Nanostructured thermoset epoxy resin templated by an amphiphilic poly(ethylene oxide)‐block‐poly(dimethylsiloxane) diblock copolymer

An amphiphilic poly(ethylene oxide)‐block‐poly(dimethylsiloxane) (PEO–PDMS) diblock copolymer was used to template a bisphenol A type epoxy resin (ER); nanostructured thermoset blends of ER and PEO–PDMS were prepared with 4,4′‐methylenedianiline (MDA) as the curing agent. The phase behavior, crystallization, hydrogen‐bonding interactions, and nanoscale structures were investigated with differential scanning calorimetry, Fourier transform infrared spectroscopy, transmission electron microscopy, and small‐angle X‐ray scattering. The uncured ER was miscible with the poly(ethylene oxide) block of PEO–PDMS, and the uncured blends were not macroscopically phase‐separated. Macroscopic phase separation took place in the MDA‐cured ER/PEO–PDMS blends containing 60–80 wt % PEO–PDMS diblock copolymer. However, the composition‐dependent nanostructures were formed in the cured blends with 10–50 wt % PEO–PDMS, which did not show macroscopic phase separation. The poly(dimethylsiloxane) microdomains with sizes of 10–20 nm were dispersed in a continuous ER‐rich phase; the average distance between the neighboring microdomains was in the range of 20–50 nm. The miscibility between the cured ER and the poly(ethylene oxide) block of PEO–PDMS was ascribed to the favorable hydrogen‐bonding interaction. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3042–3052, 2006     

Water‐resistant conducting hybrids from electrostatic interactions

Conductive hybrids were prepared in a water/ethanol solution via the sol–gel process from an inorganic sol containing carboxyl groups and water‐borne conductive polyaniline (cPANI). The inorganic sol was prepared by the hydrolysis and condensation of methyltriethoxysilane with the condensed product of maleic anhydride and aminopropyltriethoxysilane as a catalyst, for which the carboxyl counterion along the cPANI backbone acted as an electrostatic‐interaction moiety. The existence of this electrostatic interaction could improve the compatibility of the two components and contribute to the homogeneous dispersion of cPANI in the silica phase. The electrostatic‐interaction hybrids displayed a conductivity percolation threshold as low as 1.1 wt % polyaniline in an emeraldine base, showing 2 orders of magnitude higher electrical conductivity than that without electrostatic interactions. The electrostatic‐interaction hybrids also showed good water resistance; the electrical conductivity with a cPANI loading of 16 wt % underwent a slight change after 14 days of soaking in water. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1424–1431, 2007     

Electrical and optical properties of ceramic–polymer nanocomposite coatings

Transparent, conductive composite coatings were fabricated from suspensions of poly(vinyl acetate‐acrylic) (PVAc‐co‐acrylic) copolymer latices (50–600 nm) and nanosized antimony‐doped tin oxide (ATO) particles (～15 nm). The suspensions were deposited as coatings onto poly(ethylene terephthalate) substrates and dried at 50 °C. Microstructure studies using field emission scanning electron microscopy and tapping‐mode atomic force microscopy (TMAFM) indicated that the latex particles coalesced during drying and forced the ATO particles to segregate into the boundaries between the latex particles. Low phase contrast was observed with TMAFM; this result was consistent with the presence of PVAc‐co‐acrylic in the ATO‐rich phase of the composite. The conductivity of the composite coatings followed a percolation power‐law equation, with the percolation threshold between 0.05 and 0.075 volume fractions of ATO and the critical conductivity exponent ranging from 1.34 to 2.32. The highest direct‐current conductivity of the composite coatings was around 10^?2 S/cm. The optical transmittance and scattering behavior of the coatings were also investigated. Compared with the PVAc‐co‐acrylic coating, the composite coatings had lower transparency because of the Rayleigh scattering. The transparency of the composite coatings was improved by a reduction in the coating thickness. The best transparency for the coatings with a direct‐current conductivity of approximately 10^?2 S/cm was around 85% at a wavelength of 600 nm. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1744–1761, 2003     

Phase behavior,crystallization, and morphology in thermosetting blends of a biodegradable poly(ethylene glycol)‐type epoxy resin and poly(ϵ‐caprolactone)

