Effects of the solubility parameter of polyimides and the segment length of siloxane block on the morphology and properties of poly(imide siloxane)

The dependence of morphology of the poly(imide siloxane)s (PISs) on the solubility parameter of unmodified polyimides and the molecular weight and content of α,ω‐bis(3‐aminopropyl) polydimethylsiloxane (APPS) has been studied. The effect of the morphology on the mechanical properties is also under investigation. The domain formation in the PISs with the APPS molecular weight M_n = 507 g/mol is not found until the mol ratio of APPS/PIS ≥ 0.5% in the pyromellitic dianhydride/p‐phenylene diamine (PMDA/p‐PDA)‐based PISs, and at a mol ratio ≥ 2.7% in the 3,3′,4,4′‐benzophenone tetracarboxylic dianhydride/2,2′‐bis[4‐(3‐aminophenoxy) phenyl] sulfone (BTDA/m‐BAPS)‐based PISs. As the APPS M_n = 715 g/mol, the critical APPS concentrations of the domain formation in both types of PISs are equal to 0.1 and 1.1%, respectively. The critical concentration is equal to 0.6% in the BTDA/m‐BAPS‐based PIS film with the APPS M_n = 996 g/mol. The isolated siloxane‐rich phase in the BTDA/m‐BAPS‐based PISs becomes a continuous phase as the mol ratio of APPS/PIS ≥ 7.7, 10.0, and 16.6% as the APPS M_n = 996, 715, and 507 g/mol, respectively. Dynamic Mechanical Analysis (DMA) shows two T_gs in the PIS films having phase separation: one at −118 ∼ –115°C, being the siloxane‐rich phase, the other at 181–244°C, being the aromatic imide‐rich phase. The SEM micrographs show a significant deformation on the fractured surfaces of the BTDA/m‐BAPS‐based PIS films with a continuous siloxane‐rich phase. This phenomenon of plastic deformation is also observed in the tensile tests at −118°C and at room temperature. The highest elongation in the PIS films is found at the critical siloxane content of the continuous siloxane‐rich phase formation. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2832–2847, 1999     

Thermotropic polyester carbonates. III. Thermotropic polyester carbonates as self-reinforced plastics

Thermotropic polyester carbonates derived from t-butylhydroquinone, methylhydroquinone, diphenyl terephthalate, and diphenyl carbonate in the molar ratio of 50 : 50 : 55 : 45; 50 : 50 : 57.5 : 5 : 42.5 and 50 : 50 : 60 : 40 can be injection molded successfully from temperatures 10°C below melting to 30–40°C above melting. Normally the best molding temperatures are 10–20°C above melting. If the molding conditions are controlled properly, tensile strengths as high as 1.8 × 10⁴ psi, tensile moduli as high as 7.4 × 10⁵ psi, and flex moduli as high as 1.1 × 10⁶ psi can be obtained.     

Synthesis and properties of highly branched poly(urethane–imide) via A2 + B3 approach

A series of highly branched poly(urethane–imide) (HBPUI) were synthesized via A₂ + B₃ approach using isophorone diisocyante (IPDI), polycarbonatediol (PCDL), 3,3′,4,4′-Benzophen-onetetracarboxylic dianhydride (BTDA), and poly(oxyalkylene) triamine (ATA) as materials. The structure of the products was characterized by FT-IR and ¹³C-NMR. The molecular weights were characterized by gel permeation chromatograph (GPC). The solution viscosity, thermal, and mechanical properties were measured by rotational rheometer, differential scanning calorimetry (DSC), thermal gravimetric analysis (TGA), tensile tests, and dynamic mechanical analysis (DMA), respectively. The HBPUI showed lower viscosity than that of linear poly(urethane–imide) (LPUI), nevertheless T _g of HBPUI was higher than that of LPUI. TGA indicated that the thermal degradation of poly(urethane–imide) occurred above 300 °C, which was higher than conventional polyurethane. The tensile strength of HBPUI was obviously improved by increasing the content of BTDA and the molar ratio of [A₂]/[B₃]. The effects of the content of BTDA and the molar ratio of [A₂]/[B₃] on the storage modulus of the polymers were also studied.     

