Influence of interfacial structure on morphology and deformation behavior of SBS block copolymers

Linear styrene-block-butadiene-block-styrene (SBS) triblock copolymers having different interfacial structures were investigated. In spite of the nearly equivalent chemical composition (about 70 vol% of styrene), these copolymers show significantly different morphologies. It was shown that the origin of the modified morphology in asymmetric block copolymers is the intermixing of short polystyrene (PS) chains or chain segments into the polybutadiene (PB) phase. It has a consequence of an increase in the glass transition temperature of the soft phase (PB phase here) and a significant decrease of the whole relaxation time of the materials. The larger the interfacial volume, the more PS molecules can mix into the PB phase. Moreover, it seems that the extent of the stress transfer in heterogeneous polymeric systems is crucially influenced by the interface. The tapered interface in an SBS block copolymer, for example, permits a more effective stress transfer compared to the sharp interface resulting in a higher degree of orientation in the individual phases of the materials.     

Some anomalies in pressure-induced ordering of glassy spheres in a rubbery matrix of a microphase-separated triblock copolymer

We report experimental results of pressure-induced ordering of spheres on body-centered cubic (bcc) superlattice in a microphase-separated polystyrene-block-poly(ethylene-co-but-1-ene)-block-polystyrene (SEBS) triblock copolymer. After well-ordered bcc superlattice was prepared by annealing as-cast samples at 140 °C for 10 h, the samples were further pressurized at 50.7, 101.3, 202.7 and 405.3 MPa at room temperature for 24 h. Small-angle X-ray scattering (SAXS) measurements revealed further ordering of the bcc spheres for the samples pressurized at 202.7 and 405.3 MPa, while the bcc regularity became worse for the samples pressurized at 50.7 and 101.3 MPa. On the other hand, starting with an ill-ordered sample, no change in the SAXS profile was detected upon pressurizing at 405.3 MPa up to 27.5 h. Thus, it turned out that the effect of pressure on the ordering of spherical microdomains is not straightforward.     

The effect of polystyrene-block-poly(4-vinylpyridine) prepared by a RAFT method in the dispersion polymerization of MMA

The dispersion polymerization of methyl methacrylate (MMA) has been carried out using polystyrene-block-poly(4-vinylpyridine) copolymer [P(S-b-4VP)], which was prepared by a reversible addition-fragmentation chain transfer (RAFT) method, as a steric stabilizer in an alcohol media. The stable polymer particles were obtained when the block copolymer concentrations increased from 1 to 10 wt% relative to the monomer and the average particle sizes decreased from 5.3 to 3.4 μm with the increasing concentration of the block copolymer. In particular, the incorporation of 2 wt% polystyrene-block-poly(4-vinylpyridine) produced 4.3 μm of monodisperse PMMA particles with 2.14% of C_v. Thus, the P(S-b-4VP) block copolymer prepared by the RAFT method is working not only as a steric stabilizer, but also in providing monodisperse micron-sized PMMA particles.     

Grafting of poly(ethylene-block-ethylene oxide) onto a vapor grown carbon fiber surface by γ-ray radiation grafting

To modify the surface of vapor grown carbon fiber (VGCF), poly(ethylene-block-ethylene oxide) (PE-b-PEO, M_n=1400, PEO content=50 wt%) was successfully grafted onto the surface by using γ-ray irradiation of the PE-b-PEO-adsorbed VGCF in solvent-free system. It is found that the percentage of polymer grafting reached 15.0% when the PE-b-PEO-adsorbed VGCF was irradiated by γ-ray over 40 kGy dose at 110 °C, but at the lower irradiation temperature of 75 °C, the grafting reaction scarcely proceeded. This indicates that polymer radicals formed by γ-ray irradiation were successfully trapped by VGCF surface above melting point of PE-b-PEO. On the other hand, when the dispersion of VGCF in THF solution of PE-b-PEO was irradiated, the percentage of PE-b-PEO grafting was less than 4.0%. It was confirmed by a field-emission scanning electron microscope (FE-SEM) that the surface of the VGCF was uniformly covered by grafted PE-b-PEO. In addition, the surface free energy of ungrafted and PE-b-PEO-grafted VGCF was determined.     

