PE Crystals Research Articles

Regulating the structure of crosslinked polyethylene and its application in ultra‐high voltage cables

AbstractThe crystallinity of polyethylene has been extensively studied, but in situ experiments designed to investigate the crystallization of PE and XLPE have hardly been discussed. In this work, the crystallization behavior of PE and XLPE was investigated by designing in situ crystallization observation experiments. We have compared the crystallinity, crosslinking, viscosity properties, and gas byproducts of different XLPE insulating materials. COMSOL simulations demonstrate that the DTAP and DTBP crosslinker initiated crosslinks have better insulating properties and cable stability than the DTBC and DTBTMC crosslinkers. The formation of an insulation layer initiated by the DTAP crosslinker is beneficial for improving the breakdown strength, processing performance, and stable operation of cables. Our work is of great significance for understanding the crystallinity of XLPE and determining the correct crosslinker.Highlights In situ crystallization observation of PE and XLPE. Simulation of ultra‐high voltage cables. Finite element analysis. Investigation of gas byproducts in XLPE.

Increased interaction between Ultra-High Molecular Weight Polyethylene fibres and epoxy matrices for advanced composite materials

Ultra-High Molecular Weight Polyethylene (UHMWPE) fibre is considered as an excellent strengthening component due to its high specific stiffness and strength, good wear resistance, low coefficient of friction and great chemical resistance. However, very weak interfacial adhesion with resin has hampered the development of UHMWPE-based composites with high performance. With the aim of improving the interface adhesion properties, the surface of the fibres has been decorated with PE crystal by a suitable chemical treatment. Adhesion property has been examined by pull-out tests, while tensile tests have been performed to evaluate the strength of the fibre. Preliminary results indicate that, compared to unmodified UHMWPE fibres, the overall mechanical properties of the composite with treated UHMWPE fibres and epoxy resin have been greatly improved. Moreover, the applied treatment does not weaken the strength of the fibre. The study results imply that the modified fibres have a great potential for use as reinforcing elements in high-performance composites.

Synthesis of precision poly(1,3‐bicyclo[1.1.1]pentane alkylene)s via acyclic diene metathesis polymerization

Abstract1,3‐Disubstituted bicyclo[1.1.1]pentane (BCP) is a rigid, linear, non‐conjugated hydrocarbon unit that is usually transformed from [1.1.1]propellane. This unit has been introduced into drugs as mimics of 1,4‐disubstituted benzene moieties and used as rigid linkers in small‐molecule materials. However, the influence of this unique structure on the polymer properties has only been scarcely investigated. In this work, three symmetrical α,ω‐diene monomers containing one and two BCP units were synthesized for the first time from [1.1.1]propellane. Three types of precise poly(1,3‐bicyclo[1.1.1]pentane alkylene)s with BCPs located on every 11th and 21st chain carbons were obtained via acyclic diene metathesis (ADMET) polymerization and subsequent hydrogenation. All these polymers show higher thermal stability than linear polyethylene. For polymers containing one BCP moiety in their repeating unit, BCP acts as a defect to distort the PE crystals and decrease the melting temperature of PE. However, the polymer that containing a [2]staffane moiety (two jointed BCP units) in the polymer backbone forms a new crystalline morphology. This work elucidates the impact of BCP units on the thermal and crystallization behavior of PE, providing new insights of utilizing BCP unit to construct new polymer backbone, regulate the packing order of polymers and their properties.

Effects of diluent content on the crystallization behavior and morphology of polyethylene membrane fabricated via thermally induced phase separation process

Thermally induced phase separation technique has been widely applied to produce various commercial high-density polyethylene (HDPE) membranes based on the HDPE/diluent system. In this work, the crystallization behavior and morphological evolution of HDPE/liquid paraffin (LP) blends were systematically investigated by differential scanning calorimetry (DSC), dynamic thermomechanical analysis (DMA), two-dimensional small-angle X-ray scattering (2D-SAXS) and scanning electron microscope (SEM). It is found that the chain mobility of HDPE is promoted and the entanglement density reduces with the introduction of diluent LP. When the LP content is lower than 40%, the liquid diluent distributes randomly in HDPE melt, while as the LP content exceeds 40%, the diluent saturates the inter-molecular space of HDPE, resulting in the full growth of lateral lamellar dimension of PE crystal. On the other hand, the morphologies of HDPE/LP films change considerably with the diluent content. (1) LP content <20%: diluent lives directly in the inter-lamellar region; (2) 20% ≤ LP content ≤40%: diluent will be excluded into the inter-cluster region and leads to the formation of separated LP domains between PE clusters. (3) LP content >40%: diluent will be aggregated between the stacked clusters to create numerous interconnected LP domains which act as the pathways for the gas or liquid permeation after the removal of LP. Accordingly, we provide a new guidance for the condensed structure controlling and the development of PE membranes with diverse functionalities.

