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     

Structure development via reaction-induced phase separation in tetrafunctional epoxy/polysulfone blends

For the cure process of tetrafunctional epoxy resin/polysulfone(EP/PSF) blends, we investigated the effect of cure temperature and blend composition on the phase separation behavior by light scattering and the structure development during cure by an optical microscope. The EP/PSF blend without the curing agent was shown to exhibit an LCST-type phase behavior (LCST = 241°C). At the early stage of curing, the EP/PSF blend was homogeneous at the cure temperature. As the cure reaction proceeded, the blend was thrust into a two-phase regime by the LCST depression caused by the increase in a molecular weight of the epoxy-rich phase, and the phase separation took place via a spinodal decomposition (SD) or nucleation and growth (NG) mode, depending on the blend composition and the cure temperature. When cured isothermally at 220°C, the blend exhibited a sea-island morphology formed via the NG mode below 5 wt % PSF content, while the SD mode prevailed above 20 wt % PSF content. At the intermediate composition range, combined morphology with both sea-island and cocontinuous structure was observed. On the other hand, by lowering the cure temperature and/or increasing the content of PSF component, a two-phase structure with a shorter periodic distance was obtained. It seems that the rate of the phase separation is considerable reduced, while that of the cure reaction is not as much. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 2233–2242, 1997     

Cure reaction and phase separation behavior of cyanate ester‐cured epoxy/polyphenylene oxide blends

The cure reaction and phase separation mechanism of a cyanate ester‐cured epoxy and its blends with polyphenylene oxide (PPO) were studied. An autocatalytic mechanism was observed for the epoxy and its blends. The reaction rate of the blends was higher than that of the neat epoxy at initial stage; however, the reached conversion decreased with PPO content. FTIR analysis revealed that the cyanate functional group reactions were accelerated by adding PPO and indicated that several coreactions have occurred. This was caused by the reaction of cyanate ester with the PPO reactive chain ends. But at a later stage of cure, the reaction could not progress further due to diffusional limitation of PPO. To understand the relationship between the cure kinetics and phase separation of the blends, the morphology of the blends during cure was examined. When the homogeneous epoxy/PPO blends with low PPO content (10 phr) were cured isothermally, the blends were separated by nucleation and growth (NG) mechanism to form the PPO particle structure. But at high PPO content (30 phr), the phase separation took place via spinodal decomposition (SD). SD is favored near critical concentration and high cure rate system. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102:1139–1145, 2006     

Effects of the cure cycle and thermoplastic content on the final properties of dicyanate ester/polysulfone Semi‐IPNS

A bisphenol A dicyanate resin, BADCy, was toughened by incorporating polysulfone, PSU, at various compositions. The catalyst system used was a mixture of copper acetylacetonate and nonylphenol. Phase separation and rheokinetics were studied through curing. The blends seemed to have a LCST behavior, and the presence of PSU did not affect the polycyclotrimerization kinetics. The phase structure, thermal, and mechanical properties of the final network were investigated as a function of the PSU content and cure temperature. The toughness of the BADCy/PSU blends was closely related to their final morphology, increasing with the amount of phase inversion. The mechanical properties were not affected by the addition of the thermoplastic. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1799–1809, 2002     

Viscoelastic effects on the phase separation in thermoplastics modified cyanate ester resin

A high temperature thermosetting bisphenol-A dicyanate, BADCy was blended with a thermoplastic poly(ether imide) (PEI). The phase separation behavior of the blend was investigated by scanning electron microscopy (SEM) and time resolved light scattering (TRLS). It was found by SEM that the blend with 20 and 25 wt% PEI had a phase inversion structure. The results of TRLS displayed clearly that the phase separation took place according to a spinodal decomposition (SD) mechanism and the evolution of both scattering vector q_m and the maximum scattering intensity I_m followed Maxwell-type relaxation equation. The temperature-dependent relaxation time τ for the blends can be described by the Williams-Landel-Ferry equation. It demonstrated experimentally that the phase separation behaviors in PEI/BADCy blends were affected by viscoelastic effect.     

