Enhanced crystallization of poly(L‐lactide‐co‐ε‐caprolactone) in the presence of water

Poly(L ‐lactide‐co‐ε‐caprolactone) [P(LLA‐CL)], which is used in biodegradable biomedical materials such as drug‐delivery systems, surgical sutures, orthopedics, and scaffolds for tissue engineering, has been reported to crystallize upon storage in a dry state even at room temperature; this results in rapid changes in the mechanical properties. In biomedical applications, P(LLA‐CL) is used in the presence of water. This study investigated the effects of water on the crystallization of P(LLA‐CL) at 37°C in phosphate buffered solution, which was anticipated to alter its mechanical properties and hydrolytic degradation behavior. Surprisingly, the crystallinity of P(LLA‐CL) in the presence of water rapidly increased in 6–12 h and then slowly increased up to 120 h. The period of time for the initial rapid crystallization increase in the presence of water was much shorter than that in the absence of water. The obtained information would be useful for the selection, preparation, and use of P(LLA‐CL) in various biomedical applications. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Microstructural characteristics and crystallization behaviors of poly(l‐lactide) scaffolds by thermally induced phase separation

In this study, poly(l ‐lactic acid) (PLLA) was prepared by four typical approach systems, namely, solid–liquid phase‐separation processes from PLLA–dioxane at ?80°C, PLLA–dioxane–water at ?80°C, PLLA–tetrahydrofuran (THF) at ?80°C, and PLLA–THF at 18°C. The microstructural characteristics and crystallization behaviors of PLLA were investigated by scanning electron microscopy, differential scanning calorimetry, X‐ray diffraction, and Fourier transform infrared spectroscopy. In the PLLA–dioxane binary system and PLLA–dioxane–water ternary system, the solvent froze immediately after quenching to a low temperature, and this restricted the PLLA chain arrangement. Thus, the PLLA amorphous phase dominated in the scaffolds, and solid‐walled structures were produced. THF was liquid throughout the entire process, which enabled free PLLA chain arrangement and further crystallization. Single crystals aggregated by crystal nucleation and growth at a critical temperature (T_c) of 18°C; this resulted in its most common and stable polymorph, the α form. However, α′‐form crystals, which were assumed to be limit‐disordered crystals of the α form, were produced at a low T_c (?80°C). Scaffolds with a plateletlike structure were produced at a T_c of 18°C, whereas a nanofibrous network was obtained at ?80°C. PLLA crystallization competed with phase separation; thus, the crystal structure and scaffold morphology depended on the codevelopment of these two processes. Finally, the effects of the scaffold morphologies on the cell behaviors were studied, and the nanofibrous scaffold was found to have better cell adhesion and viability than the other three scaffolds. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39436.     

Morphological and structural development of recycled crosslinked polyethylene during solid‐state mechanochemical milling

Waste crosslinked polyethylene (XLPE) was partially decrosslinked to obtain a thermoplastic recycled material through solid‐state mechanochemical milling with pan‐mill equipment at ambient temperature. The gel fraction and size exclusion chromatography measurements showed that the gel content of XLPE decreased remarkably with increasing cycles of mechanochemical milling, whereas the molecular weight of the sol fraction was not significantly reduced; this indicated the realization of partial decrosslinking during mechanochemical milling. Differential scanning calorimetry and X‐ray diffraction analysis showed that the melting temperature of decrosslinked polyethylene increased by 3.5°C because the bigger crystallites size resulting from the higher mobility of the chain segment. The improved thermoplastic characteristic of XLPE after mechanochemical milling were confirmed by scanning electron microscopy and rheological measurement. The mechanical properties of recycled XLPE also achieved significant improvement after mechanochemical milling. Solid‐state mechanochemical milling is a cost‐effective, reliable, and environmentally friendly method for recycling XLPE at ambient temperature without any additional materials or chemicals. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Influence of extrusion temperature on molecular architecture and crystallization behavior of peroxide‐induced slightly crosslinked poly(L‐lactide) by reactive extrusion