Polyimide foams with ultralow dielectric constants

To explore ultralow dielectric constant polyimide, the crosslinked polyimide foams (PIFs) were prepared from 3,3′,4,4′‐benzophenonetetracarboxylic dianhydride (BTDA), 4,4′‐oxydianiline (ODA), and 2,4,6‐triaminopyrimidine (TAP) via a poly(ester–amine salt) (PEAS) process. FTIR measurements indicated that TAP did not yield a negative effect on imidization of PEAS precursors. SEM measurement revealed the homogeneous cell structure. Through using TAP as a crosslinking monomer, the mechanical properties of PIFs could be improved in comparison with uncrosslinked BTDA/ODA based PIF. The crosslinked PIFs still exhibited excellent thermal stability with 5% weight loss temperatures higher than 520°C. In the field with frequency higher than 100 Hz, the dielectric constants of the obtained PIFs ranged from 1.77 to 2.4, and the dielectric losses were smaller than 3 × 10^?2 at 25–150°C. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1734–1740, 2006     

Isothiocyanate derivatives of soybean oil triglycerides: Synthesis,characterization, and polymerization with polyols and polyamines

In this article, a novel two step synthesis of soy oil based isothiocyanate is described. Allylicaly brominated soybean oil (ABSO) was reacted first with ammonium thiocyanate in tetrahydro furan to form allylic thiocyanates. These compounds were then converted to isothiocyanated soybean oil (ITSO) by a thermal rearrangement. Conversion was found to be 70%. The structure of the ITSO was characterized by IR and ¹ H‐NMR techniques. Then ITSO was reacted with ethylene glycol, glycerol, and castor oil to produce polythiourethanes and ethylene diamine and triethylene tetra amine to produce polythioureas. Thermal properties of the products were determined by DSC and TGA techniques. DSC traces showed T_g's for ethylene glycol polythiourethane at ?39 and 58°C, for glycerol polythiourethane at ?39 and 126°C, for castor oil polythiourethane at ?38°C and ?17°C, for ethylene diamine polythiourea at ?45°C, and for triethylene tetra amine poly thiourea at ?39°C. Additionally, DSC analysis of polythioureas showed an endotherm at around 100°C. All of the polymers started to decompose around 200°C. Tensile properties of the polymers were determined. Polythiourethanes showed higher tensile strength and lower elongation when compared with their urea analogs. Stress at break values of the polymers were 1.2 MPa for glycerol polythiourethane, 0.6 MPa for ethylene glycol polythiourethane, 0.5 MPa for ethylene diamine polythiourea, and 0.9 MPa for triethylene tetra amine polythiourea polymers. Unfortunately, polymers synthesized showed poor solvent resistance. All polymers swelled and disintegrated in CH₂Cl₂ in 5 h. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Facile fabrication of polyimide foam sheets with millimeter thickness: Processing,morphology, and properties

A series of polyimide foam sheets (PIFSs) with thickness of 0.5 mm using 3,3′,4,4′‐benzophenonetetracarboxylic dianhydride (BTDA), 3,4′‐oxydianiline (3,4′‐ODA), and polyaryl polymethylene isocyanate (PAPI) as main materials were first fabricated by liquid foaming and compression molding technology. The effects of different PAPI contents and 3,4′‐ODA contents on the structures and properties of PIFSs were investigated. The results indicated that PIFSs exhibited a structure that front surface displayed closed cells made of damaged cell walls and membranes, while internal cells were open, and elliptic vacancies were flatted in the thickness direction from the cross section. The average cellular diameter increased with increasing PAPI loading. In addition, the introduction of 3,4′‐ODA increased the average cell size of PIFSs. Further, PIFSs had density of 0.087–0.239 g/cm³, elongation at break of 3.75–8.01% and tensile toughness of 3.46 × 10^?2?13.87 × 10^?2 J/cm³. Notably, they exhibited higher tensile strength of 1.89–5.42 MPa and lower thermal conductivity of 14.727–19.25 mW/m ?K at 24°C, compared to the polyimide foams reported earlier. The sound absorption coefficients (α) of samples with different PAPI contents increased and then decreased with increasing PAPI content. At low frequencies, a certain content of 3,4′‐ ODA allowed an improvement of the acoustical behavior of PIFSs, and the α increased and then decreased with increasing density. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39881.     