Amphiphilic olefin block copolymers synthesized by successive coordinative chain transfer and ring-opening polymerizations

Introducing polarity is a necessity for widening the application scope of polyolefins specifically for developing biocompatible products. To this end, we exploit a two-step polymerization process to synthesize poly(ethylene‑b‑caprolactone) PE‑PCL block copolymers, which contain both polar and non-polar segments. First ethylene is polymerized by a generic metallocene catalyst in the presence of ZnEt2 as the chain transfer agent according to the coordinative chain transfer polymerization (CCTP) technique. Terminal zinc atoms are subsequently replaced by hydroxyl groups (PE‑OH) by exposing dormant polymer chains to oxygen. Afterward, ring-opening polymerization (ROP) of ε‑caprolactone is initiated by PE‑OH to form PE‑PCL block copolymers. Successful formation of both blocks is verified by FTIR and NMR spectroscopy. The presence of PCL blocks greatly lowers the crystallinity of ethylene sequences according to XRD and DSC results. Moreover, a second type of PE crystals with more chain folds and lower lamella thickness is found in block copolymers, which is absent in the equivalent physical blend. The diverse crystal structure of block copolymers suggest that phase separation exists between PE and PCL segments. The SEM image of the equivalent physical blend confirms the tendency of PCL and PE chains to phase separate, and infers a compatibilization in the presence of PE‑PCL block copolymers. This phase separation is detected by rheological measurements, as well, where block copolymers show deviations from Maxwell behavior in the terminal relaxation zone at low frequencies. Rheology results also show that the order-disorder transition temperature (TODT) of these block copolymers is higher than 180 °C. These results provide a clear picture from the morphology and utility of such block copolymers specifically for compatibilizing blends of polar polymers and non-polar polyolefins, which significantly broaden the utility of polyolefins.

The effect of phase separation on crystallization of polyethylene/poly(ethylene-alt-propylene) blend

The influence of liquid–liquid phase separation (LLPS) on crystallization kinetics in off-critical and near-critical blends of polyethylene/poly(ethylene-alt-propylene) (PE/PEP) is studied to explore the origin of the two crystallization peaks in differential scanning calorimetry with the same long period. The PE/PEP blend systems show upper critical solution temperature (UCST) type of phase diagram and the crystallization temperature of PE component is much lower than the UCST, LLPS occurs first. The crystal nuclei first form at the interface region of two phases and then it is necessary for the PE chains to diffuse there to continue the crystallization process from both PE-rich and PEP-rich regions. As a result, the crystallization kinetics pathway is dynamically influenced by LLPS period of time, quench depth and initial composition because they control inter-diffusion coefficient in both phases. In the off-critical blend, the LLPS is extremely slow. The area ratio of the two DSC crystallization peaks doesn't fit with the ratio of coexistence compositions of PE in PE-rich and PEP-rich phases until LLPS has reached its equilibrium before crystallization. The crystallization of PE dominates the final morphology. Small and randomly dispersed crystals could be observed because the inter-diffusion of PE chains in PEP-rich phase is greatly hindered and they could not contribute to the formation of more perfect crystals. In the near-critical blend, LLPS kinetics is comparatively much faster, so the area of the two DCS crystallization peaks agrees with the coexistence compositions of PE. LLPS is the key factor to determine the final morphology.