Adhesion properties of UV crosslinked polystyrene-block-polybutadiene-block-polystyrene copolymer and tackifier mixture

The peel and tack properties of mixtures of polystyrene-block-polybutadiene-block-polystyrene (SBS) and a tackifier were investigated after these were crosslinked by ultraviolet (UV) irradiation at various amounts of benzophenone (BP) as a photoinitiator and trimethylolpropane mercaptopropionate (TRIS) as a crosslinking agent.The degree of crosslinking of polybutadiene (PB) block in the SBS mixture was qualitatively estimated from the amount of gel fraction as well as the change in the glass transition temperature of the PB block. The crosslinking of the PB block was done within 3 min after UV irradiation and the peel strength of crosslinked specimens was as low as 45[percnt] of specimens without crosslinking. Nano-tack and bulk tack properties as well as the surface tension of mixtures were measured depending upon amounts of BP and TRIS.     

Low temperature synthesis and dielectric, ferroelectric and piezoelectric study of microwave sintered BaTiO3 ceramics

Barium titanate (BaTiO₃/BT) ferroelectric system was synthesized in single perovskite phase at low temperature by using powders derived from modified solid state reaction (MSSR) and sintered by microwave (MW) processing routes. Conventional calcination temperature was optimized at 900 °C for 4 h. MW sintering of BT samples was carried out at 1100 °C for 30 min to get dense (98% density) ceramics. Room temperature (RT) dielectric constant (?_r) and dielectric loss (tan δ) at 1 kHz frequency of MW sintered BT samples was found to be ∼2500 and 0.03, respectively. Saturated polarization vs. electric field (P-E) loops with remnant polarization (P_r) ∼6 μC/cm² and coercive field (E_c) ∼1.45 kV/cm confirmed the ferroelectric nature of MW sintered BT samples. Piezoelectric coefficient from strain vs. electric field (S-E) loops study was found to be 335 pm/V.     

Solid state structure-property behavior of semicrystalline poly(ether-block-amide) PEBAX thermoplastic elastomers

The solid state structure-property behavior was investigated of a series of poly(ether-block-amide) PEBAX^® thermoplastic elastomers based on nylon 12 and poly(tetramethylene oxide) with varying hard segment content. Particular emphasis was placed on better defining the morphological features of this entire series of commercially available materials. Compression molded and solution cast samples were studied by the techniques of DMA, DSC, WAXS, SAXS, AFM, SALS and stress-strain response. The strain-induced crystallization behavior of the soft polyether (PE) segments was also investigated. All samples exhibited a microphase separated morphology over a broad temperature range. As expected, an increase in the interconnectivity of the polyamide hard phase was greatly controlled by the polyamide (PA) content. Due to the crystallization of the PA hard segment, the formation of PA lamellar crystals was noted in both melt and solution cast films. At the higher PA contents, a distinct spherulitic superstructure was also observed but this form of morphological texture was diminished as the PE soft segment content increased. Limited studies of the deformation/recovery behavior of the spherulitic superstructure provided further information concerning the interaction between the hard and soft segments.     

Temperature sensitive poly(N-t-butylacrylamide-co-acrylamide) hydrogels: synthesis and swelling behavior

A series of temperature sensitive hydrogels was prepared by free-radical crosslinking copolymerization of N-t-butylacrylamide (TBA) and acrylamide in methanol. N,N′-methylenebis(acrylamide) was used as the crosslinker. It was shown that the swelling behavior of the hydrogels can be controlled by changing the amount of TBA units in the network chains. Hydrogels immersed in dimethylsulfoxide (DMSO)-water mixtures exhibited reentrant swelling behavior, in which the gels first deswell then reswell if the DMSO content of the solvent mixture is continuously increased. In water over the temperature range of 2-64 °C, hydrogels with less than 40[percnt] TBA by mole were in a swollen state while those with TBA contents higher than 60[percnt] were in a collapsed state. Hydrogels with 40-60[percnt] TBA exhibited swelling-deswelling transition in water depending on the temperature. The temperature interval for the deswelling transition of 60[percnt] TBA gel was found to be in the range from 10 to 28 °C, while for the 40[percnt] TBA gel, the deswelling started at about 20 °C and continued until the onset of the hydrolysis of the network chains at around 64 °C. It was shown that the Flory-Rehner theory of swelling equilibrium provides a satisfactory agreement to the experimental swelling data of the hydrogels, provided that the sensitive dependence of the χ parameter on both temperature and polymer concentration is taken into account.     