Flax fiber‐reinforced polylactide stereocomplex composites with enhanced heat resistance and mechanical properties

Polylactide stereocomplex (sc‐PLA) prepared by blending equivalent proportion of poly(l ‐lactic acid)/poly(d ‐lactic acid) (PLLA/PDLA) and its composites reinforced with 10, 20, and 30% flax fibers were fabricated by melt compounding and followed by injection molding. The mechanical properties, crystallinity, cross‐section morphology, and heat resistance of sc‐PLA and flax/sc‐PLA composites were compared. The results showed that homocrystallites (hc) and stereocomplex crystallites (sc) were formed simultaneously in sc‐PLA and its composites, with a melting temperature at ∼170 and ∼210°C, respectively. The crystallinity and sc content of composite increased with the increasing content of the flax fibers. The sc content of 30% flax/sc‐PLA composite could reach 98.4%, 32% higher than that of sc‐PLA (66.4%). When compared with nonblended PLLA, heat resistance of sc‐PLA increased slightly, but at the expense of mechanical properties. By the addition of flax fibers, the mechanical properties of flax/sc‐PLA composite improved significantly. The highest tensile strength, Young's modulus, and notched Izod impact strength of flax/sc‐PLA composite were 52.90 MPa, 6.42 GPa, and 5.27 kJ/m², respectively, improved by 54, 132, and 343% when compared with sc‐PLA. Moreover, the heat resistance of composite was also improved greatly by reinforcing with flax fibers. The Vicat softening temperature of 30% flax/sc‐PLA composite could achieve 162.5°C, nearly 100°C higher than that of PLLA. POLYM. COMPOS., 38:472–478, 2017. © 2015 Society of Plastics Engineers     

Polyether–polyimide thermoplastic elastomers. I. Synthesis and properties

A series of polyether–polyimides based on polycondensation of poly(tetramethylene oxide) glycol di-p-aminobenzoate with different molecular weights (650, 1000, 2000) and benzenetetracarboxylic acid dianhydride (BTDA) or 3,3′,4,4′-benzenetetracarboxylic acid anhydride (BPTDA) was synthesized. Infrared spectroscopy (IR), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and stress–strain tests were used to follow the imidization process and to study the structure–property relations of this family of polymers. FTIR data showed that the imidization was completed after 6 h at 140°C, which is a much lower temperature than that required for polyimides synthesized from low molecular weight diamines. DSC and DMA results indicated that the block copolymer exhibited a well-phase-separated structure and had a broad rubbery plateau from about ?70°C to 260°C, which varied with dianhydride type and hard-segment content. The BTDA series had enhanced mechanical properties compared to the BPTDA series. The excellent tensile properties of the polyether–polyimides suggest that they could be potentially used as heat-resistant thermoplastic elastomers.     

Supercritical fluid extraction of cyclic oligomers from depolymerizing PBT

Cyclic oligomers of polyester show great potential for a reaction‐injection‐molding process, because of their initial low viscosity and rapid ring‐opening polymerization at low temperatures (180°C) without exothermic reaction or condensates. In this work, we report the synthesis of cyclic oligo(butylene terephthalate) (COBT) from linear poly(butylene terephthalate) by a formation–extraction process employing supercritical fluids (SCF) CO₂ and pentane at T = 230°C and P = 250 bar. Following this, depressurization of SCF leads to easy recovery of the COBTs. When compared with SCF CO₂, SCF pentane is found to be an attractive solvent because of its higher solubilizing capacity (0.8 mg COBT dimer/g pentane) for the COBTs. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 4487–4492, 2006     

Synthesis and characterization of copolymeric aliphatic–aromatic esters derived from terephthalic acid, 1,4‐butanediol,and ε‐caprolactone by physical,thermal, and mechanical properties and NMR measurements

