Thermally Robust yet Deconstructable and Chemically Recyclable High-Density Polyethylene (HDPE)-Like Materials Based on Si-O Bonds

Polyethylene (PE) is the most widely produced synthetic polymer. By installing chemically cleavable bonds into the backbone of PE, it is possible to produce chemically deconstructable PE derivatives; to date, however, such designs have primarily relied on carbonyl- and olefin-related functional groups. Bifunctional silyl ethers (BSEs; SiR2 (OR'2 )) could expand the functional scope of PE mimics as they possess strong Si-O bonds and facile chemical tunability. Here, we report BSE-containing high-density polyethylene (HDPE)-like materials synthesized through a one-pot catalytic ring-opening metathesis polymerization (ROMP) and hydrogenation sequence. The crystallinity of these materials can be adjusted by varying the BSE concentration or the steric bulk of the Si-substituents, providing handles to control thermomechanical properties. Two methods for chemical recycling of HDPE mimics are introduced, including a circular approach that leverages acid-catalyzed Si-O bond exchange with 1-propanol. Additionally, despite the fact that the starting HDPE mimics were synthesized by chain-growth polymerization (ROMP), we show that it is possible to recover the molar mass and dispersity of recycled HDPE products using step-growth Si-O bond formation or exchange, generating high molecular weight recycled HDPE products with mechanical properties similar to commercial HDPE.

Nanoscale Control of the Surface Functionality of Polymeric 2D Materials

Typically, 2D nanosheets have a homogeneous surface, making them a major challenge to structure. This study proposes a novel concept of 2D organic nanosheets with a heterogeneously functionalized surface. This work achieves this by consecutively crystallizing two precisely synthesized polymers with different functional groups in the polymer backbone in a two-step process. First, the core platelet is formed and then the second polymer is crystallized around it. As a result, the central area of the platelets has a different surface functionality than the periphery. This concept offers two advantages: the resulting polymeric 2D platelets are stable in dispersion, which simplifies further processing and makes both crystal surfaces accessible for subsequent functionalization. Additionally, a wide variety of polymers can be used, making the process and the choice of surface functionalization very flexible.

Design, Synthesis and Actual Applications of the Polymers Containing Acidic P-OH Fragments: Part 1. Polyphosphodiesters

Among natural and synthetic polymers, main-chain phosphorus-containing polyacids (PCPAs) (polyphosphodiesters), stand in a unique position at the intersection of chemistry, physics, biology and medicine. The structural similarity of polyphosphodiesters PCPAs to natural nucleic and teichoic acids, their biocompatibility, mimicking to biomolecules providing the 'stealth effect', high bone mineral affinity of polyphosphodiesters resulting in biomineralization at physiological conditions, and adjustable hydrolytic stability of polyphosphodiesters are the basis for various biomedical, industrial and household applications of this type of polymers. In the present review, we discuss the synthesis, properties and actual applications of polyphosphodiesters.

Terpyridine-Induced Folding of Anisotropic Polyphosphoester Platelets

The folding of macromolecules is of great importance in nature. Also in synthetic polymer chemistry, single-chain nanoparticles, i.e. folding synthetic macromolecules, are a current research topic to mimic protein folding and to generate well-defined structures. Here, we present the "folding" of anisotropic polymer platelets to further mimic natural folding processes on the (sub)micrometer scale. We report on the synthesis of terpyridine-functionalized long-chain polyphosphoesters by acyclic diene metathesis polymerization that can crystallize in dilute solution into anisotropic polymer crystal platelets. As the terpyridine units are expelled to the platelet surface, terpyridine-metal interactions could be induced by adding nickel(II) bis(acetylacetonate) (Ni(acac)₂) to the platelet dispersion in ethyl acetate. These polymer crystals were "folded" to homogeneous nanoparticles with a wrinkled structure, which were visualized by transmission electron microscopy (TEM). The size and size distribution of the obtained assemblies could be altered by varying the concentration of Ni(acac)₂. In contrast, no wrinkled structures but rather intrachain cross-linking was observed, when Ni(acac)₂ was added to the homogeneous polymer solution before crystallization. We believe that this concept of "folding" anisotropic polymer platelets will further enhance the control of morphologies on (sub)micrometer particles and might be useful for catalysis or separation.