The influence of temperature during reactive extrusion of poly(L ‐lactide) (PLLA) on the molecular architecture and crystallization behavior was investigated for OO‐(t‐butyl) O‐(2‐ethylhexyl) peroxycarbonate‐modified polymer. The long chain–branched PLLA (LCB‐PLLA) content and its structure in the resulting slightly crosslinked PLLA (χ‐PLLA) containing linear and LCB‐PLLA were characterized by both analyses, size exclusion chromatography equipped with multiangle laser light scattering and rheological measurements. A reduction of LCB‐PLLA content in χ‐PLLA and an increase of number of branches in LCB‐PLLA were found with increasing the extrusion temperature. An increase of extrusion temperature induces different process in the polymer: decrease of the lifetime of peroxide, increase of the radical concentration due to rapid peroxide decomposition rate, and increase of the chain diffusion to the amorphous phase. Among these indices, the lifetime of peroxide is a good index for crosslinking behavior of PLLA during extrusion. As for the isothermal crystallization behavior from the melt, the Avrami crystallization rate constant of χ‐PLLA increases as an increase of LCB‐PLLA content in χ‐PLLA. This implies that LCB‐PLLA acts as a nucleating agent for PLLA. Furthermore, regime analysis and the free energy of nucleus of χ‐PLLA were investigated using Hoffman–Lauritzen theory. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Process–structure–property relationship of melt spun poly(lactic acid) fibers produced in the spunbond process

We report on the process–structure–property relationships for Poly(lactic acid) (PLA) filaments produced through the spunbond process. The influence of spinning speed, polymer throughput, and draw ratio on crystallinity and birefringence of fibers were evaluated. We established that increasing spinning speed increases crystallinity and birefringence of fibers. We also investigate the role of fiber structures on fiber tensile properties—breaking tensile strength, strain at break, initial modulus, and natural draw ratio. An increase in spinning speed leads to a higher breaking tensile strength, higher initial modulus and lower strain at break. We have shown an almost linear relationship between breaking tensile strength of PLA fibers and birefringence. This indicates that improved tensile properties at high spinning speeds can be attributed to enhanced molecular orientation. The dependency of fiber breaking tensile strength and strain at break on spun orientation were explained with natural draw ratio, as a measure of spun orientation. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44225.     

Crystallization behavior of poly(p‐dioxanone)‐PU/montmorillonite nanocomposites prepared by chain‐extending reaction

Organo‐modified montmorillonites and poly(p‐dioxanone) (PPDO) diol prepolymers were used to prepare Poly(p‐dioxanone)‐PU/organic montmorillonite (PPDO‐PU/OMMT) nanocomposites by chain‐extending reaction. The crystallization behavior and spherulitic morphology of PPDO‐PU/OMMT nanocomposites were investigated by WXRD, differential scanning calorimetry, and polarized optical microscopy. The results show that the regularity of the chain structure plays a dominant role during the crystallization process rather than that of OMMT content and its dispersion status in PPDO matrix. With similar molecular weight and same OMMT content, PPDO‐PU/OMMT nanocomposite, which derived from lower molecular weight PPDO prepolymer, exhibits lower crystallization rate, melting point, and crystallinity. The influence of the clay content on the crystallization behavior highly depends on its dispersing state. The nucleating effect of OMMT can be only observed at high loading percentage. For the nanocomposites with low clay loading percentage, the retarding effect of exfoliated platelets on the chain‐ordering into crystal lamellae became the key factor. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Effect of the comonomer content on the solid‐state mechanical and viscoelastic properties of poly(propylene‐co‐1‐butene) films

In this study, we quantified the thermal and solid‐state mechanical and viscoelastic properties of isotactic polypropylene (i‐PP) homopolymer and poly(propylene‐1‐butene) copolymer films having a 1‐butene ratio of 8, 12, and 14 wt %, depending on the comonomer content. The uniaxial tensile creep and stress‐relaxation behaviors of the samples were studied in a dynamic mechanical analyzer at different temperatures. The creep behaviors of the samples were modeled with the four‐element Burger equation, and the long‐term creep strains were predicted with the time–temperature superposition method. The short‐term mechanical properties of the samples were also determined with tensile and impact testing at room temperature. We found that the Young's modulus and ultimate strength values of the samples decreased with increasing amount of 1‐butene in the copolymer structure. On the other hand, the strain at break and impact strength values of the samples improved with increasing amount of 1‐butene. Creep analysis showed that i‐PP exhibited a relatively lower creep strain than the poly(propylene‐co‐1‐butene)s at 30 °C. However, interestingly, we discovered that the temperature increase resulted in different effects on the creep behaviors. We also found that short‐chain branching improved the creep resistance of polypropylene at relatively high temperatures. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46350.     

