观活化能为68.11 kJ/mol,固化反应级数为0.860(接近于1级反应);环氧树脂(EP)可促进CE固化,当固化工艺条件为"150℃/3 h→180℃/2 h"时,改性树脂体系可以固化完全。     

Morphology profiles obtained by reaction‐induced phase separation in epoxy/polysulfone/poly(ether imide) systems

The reaction‐induced phase separation in epoxy/aromatic diamine formulations simultaneously modified with two immiscible thermoplastics (TPs), poly(ether imide) (PEI) and polysulfone (PSF), has been studied. The epoxy monomer was based on the diglycidyl ether of bisphenol A (DGEBA) and the aromatic diamine was 4,4′‐methylenebis(3‐chloro 2,6‐diethylaniline) (MCDEA). Phase‐separation conversions are reported for various PSF/PEI proportions for blends containing 10 wt% total TP. On the basis of phase‐separation results, a conversion–composition phase diagram at 200 °C was compiled. This diagram was used to design particular cure cycles in order to generate different morphologies during the phase‐separation process. It was found that, depending on the PSF/PEI ratio employed, a particulate or a morphology characterized by a distribution of irregular PEI‐rich domains dispersed in an epoxy‐rich phase was obtained for initially miscible blends. Scanning electron microscopy (SEM) characterization revealed that the PEI‐rich phase exhibits a phase‐inverted structure and the epoxy‐rich matrix presents a bimodal size distribution of TP‐rich particles. For PSF/PEI ratios near the miscibility limit, slight temperature change result in morphology profiles. Copyright © 2005 Society of Chemical Industry     

氮化硼粒子增强氰酸酯树脂基复合材料的研究

在玻璃布增强氰酸酯树脂（CE）基复合材料中加入氮化硼(BN)粒子,制得CE/玻璃布/BN复合材料。研究了BN粒子含量对复合材料性能的影响。结果表明,经偶联剂处理的BN粒子使体系凝胶时间缩短,反应活性略有提高。BN粒子的加入可以明显提高复合材料的弯曲强度和层间剪切强度,在BN加入量为8 %时,复合材料的弯曲强度和层间剪切强度达到最大值,分别提高了5 %和36 %。加入BN粒子后,复合材料的起始热分解温度都较未填充体系有所提高,耐热指数升高,热稳定性相应提高。     

Viscoelastic phase separation in soft matter: Numerical-simulation study on its physical mechanism

Viscoelastic phase separation is a new type of phase separation, which may be universal to any dynamically asymmetric mixture composed of slow and fast components. Dynamic asymmetry can arise from (i) a large size disparity between the components and (ii) a large difference in glass-transition temperature. Origin (i) often exists in the so-called soft matter, while origin (ii) can exist in any material including oxide, metallic, and molecular glass formers. For case (i), phase separation generally leads to the formation of a long-lived “interaction network” (transient gel) of the slow components, if the concentration is high enough and attractive interactions between them are strong enough. This new type of phase separation allows us to form a network structure of the minority slow-component-rich phase, contrary to the conventional wisdom on phase separation. This has a significant technological impact on the morphological control of multi-phase materials. Here we review our numerical simulation studies on viscoelastic phase separation. Effects of transient gelation on phase-separation kinetics are studied by numerical simulations based on the coarse-grained two-fluid model. We find that the bulk mechanical stress originating from connectivity of the slow components of a mixture plays a crucial role in pattern evolution of viscoelastic phase separation. We also discuss how we can control the phase-separation morphology by controlling the viscoelastic properties of component materials. This coarse-grained model cannot describe how a transient gel itself is formed. Thus, to study the formation process of a transient gel in colloidal suspensions, we develop a new simulation method (“fluid particle dynamics (FPD) method”), which can properly treat interparticle hydrodynamic interactions. This new method can be applied to various fields of colloidal science, where hydrodynamic interactions play important roles. Our FPD simulations of colloidal aggregation clearly indicate that hydrodynamic interactions play crucial roles in the formation of a transient gel. We emphasize that the percolation threshold is crucially affected by hydrodynamic interactions. We point out that viscoelastic phase separation should be universally observed in not only polymer solutions and mixtures but also colloidal suspensions, emulsions, and protein solutions.     