Thermosetting blends of a biodegradable poly(ethylene glycol)‐type epoxy resin (PEG‐ER) and poly(?‐caprolactone) (PCL) were prepared via an in situ curing reaction of poly(ethylene glycol) diglycidyl ether (PEGDGE) and maleic anhydride (MAH) in the presence of PCL. The miscibility, phase behavior, crystallization, and morphology of these blends were investigated. The uncured PCL/PEGDGE blends were miscible, mainly because of the entropic contribution, as the molecular weight of PEGDGE was very low. The crystallization and melting behavior of both PCL and the poly(ethylene glycol) (PEG) segment of PEGDGE were less affected in the uncured PCL/PEGDGE blends because of the very close glass‐transition temperatures of PCL and PEGDGE. However, the cured PCL/PEG‐ER blends were immiscible and exhibited two separate glass transitions, as revealed by differential scanning calorimetry and dynamic mechanical analysis. There existed two phases in the cured PCL/PEG‐ER blends, that is, a PCL‐rich phase and a PEG‐ER crosslinked phase composed of an MAH‐cured PEGDGE network. The crystallization of PCL was slightly enhanced in the cured blends because of the phase‐separated nature; meanwhile, the PEG segment was highly restricted in the crosslinked network and was noncrystallizable in the cured blends. The phase structure and morphology of the cured PCL/PEG‐ER blends were examined with scanning electron microscopy; a variety of phase morphologies were observed that depended on the blend composition. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2833–2843, 2004     

Polymer electrolyte membranes by in situ polymerization of poly(ethylene carbonate‐co‐ethylene oxide) macromonomers in blends with poly(vinylidene fluoride‐co‐hexafluoropropylene)

Salt‐containing membranes based on polymethacrylates having poly(ethylene carbonate‐co‐ethylene oxide) side chains, as well as their blends with poly(vinylidene fluoride‐co‐hexafluoropropylene) (PVDF‐HFP), have been studied. Self‐supportive ion conductive membranes were prepared by casting films of methacrylate functional poly(ethylene carbonate‐co‐ethylene oxide) macromonomers containing lithium bis(trifluorosulfonyl)imide (LiTFSI) salt, followed by irradiation with UV‐light to polymerize the methacrylate units in situ. Homogenous electrolyte membranes based on the polymerized macromonomers showed a conductivity of 6.3 × 10^?6 S cm^?1 at 20 °C. The preparation of polymer blends, by the addition of PVDF‐HFP to the electrolytes, was found to greatly improve the mechanical properties. However, the addition led to an increase of the glass transition temperature (T_g) of the ion conductive phase by ～5 °C. The conductivity of the blend membranes was thus lower in relation to the corresponding homogeneous polymer electrolytes, and 2.5 × 10^?6 S cm^?1 was recorded for a membrane containing 10 wt % PVDF‐HFP at 20 °C. Increasing the salt concentration in the blend membranes was found to increase the T_g of the ion conductive component and decrease the propensity for the crystallization of the PVDF‐HFP component. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 79–90, 2007     

Electrical conductivity of poly(ethylene terephthalate)/expanded graphite nanocomposites prepared by in situ polymerization

Nanocomposites based on poly(ethylene terephthalate) (PET) and expanded graphite (EG) have been prepared by in situ polymerization. Morphology of the nanocomposites has been examined by electronic microscopy. The relationship between the preparation method, morphology, and electrical conductivity was studied. Electronic microscopy images reveal that the nanocomposites exhibit well dispersed graphene platelets. The incorporation of EG to the PET results in a sharp insulator‐to‐conductor transition with a percolation threshold (?_c) as low as 0.05 wt %. An electrical conductivity of 10^?3 S/cm was achieved for 0.4 wt % of EG. The low percolation threshold and relatively high electrical conductivity are attributed to the high aspect ratio, large surface area, and uniform dispersion of the EG sheets in PET matrix. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Volume‐exclusion effects in polyethylene blends filled with carbon black,graphite, or carbon fiber