Evolution of interphase in styrene-butadiene block copolymers as revealed by H solid-state NMR: Effect of temperature and molecular architecture

¹H spin-diffusion solid-state NMR, in combination with other techniques, was utilized to investigate the effect of molecular architecture and temperature on the interphase thickness and domain size in poly(styrene)-block-poly(butadiene) and poly(styrene)-block-poly(butadiene)-block-poly(styrene) copolymers (SB and SBS) over the temperature range from 25 to 80 °C. These two block copolymers contain equal PS weight fraction of 32 wt%, and especially, polystyrene (PS) and polybutadiene (PB) blocks are in glass and melt state, respectively, within the experimental temperature range. It was found that the domain sizes of the dispersed phase and interphase thicknesses in these two block copolymers increased with increasing temperature. Surprisingly we found that the interphase thicknesses in these two block copolymers were obviously different, which was inconsistent with the theoretical predictions about the evolution of interphase in block copolymer melts by self-consistent mean-field theory (SCFT). This implies that the interphase thickness not only depends strongly on the binary thermodynamic interaction (χ) between the PS and PB blocks, but also is influenced by their molecular architectures in the experimental temperature range.     

Association behavior of poly(methyl methacrylate-b-methacrylic acid-b-methyl methacrylate) in aqueous medium

ABA type triblock amphiphilic polyelectrolyte consisting of poly(methyl methacrylate-block-methacrylic acid-block-methyl methacrylate) (P(MMA-b-MAA-b-MMA)) was synthesized by atom transfer radical polymerization technique and the self-assembly behavior of the polymers in aqueous solution was studied over the course of neutralization. Combination of potentiometric and conductometric titrations along with dynamic light scattering techniques were used to investigate the size and shape of aggregates at various degrees of neutralization. The effect of hydrophobic-hydrophilic (MMA-MAA) ratio and polymer chain length on the aggregation behavior during neutralization was studied. P(MMA-b-MAA-b-MMA) with longer MMA segment self-assembles via the closed association mechanism through stronger self-entanglement of MMA chains, whereas P(MMA-b-MAA-b-MMA) with shorter MMA chain self-assembles via the open association mechanism, as confirmed by transmission electron microscopy. Conductometric titration was used to determine the counterion condensation during the course of neutralization. When the charge density of micelle approaches a critical value as neutralization progresses, counterion condensation of Na⁺ ions on the polymer chains occurs. The effect of counterion condensation on the aggregation behavior during neutralization was elucidated.     

Nano- and bulk-tack adhesive properties of stimuli-responsive, fullerene-polymer blends, containing polystyrene-block-polybutadiene-block-polystyrene and polystyrene-block-polyisoprene-block-polystyrene rubber-based adhesives

Nano-tack (measured using AFM) and bulk-tack adhesive forces of blends of C₆₀ and either polystyrene-block-polybutadiene-block-polystyrene (SBS) or polystyrene-block-polyisoprene-block-polystyrene (SIS) triblock copolymer pressure sensitive adhesives were measured after exposure to white light irradiation. The nano-tack adhesive forces in C₆₀-SIS/SBS were found to decrease with increasing C₆₀ concentration and exposure time, approaching the value for 100% polystyrene, providing an indication that significant surface hardening and crosslinking of the soft isoprene and butadiene phases occurs in the presence of C₆₀. Films produced during the study were smooth, having low RMS surface roughness, and showed nanoscale phase separation between the soft (diene) and hard (styrene) segments. This phase separation disappeared after addition of C₆₀ sensitizer and white light irradiation. Bulk adhesive measurements (tack and peel strength) showed a similar trend with C₆₀ concentration and exposure time, and in irradiated systems containing as little as 0.2 wt% C₆₀, a significant decrease in adhesion was observed. Estimated T_g (measured using DMA, shear mode) of the soft-block shifts to higher temperatures (increasing by 30-40 °C), and high gel fractions were obtained, indicating the presence of chemically crosslinked networks.     

