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Unformatted post-print version of the accepted article Solid-solid transitions in poly (hexamethylene carbonate) (PC6) and poly (octamethylene carbonate) (PC8), denoted δ to α transition, have been investigated, using self-nucleation and Successive Self-nucleation and Annealing (SSA) technique. The SSA protocol was performed in-situ for thermal (differential scanning calorimetry (DSC)), structural (Wide-angle X-ray Scattering (WAXS)), and conformational (Fourier-transformed Infrared Spectroscopy (FT-IR)) characterization. The final heating after SSA fractionation displayed an enhanced (compared to a standard second DSC heating scan) endothermic and unfractionated peak signal at low temperatures corresponding to the δ to α transition. The improved (i.e., higher enthalpy and temperature than in other crystallization conditions) δ to α transition signal is produced by annealing the thickest lamellae made up by α and β phase crystals after SSA treatment. As thicker lamellae are annealed, more significant changes are produced in the δ to α transition, demonstrating the transition dependence on crystal stability, thus, on the crystallization conditions. The ability of SSA to significantly enhance the observed solid-solid transitions makes it an ideal tool to detect and study this type of transitions. In-situ WAXS reveals that the δ to α transition corresponds to a change in the unit cell dimensions, evidenced by an increase in the d-spacing. This implies a more efficient chain packing in the crystal, for both samples, in the δ phase (lower d-spacing at low temperatures) than in the α phase (higher d-spacing at high temperatures). The chain packing differences are explained through in-situ FT-IR measurements that show the transition from ordered (δ phase) to disordered (α phase) methylene chain conformations. We would like to acknowledge financial support provided by the National Key R&D Program of China (2017YFE0117800) and the National Natural Science Foundation of China (51820105005, 21922308, and 52050410327). We also acknowledge financial support from the BIODEST project; this project has received funding from the European Union’s Horizon 2020 research and innovation program under the Marie Skłodowska-Curie Grant Agreement No. 778092. This work has also received funding from MINECO through project MAT2017-83014-C2-1-P and from the Basque Government through grant IT1309-19. R.A.P.-C is supported by the China Postdoctoral Science Foundation (2020M670462). G.L. is grateful to the Youth Innovation Promotion Association of the Chinese Academy of Sciences (Y201908). We also thank the BSRF (beamline 1W2A) for providing beamtime.

Unformatted post-print version of the accepted article Poly (hexamethylene carbonate) (PC6) and poly (octamethylene carbonate) (PC8) were studied under different crystallization conditions. Using differential scanning calorimetry (DSC), a new solid-solid transition, denoted α to δ transition, was detected at low temperatures (

Unformatted post-print version of the accepted article The inclusion of polymer-grafted nanoparticles (PGNPs) can impart various functional properties to polymer nanocomposites (PNCs). For semicrystalline polymers, we can control the spatial dispersion of PGNPs and presumably use it to modulate the nucleation rate of the polymer. In this work, the correlation between the dispersion quality of poly(ethylene glycol) (PEG) grafted silica (PEG-g-SiO2) nanoparticles and the crystallization ability of poly(ethylene oxide) (PEO) nanocomposites is systematically investigated by varying the grafting density (σ, chains/nm2) and the value of P/N (P: molecular weight of matrix chains, N: molecular weight of grafted chains). The variation of PEG-g-SiO2 dispersion state was studied by morphological characterization and small-angle X-ray scattering (SAXS). It was found that, in contrast to the unmodified SiO2 and poly(methyl methacrylate) grafted silica (PMMA-g-SiO2), PEG-g-SiO2 (high σ and low P/N) can increase the nucleation rate of PEO even under conditions where they are well dispersed in the PEO matrix. Evidently, the nature of the graft, i.e., amorphous PMMA vs. crystallizable PEO, has profound consequences in this context, a novel result that has not been anticipated based on previous work. NP aggregation occurs at higher P/N values and limits the effectiveness of the grafted PEG on the crystallization ability of PEO nanocomposites. Based on differential scanning calorimetry (DSC) and polarized light optical microscopy (PLOM) characterization, we deduced that the increased nucleation density at high σ and low P/N has a strong impact on accelerating the overall crystallization of PEO nanocomposites. This project is supported by the Ministry of Science and Technology of China (2017YFE0117800) and the National Natural Science Foundation of China (21574141). We would like to thank the financial support provided by the BIODEST project; this project has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 778092. The authors thank Prof. Yongfen Men (CIAC) for providing the SAXS beam time and helps during experiments. The discussion of TEM data with Andrew M. Jimenez (Columbia University, New York, NY) is gratefully acknowledged. We also thank B. Guan, J. L. Yue and K. A. Liu for help in cryo-TEM experiments.

