Long Chen

The heterogenization of homogeneous transition‐metal catalysts is a well‐established strategy for enabling oriented synthesis and precise morphological control of high‐molecular‐weight polyolefins. To date, however, the development of covalent organic framework (COF)‐supported late‐transition‐metal catalysts has remained unexplored. Herein, we report the facile construction of a heterogeneous Ni@PY‐COF catalyst via straightforward coordinated post‐synthetic modification of a dipyridyl‐functionalized COF. This system delivers highly active (10 ⁶ g mol ⁻¹ h ⁻¹ ) and thermally stable (up to 100°C) Ni catalytic sites without requiring bulky steric substituents on the ligand. The catalyst produces semicrystalline, predominantly methyl‐branched polyethylene featuring high molecular weight (29–297 kg mol ⁻¹ ), high melting points (121°C–128°C), low branching density (≤ 25/1000 C), and well‐controlled particle morphology. Structural analysis reveals that the confined nanoscale environment of the highly porous COF framework suppresses β ‐H elimination, the dominant chain transfer and termination pathway in late‐transition‐metal‐catalyzed olefin polymerization. This work demonstrates the feasibility of integrating late‐transition‐metal active sites into an atomically precise COF material to enable heterogeneous olefin polymerization rather than oligomerization, thereby establishing a transformative paradigm for advancing high‐performance and industrially relevant polyolefin catalysts.

The heterogenization of homogeneous transition‐metal catalysts is a well‐established strategy for enabling oriented synthesis and precise morphological control of high‐molecular‐weight polyolefins. To date, however, the development of covalent organic framework (COF)‐supported late‐transition‐metal catalysts has remained unexplored. Herein, we report the facile construction of a heterogeneous Ni@PY‐COF catalyst via straightforward coordinated post‐synthetic modification of a dipyridyl‐functionalized COF. This system delivers highly active (10 ⁶ g mol ⁻¹ h ⁻¹ ) and thermally stable (up to 100°C) Ni catalytic sites without requiring bulky steric substituents on the ligand. The catalyst produces semicrystalline, predominantly methyl‐branched polyethylene featuring high molecular weight (29–297 kg mol ⁻¹ ), high melting points (121°C–128°C), low branching density (≤ 25/1000 C), and well‐controlled particle morphology. Structural analysis reveals that the confined nanoscale environment of the highly porous COF framework suppresses β ‐H elimination, the dominant chain transfer and termination pathway in late‐transition‐metal‐catalyzed olefin polymerization. This work demonstrates the feasibility of integrating late‐transition‐metal active sites into an atomically precise COF material to enable heterogeneous olefin polymerization rather than oligomerization, thereby establishing a transformative paradigm for advancing high‐performance and industrially relevant polyolefin catalysts.

To enhance the thermal‐oxidative stability of polypropylene (PP) fiber, several nitrogen‐heterocyclic polypropylene copolymers were synthesized as blending modifiers, containing pyrrole (Py), indole (Id), and carbazole (Cz) groups. The large steric hindrance of indole and carbazole groups reduces the negative effect of heteroatoms on the catalytic center, with the highest polymerization activity of 2.33 × 10 ⁴ kg _polymer mol _Zr ⁻¹ h ⁻¹ . Compared with PP, the 5% mass loss temperature ( T _5% ) of PPPy and PPId is increased, while only PPPy is capable of further delaying oxygen permeation. The steady‐state shear curves indicate that the cross‐linked structure between PPPy molecular chains inhibits the flow of PP/NHPP melt, while the indole and carbazole groups promote the flow of PP/NHPP melt. All PP/NHPP blends are successfully prepared into fibers. The mechanical properties of PP/PPPy fiber are well maintained due to the cross‐linked structure. The thermo‐oxidative stability of PP/NHPP fibers can be enhanced at a low blend content of 5 wt%, with the maximum rise of 13°C in T _5% and 10.7 min in oxidation induction time, which is expected to be applied in engineering fields requiring high‐temperature stability.

Efficient glycolytic depolymerization of waste polyethylene terephthalate (PET) is critical for sustainable resource recycling, yet the effect of specific surface area—a key structural parameter of PET fibers—on reaction kinetics and depolymerization mechanisms remains unclear. In this work, PET fibers with uniform crystallinity (~27%) and varying specific surface areas (0.640, 0.520, 0.307 m ² g ⁻¹ ) were prepared, and their glycolytic behavior was investigated at 165°C–180°C using zinc acetate as catalyst. Scanning electron microscopy confirmed an outside‐in depolymerization mode with oligomeric fragments detaching from fiber surfaces. Conversion curves were well‐fitted by the Avrami–Erofeev model with n = 2, corresponding to one‐dimensional heterogeneous nucleation and growth of depolymerization domains along fiber longitudinal direction. Apparent activation energies increased with decreasing specific surface area (136.8, 162.9, 172.9 kJ mol ⁻¹ , respectively). This work elucidates the structure–activity relationship of PET fibers in glycolysis, providing theoretical guidance for low‐energy, high‐efficiency waste PET recycling.