Self‐assembled fibrillar polyethylene crystals with tunable properties

AbstractDue to its simple linear chain structure, crystal morphology of linear low‐density polyethylene (LLDPE) fibers can be controlled to fulfill the needs of diverse advanced applications. This study presents a simple two‐step method to produce LLDPE fibers with self‐assembled fibrillar crystals and highly oriented amorphous phase. Rather than conventional melt spinning, fibers were treated in a two‐step eco‐friendly bath without drawing after extruded fibers emerge from the spinneret. Treated fibers through the baths demonstrated lower crystallinity, but significantly higher degree of crystal orientation when compared to control fibers of traditional melt spinning. Morphological analysis revealed that a unique microstructure was formed after spinning through a two‐step eco‐friendly bath. As‐spun fibers demonstrated spherulitic morphology which can be transformed into a fibrillar structure followed by post‐drawing process. Cross sectional images of the treated LLDPE fibers produced at 400 m/min showed fibrillar PE crystals which can be more dominant upon post‐drawing. After two‐step bath treatment, produced fibers need low draw ratios to exhibit high performance. Our novel modification followed by hot drawing process can manipulate internal structure with performance of PE fibers to an outstanding level of 0.35 GPa strength and 3 GPa modulus at a production speed of 400 m/min.

Tailored crystalline structure and enhanced impact strength of isotactic polypropylene/high-density polyethylene blend by controlling the printing speed of fused filament fabrication

Fused filament fabrication (FFF) is the most commonly used 3D printing technology. In this work, the isotactic polypropylene/high-density polyethylene blend was used for FFF for the first time. A printing platform with arrays of conical holes was designed to overcome the warpage deformation of product. In order to investigate the influences of shearing force during the nozzle-extrusion process and stretching force during deposition process on the part property, various printing speeds were selected for series of samples. WAXD, SAXS and SEM measurements were used to study the phase morphology and crystalline structure of components. Results reveal that with the increase in printing speed, the PP crystal would deform into shish-kebab structure and PE crystal would deform into epitaxy crystalline structure owing to the strong shearing and stretching forces. These structures improved the impact strength by about 5 times. The printing speed showed slight influence on the thermal behavior. This work confirms the applicability of semicrystalline polymer in FFF technology and gives a deep understanding toward the printing conditions and part property. The obtained results also provide a new method to fabricate high-performance product which will broaden the research field of FFF.

Self-assembly of linear-hyperbranched hybrid block polymers: crystallization-driven or solvent-driven?

Self-assembly of polyethylene-block-hyperbranched polyglycidol diblock polymers (PE1-b-hbPG7-OH8 and PE1-b-hbPG26-OH27) in selective or slightly selective or nonselective solvents of PE segments were investigated by microscopy (TEM, SEM and AFM). Study showed that both polymers can be assembled into a diamond-shaped lamellae driving by PE crystallization in toluene solvent, composed of PE single-crystal layer sandwiched between two hbPG layers tethered on the top and bottom basal surfaces. However, by adding the toluene solution of polymers to THF and MeOH, the morphology of the aggregate changed from lamellae to rod or sphere, indicating the change of driving force from the crystallization of PE block to the interaction parameter (χ) between hbPG block and solvent. In addition, the degree of polymerization (DP) of hbPG segments affected the thickness of the lamellae (in toluene) and the shape and size of the rodlike or spherical aggregate (in mixed solvent), determined by the relative volume fractions of PE and hbPG chains in selective solvents.

Micromechanical models for the stiffness and strength of UHMWPE macrofibrils

Ultrahigh molecular weight polyethylene (UHMWPE) fibers have a complex hierarchical structure that at the micron-scale is composed of oriented chain crystals, lamellar crystals, and amorphous domains organized into macrofibrils. We developed a computational micromechanical modeling study of the effects of the morphological structure and constituent material properties on the deformation mechanisms, stiffness and strength of the UHMWPE macrofibrils. Specifically, we developed four representative volume elements, which differed in the arrangement and orientation of the lamellar crystals, to describe the various macrofibrillar microstructures observed in recent experiments. The stiffness and strength of the crystals were determined from molecular dynamic simulations of a pure PE crystal. A finite deformation crystal plasticity model was used to describe the crystals and an isotropic viscoplastic model was used for the amorphous phase. The results show that yielding in UHMWPE macrofibrils under axial tension is dominated by the slip in the oriented crystals, while yielding under transverse compression and shear is dominated by slips in both the oriented and lamellar crystals. The results also show that the axial modulus and strength are mainly determined by the volume fraction of the oriented crystals and are insensitive to the arrangements of the lamellar crystals when the modulus of the amorphous phase is significantly smaller than that of the crystals. In contrast, the arrangement and size of the lamellar crystals have a significant effect on the stiffness and strength under transverse compression and shear. These findings can provide a guide for new materials and processing design to improve the properties of UHMWPE fibers by controlling the macrofibrillar morphologies.