Effect of mixing conditions on the rheological and optical properties of chemically modified poly(ethylene terephthalate‐co‐ethylene isophthalate)

The optical properties and rheological properties were studied for binary reactive blends composed of poly(ethylene terephthalate‐co‐ethylene isophthalate) [P(ET–EI)] and a styrene–acrylate based copolymer with glycidyl functionality. The blade rotation speed in the internal mixer greatly affected the structure and properties for the blend system. Intensive mixing at a high rotation speed enhanced the optical transparency because of the reduced particle size of the dispersed phase. The graft copolymer generated by the reaction between P(ET–EI) and the modifier was responsible for the fine morphology. Furthermore, the copolymer also enhanced the elastic nature in the molten state because it acted as a long‐chain branched polymer. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

Structure−property relationships of halogen‐free flame‐retarded poly(butylene terephthalate) and glass fiber reinforced PBT

Flame retardancy for thermoplastics is a challenging task where chemists and engineers work together to find solutions to improve the burning behavior without strongly influencing other key properties of the material. In this work, the halogen‐free additives aluminum diethylphosphinate (AlPi‐Et) and a mixture of aluminum phosphinate (AlPi) and resorcinol‐bis(di‐2,6‐xylyl phosphate) (AlPi‐H + RXP) are employed in neat and reinforced poly(butylene terephthalate) (PBT), and the morphology, mechanical performance, rheological behavior, and flammability of these materials are compared. Both additives show submicron dimensions but differ in terms of particle and agglomerate sizes und shapes. The overall mechanical performance of the PBT flame‐retarded with AlPi‐Et is lower than that with AlPi‐H‐RXP, due to the presence of larger agglomerates. Moreover, the flow behavior of the AlPi‐Et/PBT materials is dramatically changed as the larger rod‐like primary particles build a percolation threshold. In terms of flammability, both additives perform similar in the UL 94 test and under forced‐flaming combustion. Nevertheless, AlPi‐Et performs better than AlPi‐H + RXP in the LOI test. The concentration required to achieve acceptable flame retardancy ranges above 15 wt %. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Effects of nano‐TiO2 on the properties and structures of starch/poly(ε‐caprolactone) composites

Poor physical properties resulting from low interfacial interactions between hydrophilic biopolymers and hydrophobic thermoplastic matrices have been one of the biggest obstacles in preparing quality biomass materials. This study concentrates on the effects of nano‐TiO₂ on the properties and structure of starch/poly (ε‐caprolactone) (PCL) composites. The molecular and crystal structures of the composites were characterized by using Fourier transform infrared spectroscopy, differential scanning calorimeter (DSC), X‐ray diffraction (XRD), and field emission scanning electron microscope. The results indicated that an interpenetrating network structure formed by adding nano‐TiO₂ into starch/PCL composites. The DSC and XRD analysis indicated that the crystallinity degree and the crystallization rate of the composites reduced, whereas the crystal form and crystal size were unchanged. The results also showed that the mechanical properties and water resistance of the composites were improved significantly with the addition of nano‐TiO₂, whereas their transparency decreased. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 4129–4136, 2013     

Effect of solid‐state shear milling on structure and properties of HDPE/UHMWPE blends

The structure and properties of HDPE/UHMWPE blends prepared through a pan‐milling reactor in solid state at ambient temperature were compared with the blends made by melt mixing. The changes of structure and properties of the blends were investigated by FTIR, melt flow index, mechanical properties, dynamic rheological measurement, DSC, and WAXD. DSC measurement illustrated that after pan‐milling treatment, the half‐width of the melting temperature became smaller. The more content of UHMWPE added in the blend, the more evident change was observed. Combined with the dynamic rheological analysis, it was proved that, the pan‐milling treatment can improve the compatibility of the HDPE/UHMWPE blends. X‐ray diffraction analysis showed that after pan‐milling treatment some ordered structure could be induced, but after heat treatment, the induced crystalline structure disappeared. The tensile properties of pan‐milled HDPE/UHMWPE blends also achieved improvement after pan milling treatment. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39916.     

