Seon-Mi Kim

Superior Toughness and Fast Self‐Healing at Room Temperature Engineered by Transparent Elastomers

The most important properties of self-healing polymers are efficient recovery at room temperature and prolonged durability. However, these two characteristics are contradictory, making it difficult to optimize them simultaneously. Herein, a transparent and easily processable thermoplastic polyurethane (TPU) with the highest reported tensile strength and toughness (6.8 MPa and 26.9 MJ m-3 , respectively) is prepared. This TPU is superior to reported contemporary room-temperature self-healable materials and conveniently heals within 2 h through facile aromatic disulfide metathesis engineered by hard segment embedded aromatic disulfides. After the TPU film is cut in half and respliced, the mechanical properties recover to more than 75% of those of the virgin sample within 2 h. Hard segments with an asymmetric alicyclic structure are more effective than those with symmetric alicyclic, linear aliphatic, and aromatic structures. An asymmetric structure provides the optimal metathesis efficiency for the embedded aromatic disulfide while preserving the remarkable mechanical properties of TPU, as indicated by rheological and surface investigations. The demonstration of a scratch-detecting electrical sensor coated on a tough TPU film capable of auto-repair at room temperature suggests that this film has potential applications in the wearable electronics industry.

Structural and thermal properties of poly(1,4-cyclohexane dimethylene terephthalate) containing isosorbide

Poly(1,4-cyclohexanedimethylene isosorbide terephthalate) (PICT) copolymers were synthesized by melt condensation with various contents of the corn derived monomer isosorbide (ISB). Since poly(1,4-cyclohexanedimethylene terephthalate) (PCT) has disadvantageous thermal processing properties as well as a high melting temperature, ISB could be used to control Tg and Tm simultaneously. An increased content of ISB can increase the Tg and lower the Tm by affecting the crystallization behavior and structural properties of PCT. The composition of PICT was confirmed using 1H-NMR spectroscopy, and the detailed structure was analyzed with correlation spectroscopy (COSY) and heteronuclear single-quantum correlation spectroscopy (HSQC). 13C-NMR spectroscopy was used for investigating the sequence distribution and from these results, the effect of the ISB-TPA dyad on the thermal properties was revealed. Solid state cross polarization/magic angle spinning (CPMAS) 13C-NMR spectroscopy was used to investigate the free space of an atom due to environment dependent relaxation behavior, which determines whether ISB is excluded from the crystal structure. Then, WAXD was used to analyze the crystal structure, representing the effect of ISB on the crystallization. Finally, polarized optical microscopy and atomic force microscopy were used to visualize the morphological change of the crystallite resulting from ISB.

Environmentally-Friendly Synthesis of Carbonate-Type Macrodiols and Preparation of Transparent Self-Healable Thermoplastic Polyurethanes

Carbonate-type macrodiols synthesized by base-catalyzed polycondensation of co-diols and dimethyl carbonate as an environmentally-friendly route were subsequently utilized for the preparation of transparent and self-healable thermoplastic polyurethanes (TPUs) containing a carbonate-type soft segment. Three types of macrodiols, obtained from mono, dual and triple diol-monomers for target molecular weights of 1 and 1.5 kg mol−1, were analyzed by 1H NMR integration and the OH titration value. Colorless transparent macrodiols in a liquid state at a room temperature of 20 °C were obtained, except the macrodiol from mono 1,6-hexanediol. Before TPU synthesis, macrodiols require pH neutralization to prevent gelation. TPUs synthesized by a solution pre-polymer method with 4,4′-methylene(bisphenyl isocyanate) and 1,4-butanediol as a chain extender exhibited moderate molecular weights, good transparencies and robust mechanical properties. Especially, the incorporation of 3-methyl-1,5-pentanediol within carbonate-type macrodiols enhanced the transparency of the resultant TPUs by decreasing the degree of microphase separation evidenced by ATR-FTIR and DSC. Interestingly, packing density of hard segments and the degree of microphase separation determined the self-healing efficiency of TPUs, which showed good performances in the case of sourced macrodiols from triple diol-monomers.

Butanol-mediated oven-drying of nanocellulose with enhanced dehydration rate and aqueous re-dispersion

AbstractThe application potential of nanocellulose has been previously hindered by the costly and slow drying methods that this material requires, including freeze/supercritical drying process. The main issue for nanocellulose commercialization is how effectively and rapidly its high water contents (90–99%) can be removed, all of which raise its transportation and processing costs. Oven-drying is the fastest, most economical, and most scalable method for dehydrating nanocellulose, but causes strong interfibrillar aggregation and leads to poor aqueous re-dispersion. Here, we report that the problems of nanocellulose oven-drying are comprehensively overcome by adding tert-butanol (t-BuOH) to the nanocellulose solution at >90%. In a lab-scale comparison, the t-BuOH-mediated oven-drying of aqueous nanocellulose showed lower drying times by a factor of 2–12 compared to water only oven-drying and freeze drying of the same material. The dispersibility of this dried nanocellulose is as high as the never-dried material in terms of particle size, light transmittance, and sedimentation. t-BuOH reduces interfibrillar shrinkage due to the lower surface tension of t-BuOH compared to water, and a remaining t-BuOH/water mixture decreases interfibrillar adhesion and contact.n Graphical abstractThis paper suggests a strategy to improve the aqueous re-dispersibility of oven-dried nanocellulose, and to accelerate oven-drying rate.

Synthesis and biological evaluation of 3-(2-aminoethyl) uracil derivatives as gonadotropin-releasing hormone (GnRH) receptor antagonists

We investigated a series of uracil analogues by introducing various substituents on the phenyl ring of the N-3 aminoethyl side chain and evaluated their antagonistic activity against human gonadotropin-releasing hormone (GnRH) receptors. Analogues with substituents at the ortho or meta position demonstrated potent inxa0vitro antagonistic activity. Specifically, the introduction of a 2-OMe group enhanced nuclear factor of activated T-cells (NFAT) inhibition up to 6-fold compared to the unsubstituted analogue. We identified compound 12c as a highly potent GnRH antagonist with moderate CYP inhibition. Compound 12c showed potent and prolonged LH suppression after a single dose was orally administered in castrated monkeys compared to a known antagonist, Elagolix. We believe that our SAR study offers useful insights to design GnRH antagonists as a potential treatment option for endometriosis.