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Effect of chemical structure on the crystallization kinetics of triple polymorphic high-sulfur-content polythioethers

Valentina Pirela, Leire Unanue, Justine Elgoyhen, Javier Ramos, Juan Francisco Vega, Agurtzane Mugica, Manuela Zubitur, Cuong Minh Quoc Le, Abraham Chemtob, Radmila Tomovska, Günter Reiter, Jaime Martín, Alejandro J. Müller. European Polymer Journal (2025) 113721

This work studies how the chemical structure of relatively similar high-sulfur alternating polythioether homopolymers (DMDS-alt-DVE, DMDS-alt-TEGDVE, and DMDS-alt-BDDVE) affects their structural properties, morphology, polymorphism, and crystallization kinetics. Differential scanning calorimetry (DSC) and polarized light optical microscopy (PLOM) experiments revealed a complex crystallization for the samples in which up to three different polymorphic phases were identified: a very low melting crystal form (VL-Tm form), a low melting crystal form (L-Tm form) and a high melting crystal form (H-Tm form), characterized by their corresponding melting temperature ranges and confirmed via Wide-Angle X-ray Scattering (WAXS). A coexistence of negative and positive spherulites was found, and their origin was revealed by atomic force microscopy (AFM), which showed how the lamellar arrangement varied in the samples from predominantly radial to a cross-hatched morphology. (more...)
 

Post-spin Stretch Improves Mechanical Properties, Reduces Necking, and Reverts Effects of Aging in Biomimetic Artificial Spider Silk Fibers

Gabriele Greco, Benjamin Schmuck, Fredrik G. Bäcklund, Günter Reiter and Anna Rising. ACS Appl. Polym. Mater.  6 (2024) 14342–14350

Recent biotechnological advancements in protein production and development of biomimetic spinning procedures make artificial spider silk a promising alternative to petroleum-based fibers. To enhance the competitiveness of artificial silk in terms of mechanical properties, refining the spinning techniques is imperative. One potential strategy involves the integration of post-spin stretching, known to improve fiber strength and stiffness while potentially offering additional advantages. Here, we demonstrate that post-spin stretching not only enhances the mechanical properties of artificial silk fibers but also restores a higher and more uniform alignment of the protein chains, leading to a higher fiber toughness. (more...)

Mechanistically Different Mechanochromophores Enable Calibration and Validation of Molecular Forces in Glassy Polymers and Elastomeric Networks

Raphael Hertel, Maximilian Raisch, Michael Walter, Günter Reiter, Michael Sommer. Angew. Chem. Int. Ed. 2024, e202409369

Sterically distorted donor-acceptor p‑systems, termed DA springs, can be progressively planarized under mechanical load causing a bathochromic shift of the photoluminescence (PL) spectrum. By combining theory and experiment, we here use a simple linear force calibration for two different conformational mechanochromophores to determine molecular forces in polymers from the mechanochromic shift in PL wavelength during multiple uniaxial tensile tests. Two systems are used, i) a highly entangled linear glassy polyphenylene and ii) a covalent elastomeric polydimethylsiloxane network. The mean forces estimated by this method are validated using known threshold forces for the mechanochemical ring-opening reactions of two different spiropyran force probes. The agreement between both approaches underlines that these DA springs provide the unique opportunity for the online monitoring of local molecular forces present in diverse polymer matrices.(more...)

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