In this study, a series of aliphatic–aromatic poly(butylene terephthalate‐co‐ε‐caprolactone) (PBTCL) copolyesters were synthesized from various monomeric compositions of terephthalic acid (TPA), 1,4‐butanediol (BDO), and ε‐caprolactone (CL) in the presence of tetrabutyl titanate (Ti(Obu)₄) and stannous octoate (Sn(Oct)₂) as catalysts through a combination of polycondensation and ring opening polymerization. A significant increase in the melting temperature (T_m) of copolyesters was observed by increasing the TPA/(CL+TPA) molar ratio, starting from the low end (T_m 66.2°C) of pure poly‐ε‐caprolactone PCL upward. We found that PBTCL‐50, which has a TPA/(CL+TPA) 50% molar ratio and polycondensation at 260°C for 1.5 h, resulted in a proper T_m of 139.2°C that facilitates thermal extrusion from biomass or other biodegradable polymers of similar T_m. The number–average molecular weight (M_n) of 7.4 × 10⁴ for PBTCL‐50 was determined from the intrinsic viscosity [η] by using the Berkowitz model of M_n = 1.66 × 10⁵[η]^0.9. Good mechanical properties of PBTCL‐50 have been shown by tensile stretching experiment that indicates tensile strength, elongation, and Young's modulus are 11.9 MPa, 132%, and 257 MPa, respectively. Polymers with aforementioned properties are suitable for manufacturing biodegradable plastic films for downstream agricultural applications or merely for trash bag. This article reveals that the PBTCL‐50 contains all five monomers with different molar ratios and characteristical linkages between each other. The novel structure was furthermore analyzed by ¹H‐ and ¹³C‐NMR spectroscopy. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

The kinetics of polyarylate hydrolytic embrittlement

The hydrolysis of polyarylate in water between 55 and 98°C was found to be a zero-order process with an activation energy of 19.2 kcal/mol, determined by changes in molecular weight. The equation for the effect of temperature on the rate of hydrolysis is ln k = 34.1 ? 10⁴/T, where k is in day^?1. The decrease in molecular weight is accompanied by a loss in ductility. The transition from a ductile to brittle failure in tension occurs at M?_w of about 35,000 and M?_n of 12,700. At 27°C (80°F) and high humidity environment this would occur after 21 years. But during injection molding, the material, if not properly dried, would embrittle in a matter of seconds.     

Thermal properties of a tough,new semicrystalline polyimide

Thermal properties of a new semicrystalline polyimide synthesized from 3,3′,4,4′-benzophenonetetracarboxylic dianhydride ( BTDA ) and 2,2-dimethyl-1,3-(4-aminophenoxy)propane ( DMDA ) have been studied. Heat capacities in the solid and liquid states of BTDA - DMDA have been measured. The heat capacity increase at the glass transition temperature (T_g = 230°C) is 145 J/°Cmol for amorphous BTDA - DMDA . The equilibrium heat of fusion of the BTDA - DMDA crystals has been obtained using wide-angle X-ray diffraction and differential scanning calorimetry measurements, and is 75.8 kj/mol. Based on the information on crystallinity and the heat capacity increase at T_g, a rigid amorphous fraction is identified in semicrystalline BTDA - DMDA samples, which represents an interfacial region between the crystalline and amorphous states. In particular, this fraction increases with the crystallinity of the sample, which should be associated with crystal sizes, and therefore with crystal morphology. It has also been found that this polymer has a high-temperature crystal phase upon annealing above its original melting temperature. The thermal degradation activation energies of BTDA - DMDA in nitrogen and air are determined to be 154 and 150kJ/mol, respectively.     

Melting,regelling, and remelting of poly(vinyl alcohol) hydrogels

The melting behaviors of hydrogels of syndiotacticity-rich poly(vinyl alcohol) (s-PVA), derived from vinyl trifluoroacetate, during heating at various rates of rising temperature were examined. For the hydrogels with the polymer concentrations above 5 g/dL chilled at the temperatures of 0 ∼ 40°C, the melting temperature increased with a decrease in the rate of rising temperature. During rising temperature at lower rates, the phase separation with spinodal decomposition progressed even in gels and the microcrystals, which play an important role as the junction points, propagated to thermally more stable size. The small, broad exothermic peaks during rising temperature of s-PVA hydrogels in DSC thermograms was found at the temperature ranges of 10 ∼ 30 and 45 ∼ 60°C. © 1996 John Wiley & Sons, Inc.     