Crystallization behavior of precision polymers containing azobenzene defects

The crystallization of precision polymers containing (cis/trans)-azo-benzenes as defects within a polyalkylene-chain, prepared via ADMET and subsequent hydrogenation, is reported. The polymers are designed such that after exactly 18 –CH2− units an azobenzene-moiety (bearing either an o,o-dihydrogen (H-azo) or an o,o-difluorinated azo-moiety (F-azo) is placed, able to photochemically switch cis/trans configuration, thus changing the geometrical constraint exerted on the alkyl-moiety during crystallization and its crystal packing. The morphology of these polymers (Mn=3100 to 17,000g/mol) is investigated using differential scanning calorimetry (DSC), wide-angle X-ray scattering (WAXS) and successive self-nucleation and annealing (SSA) experiments, putting special emphasis on the crystallization of the alkyl moieties. H/F-azo defects within the poly(alkyl)-chains significantly increase the melting point of the polymers compared to ADMET polymers without defect. Successive self-nucleation and annealing (SSA) and WAXS analysis show inclusion of the azo-moieties into the PE crystal. Changing the aromatic azo units from hydrogen (H-azo) to fluorine (F-azo) atoms also increases the enthalpy of melting and the melting point of the azo-polymers. Photochemical trans-to-cis isomerization of the (F-azo)-polymers increases lattice disorder throughout the entire sample to an extent sufficient to disrupt the long-range structuring of the sample, thus causing the reduction in their crystallinities.

Effect of magnetic field on phase transitions in solutions and melts of flexible polymers

The effect of the magnetic field on the phase diagrams of flexible-chain polymer–solvent systems is observed for the first time. Phase transitions in systems with the crystalline-phase separation (PE–o-xylene, PE–n-hexane, PE–chloroform, PE–o-dichlorobenzene, PEG–1,4-dioxane, PEG–toluene) and the amorphous demixing (PS–methyl acetate, PVA–ethanol, PDMS–butanone) are studied. The magnetic field increases the temperatures of crystallization of PE and PEG from solutions and melts but has no effect on phase transitions in PS, PVA, and PDMS solutions. The structures of polymer entities isolated from solutions and melts are studied. Under application of the magnetic field to PEG solutions, spherulites of substantially smaller sizes than those formed outside the field appear. The magnetic field increases the degree of crystallinity of PEG, but the degree of crystallinity and size of PE spherulites remain unchanged.

Effects of crystal structure of poly(β-propiolactone) blocks on the cooperative crystallization of a polyethylene-block-poly(β-propiolactone) diblock copolymer

The crystalline morphology of a double crystalline polyethylene-block-poly(β-propiolactone) diblock copolymer (PE-b-PPL) was examined using synchrotron small-angle X-ray scattering (SR-SAXS), where the PPL block crystallized into δ- or β-form according to the thermal history during sample preparation. Furthermore, the isothermal crystallization process of PE-b-PPL was pursued using simultaneous time-resolved SR-SAXS and wide-angle X-ray diffraction (SR-WAXD). The crystallization behavior of δPPL blocks (i.e., PPL blocks to crystallize into δ-form) was similar to that of PE blocks without any detectable induction time, so simultaneous crystallization of PE and δPPL blocks was observed on quenching from a lamellar microdomain structure (LMS), yielding a largely distorted LMS (with the standard deviation of each lamella thickness ∼ 36%). On the other hand, the βPPL blocks (i.e., PPL blocks to crystallize into β-form) started to crystallize after an appreciable induction time, showing sequential crystallization (i.e., advance crystallization of PE blocks and subsequent crystallization of βPPL blocks) to form a slightly distorted LMS (18%). Consequently, the final crystalline morphology was significantly different depending on the crystal structure of PPL blocks, though the crystallization started from an identical LMS. The crystallization mechanism of PE-b-PPL was discussed by considering the difference in crystallization kinetics between PE blocks and PPL (δPPL or βPPL) blocks.