Phase separation,cure kinetics,and morphology of epoxy/poly(vinyl acetate) blends

Epoxy based on diglycidyl ether of bisphenol A + 4,4′diaminodiphenylsulfone blended with poly(vinyl acetate) (PVAc) was investigated through differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA) and environmental scanning electron microscopy (ESEM). The influence of PVAc content on reaction induced phase separation, cure kinetics, morphology and dynamic‐mechanical properties of cured blends at 180°C is reported. Epoxy/PVAc blends (5, 10 and 15 wt % of PVAc content) are initially miscible but phase separate upon curing. DMTA α‐relaxations of cured blends agree with T_g results by DSC. The conversion‐time data revealed the cure reaction was slower in the blends than in the neat system, although the autocatalytic cure mechanism was not affected by the addition of PVAc. ESEM showed the cured epoxy/PVAc blends had different morphologies as a function of PVAc content: an inversion in morphology took place for blends containing 15 wt % PVAc. The changes in the blend morphology with PVAc content had a clear effect on the DMTA behavior. Inverted morphology blends had low storage modulus values and a high capability to dissipate energy at temperatures higher than the PVAc glass‐transition temperature, in contrast to the behavior of neat epoxy and blends with a low PVAc content. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1507–1516, 2007     

Thermally induced phase separation in liquid crystalline polymer/polycarbonate blends

Thermally induced phase separation in liquid crystalline polymer (LCP)/polycarbonate (PC) blends was investigated in this study. The LCP used is a main‐chain type copolyester comprised of p‐hydroxybenoic acid and 6‐hydroxy‐2‐naphthoic acid. Specimens for microscopic observation were prepared by melt blending. The specimens were heated to a preselected temperature, at which they were held for isothermal phase separation. The preselected temperatures used in this study were 265, 290, and 300°C. The LCP contents used were 10, 20, and 50 wt %. These parameters corresponded to different positions on the phase diagram of the blends. The development of the phase‐separated morphology in the blends was monitored in real time and space. It was observed that an initial rapid phase separation was followed by the coarsening of the dispersed domains. The blends developed into various types of phase‐separated morphology, depending on the concentration and temperature at which phase separation occurred. The following coarsening mechanisms of the phase‐separated domains were observed in the late stages of the phase separation in these blends: (i) diffusion and coalescence of the LCP‐rich droplets; (ii) vanishing of the PC‐rich domains following the evaporation‐condensation mechanism; and (iii) breakage and shrinkage of the LCP‐rich domains. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Effect of different curing systems on heat shrinkability and mechanical properties of ethylene vinyl acetate/epoxidized natural rubber blends

Ethylene vinyl acetate (EVA)/epoxidized natural rubber (ENR) blends containing 10 and 30 wt % ENR were prepared by using an internal mixer. Five different types of curing systems were employed: dicumyl peroxide (DCP), sulfur (S), phenolic resin (Ph), DCP + S, and DCP + Ph. DCP could crosslink with both EVA and ENR while S and Ph were curing agents for ENR. The DCP system provided the lowest tensile properties and tear strength because of low crosslinking in ENR phase. Addition of sulfur or phenolic resin increased the mechanical properties due to a better vulcanization of the rubber phase. The mechanical properties of the blends decreased with increasing ENR content. The rubber particle size in the blends containing 30% ENR played a more important role in the mechanical properties than the blends containing 10% ENR. ENR particle size did not affect heat shrinkability of EVA and a well vulcanized rubber phase was not required for high heat shrinkage. Furthermore, heat shrinkage of the blends slightly changed as the ENR content increased for all curing systems. With regard to the mechanical properties and heat shrinkability, the most appropriate curing system was DCP + Ph and in the case the 10 wt % ENR content produced a more favorable blend. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Morphology and thermal behavior of dicyanate ester‐polyetherimide semi‐IPNS cured at different conditions

