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We present results concerning the fabrication of a new magnetorheological fluid with FeCo magnetic nanoparticles (NPs) as magnetic fillers. These NPs have been fabricated by using the chemical reduction technique and show a pure crystalline phase with size ranging among 30–50 nm and high magnetization, 212 ± 2 A m2 kg−1. They agglomerate due to the strong magnetic dipolar interaction among them. These FeCo nanoparticles were used to synthesize a magnetorheological fluid by using oleic acid as surfactant, mineral oil as carrier liquid and Aerosil 300 as additive to control the viscosity of the fluid. The synthesized fluid showed a strong magnetorheological response with increasing shear stress values as the magnetic field intensity increases. Thus, we have measured a superior performance up to 616.7 kA m−1, with a yield stress value of 2729 Pa, and good reversibility after demagnetization process. This value competes with the best ones reported in the most recent literature. We have compared the obtained results with our previous reported ones by using high magnetization Fe NPs fabricated by the electrical explosion of wire method (Fe-EEW)., J. Berasategi, A. Gómez and M. M. Bou-Ali would like to thank the financial support provided by the Basque Government under research project PI-2017-1-0055 and MMMfavIN (KK-2020/00099, Elkartek program). V. Vadillo, J. Gutiérrez, J.M. Barandiarán, M. Insausti and I. Gil de Muro would like to thank the financial support provided also by the Basque Government under PI-2017-1-0043, the MMMfavIN (KK-2020/00099, Elkartek program) and Research Groups (IT1245-19 and IT1226-19) research projects. A. A. and A. I. gratefully acknowledge the financial support of the Basque Government (Research Groups IT-1175-19) and the Ministerio de Economía y Competitividad (PGC2018-094548-B-I00, MCIU/AEI/FEDER, UE).

Organic solar cells incorporating non-fullerene acceptors (NFAs) have reached remarkable power conversion efficiencies of over 18%. Unlike fullerene derivatives, NFAs tend to crystallize from solutions, resulting in bulk heterojunctions that include a crystalline acceptor phase. This must be considered in any morphology-function models. Here, it is confirmed that high-performing solution-processed indacenodithienothiophene-based NFAs, i.e., ITIC and its derivatives ITIC-M, ITIC-2F, and ITIC-Th, exhibit at least two crystalline forms. In addition to highly ordered polymorphs that form at high temperatures, NFAs arrange into a low-temperature metastable phase that is readily promoted via solution processing and leads to the highest device efficiencies. Intriguingly, the low-temperature forms seem to feature a continuous network that favors charge transport despite of a poorly order along the π–π stacking direction. As the optical absorption of the structurally more disordered low-temperature phase can surpass that of the more ordered polymorphs while displaying comparable—or even higher—charge transport properties, it is argued that such a packing structure is an important feature for reaching highest device efficiencies, thus, providing guidelines for future materials design and crystal engineering activities., This work is supported by the Ministerio de Ciencia e Innovacion/FEDER (under Ref. PGC2018-094620-A-I00 and PGC2018-095411-B-I00, CEX2019-000917-S and PGC2018- 095411-B-100) and the Basque Country Government (Ref. PIBA19-0051). S.M. is grateful to POLYMAT for the doctoral scholarship. The authors thank A. Arbe, A. Alonso-Mateo, L. Hueso for their support and access to characterization tools. The authors also thank the technical and human support provided by SGIker of UPV/EHU and European funding (ERDF and ESF). GIWAXS experiments were performed at BL11 NCD-SWEET beamline at ALBA Synchrotron (Spain) with the collaboration of ALBA staff. J.M and E.F.-G. acknowledge support through the European Union's Horizon 2020 research and innovation program, H2020-FETOPEN 01- 2018-2020 (FET-Open Challenging Current Thinking), ‘LION-HEARTED', grant agreement n. 828984. J.M and N.S. would like to thank the financial support provided by the IONBIKE RISE project, which has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement No 823989. N.S. and A.K. and A.B. furthermore are grateful to the U.S. National Science Foundation (NSF) for support via project # 1905901 within NSF’s Division of Materials Research. A. S. and M. C. acknowledge financial support by the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program “HEROIC,” grant agreement 638059. This work was partially carried out at Polifab, the micro- and nanotechnology center of the Politecnico di Milano. .C.M. thanks the Knut and Alice Wallenberg Foundation for funding through the project “Mastering Morphology for Solution-borne Electronics”.