UHMW Ziegler–Natta polyethylene: Synthesis, crystallization, and melt behavior

Abstract The fabrication of normal and UHMW PE end-products involves melting and crystallization of the polymer. Therefore, the melt behavior and crystallization of as-synthesized UHMW PE, and NMW PE and E-1-hexene copolymer have been studied using a new nonisothermal crystallization model, Flory's equilibrium theory and ethylene sequence length distribution concept (SLD), Gibbs–Thompson equation, and DSC experiments. By using this approach, the effects of MW, 1-hexene incorporation, ethylene SLD, the level of undercooling θ , and crystal surface free energy D on crystallite stability, relative crystallinity α , instantaneous crystallinity χ , the crystallization kinetic triplet, crystallization entropy, and lamellar thickness distribution (LTD) have been evaluated. Consequently, this study reports insightful new results, interpretations, and explanations regarding the melting and crystallization of the aforementioned polymers. The UHMW PE results significantly differ from the NMW PE and E-1-hexene copolymer ones. Ethylene sequences shorter than the so called minimum crystallizable ethylene sequence length , irrespective of E-1-hexene copolymer MW, can also crystallize. Additionally, the polymer preparation shows that the catalyst coordination environment and symmetry, as well as achiral ethylene versus prochiral α -olefin steric encumbrance and competitive diffusion affect the synthesis of UHMW PE, particularly the corresponding UHMW copolymers.

Nucleation and mechanical enhancements in polyethylene-graphene nanoplate composites

Abstract Graphene nanoplatelets (GNP) dispersed in high-density polyethylene (HDPE) were found to significantly enhance nucleation of PE crystallization, and thermal/mechanical properties of HDPE-GNP nanocomposites. Excellent dispersion of GNPs was achieved by combining solution blending and twin-screw extrusion homogenization. The dispersion state was confirmed by bimodal AFM and also by the resulting improvements in thermal, mechanical, and transport properties. The crystallization rates were shown to markedly increase at low GNP content (0.1 wt%) and continued to increase with GNP loading up to 15 wt%. The size of secondary structures, or spherulites, decreased with GNP loading. Smaller spherulite sizes and faster kinetics suggested enhanced nucleation with GNP addition. 30–40% reductions in permeability and up to 60% higher Young’s moduli were found in these HDPE-GNP nanocomposites. Restricted polyethylene mobility and enhanced thermal stability with increasing GNP loading were also indicated in these HDPE-GNP nanocomposites.

Graphene-induced tiny flowers of organometallic polymers with ultrathin petals for hydrogen peroxide sensing

A facile and efficient approach for scalable synthesis of polymer flowers decorated with Prussian blue (PB) and graphene nanosheets is reported for the first time. This approach involved graphene-induced crystallization of polyethylene capped with a cyanoferrate complex (PE–Fe), followed by in situ coordination polymerization of cyanoferrate complex with Fe3+ on the surface. The morphological and thermal analyses demonstrated that graphene nanosheets prompted the crystallization of PE–Fe, affording the formation of hybrid flowers of 3μm. The tiny flowers were comprised of ultrathin petals of 10nm in thickness, which consisted of a single polyethylene lamella sandwiched between two PB/graphene nanolayers. Hybrid flowers exhibited excellent electrocatalytic activity toward reduction of hydrogen peroxide. Maximum reduction current of hybrid flowers was two orders of magnitude higher compared with conventional PB particles. Moreover, the sensors based on hybrid flowers showed by far higher successive performance ability as contrast to conventional PB particles. Such graphene-induced flower-like nanoarchitectures offer a catalog of functional nanomaterials useful for biosensing and nanodevices.

Crystallization behavior of poly(β-propiolactone)-block-polyethylene copolymers with varying polyethylene crystallinities

The crystallization behavior of poly(β-propiolactone)-block-polyethylene (PPL-b-PE) copolymers with high PE crystallinities χPE (>0.30) has been examined using time-resolved synchrotron small-angle X-ray scattering and Fourier transform infrared spectroscopy, where the PE block crystallized first and subsequently the PPL block crystallized on quenching from a strongly segregated melt. The crystallization of PE blocks destroyed the lamellar microdomain structure (LMS) existing in the melt to form the crystalline lamellar morphology (CLM), and then PPL blocks crystallized within CLM. This morphology formation was compared to our previous results for the crystallization of PPL-b-PE copolymers with low χPE (0.12 < χPE < 0.26), where the crystallizability of PE blocks was not sufficiently large to destroy LMS. As a result, PE blocks crystallized promptly within LMS to reinforce and stabilize it against the subsequent crystallization of PPL blocks, yielding the confined crystallization of both blocks within LMS. We summarize these results including the case of χPE = 0, and propose three mechanisms of morphology formation occurring in PPL-b-PE copolymers according to χPE (i.e., high, low, or zero).