A high‐temperature thermosetting bisphenol‐A dicyanate, BADCy was modified with polyetherimide, PEI, at various compositions. Phase separation and rheokinetics through curing were studied by optical microscopy, dynamic and isothermal differential scanning calorimetry, and rheological measurements. The PEI phase separated at the early stages of curing, well before gelation, and did not affect the polycyclotrimerization kinetics. The phase structure and thermal properties of the final network were investigated as a function of the PEI content and cure temperature. For this purpose, dynamic mechanical analysis, scanning electron microscopy studies, and thermogravimetrical analysis were carried out. The morphological changes were interpreted in terms of a spinodal decomposition mechanism in the composition range studied. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1037–1047, 2000     

Epoxy and hyperbranched polymer blends: Morphology and free volume

In this work, the phase separation of an epoxy‐functionalized hyperbranched polymer (HBP) in a blend with a conventional epoxy resin is examined. Morphology development with the advancement of curing reaction was investigated by hot‐stage polarized optical microscope, where it was found that HBP is miscible in epoxy resin solvent at 120°C and undergoes phase separation during the curing reaction, leading to a two‐phase microstructure which maintains a dispersed morphology up to 20 wt % HBP. The degree of phase separation and morphology were also investigated using differential scanning calorimetry, and the resultant microstructure was confirmed by atomic force microscopy. The epoxy/HBP blends were characterized by positron annihilation lifetime spectroscopy for their free volume characteristics where behavior typical of miscible blends was seen, likely due to chemical bonding between the two phases. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Phase separation of unsaturated polyester resin blended with poly(vinyl acetate)

The behavior of phase separation during the curing reaction of unsaturated polyester (UPE) resin in the presence of low profile additive, that is, poly(vinyl acetate) (PVAc), was studied by low-angle laser light scattering (LALS) and scanning electron microscopy (SEM). The experimental results revealed that the PVAc-rich phase was regularly dispersed in the cured styrene–UPE matrix for styrene–UPE resin blended with 5 wt % of PVAc. As the PVAc content was increased higher than 10 wt %, a cocontinuous PVAc and cured styrene–UPE phase was observed for the cured systems. The LALS observations were carried out in situ at a curing temperature of 100°C; thus, the effect of the rate of exothermic heat released from curing reaction on the morphology of curing system was investigated and reported in this work. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 2413–2428, 1999     

Dynamic mechanical properties and morphology of poly(benzyl methacrylate)/epoxy thermoset blends

Poly(benzyl methacrylate) (PBzMA)/epoxy thermoset blends of composition 5 to 25 wt% of PBzMA were prepared curing with 4,4′diaminodiphenylmethane (DDM), to study the influence of composition on the morphology and dynamic‐mechanical properties of the blends. The cured blends are phase separated in PBzMA‐rich phase and epoxy rich‐phase. As the PBzMA content increases, the morphology evolves from nodular, to combined and to totally inverted. The analysis of the α‐mechanical relaxations indicates that the glass transition temperatures (T_g) of PBzMA and of epoxy in the blends are different from the neat polymers, this is related to a noncomplete phase separation on curing. The profiles of the loss modulus‐temperature curves are correlated with the change in morphology that appears increasing the PBzMA content. The storage modulus‐temperature curves are highly dependent on the morphology of the samples. The storage modulus‐composition dependence is predicted using several models for two phase composites. POLYM. ENG. SCI., 50:1820–1830, 2010. © 2010 Society of Plastics Engineers     

Reactive compatibilization of the polyamide 6/poly(phenylene oxide) blend by means of styrene–maleic anhydride copolymer

The compatibilization of the polymer blend polyamide 6/poly(phenylene oxide) (PA-6/PPO) system has been studied using the reactive random copolymer styrene–maleic anhydride (SMA) as a compatibilizer precursor. SMA is miscible with PPO when the MA content of SMA is not higher than 8 wt %. The anhydride groups of SMA react with the amino end groups of PA-6 during melt blending to form a graft copolymer at the interface with a compatibilizing effect as a result. Two different blending procedures were compared to each other and the compatibilizing effect of the added SMA was evaluated for a matrix/dispersed particle type of morphology. The effect of the different material parameters such as the functionality of SMA (wt % MA in SMA) and the molecular weight of PA-6, and blending parameters such as the extrusion time was analyzed with respect to the blend phase morphology. Finally, the amount of reacted MA groups in the blends PA-6/(PPO/SMA) was determined with FTIR after the use of an extraction method to remove the PA-6 matrix phase. The comparison between the morphological data (particle size reduction of the dispersed PPO/SMA phase) and the FTIR data (amount of reacted MA groups) of the blends considered, turned out to be very logical. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 889–898, 1999     