Shrinkage behavior after the heat setting of biaxially stretched poly(ethylene 2,6‐naphthalate) films and bottles

Amorphous preforms of poly(ethylene 2,6‐naphthalate) (PEN) were biaxially drawn into bottles up to the desired volume under industrial conditions. These bottles were used to characterize the shrinkage behavior of the drawn bottles with or without heat treatment and to study structural variations during heat setting. During drawing, a rigid phase structure was induced, and the amount of the induced rigid phase structure was linearly related to the square root of the extra first strain invariant under equilibrium conditions. During the production of these bottles, this equilibrium was not attained because of high stretching conditions and rapid cooling after stretching. The structure after orientation contained a rigid amorphous phase and an oriented amorphous phase. The shrinkage behavior was a function of the temperature and time of heat setting. Long heat‐setting times, around 30 min, were used to characterize the possible structural variations of the oriented PEN after heat setting at equilibrium. Under the equilibrium conditions of heat setting, the start temperature of the shrinkage was directly related to the heat‐setting temperature and moved from 60°C without heat treatment up to a temperature of 255°C by a heat‐setting temperature of 255°C; this contrasted with poly(ethylene terephthalate) (PET), for which the start temperature of shrinkage was always around 80°C. For heat‐setting temperatures higher than 220°C, the structural variations changed rapidly as a function of the heat‐setting time, and the corresponding shrinkage of the heat‐set samples sank below 1% in a timescale of 30–60 s for a film thickness of 500 μm. The heat treatment of the oriented films taken out of the bottle walls with fixed ends stabilized the induced structures, and the shrinkage of these heat‐set films was zero for temperatures up to the heat‐setting temperature, between 220 and 265°C, if the heat‐setting time was sufficient. According to the results obtained, a heat‐setting time of 30 s, for a film thickness of 500 μm, was sufficient at a heat‐setting temperature of 255°C to stabilize the produced biaxially oriented PEN bottles and to take them out the mold without further shrinkage. During the drawing of PEN, two different types of rigid amorphous phases seemed to be induced, one with a mean shrinkage temperature of 151°C and another rigid amorphous phase, more temperature‐stable than the first one, that shrank in the temperature range of 200–310°C. During heat setting at high temperatures, a continuous transformation of the less stable phase into the very stable phase took place. The heat‐set method after blow molding is industrially possible with PEN, without the complicated process of subsequent cooling before the molds are opened, in contrast to PET. This constitutes a big advantage for the blow molding of PEN bottles and the production of oriented PEN films. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1462–1473, 2003     

Mechanical and thermal properties of thermoplastic random copolyesters made from lipid‐derived Medium and long chain poly(ω‐hydroxyfatty acid)s

The physical properties of novel thermoplastic random copolyesters [‐(CH₂)_n‐COO‐/‐(CH₂)_n‐COO‐]_x made of long (n = 12) and medium (n = 8) chain length ω‐hydroxyfatty esters [HO‐(CH₂)_n‐COOCH₃] derived from bio‐based vegetable oil feedstock are described. Poly(ω‐hydroxy tridecanoate/ω‐hydroxy nonanoate) P(?Me13?/?Me9?) random copolyesters (M_n = 11,000–18,500 g/mol) with varying molar ratios were examined by TGA, DSC, DMA and tensile analysis, and WAXD. For the whole range of P(?Me13?/?Me9?) compositions, the WAXD data indicated an orthorhombic polyethylene‐like crystal packing. Their melting characteristics, determined by DSC, varied with composition suggesting an isomorphic cocrystallization behavior. TGA of the P(?Me13?/?Me9?)s indicated improved thermal stability determined by their molar compositions. The glass transition temperature, investigated by DMA, was also found to vary with composition. The crystallinities of P(?Me13?/?Me9?)s however, were unaffected by the composition. The stiffness (Young's modulus) of these materials was found to be related to their degrees of crystallinity. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40492.     