氰酸酯树脂增韧改性研究进展

主要介绍了氰酸酯(CE)树脂的增韧机制,综合分析了国内外CE树脂的增韧改性研究成果(包括热固性树脂改性CE、热塑性树脂改性CE、橡胶弹性体改性CE和纳米无机材料改性CE等),并对CE树脂的发展前景进行了展望。     

Polymerization induced phase separation in poly(ether imide)-modified epoxy resin cured with imidazole

This paper studies the phase separation in poly(ether imide) (PEI) modified epoxy resin using imidazole (C₁₁Z-CNS) as epoxy hardener to control its morphology. The sponge-like phase structures were founded at higher PEI concentration (10-25 phr), while homogeneous structures are formed at low PEI concentration (5 phr). The effects of PEI concentration on curing kinetics and phase structures were studied by differential scanning calorimeters (DSC) and scanning electron microscopy (SEM). It is shown that although the addition of PEI does not change the curing mechanism, the separated morphology becomes finer at high PEI concentration. The curing rate and conversion decrease with the increase of the content of PEI. The chain growth polymerization of these systems caused an early gelation (conversion <10%) and early freezing of morphologies. The evolution of phase separation in the early stage was monitored by synchrotron radiation small angle X-ray scattering (SR-SAXS) and transmission electronic microscopy (TEM). It is suggested that the formation of sponge-like phase structure could be attributed to the strong viscoelastic effects in the early stage of phase separation.     

Biobased nanocomposites from clay modified blend of epoxidized soybean oil and cyanate ester resin

Novel bio-based nanocomposites were prepared by blending surface modified natural clay with epoxidized soybean oil (ESO) and cyanate ester resin (CE). A convenient method was employed to modify the attapulgite (ATT) clay by adsorbing the poly(ethylene glycol) diglycidyl ether (PEGDE) onto the clay surface, which was confirmed by the appearance of a new peak of infrared spectroscopy due to hydrogen bonding and chelation. Thermogravimetic analysis (TGA) showed that the amount of PEGDE adsorbed on ATT was influenced by PEGDE concentration in acetone solution. Scanning electron microscope (SEM) and transmission electron microscope (TEM) results showed that nanoscaled ATT dispersed well in the blend of epoxidized soybean oil (ESO) before and after curing. The thermal-physical and mechanical properties were evaluated by dynamic mechanical analysis (DMA), TGA and tensile mechanical test. The nanocomposites showed higher glass transition temperature and modulus, and the tensile strength of the nanocomposites was reinforced as compared to that of ESO/CE blends.     

Mechanisms of moisture absorption by cyanate ester modified epoxy resin matrices: the clustering of water molecules

One of the important factors, which determine the concentration of moisture that a polymer will absorb, is the effect of non-random mixing whereby water-clustering is said to occur. The Flory-Huggins theory cannot predict the isotherms observed for highly polar polymers since the theory assumes complete random mixing. The complementary model of Brown [Brown GL. In: Rowland SP, editor. Water in polymers. Washington, DC: American Chemical Society; 1980. p. 441. [1]] considers the moisture distribution in polar polymers, consists of components associated with random mixing (Flory-Huggins theory) and clustering of the water molecules. Moisture sorption isotherms of cyanate ester/epoxy blends at different relative humidities have been analysed by the clustering theory of Brown [Brown GL. In: Rowland SP, editor. Water in polymers. Washington, DC: American Chemical Society; 1980. p. 441. [1]] and the dual mode sorption theory of Zimm [Zimm BH. J Chem Phys 1953;21:934. [2]]. Clustering was found to occur in cyanate ester/epoxy blends conditioned at relative humidities of 40% and higher. The Cluster size indicates that the majority of the absorbed water in a cured cyanate ester/epoxy blend was not clustered but present in monomeric form through hydrogen bonding to polar sites. It is postulated that the phenomenon of thermal spiking enhanced moisture absorption can be explained by an equilibrium between cluster formation and declustering associated with network relaxation at the spike-temperature.     

环氧树脂改性氰酸酯树脂固化体系研究

采用差示扫描量热(DSC)法对脂环族环氧树脂(L2)改性双酚A型氰酸酯树脂(CE)的固化反应历程进行了研究,并探讨了L2用量对CE耐热性能和粘接强度等影响。结果表明:L2对CE的固化反应具有催化作用,但当w(L2)≥30%时,其催化效果因稀释作用而降低;纯CE和CE/L2体系在等温(210℃)固化反应过程中,其转化率在起始反应10 min内分别达到80%和91%左右;当w(L2)=10%时,CE/L2改性体系的拉伸剪切强度(22.80 MPa)和压缩剪切强度(44.40 MPa)较高,同时其耐热性能较好。     

Microphase separation in amorphous poly(imide siloxane) segmented copolymers

A series of amorphous poly(imide siloxane) (PIS) segmented copolymers with various segmental lengths and contents of poly(dimethyl siloxane) (PDMS) were synthesized by condensation polymerization. Extraction was utilized to obtain highly pure PISs for a study of phase separation. The PISs self-assemble from dilute solutions that are initially rod-like structures and then rapidly transform to vesicles. Moreover, the vesicles change to solid spheres as the PDMS content increases. A variety of morphologies of the PIS films, including unilamellar vesicle, multilamellar vesicle, sea-island and others, are found as a function of the content and the segmental length of PDMS. Small angle X-ray scattering demonstrates the coexistence of large-scale phase separations and nano-scale phase separations of approximately 20 nm. The DSC results reveal that the phase separation is induced and dominated by the aggregation of PDMS segments. Furthermore, the surfaces of the hard phases in the PDMS-900 PISs are found to be fractal.     