Conductive polymer composites possessing a low percolation‐threshold concentration as a result of double percolation of a conductive filler and its host phase in an immiscible polymer blend afford a desirable alternative to conventional composites. In this work, blends of high‐density polyethylene (HDPE) and ultrahigh molecular weight polyethylene (UHMWPE) were used to produce ternary composites containing either carbon black (CB), graphite (G), or carbon fiber (CF). Blend composition had a synergistic effect on electrical conductivity, with pronounced conductivity maxima observed at about 70–80 wt % UHMWPE in the CB and G composites. A much broader maximum occurred at about 25 wt % UHMWPE in composites prepared with CF. Optical and electron microscopies were used to ascertain the extent to which the polymers, and hence filler particles, are segregated. Differential scanning calorimetry of the composites confirmed that the constituent polymers are indistinguishable in terms of their thermal signatures and virtually unaffected by the presence of any of the fillers examined here. Dynamic mechanical analysis revealed that CF imparts the greatest stiffness and thermal stability to the composites. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1013–1023, 2002     

Synthesis of a novel block copolymer poly(ethylene oxide)‐block‐poly(4‐vinylpyridine) by combination of anionic ring‐opening and controllable free‐radical polymerization

The block copolymer poly(ethylene oxide)‐b‐poly(4‐vinylpyridine) was synthesized by a combination of living anionic ring‐opening polymerization and a controllable radical mechanism. The poly(ethylene oxide) prepolymer with the 2,2,6,6‐tetramethylpiperidinyl‐1‐oxy end group (PEO_T) was first obtained by anionic ring‐opening polymerization of ethylene oxide with sodium 4‐oxy‐2,2,6,6‐tetramethylpiperidinyl‐1‐oxy as the initiator in a homogeneous process. In the polymerization UV and electron spin resonance spectroscopy determined the 2,2,6,6‐tetramethylpiperidinyl‐1‐oxy moiety was left intact. The copolymers were then obtained by radical polymerization of 4‐vinylpyridine in the presence of PEO_T. The polymerization showed a controllable radical mechanism. The desired block copolymers were characterized by gel permeation chromatography, Fourier transform infrared, and NMR spectroscopy in detail. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 4404–4409, 2002     

Grafting of polycaprolactone onto poly(ethylene‐co‐vinyl alcohol) and application to polyethylene‐based bioerodable blends

Poly(ethylene‐co‐vinyl acetate) (EVA) powders containing 10 and 20 wt % of vinyl acetate (VAc) units was saponified in ethanol/KOH solution in a heterogeneous manner. Intermolecular interaction between vinyl alcohol(VOH) units in the produced poly(ethylene‐co‐vinyl alcohol) (EVOH) promoted the crystallization of intervening segments composed of ethylene units. Ring opening polymerization of caprolactone (CL) in the presence of EVOH gave EVOH‐g‐PCL graft copolymers with relatively short chain branches. Even though the graft copolymerization was carried out in a homogeneous solution, all the VOH units were not equally reactive for the PCL grafting. And the unreacted VOH units decreased very slowly with the graft copolymerization time. EVOH‐g‐PCL decreased the domain size of the dispersed phase in low density polyethylene (PE)/biodegradable master batch (MB) blends, and thus increased their tensile properties significantly. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2561–2569, 2002     

Solvent‐ and interface‐induced surface segregation in blends of isotactic polypropylene with poly(ethylene‐co‐propylene) rubber

The surface compositions and morphologies of melt‐quenched blends of isotactic polypropylene (iPP) with aspecific poly(ethylene‐co‐propylene) rubber (aEPR) were characterized by atomic force microscopy, optical microscopy, and X‐ray photoelectron spectroscopy. The surface morphologies and compositions formed in the melt are frozen‐in by crystallization of the iPP component and, depending on the processing conditions, are enriched in iPP or aEPR or contain a phase‐separated mix of iPP and aEPR. Enrichment of iPP is observed for blends melted in open air, in agreement with earlier work showing the high surface activity of atactic polypropylene at open interfaces. Surface segregation of iPP is suppressed at confined interfaces. Blends melt‐pressed between hydrophilic and hydrophobic substrates have phase‐separated iPP and aEPR domains present at the surface, which grow in size as the melt time increases. Surface enrichment of aEPR is observed after exposing melt‐pressed blends to n‐hexane vapor, which preferentially solvates aEPR and draws it to the surface. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 421–432, 2004     