The determination of intrinsic chain stiffness of conjugated polymers is challenging, in particular, for scattering techniques because of their strong light absorption and structural instability du...

The orientation of polymers under confinement is a basic, yet not fully understood phenomenon. In this work, the texture of poly(ethylene oxide) (PEO) infiltrated in nanoporous anodic alumina oxide (AAO) templates was investigated by X-ray pole figures. The influence of geometry and crystallization conditions, such as pore diameter, aspect ratio, and cooling rates, was systematically examined. All the samples exhibited a single, volume-dependent crystallization temperature (Tc) at temperatures much lower than that exhibited by bulk PEO, indicating “clean” microdomains without detectable heterogeneous nucleation. An “orientation diagram” was established to account for the experimental observations. Under very high cooling rates (quenching), crystallization of PEO within AAO was nucleation-controlled, adopting a random distribution of crystallites. Under low cooling rates, growth kinetics played a decisive role on the crystal orientation. A relatively faster cooling rate (10 °C/min) and/or smaller pores lead to the * ║ pore axis (n⃗) mode (uniaxial orientation). When the cooling rate was lower (1 °C/min), and/or the pores were larger, a mixed orientation, with a coexistence of * ║ n⃗ and * ║ n⃗ , was observed. The results favor the kinetic model where the fastest growth direction tends to align parallel to the pore axis. This work is supported by the National Natural Science Foundation of China (NSFC, 21873109, 51820105005, 21274156). G. L. is grateful to the Youth Innovation Promotion Association of the Chinese Academy of Sciences (2015026). G. L., D. W., and A. J. M. also acknowledge European funding by the RISE BIODEST project (H2020-MSCA-RISE-2017-778092). The authors thank Dr. Zhongkai Yang for assistance with pole figure measurement.

Understanding the deformation mechanism of conjugated polymers is essential for developing flexible or stretchable electronic devices. In this work, the mechanical properties of poly(3-dodecylthiophene) (P3DDT) and poly(3-hexylthiophene) (P3HT) are measured at different temperatures, and the underlying deformation mechanism is explored by using in situ X-ray scattering and pole figure. It is observed that the modulus and fracture strength of P3DDT decrease with increasing stretching temperature. The elongation at break of P3DDT exhibits a sharp increase when the stretching temperature reaches 45 °C. The general deformation process of the two polymers is in line with the traditional deformation mechanism established for flexible crystalline polymers with several special features. Well-defined yielding is not detected even at temperatures below the main-chain glass transition temperature, which corresponds to the microscopic observation of the absence of a well-defined lamellar–fibrillar transition. By anal...

Reversible periodic structures in a symmetric poly(butylene succinate)-co-poly(e-caprolactone) (PBS-co-PCL) multiblock copolymer have been detected for the first time. A phase-segregated structure can be observed under the phase contrast optical microscope at 150 °C, but it has no significant effect on the subsequent crystallization behavior of the PBS component, which can break out at lower temperatures (i.e., 82 °C) forming spherulites that contain the molten PCL component within them. During PBS chains crystallization at 82 °C, two peaks are detected by SAXS experiments. The high-q peak corresponds to a periodic structure formed within PBS-rich domains consisting of PBS lamellae and amorphous regions containing PBS and molten PCL chains. The low-q peak arises from a periodic structure formed within PCL-rich domains consisting of PBS lamellae and thick amorphous layers needed to accommodate the large fraction of molten PCL chains at 82 °C. When the temperature is decreased to 36 °C, the PCL component cr...

The crystallization of poly(e-caprolactone) (PCL) and isotactic polypropylene (iPP) infiltrated in nanoporous anodic alumina oxide (AAO) templates was reexamined to demonstrate the importance of obtaining polymer-free, clean AAO surfaces on the nucleation, size dependence of crystallization temperature (Tc), and texture. The AAO pore diameters cover a broad range from 400 to 20 nm. When the AAO templates were completely free of any residual polymer on their surfaces, differential scanning calorimetry (DSC) experiments exhibited a single crystallization peak for all the samples with different AAO pore sizes. A drastic decrease in Tc with density of domains indicated a transition from heterogeneous to homogeneous/surface nucleation. A regular decrease of Tc with pore size was observed in the low Tc regime, as a result of the volume dependence of nucleation events. The chain alignment of the two polymers infiltrated in AAO was studied by two-dimensional wide-angle X-ray scattering (WAXS). By comparing the ex...

