Sang-Ho Lee

Achieving both high optical transparency and high glass-transition temperature (Tg) remains challenging in cyclic olefin polymers. Here, ring-opening metathesis polymerization (ROMP)-derived oxanorbornene polymers enable modular tuning of these competing properties through imide N-substitution and comonomer architecture. P-OCy exhibited a Tg of 224.5 °C with 94.9% transmittance at 400 nm. Flexible ester comonomers improved transparency but reduced Tg to 121.1–146.4 °C, whereas rigid MMETCD preserved Tg near 210 °C while increasing P-OPh transmittance from 61.0% to 90.0%. These systematic comparisons reveal distinct structural contributions to thermal rigidity and optical clarity, establishing practical design guidelines for transparent, high-Tg oxanorbornene polymers.

Polyurethanes (PUs) are indispensable polymeric materials widely employed across diverse industrial sectors due to their excellent thermal stability, chemical resistance, adhesion, and mechanical durability. However, the intrinsic three-dimensional crosslinked network that underpins their performance also presents a fundamental barrier to reprocessing and recycling. Consequently, most end-of-life PU waste is currently managed through landfilling or incineration, resulting in significant resource loss and environmental impact. To address these challenges, this review presents an integrated perspective on sustainable PU systems by unifying green synthesis strategies with closed-loop recovery approaches. First, recent advances in bio-based polyols and phosgene-free isocyanate synthesis derived from renewable resources—such as plant oils, carbohydrates, and lignin—are discussed as viable means to reduce dependence on petrochemical feedstocks and mitigate toxicity concerns. Next, emerging chemical recycling methodologies, including acidolysis and aminolysis, are reviewed with a focus on the selective recovery of high-purity monomers. Finally, PU vitrimers and dynamic covalent polymer networks (DCPNs) based on urethane bond exchange reactions are examined as reprocessable architectures that combine thermoplastic-like processability with the mechanical robustness of thermosets. By integrating synthesis, recovery, and reuse within a unified framework, this review aims to outline a coherent pathway toward establishing a sustainable circular economy for PU materials.

Poly(lactic acid) (PLA) has emerged as a leading bio-based polymer due to its renewability, processability, and biodegradability, yet its broader adoption remains constrained by limitations in thermal stability, mechanical performance, and end-of-life control. This review provides a comparative and application-oriented overview of recent advances in PLA from synthesis and catalyst landscapes to structure–property–biodegradation relationships and practical applications. Representative polymerization routes and catalyst systems are critically compared in terms of achievable molecular weight, stereochemical control, scalability, and sustainability. Key structure–property modification strategies—including stereocomplex formation, blending, and copolymerization—are quantitatively evaluated with respect to thermal and mechanical properties, highlighting inherent trade-offs. Importantly, environment-specific biodegradation behaviors are assessed using representative quantitative metrics under industrial composting, soil, marine, and enzymatic conditions, underscoring the strong dependence of degradation on both material design and testing environment. Finally, application-driven requirements for food packaging, fibers, and agricultural materials are discussed alongside regulatory considerations, processing constraints, and qualitative cost positioning relative to conventional polymers. By integrating recent representative studies into comparative tables and synthesis-driven discussions, this review offers design guidelines for tailoring PLA-based materials toward targeted performance and sustainable deployment.