Super porous organic-inorganic poly(N-isopropylacrylamide)-based hydrogel with a very fast temperature response

Porous organic-inorganic (O-I) hydrogels showing a very fast temperature response, including very fast reswelling were prepared: only 6 s are needed for 72% deswelling (gel collapse) as well as for 72% reswelling. Both deswelling and reswelling are practically complete in 14 s. The gels were prepared from N-isopropylacrylamide (NIPA), N,N′-methylenebisacrylamide (BAA) and tetramethoxysilane (TMOS) by simultaneous radical polymerization and hydrolytic polycondensation of TMOS. The syntheses were carried out at temperatures below the lower critical solution temperature (LCST) of poly(NIPA) in two steps: during the first stage the temperature was held at T = +15 °C and during the second the temperature was lowered below the freezing point of the reaction mixture, T = −18 °C. The ice crystals, which grew during the second stage, served as the pore-forming agent. The best samples were obtained if the second stage was started shortly before the gel point of the reaction mixture. The introduction of the inorganic phase (silica) is necessary for the ability of fast reswelling and also results in a strong improvement of the hydrogels' mechanical properties, while the maximum swelling degree remains nearly unaffected.     

Electrochemical and thermal studies of Li[NixLi(1/3−2x/3)Mn(2/3−x/3)]O2 (x = 1/12, 1/4, 5/12, and 1/2)

Samples of the layered cathode materials, Li[Ni_xLi_(1/3−2x/3)Mn_(2/3−x/3)]O₂ (x = 1/12, 1/4, 5/12, and 1/2), were synthesized at 900 °C. Electrodes of these samples were charged in Li-ion coin cells to remove lithium. The charged electrode materials were rinsed to remove the electrolyte salt and then added, along with EC/DEC solvent or 1 M LiPF₆ EC/DEC, to stainless steel accelerating rate calorimetry (ARC) sample holders that were then welded closed. The reactivity of the samples with electrolyte was probed at two states of charge. First, for samples charged to near 4.45 V and second, for samples charged to 4.8 V, corresponding to removal of all mobile lithium from the samples and also concomitant release of oxygen in a plateau near 4.5 V. Li[Ni_xLi_(1/3−2x/3)Mn_(2/3−x/3)]O₂ samples with x = 1/4, 5/12 and 1/2 charged to 4.45 V do not react appreciably till 190 °C in EC/DEC. Li[Ni_xLi_(1/3−2x/3)Mn_(2/3−x/3)]O₂ samples charged to 4.8 V versus Li, across the oxygen release plateau, start to significantly react with EC/DEC at about 130 °C. However, their high reactivity is similar to that of Li_0.5CoO₂ (4.2 V) with 1 μm particle size. Therefore, Li[Ni_xLi_(1/3−2x/3)Mn_(2/3−x/3)]O₂ samples showing specific capacity of up to 225 mAh/g may be acceptable for replacing LiCoO₂ (145 mAh/g to 4.2 V) from a safety point of view, if their particle size is increased.     

The effects of the selectivity of the toluene/ethanol mixture on the micellar and the ordered structures of an asymmetric poly(styrene-b-4-vinylpyridine)

The effects of the solvent selectivity of toluene/ethanol mixtures on the micellar and ordered structures of an asymmetric diblock copolymer of PS(19.6 K)-b-P4VP(5.1 K) in the dilute (1 wt%) and semi-dilute (8 wt%) solutions, as well as in the gel and solid films, were studied using small angle X-ray scattering (SAXS), generalized indirect Fourier transform (GIFT), and transmission electron microscopy (TEM) methods. The solvent selectivity was controlled by ? (weight percentage of ethanol in toluene/ethanol mixture). Individual micelles, space-filled micellar structure (without three-dimensional order), and three-dimensionally ordered gel and solid structures were observed from the 1 and 8 wt% solutions, the gel, and the solid film, respectively. In the 1 wt% solution, the individual micellar structures were strongly dependent on ?; the spherical micelles with P4VP core at ? = 0, the unimer state at 10 ≤ ? ≤ 50, the spherical micelles with PS core at ? = 60, the cylindrical micelles with PS core at ? = 70 and 80, and precipitation at ? = 90 and 100 were observed. The 8 wt% solution was close to overlap concentration with the unimer state in the regions of 20 ≤ ? ≤ 40. In the gel, the ordered structure was observed in the sequence of bcc, hexagonal, gyroid, lamellar, reverse hexagonal and random as ? increased, and could be explained by the change of the relative volume fraction of each block as ? changed, similar to the phase sequence in the phase diagram of the diblock copolymer. The solid films showed the various kinetically frozen ordered microstructures such as randomly packed sphere, hexagonal, gyroid, hexagonally perforated lamella, reversed hexagonal, and randomly packed cylinder, which were controlled by the solvent quality in the gel before solidification. We believe that these results can be applied to photonic crystals, self-assembled nano-patterning, and functional nanoparticles in which the structural control is most important.     