We have investigated how variations in primary structure (distribution of monomeric units, chain length) and degree of branching affect the crystallization behavior of polysulfides. In particular, we have used copolymers of crystallizable (ethylene sulfide, ES) and non-crystallizable (propylene sulfide, PS) units, prepared via anionic ring-opening mechanism. PS units interrupt the crystallization of ES sequences; therefore, strong differences in thermal properties are expected between copolymers with a gradient (single addition of ES/PS mixtures) or a semirandom structure (sequential additions, which yield a more constant composition along the chain). Additionally, we prepared different chain topologies: linear, 4- and 8-armed stars, and combs with 10, 15, and 20 arms, in a comparison where each arm had a gradient primary structure and degree of polymerization (DP) of 10, 20, and 30. The influence of these variables (topology, number of arms, and DP) on the thermal properties was studied by polarized light optical microscopy (PLOM), standard and advanced DSC techniques (i.e., self-nucleation and successive self-nucleation and annealing (SSA)), and small and wide angle X-ray scattering (WAXS and SAXS). First, we have confirmed the much higher order obtained in gradient polymers, in comparison to the semirandom ones. Second, we have seen that the type of crowding of polymer chains affected the level of order achievable. In star polymers, an increasing number of arms increased topological restrictions, which in turn decreased crystallization and melting temperatures, crystallinity, and lamellar thickness. For combs, which are characterized by a more parallel than convergent crowding of the chains, the increase in arms number did not produce a significant decrease in crystalline order; on the contrary, the higher density of chains caused moderate increases in crystallization and melting temperatures, crystallinity, and lamellar thickness., The POLYMAT/UPV/EHU team would like to acknowledge funding from the following projects: UPV/EHU Infrastructure: INF 14/38; Mineco/FEDER: SINF 130I001726XV1/Ref: UNPV13-4E-1726; and Mineco MAT2017-83014-C2-1-P*. R.A.P.-C. gratefully acknowledges the award of a Ph.D. fellowship by POLYMAT Basque Center for Macromolecular Design and Engineering. A.A. and A.I. acknowledge financial support from IT-654-13 and MAT2015-63704-P (MINECO/ FEDER, UE). We gratefully acknowledge the ALBA synchrotron facility (Proposal Number: 2018022683) for the funding and help to perform experiments at BL11-NCDSWEET beamline with the collaboration of ALBA staff.