Triple crystalline triblock terpolymers are materials with remarkable semicrystalline superstructures. In this work, we report for first time the alternating triple lamellar morphology that self-assembles inside spherulites of a triblock terpolymer composed of poly(ethylene oxide) (PEO), poly(e-caprolactone) (PCL), and poly(l-lactide) (PLLA). The morphology of the PEO-b-PCL-b-PLLA triblock terpolymer is compared to an analogous PCL-b-PLLA diblock copolymer. Both diblock and triblock form a single phase in the melt. Two crystallization protocols were employed to create particular crystalline morphologies. In both cases, the isothermal crystallization of the PLA block is induced first (at 81 °C, a temperature above the melting points of both PCL and PEO blocks) and PLLA spherulites form a template, whereupon cooling the other two blocks can crystallize within the PLLA interlamellar spaces. WAXS analysis demonstrated the double crystalline and triple crystalline nature of the materials. The lamellar structur...

The classic deformation mechanism of the Gaussian model of Haward and Thackray was utilized to treat the true stress−strain behaviors of a family of novel polyether-b-amide segmented copolymers based on the crystalline hard segments of polyamide1012 and the amorphous soft segments of poly(tetramethylene oxide). The results showed that the deformation behaviors of the plastic copolymers abided by the Gaussian model, causing the modulus G of the strain-induced hardening process to depend on the weight percentage of the polyamide segments in the copolymers. By contrast, the deformation of elastomeric copolymers deviated from the model because of the occurrence of strain-induced crystallization in the soft polyether sections at large strains, which negated the Gaussian assumption; i.e., the random coil conformation was maintained even under substantial stretching. The onset point of deviation was, for the first time, quantitatively identified by in situ FTIR and further confirmed by in situ WAXD/SAXS.

The structural transitions in solution-cast film of poly[5,5′-bis(2-butyloctyl)-(2,2′-bithiophene)-4,4′-dicarboxylate-alt-5,5′-2,2′-bithiophene] (PDCBT) copolymer have been systematically studied by a combination of differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), in situ Fourier transform infrared spectroscopy (FTIR), UV–vis spectroscopy, and in situ wide-angle X-ray scattering (WAXS). The glass transition temperature of the main chain as well as the melting and crystallization temperatures of the polymer were determined as 10, 238, and 221 °C, respectively. The out-of-plane deformation vibration of PDCBT Cβ–H groups in FTIR has been manifestly assigned for the first time. A broad endothermic peak between 30 and 120 °C was observed during DSC heating process and was attributed to the enthalpic relaxation of the twist glass transition, which resulted in a small negative effect on the power conversion efficiency (PCE) of solar cells. A reorganization process in the crystalline re...

The crystallization behavior of poly(l-lactic acid) (PLLA) infiltrated in anodic alumina oxide templates (AAO) was investigated by differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD). During heating from the glassy state, the crystallization of infiltrated PLLA was unexpectedly enhanced as compared with bulk PLLA. The cold crystallization temperature of infiltrated PLLA from the glassy state was much lower than that of bulk PLLA. The half-crystallization time (t1/2) of infiltrated PLLA at 75 °C decreased with the diameter of AAO nanopores. The glass transition temperature of PLLA was not influenced by the geometrical confinement. The enhanced crystallization from the glassy state was explained by surface-induced nucleation of AAO walls on PLLA. Our results provide the first observation of enhanced cold crystallization of polymers in confined geometry.

Multiblock copolymers consisting of crystalline poly(butylene succinate) and amorphous poly(1,2-propylene succinate) (PBS-co-PPS) are synthesized. The microstructure of the materials is investigated by the combination of thermal analysis and wide-angle/small-angle X-ray scattering (WAXS/SAXS). The noncrystalline PPS blocks are found to locate predominately in the amorphous phase between crystalline lamellae of PBS. By means of in situ WAXS coupled with optical-assisted strain measurement, the deformation process of PBS-co-PPS is studied. The stiffness and strength of PBS-co-PPS decrease with increasing PPS fraction, while the strain recovery behavior of PBS-co-PPS is similar to PBS homopolymer. Transition from α crystal to β crystal is observed for all the PBS-co-PPS samples. The critical stress for α–β transition of PBS-co-PPS is determined, which is found to be independent of PPS blocks. The universal critical stress for crystal transition is interpreted through a single-microfibril-stretching mechanism.