In situ UV-vis spectroelectrochemistry of poly(o-phenylenediamine-co-m-toluidine)

Results of in situ UV-vis spectroelectrochemical studies of the electropolymerization of o-phenylenediamine (OPD), m-toluidine (MT) and the copolymerization of OPD with MT are reported. Electropolymerization was performed in aqueous acidic medium at a constant potential of E_SCE = 1.0 V at an indium doped tin oxide (ITO) coated glass electrode. The course of homopolymerization was followed for MT and OPD solutions with various monomer concentrations. The spectral characteristics of the mixed solutions were studied at a constant concentration of MT and various concentrations of OPD in the comonomer feed. An absorption band at λ = 497 nm was assigned to the head-to-tail mixed dimer/oligomer resulting from the cross reaction between OPD and MT cation radicals. UV-vis spectra recorded during copolymerization show dependence of the growth of the band at λ = 497 nm on OPD concentration in the feed. At lower OPD feed concentration it appears as the major band in the corresponding spectra. The UV-vis spectra recorded for the copolymer films suggest the incorporation of both monomer units in the copolymer. The FT-IR spectra of the copolymers show the presence of phenazine type structures in the copolymer backbone.     

Microstructure and dielectric properties of Dy/Mn doped BaTiO3 ceramics

Dy/Mn doped BaTiO₃ with different Dy₂O₃ contents, ranging from 0.1 to 5.0 at% Dy, were investigated regarding their microstructural and dielectric characteristics. The content of 0.05 at% Mn was constant in all the investigated samples. The samples were prepared by the conventional solid state reaction and sintered at 1290°, and 1350 °C in air atmosphere for 2 h. The low doped samples (0.1 and 0.5 at% Dy) exhibit mainly fairly uniform and homogeneous microstructure with average grain sizes ranged from 0.3 μm to 3.0 μm. At 1350 °C, the appearance of secondary, abnormal, grains in the fine grain matrix and core–shell structure were observed in highly doped Dy/BaTiO₃. Dielectric measurements were carried out as a function of temperature up to 180 °C. The low doped samples sintered at 1350 °C, display the high value of dielectric permittivity at room temperature, 5600 for 0.1Dy/BaTiO₃. A nearly flat permittivity–temperature response was obtained in specimens with 2.0 and 5.0 at% additive content. Using a Curie–Weiss and modified Curie–Weiss low, the Curie constant (C), Curie like constant (C′), Curie temperature (T_C) and a critical exponent (γ) were calculated. The obtained values of γ pointed out the diffuse phase transformation in highly doped BaTiO₃ samples.     

Nonlinear stress properties of poly(styrene-block-butadiene-block-styrene) melt under elongational and shear deformation

Effects of block copolymerized structure on nonlinear stress properties under elongational and shear deformation were investigated. Samples used in this study were poly(styrene-block-butadiene-block-styrene) (SBS, weight rate of S/B = 40/60) and polystyrene (PS) as a reference. Tensile stress–strain and shear stress relaxation properties were measured at the molten state. SBS showed high elasticity after reaching the yield point under elongational deformation at room temperature. PS melt showed substantial tensile stress increase after the yield point as strain rates increased. However, SBS melt did not exhibit noticeable tensile stress rise at higher elongation, and this property was almost independent of strain rates. Stress relaxation experiments revealed that the damping function of SBS melt was more strain-softening than that of PS melt. The results suggested that the block copolymerized structure decreases melt elasticity under elongational and shear deformation. A transmission electron micrograph indicated that the lack of melt elasticity in SBS melt is caused by orientation of the lamellar structure toward the stretched direction during deformation. © 1995 John Wiley & Sons, Inc.     

Flow and aggregation characteristics of thermo-responsive poly(N-isopropylacrylamide) spheres during the phase transition