Herein, we elucidate the impact of tubular confinement on the structure and relaxation behavior of poly(vinylidene difluoride) (PVDF) and how these affect the para-/ferroelectric behavior of this polymer. We use PVDF nanotubes that were solidified in anodic aluminum oxide (AAO) templates. Dielectric spectroscopy measurements evidence a bimodal relaxation process for PVDF nanotubes: besides the bulk-like α-relaxation, we detect a notably slower relaxation that is associated with the PVDF regions of restricted dynamics at the interface with the AAO pore. Strikingly, both the bulk-like and the interfacial relaxation tend to become temperature independent as the temperature increases, a behavior that has been observed before in inorganic relaxor ferroelectrics. In line with this, we observe that the real part of the dielectric permittivity of the PVDF nanotubes exhibits a broad maximum when plotted against the temperature, which is, again, a typical feature of relaxor ferroelectrics. As such, we propose that, in nanotubular PVDF, ferroelectric-like nanodomains are formed in the amorphous phase regions adjacent to the AAO interface. These ferroelectric nanodomains may result from an anisotropic chain conformation and a preferred orientation of local dipoles due to selective H-bond formation between the PVDF macromolecues and the AAO walls. Such relaxor-ferroelectric-like behavior has not been observed for nonirradiated PVDF homopolymer; our findings thus may enable in the future alternative applications for this bulk commodity plastic, e.g., for the production of electrocaloric devices for solid-state refrigeration which benefit from a relaxor-ferroelectric-like response., J.M. acknowledges support from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant, agreement No. 654682. A.A. and A.I. acknowledge financial support from the Spanish Ministry Ministerio de Economia y Competitividad (MINECO) (code: MAT2015-63704-P (MINECO/FEDER, UE)) and the Eusko Jaurlaritza (Basque Government) (code: IT-654-13). A.C. would like to acknowledge the financial support of the EPSRC (EP/M014142/1). A.N., T.A.E., and C.M. acknowledge financial support from MINECO (codes: MAT2014-59187-R, MAT2015-66443-C02-1-R, and MAT2014-53437-C2-1P, respectively). N.S. is in addition grateful for support from a European Research Council ERC Starting Independent Research Fellowship under the grant agreement No. 279587.

A hydrothermal reaction between the monolacunary polyoxometalate [SiW11O39]8–, a copper(II) salt, and 1,4,8,11-tetraazacyclotetradecane (cyclam) affords the first example of a hybrid compound combining metal complexes of such an N4-tetradentate macrocyclic ligand and Keggin-type clusters, namely, [Cu(cyclam)(H2O)][{Cu(cyclam)}2SiW11O39Cu(H2O)]·5H2O (1). This compound has been characterized by infrared spectroscopy and thermal and elemental analyses. Single-crystal X-ray diffraction (scXRD) reveals a layered crystal packing made of corrugated two-dimensional covalent grids in which four octahedral {Cu(cyclam)}2+ bridging moieties connect copper(II)-monosubstituted {SiW11O39Cu(H2O)}6– polyanions to four adjacent clusters, and additional [Cu(cyclam)(H2O)]2+ square-pyramidal counterions are embedded into square-like grid voids. Thermostructural analyses confirm the presence in the 130–250 °C temperature range of a stable and crystalline anhydrous phase, which displays a diffraction pattern different from that of 1. This thermally triggered phase transition proceeds through a single-crystal to single-crystal transformation pathway, which according to scXRD, involves not only the release of water molecules, but also the cleavage and formation of Cu–O bonds induced by the rotation of Keggin-type anions. These modifications fully dismantle the parent two-dimensional covalent assembly to result in the neutral, discrete [{Cu(cyclam)}3SiW11O39Cu] hybrid species (2), in which the cluster exhibits three square-pyramidal {Cu(cyclam)}2+ decorating moieties grafted at its surface. This species must display a five-coordinated copper(II) center in the Keggin skeleton, and therefore, it constitutes one of the scarce examples of such type of coordinatively unsaturated substituted cluster observed in the solid state. The irreversibility of the phase transition has been confirmed by combined thermal and diffractometric analyses, which evidenced also the great flexibility of the supramolecular framework of 2, as this anhydrous phase is able to adsorb up to six water molecules per cluster to lead to the hydrated derivative [{Cu(cyclam)}3SiW11O39Cu(H2O)]·5H2O (2h) without any significant alteration in its cell parameters, nor in its crystalline structure., This work was funded by Eusko Jaurlaritza/Gobierno Vasco (EJ/GV, Grants IT1291-19 and PIBA2018-59) and Ministerio de Ciencia, Innovacion y Universidades (Grant MAT2017- 89553-P). L.F.N. and E.R.B. are indebted to EJ/GV for their predoctoral fellowships (PRE_2019_1_0106 and PRE_2018_1_0143).