Effect of pine resin derivatives on the structural,thermal, and mechanical properties of Mater-Bi type bioplastic

The effect of three additives derived from pine resin, namely, gum rosin (GR) and two pentaerythritol ester of GR, Lurefor (LF) and Unik Tack (UT), in 5, 10, and 15 wt %, on the properties of Mater-Bi, based on plasticized starch, poly(butylene adipate-co-terephthalate), and poly(ε-caprolactone) (PCL), obtained by injection molding processes, was studied. The mechanical, microstructural, and thermal properties were evaluated. LF had a cohesive behavior with the components of Mater-Bi, increasing the toughness of the material up to 250% accompanied by an increase of tensile modulus and tensile strength. UT had an intermediate behavior, conferring cohesive and plasticizing effects, allowing an increase of 105% in impact resistance. GR had a more marked plasticizing effect. This allows processing temperatures of about 50 °C lower than those used for neat Mater-Bi. In addition, an increase of the elongation at break, toughness, and impact resistance in 370, 480, and 250%, respectively, was achieved. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48236.     

Peroxide crosslinking of rigid poly(vinyl chloride)

The optimum conditions for crosslinking rigid poly(vinyl chloride) with trimethylolpropane trimethacrylate (TMPTMA) and peroxide have been examined. The extent of crosslinking was measured by determining gel content by Soxhlet extraction in tetrahydrofuran. Mechanical properties were measured at 130°C and dynamic viscoelastic measurements were carried out to detect changes in the glass transition temperature (T_g). It was found that 15 phr of TMPTMA and 0.3 phr of peroxide were optimum concentrations for maximizing the extent of crosslinking, tensile strength, and T_g. The lower molding temperature of 170°C was preferred to minimize thermal degradation. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2904–2909, 2007     

Processing and thermal properties of composites based on recycled PET,sisal fibers,and renewable plasticizers

This investigation focuses on the preparation of bio‐based composites from recycled poly (ethylene terephthalate) (PET) and sisal fibers (3 cm, 15 wt %), via thermopressing process. Plasticizers derived from renewable raw materials are used, namely, glycerol, tributyl citrate (TBC) and castor oil (CO), to decrease the melting point of the recycled PET (T_m ∼ 265°C), which is sufficiently high to initiate the thermal decomposition of the lignocellulosic fiber. All used materials are characterized by thermogravimetric analysis and differential scanning calorimetry, and the composites are also characterized via dynamic mechanical thermal analysis. The storage modulus (30°C) and the tan δ peak values of CT [PET/sisal/TBC] indicate that TBC also acts as a compatibilizing agent at the interface fiber/PET, as well as a plasticizer. To compare different processing methods, rheometry/thermopressing and compression molding are used to prepare the recycled PET/sisal/glycerol/CO composites. These two different methods of processing show no significant influence on the thermal properties of these composites. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40386.     

Simple dilatometer for polymer density and thermal expansivity measurements

A dilatometer is described to study the temperature dependence of density (ρ) of solid and semiliquid polymers and the following linear relations have been established. Atactic poly(vinylisobutyl ether) (25–90°C): ρ = 0.9166 ? 7.15 × 10^?4 × T. Isotactic poly(vinylisobutyl ether) (25–70°C): ρ = 0.9184 ? 7.13 × 10^?4 × T. Poly(n-butyl methacrylate) (90–150°C): ρ = 1.0622 ? 8.41 × 10^?4 × T. Poly(dimethyl siloxane) (30–51°C, using Lipkins pycnometer): ρ = 0.9846 ? 8.81 × 10^?4 × T; where ρ is in g.cm^?3, temperature T is in Celsius, and the linearity correlation coefficient r is better than 0.9998. Their volume–temperature plots are also linear. As the plots of polyn-butyl methacrylate curved slightly near its glass transition (20°C), the quadratic equation ρ = 1.0402 ? 4.79 × 10^?4 × T ? 1.46 × 10^?6 × T² (standard deviation = 1.57 × 10^?3) has been suggested for the entire range of 30–150°C scrutinized in this study. The data have been utilized to derive thermal expansivity and some equation-of-state parameters of the polymers at the reference temperature (ca. 20°C).     