The epitaxy forced crystallization behavior of thin film olefin block copolymer (OBC) samples was investigated in the presence of benzoic acid (BA). The investigated OBC samples show apparent phase separation in the melt. However, their dissimilar comonomer difference between hard and soft segments (ΔC8) and block lengths results in different segregation strength, which controls their crystallization behavior. Independent of the crystallization conditions, for both OBCs the BA substrate induces highly oriented and epitaxially grown lamellar crystals. In case of the weakly melt segregated OBC, crystallization always breakout the melt separated phase domains, and crystals are homogeneously distributed in the entire sample. For strongly melt segregated OBC, on the other hand, phase separation is maintained when quenching the samples, and only isolated crystalline domains are formed. However, subsequent annealing of quenched samples, slow cooling from the melt, or isothermal crystallization at low supercoolin...

The structural evolution of poly(butylene succinate) (PBS) during tensile deformation was investigated by in situ synchrotron X-ray scattering. Crystal transition during stretching was identified at 30–90 °C. An increase of long period was observed during the α–β crystal transition, which was attributed to the increase of both amorphous layer thickness and crystalline layer thickness (lamellar thickness). The reversibility of crystal transition and correlation of lamellar thickening with crystal transition were confirmed by a “step-cycle” deformation measurement. The variation of the amorphous layer was partially recoverable, while the variation of lamellar thickness was nearly fully recoverable. The different repeating length in unit cell along the chain axis in different crystal forms resulted in the variation of the lamellar thickness. The different recoverability of structural parameters was interpreted by the different dynamics of the amorphous and crystalline phase.

The β-form of isotactic polypropylene (iPP) is a technologically useful material. In this context, pathways to produce this material have been intensively studied for at least two decades. One method, developed by Varga, is to selectively nucleate β-iPP on preexisting α-iPP row nuclei. 1-5 This method utilizes the different temperature dependences of crystal growth rates of α- and β-iPP, there being a narrow temperature window, 100-140 °C, in which the growth of the β-phase is faster than that of the α-phase. 1.6 It is required then only to provide the β-form nuclei in this regime, for β-form growth to outstrip that of α and become the predominant phase. A simple procedure for growing β material is to embed existing, oriented α-iPP fibers into an iPP melt and then lower the temperature into the temperature region which favors β-form growth. 7-9 With this method, it has been shown that the oriented fibers must be partially melted, by insertion into the existing melt at temperatures above 170 °C, in order to successfully nucleate β-crystallization at a lower temperature. 8 Nothing has been reported on the β-nucleation process for PP β-crystallization induced by oriented fibers. In the work reported here, we explore the role of matrix iPP on this process and, on the basis of these results, suggest a role of the matrix polymer in the nucleation process.

We report a simple method to prepare biodegradable polymer−amphiphile complexes by solution mixing of poly(propylene carbonate) (PPC) with octadecanoic acid (OA). The complexes were characterized by combination of thermogravimetry analysis (TGA), differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), small-angle X-ray scattering (SAXS), polarizing optical microscopy (POM), transmission electron microscopy (TEM), and Fourier transform infrared spectroscopy (FT-IR). Compared with the amorphous PPC copolymer, the PPC−OA-x complexes show excellent thermal stability and form thermotropic liquid crystalline state without rigid mesogenic units. The corresponding mechanism has been proposed to elucidate the observed phenomena. The stabilization effect induced by hydrogen-bonding interactions between PPC and OA molecules is responsible for the thermostability and formation of liquid crystalline state. The present findings may extend the applications of such biodegradable aliphatic polycarbon...

The crystalline morphology and the liquid−liquid phase separation (LLPS) of an isotactic polypropylene/poly(ethylene-co-octene) (iPP/PEOc) polymer alloy prepared on a single multicatalyst reactor granule were studied by polarized optical microscope, phase contrast optical microscope, and scanning electron microscopy (SEM). We found that the LLPS process had a dominant effect on the final crystalline morphology of the iPP/PEOc polymer alloy. As the LLPS time was increased at 160 °C, more and more elastomer component was dispersed uniformly in the iPP spherulites as droplets, instead of being rejected to the outside and concentrated at the boundaries of the spherulites, when the sample was isothermally crystallized at 140 °C. The morphologies can be explained by the phase separation and crystallization kinetics. By simply changing the LLPS time, we could control the size of the elastomer droplets (for example between 1 and 10 μm) that dispersed in the iPP spherulites. Meanwhile, a special structural feature...