Cyclic polymers behave different than linear polymers due to the lack of end groups and smaller coil dimensions. Herein, we demonstrate that cyclic polyethylene glycol (PEG) can be used as an alternative of classical linear PEG ligands for gold nanoparticle (AuNP) stabilization. We observed that the brush height of cyclic PEG on AuNPs of diameter 4.4 and 13.2 nm increases identically as that of linear brushes with (Nσ1/2)0.7 (N, number of monomers in a chain and σ, grafting density) and that cyclic brushes are more stretched than their linear analogues when compared to their unperturbed dimensions. Such structural effect and the reduced footprint diameter in cyclic brushes with the entire chain in a concentrated polymer brush regime explains the distinct response of NPs to ionic strength and temperature, respectively, compared to linear analogues. These experiments are an important step in understanding the effect of polymer brush topology on colloidal properties., We gratefully acknowledge support from the Spanish Ministry “Ministerio de Ciencia, Innovación y Universidades” (PGC2018-094548-B-I00, MICIU/AEI/FEDER, UE), Basque Government (IT-1175-19 and PIBA 2018-34) and Diputación Foral de Guipúzcoa (RED 2018).

By means of intramolecular folding/collapse of individual polymer chains (precursors), ultra-small soft nano-objects called single-chain nano-particles (SCNPs) can be synthesized. Here we present a combination of scattering techniques [small angle X-Ray and neutron scattering (SAXS and SANS), neutron spin echo (NSE) and dynamic light scattering (DLS)] to investigate the structure and dynamics of SCNPs in solution and their linear precursors as reference. Coarse-grained molecular dynamics (MD) simulations have also been carried out to complement this study. The application of SANS and SAXS has proved the compaction of the macromolecules upon creation of internal cross-links. However, the SCNPs obtained by different routes exhibit a far from globular topology in good solvent. Regarding the dynamics, we report on the first experimental investigation of the dynamic structure factor of SCNPs in solution. It reveals a clear impact of internal cross-links through (i) a reduction of the translational diffusion coefficient and (ii) an important slowing down of the internal modes. The data have been analyzed in terms of theoretical approximations based on the Zimm model. Both, structurally and dynamically, SCNPs show striking resemblances with intrinsically disordered proteins: similar scaling properties reflecting sparse morphologies and an extremely high internal friction.

The synthesis of symmetric cyclo poly(ε-caprolactone)–block–poly(l(d)-lactide) (c(PCL–b–PL(D)LA)) by combining ring-opening polymerization of ε-caprolactone and lactides and subsequent click chemistry reaction of the linear precursors containing antagonist functionalities is presented. The two blocks can sequentially crystallize and self-assemble into double crystalline spherulitic superstructures. The cyclic chain topology significantly affects both the nucleation and the crystallization of each constituent, as gathered from a comparison of the behavior of linear precursors and cyclic block copolymers. The stereochemistry of the PLA block does not have a significant effect on the nonisothermal crystallization of both linear and cyclo PCL-b-PDLA and PCL-b-PLLA copolymers., The authors acknowledge funding by the following projects: MAT2014-53437-C2-P and MAT2015-63704-P (Spanish MINECO); IT-654-13 (Basque Government), the Science Policy Office of the Belgian Federal Government (PAI 7/5), and the Belgian FRFC-FNRS (No. 2.4508.12). O.C. is Research Associate of the F.R.S.-FNRS. N.Z. acknowledges the fellowship from the UPV/EHU.