Influence of 1,5‐naphthalenediamine on thermomechanical properties of epoxy/copolyethersulphone blends

The use of 1,5‐naphthalenediamine (ND) as curing agents for epoxy blends was studied. The epoxy monomer was a standard diglycidyl ether of bisphenol A while as modifier a laboratory made copolyethersulphone (coPES) was considered. The coPES was added at three percentages: 10, 20, and 30% wt. The stiff structure of ND increased both viscosity and glass transition temperature of the blends. The blends cured by ND showed higher viscosity compared to resins cured by 3,3′‐diammino diphenylsulfone or 4,4′‐methylenebis(2,6‐diethylaniline). Blends with higher coPES content (20 and 30% wt) showed viscosity fluctuation suggesting phase separation initiation but the combination of high viscosity and reactivity hindered the demixing process. This effect resulted in single glass transition for all formulations confirming the absence of phase separation. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers     

Cure kinetics,phase behaviors,and fracture properties of bismaleimide resin toughened by poly(phthalazinone ether ketone)

Poly(phthalazinone ether ketone)s (PPEK) were used to toughen bismaleimide (BMI) resin composed of 4,4′‐bismaleimidodiphenyl methane (BMDM) and O,O′‐diallyl bisphenyl A (DABPA). Dynamic differential scanning calorimetry (DSC) of the blends was carried out for kinetic analysis of the curing reaction. The reaction activation energy indicated that the reaction mechanism remained the same even after the incorporation of PPEK. The reaction‐induced phase separation process in BMI/PPEK blends was investigated by optical microscopy (OM). The primary phase structure of the blends was fixed at the early stage of phase separation, and a secondary phase separation was observed as a result of the high viscosity of the blends. Scanning electron microscope (SEM) graphs showed that the morphology of the cured resin changed from a dispersed structure to a phase‐inverted structure with the increase of PPEK content. Compared with the neat resin, the fracture toughness of the modified resin exhibits a moderate increase when PPEK was incorporated. Several toughening mechanisms, such as local plastic deformation, crack deflection, and branches, presumably took part in improving the toughness of BMI/PPEK blends on the basis of the morphology. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Cure kinetics and morphology of blends of epoxy resin with poly (ether ether ketone) containing pendant tertiary butyl groups

The cure kinetics and morphology of diglycidyl ether of bisphenol-A (DGEBA) epoxy resin modified with a poly (ether ether ketone) based on tertiary butyl hydroquinone (PEEK-T) cured with diamino diphenyl sulphone (DDS) were investigated using differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and dynamic mechanical thermal analysis (DMTA). The results obtained from DSC were applied to autocatalytic and diffusion controlled kinetic models. The reaction mechanism broadly showed autocatalytic behaviour regardless of the presence of PEEK-T. At higher PEEK-T concentration, more diffusion controlled mechanism was observed. The rate of curing reaction decreased with increase in thermoplastic content and also with the lowering of curing temperature. The activation energies of the blends are higher than that of the neat resin. The blends showed a phase separated morphology. The dispersed phase showed a homogeneous particle size distribution. The T_g of the neat resin decreased with the decrease in cure temperature. Two T_g's corresponding to the epoxy rich and thermoplastic rich phases were observed in the dynamic mechanical spectrum. The storage modulus of 10 and 20 phr PEEK-T blends are found to be greater than the neat resin.     

