ACS Macro Letters最新文献

In ring opening metathesis polymerization (ROMP), vinyl and enol ethers have been predominantly used to terminate the polymerization. However, contrary to convention, we have previously reported ROMP of a cyclic enol ether, 2,3-dihydrofuran, to give an acid degradable poly(enol ether). Herein, we describe the use of linear, hetero bifunctional enol ethers as chain transfer agents to synthesize heterotelechelic poly(enol ether). Unidirectional chain transfer was achieved by leveraging regioselective addition of enol ethers to the Grubbs complexes. Excellent regioselectivity in producing the desired heterotelechelic polymers was confirmed by high-resolution mass spectroscopy and NMR spectroscopy. We demonstrate various tranformations of the end group functionalities without causing unwanted degradation of the poly(enol ether) backbone. The end group functionalities were also used to synthesize fully degradable block copolymers, where each block can be degraded under orthogonal conditions. The unique unidirectional chain transfer allows for the installation of functionalities at one or both chain ends, facilitating further applications of readily synthesized poly(enol ether) as a sustainable polymer.

We observed individual macromolecular chains with distinct ring topology when studying cryogenic electron microscopy (Cryo-EM) images of a high molar mass polyorganophosphazene in its vitrified aqueous solution. The presence of monocyclic chains was confirmed by visualizing samples of the same macromolecule in its absorbed form by using atomic force microscopy (AFM). The polymer, poly[di(carboxylatophenoxy)phosphazene], PCPP, is synthesized via a two-stage process, which includes a ring-opening polymerization (ROP) and a subsequent macromolecular substitution transformation. The visualization of macrocycles, which are 20–60 nm in diameter, provides direct proof of a ring extension polymerization (REP) mechanism occurring in the chain-growth process commonly employed for the synthesis of high molar mass polyphosphazenes. Asymmetric flow field flow fractionation (AF4) analysis shows the presence of a faster moving fraction, which can be potentially attributed to macrocycles.

Biomolecular condensates are complex droplets comprising diverse molecules that interact by various mechanisms. Condensation is often driven by short-range attraction, but net charges can also mediate long-range repulsion. Using molecular dynamics simulations and an equilibrium field theory, we show that such opposing interactions can suppress coarsening, so many droplets of equal size coexist at equilibrium. This size control depends strongly on the charge asymmetry between molecular constituents, while the strength of the short-range attractions has a weak influence. The mechanism relies on droplets expelling ions; therefore, they cannot screen electrostatics effectively, implying that droplets acquire a net charge and cannot grow indefinitely. Our simulations indicate that this effect is likely less prevalent in biomolecular condensates within cells, although we still observe stable small clusters in this case. Taken together, our work reveals that electrostatic effects through molecular charge asymmetries can control droplet size, which contributes to our understanding of biomolecular condensates and the creation of synthetic patterns in chemical engineering.

Non-Newtonian viscoelastic behavior of disordered spherical micelle dispersions composed of complex coacervate core micelles (C3Ms) in aqueous media is investigated by combining rotational rheometry and microfluidic particle focusing measurements. C3Ms were prepared by mixing oppositely charged block copolymers, resulting in spherical micelles with electrostatically neutral coacervate cores surrounded by hydrophilic coronas. Despite the spherical morphology and dispersion in low-viscosity solvents, lateral migration of micrometer-sized particles in microfluidic flow revealed measurable elasticity. The relaxation time (λ), quantified from particle focusing behavior, increased with micelle concentration and scaled with the short-time Brownian diffusion time scale. This suggests that viscoelasticity in C3M solutions originates from diffusive colloidal dynamics consistent with hard-sphere-like interactions. Upon salt addition, micelle dimension and λ decreased significantly, while solution viscosity remained nearly constant. These results demonstrate that λ can be a quantitative indicator of capturing micellar structural changes under external stimuli. This study highlights the use of centerline particle migration as a sensitive probe for weak viscoelasticity in micellar systems and establishes a quantitative link between micellar structure and relaxation dynamics.

In 2024, the American Chemical Society (ACS), Division of Polymeric Materials: Science and Engineering (PMSE), celebrated its centennial. This historic occasion was marked at the 2024 Spring ACS Meeting in New Orleans with a Centennial Symposium entitled “PMSE Centennial: Celebration of Success and New Frontiers in Polymeric Materials Science and Engineering”. The symposium reflected on past scientific breakthroughs, technological advancements, and new frontiers in the field of polymeric materials science and engineering. Eight thematic areas comprised the symposium: Advanced Manufacturing, AI and Materials Discovery, Biomaterials, Electronic Materials, Energy, Entrepreneurship, Smart Materials, and Sustainability. The 31 distinguished speakers, representing academia, industry, and national laboratories, shared their unique perspectives. Within this Viewpoint, distinguished speakers have expanded on the symposium’s themes, summarizing key takeaways, identifying critical challenges, and exploring opportunities for continued advancements in polymer science.