et al., The sequential crystallization of poly(ethylene oxide)-b-poly(ε-caprolactone)-b-poly(l-lactide) (PEO-b-PCL-b-PLLA) triblock terpolymers, in which the three blocks are able to crystallize separately and sequentially from the melt, is presented. Two terpolymers with identical PEO and PCL block lengths and two different PLLA block lengths were prepared, thus the effect of increasing PLLA content on the crystallization behavior and morphology was evaluated. Wide angle X-ray scattering (WAXS) experiments performed on cooling from the melt confirmed the triple crystalline nature of these terpolymers and revealed that they crystallize in sequence: the PLLA block crystallizes first, then the PCL block, and finally the PEO block. Differential scanning calorimetry (DSC) analysis further demonstrated that the three blocks can crystallize from the melt when a low cooling rate is employed. The crystallization process takes place from a homogenous melt as indicated by small angle X-ray scattering (SAXS) experiments. The crystallization and melting enthalpies and temperatures of both PEO and PCL blocks decrease as PLLA content in the terpolymer increases. Polarized light optical microscopy (PLOM) demonstrated that the PLLA block templates the morphology of the terpolymer, as it forms spherulites upon cooling from the melt. The subsequent crystallization of PCL and PEO blocks occurs inside the interlamellar regions of the previously formed PLLA block spherulites. In this way, unique triple crystalline mixed spherulitic superstructures have been observed for the first time. As the PLLA content in the terpolymer is reduced the superstructural morphology changes from spherulites to a more axialitic-like structure., We gratefully acknowledge funds received through the following projects: “MAT2014-53437-C2-P, MAT2012-31088 (Spanish-MINECO and EU)”, UPV/EHU (UFI 11/56) and GIC IT-586-13, IT-654-13 (Basque Government).

Ring closure click chemistry methods have been used to produce cyclic c-PLLA and c-PDLA of a number-average molecular weight close to 10 kg/mol. The effects of stereochemistry of the polymer chains and their topology on their structure, nucleation, and crystallization were studied in detail employing wide-angle X-ray scattering (WAXS), small-angle X-ray scattering (SAXS), polarized light optical microscopy (PLOM), and standard and advanced differential scanning calorimetry (DSC). The crystal structures of linear and cyclic PLAs are identical to each other, and no differences in superstructural morphology could be detected. Cyclic PLA chains are able to nucleate much faster and to produce a higher number of nuclei in comparison to linear analogues, either upon cooling from the melt or upon heating from the glassy state. In the samples prepared in this work, a small fraction of linear or higher molecular weight cycles were detected (according to SEC analyses). The presence of such “impurities” retards spherulitic growth rates of c-PLAs, making them nearly the same as those of l-PLAs. On the other hand, the overall crystallization rate determined by DSC was much larger for c-PLAs, as a consequence of the enhanced nucleation that occurs in cyclic chains. The equilibrium melting temperatures of cyclic chains were determined and found to be 5 °C higher in comparison with values for l-PLAs. This result is a consequence of the lower entropy of cyclic chains in the melt. Self-nucleation studies demonstrated that c-PLAs have a shorter crystalline memory than linear analogues, as a result of their lower entanglement density. Successive self-nucleation and annealing (SSA) experiments reveal the remarkable ability of cyclic molecules to thicken, even to the point of crystallization with extended collapsed ring conformations. In general terms, stereochemistry had less influence on the results obtained in comparison with the dominating effect of chain topology., The UPV/EHU team acknowledges funding from the following projects: “UPV/EHU Infrastructure: INF 14/38”; “Mineco/FEDER: SINF 130I001726XV1/Ref: UNPV13-4E-1726” and “Mineco MAT2014-53437−C2-P”, ’Ministerio de Economia y Competitividad (MINECO), code: MAT2015-63704-P (MINECO/FEDER, UE) and by the Eusko Jaurlaritza (Basque Government), code: IT-654-13. O.C. acknowledges financial support from the European Commission and Region Wallonne FEDER program (Materia Nova) and OPTI2 MAT program of excellence, by the Interuniversity Attraction Pole Program (P7/ 05) initiated by the Belgian Science Policy office and by the FNRS-FRFC. O.C. is a Research Associate of the F.R.S.-FNRS. The Organic Synthesis and Mass Spectrometry Laboratory thanks F.R.S.-FNRS for the financial support for the acquisition of the Waters QToF Premier and Synapt-G2Si mass spectrometers and for continuing support. Finally, all authors acknowledge Research and Innovation Staff Exchange (RISE) H2020-MSCA-RISE-2017-778092, project BIODEST, for promoting cooperation between the Mons team and the UPV/EHU team.