Systematic investigation on the compositional heterogeneity, phase structure, the crystallization and subsequent melting behavior of two commercial in-reactor alloys EB−P and EP−P (ethylene-co-butylene polypropylene and ethylene-co-propylene polypropylene) from Basell were conducted. The composition of the alloys and the chain structure of each component were characterized by combinatorial using of preparative TREF and 13C NMR technique. The compositional heterogeneities of both samples were further studied by SSA technique, and possible thermal fractionation mechanisms were then inferred. Correlations between the mechanical properties and the molecular architectures and phase structures were discussed. The results show that the excellent balance between toughness and rigidity of sample EB−P primarily benefits from the crystalline polyethylene homopolymer (HPE) phase and the amorphous ethylene-α-olefin copolymer (EC) component, which is proved to be enriched at the interface between the dispersed polyprop...

The influence of the rigidity of polymer backbones on the side-chain crystallization and phase transition behavior was systematically investigated by a combination of differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), Fourier transform infrared spectroscopy (FTIR), and high-resolution solid-state nuclear magnetic resonance spectroscopy (NMR). DSC investigation indicated that the crystallization number of alkyl carbon atoms of the side chains grafted onto the rigid polymer backbone, poly(p-benzamide) (PBA), is much lower than that of the alkyl carbon atoms of the side chains grafted onto the flexible polymer backbone, poly(ethyleneimine) (PEI), implying that the conformational state of the polymer backbones has a strong effect on the side-chain crystallization behavior in comblike polymers. WAXD and FTIR results proved that these two comblike polymers pack into hexagonal (PBA18C) and orthorhombic (PEI18C) crystals, respectively, depending on the adjusting ability of the polymer backbones for particular conformational states. It was also found that the presence of the crystalline-amorphous interphase (delta = 31.6 ppm) in PBA18C detected by solid-state C-13 NMR spectroscopy can be attributed to the rigid PBA backbone, which restricts the mobility of the alkyl side chains.

Through introducing the iPP fibers having different molecular weights into their supercooled or molten matrices, fiber/matrix single polymer composites of iPP have been prepared, and the obtained interfacial morphologies were studied by means of polarized light microscopy. It was found that the interfacial supramolecular structure was affected by not only the introduction temperature but also the molecular weight of the iPP fibers. At low fiber introduction temperatures, solid iPP fiber induces the growth of α-iPP crystals and results in the formation of pure α-iPP transcrystallization layer in the vicinity of iPP fiber regardless of its molecular weight. At high fiber introduction temperatures, completely molten iPP fiber, with either high or low molecular weight, loses its nucleation ability toward iPP matrix. The interfacial structure induced by incomplete molten iPP fibers is different from fiber to fiber. This has been explained in terms of different relaxation behavior of the fiber, which has been f...

A series of branched poly(ethyleneimine) (PEI) derived polymers with different lengths of n-alkyl side chains, denoted as PEI(n)Cs (n = 12, 14, 16, 18, 20, number of carbon atoms in alkyl side group), have been prepared by a N-alkylation method, and systematically characterized by differential scanning calorimertry (DSC) and wide-angle X-ray diffraction (WARD) as well as Fourier transform infrared spectroscopy (FTIR). The side chains grafted on these comblike polymers are long enough to form crystalline phase composed of paraffin-like crystallites. The crystallization of the side chains forces the branched poly(ethyleneimine) molecules to pack into layered structure, between which the crystallites are located. The melting temperatures of the side chain crystallites increase from -12.36 to +51.49 degreesC with increasing the length of the side chains from n. = 12 to n = 20, which are a little bit lower than the corresponding pristine n-alkanes. PEI18C was taken as an example in this work for the investigation of phase transition and conformational variation of the side chains with temperature changing.