How different mesophases affect the interactive crystallisation of a block co-oligomer

An effective method for fabrication of long range ordered micro- and nanostructures on surfaces is to control the interactive crystallisation of block copolymers. In this study, the influence of different initial mesophases of a double crystalline polyethylene-block-poly (ethylene oxide) (PE-b-PEO) diblock co-oligomer on the interactive crystallisation process was studied using synchrotron radiation X-ray diffraction (SAXS/WAXD), in situ optical microscopy and differential scanning calorimetric analysis (DSC). According to the applied annealing procedure, different PE-b-PEO initial mesophases, i.e., disordered, cylindrical and spherical, have been induced. In all cases, the subsequent PEO crystallisation disrupted these initial microdomains and transformed them into crystalline lamellar morphologies with the same long periods. However, the different initial mesophases significantly affected the PEO crystallisation kinetics due to different topological confinements. An initial disordered mesophase induced the highest PEO crystallisation rate because PEO nucleation and crystal growth were limited only by chain diffusion. For an initial spherical or cylindrical mesophase, decreased PEO crystallisation rates were observed. Here, the chain diffusion was decreased by the microdomain structure. For an initial cylindrical mesophase, the earlier formed PE crystals act as a template for the subsequent PEO crystallisation and, thus, increased the PEO crystallisation as compared to the spherical mesophase where the PE was amorphous. This study demonstrates that the topological confinement of the block copolymer's initial mesophase strongly influences the crystallisation kinetics and, thus, the structures formed at the surface of drop-casted films.

Pathway mediated microstructures and phase morphologies of asymmetric double crystalline co-oligomers

Various microstructures and phase morphologies of an amphiphilic poly(ethylene oxide)-block-polyethylene (PEO-b-PE) co-oligomer, controlled by topological restriction of PE segments on the tethered PEO chains, were characterized by differential scanning calorimetry (DSC), polarized optical microscopy (POM), scanning electron microscopy (SEM), and synchrotron radiation wide-angle/small-angle X-ray scattering (WAXS/SAXS) in drop-cast films. The crystallization processes were mediated by two pathways, a one-step crystallization process (I) and a sequential crystallization process (II). Results show that the thermal procedures have great influence on the microstructures and phase morphologies of PEO-b-PE co-oligomer, e.g., negative spherulites with radial stripes were detected in the one-step crystallization process (I), while crystalline texture, which contains a large number of crystals with reduced sizes, formed in the sequential crystallization process (II). Based on our experimental data, the topological restriction effect encountered by PEO chains depends on the hard confinement of PE crystals and the soft confinement of amorphous PE in the two crystallization procedures. The formation mechanisms of the long-range order structures within the co-oligomer were elucidated through morphology models. These nano-patterned structures make the double crystalline block copolymers outstanding candidates for surface modification, micromolding, and optoelectronic devices in nanotechnological and biomedical applications.

Crystallization of double crystalline block copolymer/crystalline homopolymer blends: 1. Crystalline morphology

The crystalline morphology formed in binary blends of poly(ε-caprolactone)- block-polyethylene (PCL-b-PE) copolymers and PCL homopolymers has been examined using synchrotron small-angle X-ray scattering (SR-SAXS) and differential scanning calorimetry (DSC) as a function of the homopolymer fraction in the blend. The PE block crystallized first on quenching from a lamellar microdomain structure to set a hard lamellar morphology (PE lamellar morphology) in the blend, followed by the crystallization of PCL chains (i.e., PCL homopolymers + PCL blocks). Two binary blends were studied by considering the miscible state of PCL homopolymers in the microdomain structure: when the PCL homopolymers were uniformly mixed with PCL blocks, they formed a mixed crystal. When the PCL homopolymers were localized between PCL blocks in the microdomain structure, DSC results suggested the possible formation of separate PCL crystals in the PE lamellar morphology. The effect of the advance crystallization of PE blocks on the subsequent crystallization of PCL chains was discussed as compared with the crystalline morphology formed in PCL-block-polybutadiene copolymer/PCL homopolymer blends, where the crystallization of PCL chains started directly from a microdomain structure without forming the hard lamellar morphology.