In this paper, the preparation of PBS-ran-PCL copolyesters by enzymatic ring opening polymerization is presented for the first time. The copolyesters were produced in a wide composition range and free of metallic contaminants, so they may be regarded as potential biomaterials. The copolymers have been characterized by proton and carbon nuclear magnetic resonance (H and C NMR), gel permeation chromatography (GPC), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), polarized light optical microscopy (PLOM) and wide angle X-ray scattering (WAXS). The PBS-ran-PCL copolyesters were able to crystallize in the entire composition range and displayed a pseudo-eutectic region. Most copolymers away from the pseudo-eutectic region exhibited a single crystalline phase (PBS-rich or PCL-rich crystalline phase), while within the pseudo-eutectic region the copolymers were double crystalline. Observations by PLOM, during isothermal crystallization showed that both nucleation density and spherulitic growth rate of the copolyesters are determined by the component that constitutes the majority phase. WAXS studies revealed that d spacings of selected crystallographic planes depend on composition. Therefore, both DSC and WAXS results suggest that the copolymers are probably isodimorphic, as the PBS-rich crystalline phase may contain small inclusions of PCL co-units, while the PCL-rich crystalline domains may also contain a minor quantity of PBS co-units inside., This work received financial support from Ministerio de Economia y Competitividad (MINECO) of Spain with Grant MAT2012-38044-C03-03 and MAT2016-77345-C3-1-P and from Agència de Gestió d'Ajuts Universitaris i de Recerca (AGAUR) (Catalonia, Spain) with grant 2009SGR1469. The POLYMAT/UPV/EHU team would like to acknowledge funding from the following projects: “UPV/EHU Infrastructure: INF 14/38”; “MINECO/FEDER: SINF 130I001726XV1/Ref.: UNPV13-4E-1726” and “MINECO MAT2014-53437-C2-P”. A.A. and A.I. acknowledge financial support from the Spanish Ministry (MINECO), Ref: MAT2015-63704-P (MINECO/FEDER, UE) and by the Eusko Jaurlaritza (Basque Government), Ref: IT-654-13. C.C. wishes to acknowledge CNPq (National Research Council) Brazil for the financial support. M.S. gratefully acknowledges the award of a PhD fellowship by POLYMAT Basque Center for Macromolecular Design and Engineering. JC M-H thanks to Consejo Nacional de Ciencia y Tecnología (CONACYT) (Mexico) for the awarded PhD grant.

Two-scale multicomposite (meth)acrylate latexes containing nano-sized liquid crystalline domains were synthesized in a two step (mini)emulsion polymerization using a series of methacrylate side chain liquid crystalline monomers and mixture of short chain (meth)acrylates. Detailed characterization of the composite films obtained from the latexes using a combination of DSC, TEM, polarized light microscopy, SAXS and WAXS showed that the liquid crystalline polymers had a layered structure with a 2D-organization that was not perturbed by the amorphous polymer, which on the other hand was partially intercalated between layers. This leads to a two-scale composite with enhanced mechanical properties and higher number of degrees of freedom to fine tune the mechanical properties. The effect of liquid crystalline domains on barrier properties as well as on the water resistance of the films formed from these latexes was also investigated. The persistence of crystalline order of the liquid crystalline polymer phase up to very high temperatures leads to materials with a very broad temperature range of application, improving significantly the performance with respect to other routes based on incorporation of crystalline domains via copolymerization with comb-like monomers., Financial support of the Industrial Liaison Program on Polymerization in Dispersed Media (Akzo Nobel, Allnex, Arkema, BASF, Foresa, Nuplex Resin, Solvay, Stahl, Synthomer, Vinavil, Wacker) is gratefully acknowledged. A. A. and A. I. acknowledge financial support by the Spanish Ministry 'Ministerio de Economia y Competitividad', code: MAT2015-63704-P (MINECO/FEDER, UE) and by the Eusko Jaurlaritza, code: IT-654-13. J. R. L. acknowledges financial support from the Spanish Ministry ’Ministerio de Economia y Competitividad’, code: CTQ2014-59016-R (MINECO).