Effects of molecular weight of polysulfone on phase separation behavior for cyanate ester/polysulfone blends

The effects of molecular weight of polysulfone (PSF) on the morphology of bisphenol‐A dicyanate (BADCy)/PSF blends were studied. Because the viscosity of the blend increased and the miscibility between BADCy and PSF decreased with the increase of PSF molecular weight, these two competing effects on the phase‐separation were investigated. It was observed that the effect of viscosity was predominant: the viscosity of the blends at the onset point of phase separation increased with the increase of PSF molecular weight. The phase separation mechanism depends on the viscosity of the blends at the onset point of phase separation and determines the morphology of the blends. Because the increasing viscosity with increasing the molecular weight of PSF suppressed the nucleation and growth even with 10 phr of PSF content, phase separation occurred through spinodal decomposition to form the combined morphology having both PSF particle structure and BADCy particle structure. The combined morphology and the BADCy particle structure were obtained with a smaller amount of high molecular weight PSF content. This indicates that the viscosity of the blends at the onset point of phase separation is the critical parameter that determines the morphology of the blends. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 921–927, 2000     

Moisture absorption by cyanate ester modified epoxy resin matrices. Part I. Effect of spiking parameters

The moisture absorption of cyanate ester modified epoxy resin matrices has been studied under thermal spiking conditions. Enhanced moisture absorption has been observed at spike-temperatures above 120 °C. The results of the desorption studies on both control specimens and the spiked specimens showed that some of the water molecules remained entrained in the polymer. It is postulated that this water could be associated with that which is hydrogen bonded or from the hydrolysis of isolated residual cyanate ester groups because the concentration of entrained water remains constant at spike-temperatures below 180 °C. Above 180 °C a thermally activated process, leading to chain scission as indicated by a reduced recoverability of the glass transition temperature (T_g) on drying.On isothermal resorption, the moisture concentration was found to be similar to that achieved through thermal spiking, showing that the entrained water at the lower spike-temperatures can also be achieved under mild conditions. The T_g is reversibly recovered to within 5 °C, which indicates a degree of relaxation rather than degradation. The moisture diffusion coefficient estimated from the resorption curves is lower than those estimated from the absorption and desorption curves. The isothermal resorption diffusion coefficient also decreased with increasing spike temperature. It is proposed that thermal spiking induced a relaxation of the network but as the spike-temperature approaches the transition region of the wet polymer, further hydrolytically induced relaxation events become feasible.     

Stretching induced phase separation in poly(vinylidene fluoride)/poly(butylene succinate) blends studied by in-situ X-ray scattering

The structure evolution of poly(vinylidene fluoride)/poly(butylene succinate) (PVDF/PBS) blends during stretching above the melting point of PBS is investigated by synchrotron-based simultaneous wide angle and small angle X-ray scattering (WAXS/SAXS). Before stretching, PVDF crystallizes into the α-form, whereas the chains of molten PBS locate at the inter-lamellar amorphous phase of PVDF. Crystal transition from α to β of PVDF is observed in all samples during stretching. The morphological transformation from a lamellar structure into a fibrillar structure occurs at low and intermediate strains. With further deformation, a “stretching induced phase separation” phenomenon is observed. The final microstructure of PVDF/PBS blends contains PVDF microfibrils with PBS chains preferentially distributed in the inter-fibrillar region. The PBS molecular weight influences the onset and end strain for the transition. A new “two-step model” is proposed to describe the deformation process.     

Morphology and properties of foamed high crystallinity PEEK prepared by high temperature thermally induced phase separation

Polyetheretherketone (PEEK) is a high-performance semi-crystalline thermoplastic polymer with outstanding mechanical properties, high thermal stability, resistance to most common solvents, and good biocompatibility. A high temperature thermally induced phase separation technique was used to produce PEEK foams with controlled foam density from PEEK in 4-phenylphenol (4PPH) solutions. Physical and mechanical properties, foam and bulk density, surface area, and pore morphology of foamed PEEK were characterized and the role of PEEK concentration and cooling rate was investigated. Porous PEEK with densities ranging from 110 to 360 kg/m³ with elastic moduli and crush strength ranging from 13 to 125 MPa and 0.8 to 7 MPa, respectively, was produced.