Investigation on particular morphology of immiscible polyamide 12/polystyrene blends

In this article, a particular phase morphology of immiscible polyamide 12/polystyrene (PA12/PS) blends prepared via in situ anionic ring-opening polymerization of Laurolactam (LL) in the presence of PS was investigated. SEM and FTIR were used to analyze the morphology of the blends. The results showed that PS is dispersed as small droplets in the continuous matrix of PA12 when PS content is less than 5 wt %. When the PS content is higher than 10 wt %, two particular phase morphologies appeared. First, dispersed PS-rich particles with the spherical inclusions of PA12 can be found when PS content is between 10 wt % and 15 wt %. Then, the phase inversion (the phase morphology of the PA12/PS blends changes from the PS dispersed/PA12 matrix to PA12 dispersed/PS matrix system) occurred when PS content is higher than 20 wt %, which is completely different from traditional polymer blends prepared by melt blending. The possible reason for the particular morphology development was illuminated through phase inversion mechanism. Furthermore, the stability of the phase morphologies of the PA12/PS blends was also investigated. SEM showed that the particular morphology is instability, and it will be changed upon annealing at 230°C for 30 min. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

聚醚酰亚胺/环氧树脂体系的固化及相分离行为研究

环氧树脂固化物本征的低韧性是限制其在复合材料应用的主要缺点之一。利用高性能热塑性树脂聚醚酰亚胺(PEI)与环氧树脂共混,系统研究了PEI在环氧树脂中的溶解行为、固化行为以及相分离行为。溶解试验表明:PEI与环氧齐聚物具有良好的相互溶解性;同时,PEI的加入降低了环氧树脂固化反应的活化能,但并没有改变其固化反应的机制。扫描电镜结果显示:随着PEI含量的增加,环氧/PEI浇铸体的相形貌从明显的分散颗粒相结构演变为双连续相结构和反转相结构。     

Reaction induced phase separation in semicrystalline thermoplastic/epoxy resin blends

The phase separation behaviour and phase morphology of blends of 4,4′-diaminodiphenyl sulphone cured diglycidyl ether of bisphenol-A with poly(ε-caprolactone) were investigated by means of scanning electron microscopy, small angle light scattering and optical microscopy. The components are miscible prior to curing. High-temperature isothermal curing induces phase separation. Blends with near to critical concentrations demix via spinodal decomposition. The associated co-continuous morphology is only preserved in the actual critical compositions whereas for off-critical compositions it rapidly breaks up into spherical particles. The proceeding reaction in the separated phases induces a secondary phase separation. Occasionally, tertiary phase separation is observed as well. Off-critical compositions that are further away on either side from the critical point, phase separate via the direct formation of spherical particles, most likely as a result of the dynamic asymmetry of these blends. The influence of the amount, the molar mass of PCL and the cure temperature is discussed.     

Morphology,thermal and mechanical performance of epoxy/polysulfone composites improved by curing with two different aromatic diamines

Epoxy/polysufone (PSF) composites cured with 4,4'-diaminodiphenyl sulfone (DDS) and 4,4'-diaminodiphenyl methane (DDM) were fabricated, and the effect of dual curing reaction of diamines with epoxy on morphology, mechanical, and thermal performance was investigated. DSC results indicated that DDM was more reactive than DDS and the activation energy decreased with the rising of DDM content. Structures with small domain size at the early stage of phase separation were fixed by the fast epoxy-DDM reaction. When the DDM content was elevated to a high level, large dual structures were changed to fine bicontinuous structures, which was favorable to improve the mechanical property. The mechanical performance of epoxy composites was enhanced and the maximum values were achieved when the DDM/DDS ratio was located at 75/25 (PSF/DDS0.25-DDM0.75). The flexural and tensile strength relative to epoxy/DDM system were enhanced more than those relative to epoxy/DDS, while the increase in toughness was the opposite. TGA measurement showed that thermal stability of epoxy/PSF composites was improved because of the restricting effect of continuous PSF domains on thermal motion of epoxy. DMA analysis exhibited two relaxation peaks for PSF/DDS0.25-DDM0.75, which could be attributed to the formation of phase separated morphology and epoxy network with different cross-link density.