The synthesis of a series of methacrylate side-chain liquid crystal polymers (SCLCPs) bearing biphenyl mesogen with different spacer lengths and a fixed tail, poly[ethyl 4′-((n-(methacryloyloxy)alkyl)oxy)-[1,1′-biphenyl]-4-carboxylate]s (n-PMLCM, n = 3, 4, 5, 6), in aqueous media by free radical miniemulsion polymerization is described. This method offers the advantage of producing high molar masses (>105 Da) and full monomer conversion, not possible to achieve with conventional routes (solution polymerization). The resulting n-PMLCMs proved to have high thermal stability. The phase behaviors of the polymers were investigated by a combination of techniques including differential scanning calorimetry, polarized light microscopy, and small and wide angle X-ray scattering. The results show mesomorphic liquid crystalline behavior with a monolayer structure where the side-groups on both sides of the backbone would be interpenetrated. The liquid crystal phase transition of n-PMLCM follows the sequence smectic E (smectic E or smectic C for 4-PMLCM) ↔ smectic A ↔ isotropic liquid. The transition temperatures and the associated entropy changes exhibit a distinct odd–even effect as the length and parity of the spacer are varied, with the odd members exhibiting the higher values. The high molar masses achievable using miniemulsion polymerization translate into a more perfect and stable ordering, characterized by larger lamellar domains and higher transition temperatures, than in low molar mass SCLCPs. Compared to polymeric liquid crystals with similar mesogens but shorter tails, we found that longer tails facilitate the ordering of the mesogens and allow more efficient packing around the backbones, imparting a high stability to the smectic phases formed., The financial support from the Industrial Liaison Program on Polymerization in Dispersed Media (Akzo Nobel, Allnex, Arkema, BASF, Foresa, Nuplex Resin, Solvay, Stahl, Synthomer, Vinavil, Wacker) is gratefully acknowledged. A. A. and A. I. acknowledge financial support from the projects MAT2015-63704-P (Spanish-MINECO) and IT-654-13 (Basque Government). J. R. L. acknowledges financial support from the project CTQ2014-59016-R (MINECO).

Poly(butylene succinate-ran-butylene azelate) random copolyesters were thermally fractionated by successive self-nucleation and annealing (SSA). The samples before and after SSA were analyzed by differential scanning calorimetry (DSC) and X-ray diffraction (WAXS and SAXS). WAXS results indicate that a small degree of comonomer inclusion is present in the crystalline phases that are formed in the copolymers depending on composition: a PBS-like unit cell or/and a PBAz-like unit cell, thus confirming the isodimorphic behavior of the samples. SSA on the other hand demonstrated that the degree of comonomer exclusion during crystallization is far larger than comonomer inclusion, as judged by the increase in fractionation degree with compositions leading to the pseudo-eutectic point. Furthermore, WAXS, SAXS, and SSA results show that the isodimorphic behavior is not highly dependent on kinetic factors, as the degree of comonomer inclusion or exclusion in the samples was not significantly altered by SSA thermal fractionation, a thermal treatment that promotes annealing and molecular segregation of defects to the amorphous regions of the material., I. A. acknowledges the fellowship from the University of the Basque Country UPV/EHU. Financial support is acknowledged from UPV/EHU (UFI11/56), “UPV/EHU Infrastructure: INF 14/38”; “Mineco/FEDER: SINF 130I001726XV1/Ref: UNPV13–4E–1726” and “Mineco MAT2014-53437-C2-P”. G.M.L acknowledges the support from the Youth Innovation Promotion Association of CAS (2015026). A.A. and A.I. acknowledge financial support from the Projects MAT2012-31088 and MAT2015-63704-P (Spanish-MINECO and EU) and IT-654-13 (Basque Government).