Effect of the shape of dispersed particles on the thermal and mechanical properties of biomass polymer blends composed of poly(L‐lactide) and poly(butylene succinate)

The structure and properties of binary blends composed of poly(lactic acid) (PLA) and fibrous poly(butylene succinate) (PBS), which were prepared by an uniaxial stretching operation in the molten state, were studied and compared with those of blends having spherical particles of PBS in a continuous PLA phase. We found from electron microscope observation that PBS nanofibers with a large aspect ratio were generated in the stretched samples. Enlargement of the surface area of the PBS particles, which showed nucleating ability for PLA, led to a high degree of crystallization and enhanced the cold crystallization in the heating process. Moreover, the PBS fibers in the stretched samples had a dominant effect on the mechanical properties in the point range between the glass‐transition temperature of PLA and the melting temperature of PBS. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Strontium(II) ion uptake on poly(N‐vinyl imidazole)‐based hydrogels

In this article, we report on the extraction of Sr(II) ions from aqueous solution with a series of poly(N‐vinyl imidazole)‐based hydrogels. The hydrogels were synthesized by the crosslinking of N‐vinyl imidazole with four different crosslinkers with γ rays as initiators. The well‐characterized hydrogels were used as Sr(II) sorbents. Sr(II) uptake was determined with a colorimetric method with Rose Bengal anionic dye. Scanning electron microscopy–energy‐dispersive spectroscopy analysis of the Sr(II)‐loaded polymers was recorded to ascertain the uptake of Sr(II) ions. The experimental adsorption values were analyzed with the Freundlich and Temkin equations, and the kinetics of adsorption were investigated with a pseudo‐second‐order sorption kinetic model. The results show that the equilibrium data fit well in the Freundlich isotherm and followed a pseudo‐second‐order kinetic model. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Enhanced toughness and strength of poly (d‐lactide) by stereocomplexation with 5‐arm poly (l‐lactide)

The enhancement of mechanical properties were achieved by solution blending of poly(d ‐lactide) (PDLA) and 5‐arm poly(l ‐lactide) (5‐arm PLLA). Differential scanning calorimetry (DSC) and wide‐angle X‐ray diffraction (WAXD) results indicated almost complete stereocomplex could be obtained when 5‐arm PLLA exceeded 30wt %. Tensile test results showed that the addition of 5‐arm PLLA in linear PDLA gave dramatically improvement both on tensile strength and elongation at break, which generally could not be increased simultaneously. Furthermore, this work transformed PDLA from brittle polymer into tough and flexible materials. The mechanism was proposed based on the TEM results: the stereocomplex crystallites formed during solvent evaporation on the blends were small enough (100–200 nm), which played the role of physical crosslinking points and increased the interaction strength between PDLA and 5‐arm PLLA molecules, giving the blends high tensile strength and elongation at break. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 132, 42857.     

Role of poly(lactic acid) in the phase transition of poly(vinylidene fluoride) under uniaxial stretching

The effect of poly (lactic acid) (PLA) on the crystalline phase transition of poly (vinylidene fluoride) (PVDF) from α‐ to β‐phase under uniaxial stretching for immiscible PVDF/ PLA blends was investigated. The typical sea‐island structure in the blends was found to facilitate the necking of PVDF and the transition from α‐ to β‐phase due to the local stress distribution during stretching. The crystalline phase transition of PVDF in the blends is temperature‐dependent and is affected by the content of PLA. The highest content of β‐phase, F(β), was achieved in the samples stretched at 60°C, while the effect of PLA content on the crystalline phase transition of PVDF is more complex. F(β) increases slightly when the sample with a PLA content no more than 15 wt % is stretched at 60, 80, and 100°C, and decreases sharply for the sample containing 20 wt % PLA; in addition, the sample containing 10 wt % PLA exhibits the highest F(β) no matter what the stretching temperature is. The mechanism of the crystalline phase transition of PVDF during the stretching is interpreted from energy barrier of the transition from α‐ to β‐phase and the morphological structures in the blends. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Effects of crystallinity on solid‐state polymerization of poly(ethylene terephthalate)