The morphologies of iPP fiber/matrix homogeneity composites were studied on a lamellar level with the help of a field emission scanning electron microscope. It is found that the induced supermolecular structure of iPP depends strongly upon the fiber introduction temperature. At temperatures lower than 164 °C, no melting of the original iPP fiber takes place, and the solid iPP fiber can initiate only the growth of parallel aligned α-iPP lamellae normal to the fiber axis. At temperatures above 165 °C, the morphological change from the microfibrils to lamellae implies the occurrence of melting and recrystallization of the iPP fiber during sample preparation. At the same time, the increment of β-iPP content with the increase of fiber introduction temperature demonstrates unambiguously that the β-iPP crystallization is associated with the above-mentioned melting and recrystallization process. Combining the structural features of the recrystallized iPP fibers and the induced interfacial layers, it is suggested that the chain orientation status in the molten iPP fiber plays an important role in subsequent β-iPP crystallization.

Through introducing the iPP fibers into their supercooled homogeneity matrices, the homogeneity fiber/matrix composites of iPP have been prepared, and the resulting supermolecular structures of iPP matrices induced by their homogeneity fibers as a function of introduction temperature were studied by means of optical microscopy. The results show that the supermolecular structures of iPP matrices induced by their homogeneity fibers can be ascribed to the transcrystallization of iPP triggered by strong heterogeneous nucleation rather than the shear stress produced by fiber introduction. The morphological features demonstrate that the interfacial transcrystalline iPP is composed of purely α-form if the fibers were introduced at 138 °C. With increase of fiber introduction temperature, an increasing content of β-iPP surrounding the iPP fibers has been observed. A transcrystallization layer of mainly β-modification iPP can be obtained when the fiber introduction temperature was set at 173 °C. This is associated ...

The interfacial interactions of polymer-nanoparticles have dramatical effects on the crystallization behavior of grafted polymers. In this study, methoxy polyethylene glycol (MPEG) (molecular weights 750, 2000 and 4000 g mol−1) was grafted onto amino-modified nanosized silica (SiO2-NH2) by the “grafting to” method. The effects of the grafting density and molecular weight on the confined crystallization of grafted MPEG (MPEG-g-SiO2) were systematically investigated by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and wide-angle X-ray scattering (WAXS). It was found that confinement effects are stronger when lower molecular weights of grafted MPEG are employed. These grafted MPEG chains are more difficult to stretch out on SiO2-NH2 surfaces than when they are free in the bulk polymer. Both crystallization temperature (Tc) and crystallinity of grafted MPEG chains decrease with reductions of grafting density. Additionally, covalent bonding effects and interfacial interaction confinement effects are strengthened by the decrease in grafting density, leading to an increase in decomposition temperature and to the disappearance of the self-nucleation Domain (i.e., Domain II), when self-nucleation experiments are performed by DSC. Overall isothermal crystallization kinetics was studied by DSC and the results were analyzed with the Avrami equation. An Avrami index of n≈3 was obtained for neat MPEG (indicating that instantaneous spherulites are formed). However, in the case of MPEG-g-SiO2 with the lowest grafting density, the Avrami index of (n) was less than 1 (first order kinetics or lower), indicating that nucleation is the determining factor of the overall crystallization kinetics, a signature for confined crystallization. At the same time, the crystallization from the melt for this MPEG-g-SiO2 with the lowest grafting density occurs at Tc ≈-30 ºC, a temperature close to the glass transition temperature (Tg) of MPEG, indicating that this confined MPEG crystallizes from homogeneous nuclei. This project was supported by the National Natural Science Foundation of China (21574141) and the Ministry of Science and Technology of China (2017YFE0117800). The authors gratefully acknowledge the funding of project BIODEST, Research and Innovation Staff Exchange (RISE) H2020-MSCA-RISE-2017-778092. The authors thank beamline BL16B1 (Shanghai Synchrotron Radiation Facility) for providing the beam time and helps during experiments.