Long-spaced polycondensates generally refer to the synthetic polymers containing long methylene segments in repeating units, which are separated by functional groups such as ester, amide, and carbonate groups. Such polymers usually show the polyethylene-like crystallization behavior, mechanical property, processability, and also good chemical recyclability. Since most of the long-spaced polycondensates are highly crystalline, understanding the relationships between their chain structure, crystallization, and macroscopic properties is of fundamental importance for developing novel sustainable polymer materials. This Viewpoint focuses on discussing the crystallization and its relations to the chain structure, macroscopic performances (e.g., thermal, mechanical, barrier properties) through the case studies on long-spaced polyesters and polyamides, followed by a brief review on other long-spaced polymer families. Then, chemical recycling of long-spaced polycondensates is also commented. Finally, a conclusion of the Viewpoint and an outlook for future directions are shared. We hope that this Viewpoint can provide inspiration for future studies on advanced sustainable polymers.

The development of efficient and robust photocatalysts is critical to achieving photomediated cationic polymerization with good control. Herein, we introduce a novel family of photocatalysts based on the boranil skeleton, which enables a visible-light-mediated cationic polymerization of vinyl ethers under operationally simple conditions, affording polymers with well-controlled molecular weights and low dispersities. Mechanistic experiments and computational studies were conducted to rationalize the catalysis and initiating mechanism, and interestingly, extra activation resulting from the photoinduced opening of boric Lewis acid site was found also operative, enabling the good tolerance of this system to air and moisture. Further application of this photopolymerization method to photocuring and photopatterning is also demonstrated with success.

Self-doped conjugated polymers represent a compelling strategy for forming conductive electrostatically complexed polymer blends without the need for additional processing steps for electronic doping. Although self-doped polymers simplify processing, fundamental questions remain about structure–property relationships and the role of doping in electrostatic complexation. A class of sulfonated PEDOT derivatives was investigated to study their self-doping behavior and the ability to form electrostatically mediated complexes with cationic polyelectrolytes. Remarkably, even a subtle change in side chain architecture (differing by only a single carbon) influenced the electrical conductivity, with the shorter side chain exhibiting values up to ≈500 S cm^–1, roughly 1000 times higher than its longer-chain counterpart. Comprehensive spectroscopic and electrochemical analyses were performed to gain insight into the origin of the behavior. These self-doped conjugated polyelectrolytes maintain high electrical conductivity (≈300 S cm^–1), even after complexation with an insulating polyelectrolyte. The phase behavior of complexation revealed the ability to define an effective charge fraction of ionic groups per monomer that can guide the design of electrostatically complex conjugated polyelectrolytes.

We incorporated thiol-functionalized silica particles as macroinitiators for the construction of composites by ring-opening polymerization of thiolactones. A separate photochemical cross-linking step was employed to enhance the stability of the polymer composite material. The thermal and mechanical properties of the materials can be tuned by varying the amount of particles, and a representative formulation could be 3D printed. The polymer composite was depolymerized in the presence of a catalytic amount of thiol and 1,8-diazabicyclo(5.4.0)undec-7-ene (DBU) base to recover substantial amounts of monomer, which were repolymerized and photo-cross-linked to give a material very similar in mechanical properties to the virgin composite. The modular nature of this system and the reliability of the bond-forming and bond-breaking steps suggest that it may prove to be useful as a new type of recyclable plastic.

Forces play vital roles in regulating cellular behavior, and integrins are prime examples that cells use to sense forces. Designer scaffolds have been developed to trigger integrin-mediated mechanotransduction to control cellular functions. However, current scaffolds lack spatiotemporal control of integrin mechanostimulation in a three-dimensional matrix. In this study, a photoresponsive hydrogel scaffold in which a cell-adhesive push–pull azobenzene was covalently loaded onto the hydrogel was synthesized. The cis-trans photoisomerization of azobenzene is expected to mechanostimulate the interaction of integrins with the cell-adhesive peptides (RGD peptide; arginine-glycine-aspartic acid) bound to azobenzene. The photoresponsive behavior of the synthesized azobenzene exhibited a photoresponse immediately after the on–off switching of blue light. The efficient cross-linking of azobenzene-bearing PEG through a click reaction allowed successful cell encapsulation in the azobenzene-bearing hydrogel. Taken together, the photoresponsive hydrogel scaffold is expected to find applications in controlling cellular behaviors in four dimensions via integrin-mediated mechanotransduction.