Enhanced ionic conductivity in PEO/PMMA glassy miscible blends: Role of nano‐confinement of minority component chains

AC impedance spectroscopy was used to investigate the ionic conductivity of solution cast poly(ethylene oxide) (PEO)/poly(methyl methacrylate) (PMMA) blends doped with lithium perchlorate. At low PEO contents (below overlap weight fraction w^*), ionic conductivities are almost low. This could be due to nearly distant PEO chains in blend, which means ion transportation cannot be performed adequately. However, at weight fractions well above w^*, a significant increase in ionic conductivity was observed. This enhanced ionic conductivity mimics the PEO segmental relaxation in rigid PMMA matrix, which can be attributed to the accelerated motions of confined PEO chains in PMMA matrix. At PEO content higher than 20 wt % the conductivity measured at room temperature drops due to crystallization of PEO. However by increasing temperature to temperatures well above the melting point of PEO, a sudden increase of conductivity was observed which was attributed to phase transition from crystalline to amorphous state. The results indicate that some PEO/PMMA blends with well enough PEO content, which are structurally solid, can be considered as an interesting candidate for usage as solid‐state electrolytes in Lithium batteries. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 2065–2071, 2010     

Processing and morphological development of carbon black filled conducting blends using a binary host of poly(styrene co‐acrylonitrile) and poly(styrene)

The effects of host/filler interactions, processing, and morphological development of low percolation threshold (Φ_c) conducting blends were investigated. It was found that the value of Φ_c was dramatically reduced by the isolation of the carbon black (CB) conducting filler at the cocontinuous interface of a binary poly(styrene) (PS) and poly(styrene co‐acrylonitrile) (SAN) insulating host, resulting in a multiple percolation effect. Accumulation of the filler at the interface was possible due to the incompatibility of the CB filler with the PS phase and partial compatibility with the SAN phase. The best results were obtained by initially dispersing the CB in the PS phase during melt‐ blending, followed by the addition of the SAN phase. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 3106–3119, 2000     

Electrically conductive,melt‐processed ternary blends of polyaniline/dodecylbenzene sulfonic acid,ethylene/vinyl acetate,and low‐density polyethylene

Although polyaniline (PANI) has high conductivity and relatively good environmental and thermal stability and is easily synthesized, the intractability of this intrinsically conducting polymer with a melting procedure prevents extensive applications. This work was designed to process PANI with a melting blend method with current thermoplastic polymers. PANI in an emeraldine base form was plasticized and doped with dodecylbenzene sulfonic acid (DBSA) to prepare a conductive complex (PANI–DBSA). PANI–DBSA, low‐density polyethylene (LDPE), and an ethylene/vinyl acetate copolymer (EVA) were blended in a twin‐rotor mixer. The blending procedure was monitored, including the changes in the temperature, torque moment, and work. As expected, the conductivity of ternary PANI–DBSA/LDPE/EVA was higher by one order of magnitude than that of binary PANI–DBSA/LDPE, and this was attributed to the PANI–DBSA phase being preferentially located in the EVA phase. An investigation of the morphology of the polymer blends with high‐resolution optical microscopy indicated that PANI–DBSA formed a conducting network at a high concentration of PANI–DBSA. The thermal and crystalline properties of the polymer blends were measured with differential scanning calorimetry. The mechanical properties were also measured. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3750–3758, 2004     

Phase‐separated,conducting composites from polyaniline and benzobisthiazole rigid‐rod polymer

As an alternative method for processing polyaniline (PANI) from its conducting (protonated) state, vacuum casting of PANI from a methanesulfonic acid (MSA) solution provided films with electrical conductivity values of about 130–150 S/cm. In addition, we similarly prepared blended films of PANI · MSA and poly(p‐phenylene benzobisthiazole) (PBZT). This process eliminated the need for a subsequent protonation step and had the additional advantage that the conjugated PBZT may provide alternative conducting pathways. Conductivity values of the composite films ranged from 100 pS/cm to 124 S/cm, and the films displayed critical concentration behavior with a PANI threshold concentration of 2.75% and a critical exponent of 4. Transmission electron micrographs displayed phase‐separated regions with PANI forming a continuous network at high concentrations. Thermogravimetric analysis results demonstrated the thermal and thermooxidative stability advantage of the blends due to the PBZT component. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 2539–2548, 2001     