To date, a great many researches were focused on improving stimuli-responsive and controlled-release properties of thermo-responsive hydrogel carriers, whereas for the research on flow characteristics during the phase transition, prior reports have not been found. In this paper, poly(N-isopropylacrylamide) (PNIPAM) spheres with thermo-responsive phase transition characteristics were prepared by cross-linked polymerization. In a transparent Pyrex glass pipe with hydrophilic inner wall, flow and aggregation characteristics of PNIPAM spheres during the phase transition from low temperature which was lower than the lower critical solution temperature (LCST) to high temperature (T>LCST) was studied for the first time. Many interesting phenomena about the flow and aggregation behaviors of PNIPAM spheres were found. The velocity of PNIPAM spheres in horizontal pipe decreased from 1.07 cm/s before the phase transition to 0.65 cm/s or even became zero after the phase transition, which is what targeting drug delivery systems desired. When the initial distance was about 5.5 mm at the entrance of testing pipe section, the PNIPAM spheres could aggregate together after the phase transition and subsequently roll forward; but when the initial distance was as large as 8.5 mm, the distance became close at first during the phase transition and then far after the phase transition. Similar results were also found as mentioned above in vertical pipe. When 10 spheres aggregated together, they stopped at a certain position just after the phase transition in horizontal pipe. If the flowrate was more than 40 ml/min, the aggregation configurations such as triangle, tetrahedron, hexahedron and octahedron which formed after the phase transition at flowrate of 20 ml/min disappeared. The results provided valuable information for future applications of thermo-responsive PNIPAM spheres.     

Epoxy resin containing poly(ethylene oxide)-block-poly(?-caprolactone) diblock copolymer: Effect of curing agents on nanostructures

An amphiphilic diblock copolymer, poly(ethylene oxide)-block-poly(?-caprolactone) (PEO-b-PCL) was synthesized via the ring-opening polymerization of ?-caprolactone in the presence of a hydroxyl-terminated poly(ethylene oxide) monomethyl ether. The diblock copolymer was incorporated into epoxy thermosets. It is found that the formation of nanostructures of thermosetting blends is quite dependent on the uses of aromatic amine hardeners. For 4,4′-methylenebis(2-chloroaniline) (MOCA)-cured thermosetting system, the homogeneous morphology was obtained at the compositions investigated. Nonetheless, the nanostructured thermosets were obtained when the blends were cured with 4,4′-diaminodiphenylsulfone (DDS). The differential scanning calorimetry (DSC) showed that the nanostructured thermosets did not displayed any crystallinity although the subchains of the diblock copolymer are crystalline. The nanostructures were evidenced by means of atomic force microscopy (AFM), small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). The dependence of morphological structures on the types of aromatic amines for epoxy and PEO-b-PCL thermosetting blends were interpreted on the basis of the difference in hydrogen bonding interactions resulting from the structure of curing agents. Considering the complete miscibility of the subchains (viz. PEO and PCL) with the precursors of epoxy resin before curing, it is judged that the formation of the nanostructures in the thermosets follows the mechanism of reaction-induced microphase separation, which is in marked contrast to the mechanism of self-assembly, i.e., micelle structures of block copolymers are formed prior to curing, followed by fixing these nanostructures via curing.     

Phase morphology and toughening mechanism of polyamide 6/EPDM-g-MA blends obtained via dynamic packing injection molding

One of the most important findings in polymer-toughening is known as the critical matrix ligament thickness (τ_c) theory, which is directly related to both rubber concentration and average size of particles. All these studies assume that rubber particles are spherical and randomly distributed in the matrix. Rubber particles may be stretched and oriented along the shear flow direction in real processing. In this paper the effect of stretched and oriented rubber particles on the impact strength of PA6/EPDM-g-MA blends have been studied via dynamic packing injection molding (DPIM). The impact strength of specimens obtained by DPIM was found substantially increase at all the blends investigated, compared with the one obtained via conventional injection molding. Particularly, more than 30 kJ m⁻² increase of the impact strength was observed for specimens with a higher rubber content (more than 15 wt%). SEM results showed a remarkably decrease of rubber particle size and more uniform dispersion of the dynamic molded specimens. This can be attributed to the shear induced reaction at the interface between polyamide 6 and EPDM-g-MA during the packing stage. The rubber particles were found stretched along the melt shear flow direction when it is content above 15 wt%. A master curve can be also constructed by plotting the impact strength versus the inter-particle distance, indicating that Wu's criterion still works for blends with stretched and oriented rubber particles when the crack propagation direction is perpendicular to the orientation direction of rubber particles. The observed higher impact strength in dynamic specimens could be due to, in part, the enhanced flexural stiffness, which will absorb more energy during impact process when the fracture of IZOD bars is incomplete, but more importantly due to the existence of the stretched and oriented rubber particles, which are more efficient in slowing the velocity of crack propagation and thus cause higher impact resistance when the fracture propagation direction is perpendicular to the rubber oriented direction.