The direct melt spinning of polyamide 6 (PA6) after polymerization remains formidably challenging. The conventional hydrolysis polycondensation (HP) of ε-caprolactam (CL) requires long polymerization and postpurification times due to low conversion, while the typical alkali-metal-initiated anionic ring-opening polymerization (AROP) of CL suffers from uncontrollable molecular weight at high temperatures. Here, we proposed a controllable AROP of CL with a low Mg-initiator dosage, especially suitable for direct melt spinning. With a low initiator dosage (I₀/M₀ = 1/1000–1/3000), it enables controllable regulation of M_n (4.7–38.5 kg mol^–1) and remains stable for a relatively long period above T_m (220 °C), simultaneously maintaining high conversion (ca. 95%) and a quasi-living character. The cyclic dimer residual was restricted to an unprecedented level (<0.01 wt %). The proposed simple system is more efficient and greener than the traditional HP and AROP techniques, offering a promising approach for producing PA6 fibers via direct melt spinning.

Polyolefins are widely used polymers, with an annual global production of hundreds of millions of tons. Because they are the simplest hydrocarbon polymers, their intrinsic non-polar properties limit further applications. Coordination–insertion copolymerization of an olefin with other monomers, mediated by transition metal catalysts, is the most efficient way to synthesize polar and multi-functionalized polyolefins with enhanced material performance. Previous reviews have primarily focused on the structural design of a specific catalyst or on binary copolymerization of an olefin with a particular comonomer. However, the transition-metal-catalyzed ternary coordination–insertion polymerization of olefin monomers remains scarce. In this contribution, early transition-metal catalysts, such as Ti, Zr, Hf, and V, are employed for the terpolymerization of all-hydrocarbon or non-polar monomers to access advanced polyolefin materials with high performance. By contrast, late transition metal catalysts based on Ni and Pd, as well as rare-earth metal catalysts ligated by Sc and Y, enable the terpolymerization of olefins with a variety of heteroatom-containing monomers. Their strong tolerance empowers the development of polyolefins with multiple functionalities, thereby distinguishing these systems. The catalyst structure, catalytic process, and mechanism studies are summarized, along with the microstructure and functionality of the polymerization products, by classifying the types of termonomers employed.

Developing polydienes assembled by diversified monomer microstructures through copolymerization has been a long task in polymer synthesis catalysis, and there remains a demand for high-performance transition metal catalysts. Here, a series of well-defined cobalt complexes (Co1-Co5) bearing strong electron-donating imidazolidin-2-imine and phosphine ligands were successfully synthesized and structurally characterized through single-crystal X-ray diffraction analysis. The Co complexes are highly active and thermally stable for isoprene polymerization in the presence of a small amount of Et₂AlCl cocatalyst. It affords ultrahigh-molecular-weight polyisoprenes (M_n of up to ∼1.2 million g·mol^-1) with cis-1,4/3,4 sequences accompanied by a narrow polydispersity index (PDI = 1.01-1.55), featuring a typical "living" character. Most importantly, Co1-Co5 catalyzed the direct copolymerization of isoprene with a freshly synthesized polar-functionalized conjugated diene monomer, IP_COOMe, without using any protective masking reagent, showing their strong polarity tolerance. Polar functionalized copolymers with high molecular weight and reasonable polar monomer incorporation (2.8-11.1 mol %) are produced to demonstrate enhanced hydrophilicity compared to the typical polyisoprene-based hydrocarbon materials. These Co catalysts are promising candidates for preparing unique copolymers from different diene monomers, and the electron-donating strategy also provides a new pathway for the rational design and convenient synthesis of organometallic catalysts in the future.

Hydroxyl‐functionalized polypropylene (PPOH) is first incorporated into polypropylene (PP) to prepare modified fiber by melt spinning. Herein, PPOH with low molecular weight and wide molecular weight distribution (MWD) is prepared by controlling the reaction temperature and comonomer feed to reduce the viscoelasticity. The maximum MWD is 4.9 and the minimum weight‐average molecular weight is 28 kDa. The spinnability of the PP/PPOH blend is evaluated by rheology. The steady‐state shear curves indicate that the viscosity of the PP/PPOH blend is well maintained in the range required for melt spinning. All PP/PPOH blends are successfully prepared into as‐spun fibers. Nevertheless, PP/PPOH with higher comonomer content is impossible to undergo further hot drawing and heat setting. The presence of slight hydroxyl groups hardly hinders the orientation and crystallization of PP/PPOH fiber. However, PP/PPOH fiber exhibits better mechanical properties than pure PP fiber, especially at the low blend ratio. The tensile strength of PP/PPOH fiber with 3 wt% PPOH reaches 704 MPa, which is 31% higher than that of pure PP fiber. PPOH enhances the interfacial bonding strength between fiber and epoxy resin, making PP/PPOH fiber expected in the engineering field as a fiber‐reinforced material.

This work reports new mixed matrix membranes (MMMs) for the adsorption of enzymes from organic solvents. In this work, polyimide/hydroxyapatite (PI/HAP) MMMs were prepared via phase inversion method and further crosslinked with 3-aminopropyl triethoxysilane (APTES). The chemical and structural stability of the crosslinked PI/HAP MMMs were improved and applied for lysozyme (LZ) adsorption in organic solvent. PI/HAP MMMs were crosslinked by changing the 3-aminopropyltriethoxysilane (APTES) concentration and crosslinking time. The optimal APTES crosslinking condition for PI/HAP MMMs is 6% of concentration for 8 h. The LZ adsorption performance was studied by changing solvent types. PI/HAP MMMs possessed a high LZ adsorption in organic-solvent-aqueous solutions, and the LZ adsorption capacity reached 34.1 mg/g. The MMMs had a high desorption capacity and recovery ability. The MMMs maintained 60% of their adsorption capacity and 58% of their desorption at the fourth cycle of adsorption and desorption. The MMMs provided a new technology for the purification and separation of enzymes or proteins by MMMs in organic solvents.