Changes During Storage of Electrically Conductive Blends Polyaniline–Poly(Ethylene‐co‐vinyl Acetate)

Abstract

The electrical conductivity behavior of polyaniline–poly(ethylene‐co‐vinyl acetate) (PANI–EVA) blends was variable and dynamic during their storage. It was shown that the apparent concentration of the intrinsically conductive polymer at which a conductivity jump of the blends occurs (Φ _c ) is not a constant value over time. The electrical conductivity of the films of low PANI content (below 2.5 wt.%) increased by several (ca. 5) orders of magnitude. It was found that the PANI phase undergoes a flocculation process subsequently resulting in the formation of conductive pathways and a continuous network. Besides, the shape of percolation curves was found to change during storage of the films. Decreased conductivity deviations were registered for blends of low PANI content (<2.5 wt.%), indicating that an improvement (or decreasing number of defects) of the conductive pathways took place within the bulk of the insulating EVA matrix. These results and observed phenomena are discussed by means of the interfacial model for electrically conductive polymer blends. They supported the dispersion/flocculation phase transition within similar composite materials. The phase separation and conductivity jump are attributed to the interfacial interactions between the polymeric constituents. It was shown that the microstructure of the blends consists of highly ordered PANI paths embedded in the insulating EVA matrix. Long fibrils of PANI and interconnected fractal‐like networks were observed. It was found that the sizes of the PANI domains also varied during storage of the films. Due to the spontaneous flocculation of the primary PANI particles, conductive pathways are formed at extremely low percolation threshold (Φ _c , loading level ca. 5 × 10^?3 wt. fraction). Thus, an important property of the conductive constituent, namely its solid‐state rearrangement, was proved. This PANI self‐organization is also interpreted according to the interfacial model of polymer composites. On the other hand, the competition between self‐organization of the complex of PANI with dodecylbenzenesulfonic acid and crystallization of EVA matrix has resulted in structural changes and formation of continuous conductive networks within the blends, responsible for their significantly increased conductivity.     

Determination of percolation threshold electroactivity and phase behavior study on conducting blends of thermotropic polyesters and polyaniline

The new thermotropic polyester/polyaniline (PIn/PAni) blends have been prepared by solution blend of synthesized liquid crystalline poly[4,4′‐bis (ω‐alkoxy) biphenylisophthalate]s having four and six methylene units in spacer (PI4 and PI6) with PAni doped with camphorsolfonic acid (CSA). The percolation threshold electroactivity of prepared blend films has been determined by cyclic voltammetry. The effect of the PAni concentration, solvent nature and polyester structure on the electroactivity of the blends has been investigated. The extremely low percolation threshold of prepared PIn/PAni‐CSA blends from dimethylformamide (DMF) and m‐cresol solution was 3% weight of PAni‐CSA. The amount of conducting polymer necessary to retard the formation of the liquid crystalline (LC) phase is up to 45% by weight. Phase behavior studies by differential scanning calorimetry and polarizing microscopy show that blends with 45% of conducting polymer are both liquid crystal and conductive. The morphology of the blends has been investigated by scanning electron microscopy. Copyright © 2004 John Wiley & Sons, Ltd.     

Phase behavior of tetramethylpolycarbonate blends with styrene‐based methacrylate copolymers and their interaction energies

The miscibility of tetramethylpolycarbonate (TMPC) blends with styrenic copolymers containing various methacrylates was examined, and the interaction energies between TMPC and methacrylate were evaluated from the phase‐separation temperatures of TMPC/copolymer blends with lattice‐fluid theory combined with a binary interaction model. TMPC formed miscible blends with styrenic copolymers containing less than a certain amount of methacrylate, and these miscible blends always exhibited lower critical solution temperature (LCST)‐type phase behavior. The phase‐separation temperatures of TMPC blends with copolymers such as poly(styrene‐co‐methyl methacrylate), poly(styrene‐co‐ethyl methacrylate), poly(styrene‐co‐n‐propyl methacrylate), and poly(styrene‐co‐phenyl methacrylate) increase with methacrylate content, go through a maximum, and decrease, whereas those of TMPC blends with poly(styrene‐co‐n‐butyl methacrylate) and poly(styrene‐co‐cyclohexyl methacrylate) always decrease. The calculated interaction energy for a copolymer–TMPC pair is negative and increases with the methacrylate content in the copolymer. This would seem to contradict the prediction of the binary interaction model, that systems with more favorable energetic interactions have higher LCSTs. A detailed inspection of lattice‐fluid theory was performed to explain such phase behavior. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1288–1297, 2002     