There has been a widely held assumption that the solid‐state polymerization (SSP) rate of poly(ethylene terephthalate) (PET) decreases with increasing crystallinity. Several published articles that purported to prove this assumption were based on faulty experiments. Therefore, a proper experimental procedure has been used to study the true effects of crystallinity on the SSP of PET. The results show that, for PET in pellet and powder forms, the SSP rate increases with increasing crystallinity. This is because an increase in the crystallinity results in increased end‐group concentration in the amorphous phase, where SSP reactions take place, and decreased concentrations of inactive end groups trapped inside the crystals, thereby increasing the rates of end‐group collision and reactions. These positive effects outweigh the negative effect of the increased byproduct‐diffusion resistance because of the increase in crystallinity. As the particle size of PET is increased beyond a critical value of about 7 mm, the SSP rate actually decreases with increasing crystallinity because of the excessively increased byproduct‐diffusion resistance within the PET particles. However, this critical particle size is far greater than the pellet sizes of commercial PET resins. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 623–632, 2006     

Flexural behavior of methyl methacrylate modified unsaturated polyester polymer concrete beams reinforced with glass‐fiber‐reinforced polymer sheets

This study represents the behavior of flexural test of methyl methacrylate modified unsaturated polyester polymer concrete beam reinforced with glass‐fiber‐reinforced polymer (GFRP) sheets. The failure mode, load–deflection, ductility index, and separation load predictions according to the GFRP reinforcement thickness were tested and analyzed. The failure mode was found to occur at the bonded surface of the specimen with 10 layers of GFRP reinforcement. For the load–deflection curve, as the reinforcement thickness of the GFRP sheet increased, the crack load and ultimate load greatly increased, and the ductility index was found to be the highest for the beam with the thickness of the GFRP sheet at 10 layers (6 mm) or 13 layers (7.3 mm). The calculated results of separation load were found to match only the experimental results of the specimens where debonding occurred. The reinforcement effect was found to be most excellent in the polymer concrete with 10 layers of GFRP sheet reinforcement. The appropriate reinforcement ratio for the GFRP concrete beam suggested by this study was a fiber‐reinforced‐plastic cross‐sectional ratio of 0.007–0.008 for a polymer concrete cross‐sectional ratio of 1 (width) : 1.5 (depth). © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Influences of pre‐ordered melt structures on the crystallization behavior and polymorphic composition of β‐nucleated isotactic polypropylene with different stereo‐defect distribution

As part of continuous efforts to understand the surprising synergetic effect between β‐nucleating agent and pre‐ordered structures of isotactic polypropylene (iPP) in significant enhancement of β‐crystallization (Ordered Structure Effect, OSE), two β‐nucleated iPP with different uniformities of stereo‐defect distribution (WPP‐A and WPP‐B) were prepared, their crystallization behaviors with variation of melt structures were studied in detail. The results revealed that β‐phase can hardly form in WPP‐A (whose stereo‐defect distribution is less uniform) because of its strong tendency of α‐nucleation caused by its less uniform stereo‐defect distribution, while WPP‐B is more favorable for β‐crystallization; As fusion temperature decreases, similar variation trends of crystallization temperature and β‐phase proportion can be observed from WPP‐A and WPP‐B, indicating the occurrence of OSE behavior, which provides unsurpassed β‐nucleation efficiency and induces β‐crystallization even in WPP‐A which is less favorable for β‐crystallization; moreover, the upper and lower limiting temperatures of Region II of WPP‐A and WPP‐B are identical, suggesting the uniformity of stereo‐defect distribution has little influence on temperature window for OSE (denoted as Region II). To explore the physical nature of Region II, self‐nucleation behavior and equilibrium melting temperature of PP‐A and PP‐B were studied. The lower limiting temperatures of exclusive self‐nucleation domain of both PP‐A and PP‐B are identical with the lower limiting temperatures of Region II in OSE (168°C); moreover, the T_m⁰ of both PP‐A and PP‐B are close to their upper limiting temperatures of Region II in OSE behavior (189°C). The possible explanation was proposed. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42632.