Mechanical and viscoelastic properties of polyethylene-based microfibrillated composites from 100% recycled resources

In this study, recycled polyethylene (rPE) based microfibrillated composites (MFCs) were developed while incorporating recycled poly(ethylene terephthalate) (rPET) and recycled polyamide 6 (rPA) as the reinforcing fibrillar phases at a given weight ratio of 80 wt% (rPE)/20 wt% (rPET or rPA). The blends were first melt processed using a twin-screw extruder. The extrudates were then cold stretched at a drawing ratio of 2.5 to form rPET and rPA fibrillar structures. Next, the pelletized drawn samples were injection molded at the barrel temperatures below the melting temperatures of rPET and rPA. The tensile, three-point bending, impact strength, dynamic thermomechanical, and rheological properties of the fabricated MFCs were analyzed. The effects of injection molding barrel temperature (i.e., 150°C and 190°C) and extrusion melt processing temperature (i.e., 250°C and 275°C) on the generated fibrillar structure and the resultant properties were explored. A strong correlation between the fibrillar morphology and the mechanical properties with the extrusion and injection molding temperatures was observed. Moreover, the ethylene/n-butyl acrylate/glycidyl methacrylate (EnBAGMA) terpolymer and maleic anhydride grafted PE (MAH-g-PE) were, respectively, melt processed with rPE/rPET and rPE/rPA6 blends as compatibilizers. The compatibilizers refined the fibrillar structure and remarkably influenced mechanical properties, specifically the impact strength.     

Quaternized poly (2,6-dimethyl-1,4-phenylene oxide) crosslinked by tertiary amine and siloxane for anion exchange membranes

A series of tertiary amine and siloxane crosslinked composite anion exchange membranes were prepared by incorporating 2-(3,4-epoxycyclohexyl) ethyltrimethoxysilane (EHTMS) and N,N,N′,N′-Tetramethyl-1,6-hexanediamine (TMHDA) into N-Methyldiethanolamine (MDEA)-functionalized poly (2,6-dimethyl-1,4-phenylene oxide) (PPO) backbone via sol-gel process. The resultant membranes named as AEM-X (X = 1, 2, 3, 4), which own a three-dimensional (3D) cross-linking structure, exhibit superior swelling resistance, mechanical properties, even the thermal stability is up to 220°C. Compared with AEM-1 (contains no crosslinker), the swelling ratio of AEM-2 obviously decreases by 10.2% at 80°C, while the OH⁻ conductivity of AEM-2 has a merely 1.9% decline (20.6 mS cm⁻¹) at 80°C and can maintain 67% of its initial value in a 2 M aqueous NaOH at 80°C for 240 h. The simultaneous introduction of inorganic siloxane and organic linear crosslinker provides a new idea for the preparation of anion exchange membranes with largely improvement in dimensional stability and alkali resistance while the ionic conductivity is kept at comparatively high level.     

Structure of skin layer in injection-molded polypropylene

The structure of skin layer in injection-molded polypropylen which displayed a clear two-phase structure of skin and core has been studied by means of wide-angle x-ray diffraction, small-angle x-ray scattering, melting behavior, density, dynamic viscoelasticity, and tensile test. In skin layer, the c-axis and a^*-axis were highly oriented to the machine direction (MD), and the plane of the lamellar structure of about 160 Å in thickness was in normal to MD. The density was about 0.907 g/cm³, which was nearly the same as that of core layer. Although the majority of crystallites melted in the same temperature range as in that of the core layer, there was about 5.3% higher temperature melting structure (T_m = 182°C). The dynamic tensile modulus E′ in MD decreased more slowly with increasing temperature than that of the core layer and held high modulus in the range of ca. 30°C, just above the temperature at which E′ of the core layer suddenly dropped. E′ in MD was higher than that in TD in the temperature range below 33°C, which was slightly higher than the primary absorption temperature, and the order reversed above 33°C. The tensile yield stress in MD was 1.5 times higher than that of the core layer. The skin layer in MD ruptured just after yielding and did not show necking. The tensile yield stress in TD was about half of that in MD about 0.7 times that of the core layer. The necking stress in TD was about 0.6 times that of the core layer. In general, a polypropylene melt crystallizes under a high shear stress in injection molding. From these facts, it was concluded that the skin layer is composed of so-called “shishkebab”-like main skeleton structures, whose axis is parallel to MD, piled epitaxially with a^*-axis-oriented imperfect lamellar substructure.