Unformatted post-print version of the accepted article A series of aliphatic polyethers with different chain lengths (nCH2= 6 to 12, and 16) is studied employing differential scanning calorimetry and X-rays scattering. The calorimetric and structural behavior of samples crystallized from the melt is divided into the odd-even and saturation regions. In the odd-even region (nCH2 = 6 to 10), the odd samples (nCH2 = 7, and 9) show enhanced calorimetric properties (e.g., higher transition temperatures) and faster crystallization kinetics than the even ones (nCH2 = 6, 8 and 10). The odd samples crystallize in orthorhombic unit cells and the even ones in monoclinic unit cells. In the saturation region (nCH2 = 11 to 16), the calorimetric properties increase as nCH2 increases without alternation. However, unexpectedly, the nCH2 = 12 displayed a mixed structure (monoclinic + orthorhombic) instead of an orthorhombic one. Thus, a structural saturation effect (i.e., an orthorhombic unit cell) is not reached. This particular structural feature was investigated under varied thermal histories, induced by different cooling rates. The samples as synthesized (i.e., crystallized during precipitation from solution) exhibited a structural saturation effect since both nCH2 = 10 and 12 display an orthorhombic unit cell. But, the nCH2 = 10 exhibits a monoclinic unit cell, and the nCH2 = 12 a mixed structure when the samples crystallize from the melt at different rates. Only the nCH2 = 16 crystallizes in an orthorhombic unit cell, independently of the thermal history. Thus, the complex odd-even effects in these aliphatic polyethers are a function of the cooling rate from the melt and sample preparation procedures (solution or melt crystallization). We would like to thank the financial support provided by the BIODEST project; this project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement no. 778092. This work was also supported by Grant PID2020-113045GB-C21 funded by MCIN/AEI/10.13039/501100011033. This work has also received funding from the Basque Government through grant IT1309-19. R.A.P.-C is supported by the China Postdoctoral Science Foundation (2020M670462), and National Natural Science Foundation of China (NSFC) (52050410327). The support of the ALBA (2020024169) and SSRF synchrotron facility is gratefully acknowledged.

Unformatted post-print version of the accepted article The nucleation process of poly(lactide) (PLA) on a series of fibers was studied by means of in-situ Polarized Optical Microscope (POM) during crystallization. Several synthetic and natural fibers (PLLA stereocomplex fibers (SC), PET, carbon, Kevlar, glass, hemp, linen and cellulose) were employed, and compared to custom-spun fiber of stereocomplex enantiomeric PLA blend. Meaningful differences in the nucleating ability towards PLA could be found for all the considered fibers. Stereocomplex PLA fibers display extremely high nucleating efficiency, with the development of a continuous transcrystalline morphology on their surface, up to high crystallization temperatures. Quantitative measurement of the nucleation rate allowed a comparison of the different fiber substrates in the light of classical heterogeneous nucleation theory, by considering the interfacial free energy difference parameter, Δσ, directly related to the nucleation barrier. The topography of the fibers surface was investigated by atomic force microscopy (AFM), and tentatively related to the measured nucleation ability. While a general effect of surface roughness on lowering the heterogeneous nucleation energy barrier can be deduced, deviations can be observed, in particular for carbon and stereocomplex PLA fibers. The different fiber wettability by PLA melt suggests that chemical interactions between the substrate and the crystallizing polymer also play a meaningful role in promoting the nucleation, although this aspect is generally disregarded in the literature - in favor of surface roughness. Moreover, the specific surface topography is shown to largely affect the density of available nucleation sites along the fiber. B.W. thanks the China Scholarship Council (CSC) for funding his Ph.D scholarship.This work has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No. 778092. A.J.M. acknowledges the financial support from Spanish Ministry of Science, Innovation and Universities (MAT2017-83014-C2-1-P).

The formation of Form I nuclei of polybutene-1 (PB-1) and its copolymer with polyethylene (PB1-ran-PE) has been studied by means of modified self-nucleation protocols. Even when the self-nucleation temperature was high enough and all Form II crystals melt, re-crystallization can be accelerated if the melt-crystallized sample was annealed at low temperatures (below 60 oC for PB-1 and 75 oC for PB1-ran-PE) for just 3 min. These results suggest the formation of latent Form I nuclei within Form II crystals. This hypothesis is consistent with the observed growth of a small amount of Form I crystals during heating, after previous annealing at temperature lower than 20 °C. In addition, a peculiar phenomenon was found in PB1-ran-PE, as both Form II and Form I′ can be induced by the presence of latent Form I nuclei, due to cross-nucleation and self-nucleation effects, respectively. The final ratio of the two kinds of crystal Forms is a result of the competition between the two nucleation rates, which strongly depend on crystallization temperature. In this work, we have shown that careful design of novel self-nucleation protocols can yield evidence of the early stages of Form II to Form I transition, even when the degree of transformed crystals is below the limit of detection of conventional techniques sensitive to crystalline order (DSC, WAXD, FTIR). Financial supports from the National Science Foundation of China (Grant No. U1510207) and the Key Program for Coal-based Science and Technology of Shanxi Province (MH-2014-08) are gratefully acknowledged. We would also like to thank the support of the Research and Innovation Staff Exchange (RISE) BIODEST H2020-MSCA-RISE-2017-778092 project.