A high solids (about 30 wt %) water-borne acrylic pressure-sensitive adhesive (PSA) was prepared by emulsion polymerization using graphene oxide (GO) as a particulate surfactant and a random poly(n-butyl acrylate-stat-acrylic acid) copolymer, P(n-BA-stat-AA), as an auxiliary polymeric surfactant, thereby avoiding the colloidal instability commonly observed with conventional low-molecular-weight surfactants. FT-IR, Raman, and XPS analyses confirmed a sequential "adsorption-grafting-encapsulation" mechanism. P(n-BA-stat-AA) first adsorbs onto GO via hydrogen bonding and electrostatic attraction, then may partially grafts through radical reactions, and is finally encapsulated by the growing polymer shell. This process partially restored the π-π stacking and incorporated GO as cross-linking nodes. The resulting latex has a narrow modal particle diameter of about 200 nm and remains stable for several months. Incorporating 4 wt % GO increased the 180° peel strength to 19.11 N/25 mm, extended the shear holding time from 3 to 1388 min, and raised the shear-adhesion-failure temperature from 50.8 to 115.6 °C, demonstrating simultaneous improvements in adhesion, cohesion, and heat resistance. Thermogravimetric analysis revealed delayed backbone degradation and reduced mass-loss rates, confirming the thermal-shielding and diffusion-barrier effects of the layered filler. Overall, these findings establish a clear structure-property relationship: electrostatic repulsion from GO and steric hindrance from P(n-BA-stat-AA) together generate a nanoconfined hybrid network, imparting exceptional mechanical durability and thermal stability. This approach offers a promising pathway to high-performance water-based PSAs.

In this study, 2‐(piperidin‐1‐ylmethyl)quinoline (L_A) and 1‐(naphthalen‐2‐ylmethyl)piperidine (L_B) ligands were utilized alongside palladium(II) acetate [Pd(OAc)₂] and N,N‐Dimethylanilinium tetrakis (pentafluorophenyl)borate as a cocatalyst for the in situ addition polymerization of norbornene (NB). The ligand L_B system demonstrated superior catalytic performance compared with that of the ligand L_A system, achieving 99% versus 94% conversion for NB to polynorbornene (PNB) at 25°C in chlorobenzene. To validate the catalytic activities of these in situ catalytic systems, Pd (II) complexes, [L_APd(OAc)₂] and [L_BPd(μ‐OAc)]₂, were synthesized and characterized. X‐ray structure analysis revealed that [L_APd(OAc)₂] adopted a square planar geometry, whereas [L_BPd(μ‐OAc)]₂ exhibited a distinctive clamshell structure. These complexes were also employed for the vinyl addition polymerization of NB under the same conditions as in situ catalytic systems. The active real Pd(II) complexes demonstrated slightly lower conversions compared with those of the in situ catalytic systems, achieving over 90% conversions for both [L_APd(OAc)₂] and [L_BPd(μ‐OAc)]₂. Furthermore, both catalytic systems were subsequently used for the (co)polymerization of NB and its derivatives, such as 5‐butylbicyclo[2.2.1]hept‐2‐ene (Bu‐NB), methyl bicyclo[2.2.1]hept‐5‐ene‐2‐carboxylate (Me‐NB), and bicyclo[2.2.1]hept‐5‐en‐2‐ylmethyl acetate (AAc‐NB), yielding relatively lower conversions.

Precise control over molecular dispersity and supramolecular assembly is essential for designing nanostructures with targeted properties and functionalities. In this study, we explore the impact of molecular dispersity in BTA-oligo(AA)₃ oligomers on the formation and structural organization of Au nanomaterials in an aqueous system. Discrete and polydisperse BTA-oligo(AA)₃ samples are systematically synthesized and characterized to evaluate their role as templates for nanostructure formation. UV-vis spectroscopy and TEM analyses reveal distinct differences in the resulting nanostructures. Specifically, discrete oligomers facilitate the formation of well-defined, interconnected Au nanonetworks with high structural uniformity, even at elevated concentrations. In contrast, polydisperse oligomers facilitated the formation of isolated Au nanoparticles with limited control over morphology and connectivity. These differences are attributed to the greater molecular uniformity and enhanced self-assembly capabilities of the discrete oligomers, which serve as effective templates for directing Au precursor organization and reduction into ordered nanostructures. This study provides mechanistic insight into how molecular dispersity affects the templating and assembly of gold nanomaterials. The findings offer a promising strategy for developing tailored nanostructures with interconnected morphologies and controlled optical and structural properties, paving the way for advanced applications.