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1. Enhanced Li-Ion Transport through Selectively Solvated Ionic Layers of Single-Ion Conducting Multiblock Copolymers

   https://doi.org/10.1021/acsmacrolett.2c00288  

   Park, Jinseok; Staiger, Anne; Mecking, Stefan; Winey, Karen I. (July 2022, ACS Macro Letters)

   We demonstrate enhanced Li+ transport through the selectively solvated ionic layers of a single-ion conducting polymer. The polymer is a precisely segmented ion-containing multiblock copolymers with well-defined Li+SO3– ionic layers between crystallized linear aliphatic 18-carbon blocks. X-ray scattering reveals that the dimethyl sulfoxide (DMSO) molecules selectively solvate the ionic layers without disrupting the crystallization of the polymer backbone. The amount of DMSO (∼21 wt %) calculated from the increased layer spacing is consistent with thermogravimetric analysis. The ionic conductivity through DMSO-solvated ionic layers is >104 times higher than in the dried state, indicating a significant enhancement of ion transport in the presence of this solvent. Dielectric relaxation spectroscopy (DRS) further elucidates the role of the structural relaxation time (τ) and the number of free Li+ (n) on the ionic conductivity (σ). Specifically, DRS reveals that the solvation of ionic domains with DMSO contributes to both accelerating the structural relaxation and the dissociation of ion pairs. This study is the initial demonstration that selective solvation is a viable design strategy to improve ionic conductivity in nanophase separated, single-ion conducting multiblock copolymers. 

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2. Sustainable thermoplastic elastomers produced via cationic RAFT polymerization

   https://doi.org/10.1039/D0PY01640C  

   Spring, Scott W.; Smith-Sweetser, Red O.; Rosenbloom, Stephanie I.; Sifri, Renee J.; Fors, Brett P. (March 2021, Polymer Chemistry)

   null (Ed.)

   Plastic production continually increases its share of global oil consumption. Thermoplastic elastomers (TPEs) are a necessary component of many industries, from automotive and construction to healthcare and medical devices. To reduce the environmental burden of TPE production on the world, we developed two new ABA triblock copolymers synthesized through cationic reversable addition–fragmentation chain transfer (RAFT) polymerization from renewable monomers. Using poly(isobutyl vinyl ether) (PIBVE) as the soft block and either poly( p -methoxystyrene) (PMOS) or poly(2,3-dihydrofuran) (PDHF) as the hard blocks, we produced triblock copolymers with varying volume fractions and characterized their material properties. PDHF-PIBVE-PDHF is sourced almost entirely from simple alcohols and exhibits mechanical properties comparable to those of commercial TPEs. This effort demonstrates the utility of cationic RAFT for the production of sustainable TPEs. 

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3. Highly stretchable ionically crosslinked acrylate elastomers inspired by polyelectrolyte complexes

   https://doi.org/10.1039/D2SM00755J  

   Cai, Hongyi; Wang, Zhongtong; Utomo, Nyalaliska W.; Vidavsky, Yuval; Silberstein, Meredith N. (October 2022, Soft Matter)

   Dynamic bonds are a powerful approach to tailor the mechanical properties of elastomers and introduce shape-memory, self-healing, and recyclability. Among the library of dynamic crosslinks, electrostatic interactions among oppositely charged ions have been shown to enable tough and resilient elastomers and hydrogels. In this work, we investigate the mechanical properties of ionically crosslinked ethyl acrylate-based elastomers assembled from oppositely charged copolymers. Using both infrared and Raman spectroscopy, we confirm that ionic interactions are established among polymer chains. We find that the glass transition temperature of the complex is in between the two individual copolymers, while the complex demonstrates higher stiffness and more recovery, indicating that ionic bonds can strengthen and enhance recovery of these elastomers. We compare cycles to increasing strain levels at different strain rates, and hypothesize that at fast strain rates ionic bonds dynamically break and reform while entanglements do not have time to slip, and at slow strain rates ionic interactions are disrupted and these entanglements slip significantly. Further, we show that a higher ionic to neutral monomer ratio can increase the stiffness, but its effect on recovery is minimal. Finally, taking advantage of the versatility of acrylates, ethyl acrylate is replaced with the more hydrophilic 2-hydroxyethyl acrylate, and the latter is shown to exhibit better recovery and self-healing at a cost of stiffness and strength. The design principles uncovered for these easy-to-manufacture polyelectrolyte complex-inspired bulk materials can be broadly applied to tailor elastomer stiffness, strength, inelastic recovery, and self-healing for various applications. 

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4. Spectro‐Microscopic Characterization of Elastomers Subjected to Laser‐Induced Shock Waves

   https://doi.org/10.1002/mame.202100506  

   Huynh, Nha Uyen; Gamez, Carlos; Youssef, George (December 2021, Macromolecular Materials and Engineering)

   Abstract The core of this research is separated into three domains, the ultrahigh strain rate response of elastomeric polymers, laser‐induced shock waves , and terahertz time‐domain spectroscopy (THz‐TDS). Elastomers, e.g., polyurea, constitute an advance class of materials suitable for many applications, specifically in high impact loading scenarios, thus, a laser‐induced shock wave (LSW) experimental technique is used to investigate the mechanical response of shock‐loaded polyurea. LSW can submit samples to a strain rate exceeding 10⁶s⁻¹at low strains, enabling determination of material intrinsic failure modes. The large deformation induced during shock loading may alter the macromolecule structure, which can only be detected spectroscopically. Therefore, this research incorporated terahertz bulk spectroscopy to detect and report molecular conformational changes. Microscopy techniques were also used to elucidate changes in the microscale properties, morphology, and topography. The interpretation of the results explicated brittle failure in terms of partial and total spallation and, remarkably, ductile failure leading to plastic deformation, including plastic bulging and adiabatic shearing, not previously associated with LSW technique. Furthermore, spectral changes found in the terahertz regime substantiated the validity of terahertz spectroscopy in elucidating the underlying mechanism associated with the impact mitigating properties of dynamically loaded polyurea. 

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5. On the Fundamental Polymer Chemistry of Inverse Vulcanization for Statistical and Segmented Copolymers from Elemental Sulfur

   https://doi.org/10.1002/chem.202200115  

   Kang, Kyung‐Seok; Iyer, Krishnan_A; Pyun, Jeffrey (May 2022, Chemistry – A European Journal)

   Abstract In this concept review, the fundamental and polymerization chemistry of inverse vulcanization for the preparation of statistical and segmented sulfur copolymers, which have been actively developed and advanced in various applications over the past decade is discussed. This concept review delves into a discussion of step‐growth polymerization constructs to describe the inverse vulcanization process and discuss prepolymer approaches for the synthesis of segmented sulfur polyurethanes. Furthermore, this concept review discusses the advantages of inverse vulcanization in conjunction with dynamic covalent polymerization and post‐polymerization modifications to prepare segmented block copolymers with enhanced thermomechanical and flame retardant properties of these materials. 

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