Reduced percolation thresholds of immiscible conductive blends

The DC conductivity of polymer blends composed of poly(ethylene‐co‐vinyl acetate) (EVA) and high density polyethylene (HDPE), where a conductive carbon black (CB) had been preferentially blended into the HDPE, were investigated to establish the percolation characteristics. The blends exhibited reduced percolation thresholds and enhanced conductivities above that of the individually carbon filled HDPE and EVA. The percolation threshold of the EVA/HDPE/CB composites was between 3.6 and 4.2 wt % carbon black, where the volume resistivity changed by 8 orders of magnitude. This threshold is at a significantly lower carbon content than the individually filled HDPE or EVA. At a carbon black loading of 4.8 wt %, the EVA/HDPE/CB composite exhibits a volume resistivity which is approximately 14 and 11 orders of magnitude lower than the HDPE/CB and EVA/CB systems, respectively, at the same level of incorporated carbon black. The dielectric response of the ternary composites, at a temperature of 23°C and frequency of 1 kHz, exhibited an abrupt increase of ca. 252% at a carbon concentration of 4.8 wt %, suggesting that the percolation threshold is somewhat higher than the range predicted from DC conductivity measurements. Percolating composites with increasing levels of carbon black exhibit significantly greater relative permittivity and dielectric loss factors, with the composite containing 6 wt % of carbon black having a value of ϵ′ ≈ 79 and ϵ″ ≈ 14. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 1899–1910, 1999     

Solution processing of polymer semiconductor: Insulator blends—Tailored optical properties through liquid–liquid phase separation control

It has been demonstrated that the 0‐0 absorption transition of poly(3‐hexylthiophene) (P3HT) in blends with poly(ethylene oxide) (PEO) could be rationally tuned through the control of the liquid–liquid phase separation process during solution deposition. Pronounced J‐like aggregation behavior, characteristic for systems of a low exciton band width, was found for blends where the most pronounced liquid–liquid phase separation occurred in solution, leading to domains of P3HT and PEO of high phase purity. Since liquid–liquid phase separation could be readily manipulated either by the solution temperature, solute concentration, or deposition temperature, to name a few parameters, our findings promise the design from the out‐set of semiconductor:insulator architectures of pre‐defined properties by manipulation of the interaction parameter between the solutes as well as the respective solute:solvent system using classical polymer science principles. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 304–310     

Ductile–brittle‐transition phenomenon in polypropylene/ethylene‐propylene‐diene rubber blends obtained by dynamic packing injection molding: A new understanding of the rubber‐toughening mechanism

For a more complete understanding of the toughening mechanism of polypropylene (PP)/ethylene‐propylene‐diene rubber (EPDM) blends, dynamic packing injection molding was used to control the phase morphology and rubber particle orientation in the matrix. The relative impact strength of the blends increased at low EPDM contents, and then a definite ductile–brittle (D–B) transition was observed when the EPDM content reached 25 wt %, at which point blends should fail in the ductile mode with conventional molding. Wide‐angle X‐ray diffraction (WAXD), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM) were used to investigate the shear‐induced crystal structure, morphology, orientation, and phase separation of the blends. WAXD results showed that the observed D–B transition took place mainly for a constant crystal structure (α form). Also, no remarkable changes in the crystallinity and melting point of PP were observed by DSC. The highly oriented and elongated rubber particles were seen via SEM at high EPDM contents. Our results suggest that Wu's criterion is no longer valid when dispersed rubber particles are elongated and oriented. The possible fracture mechanism is discussed on the basis of the stress concentration in a filler‐dispersed matrix. It can be concluded that not only the interparticle distance but also the stress fields around individual particles play an important role in polymer toughening. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2086–2097, 2002