Polyphthalaldehyde: Synthesis, Derivatives, and Applications

Cyclic Polyesters with Closed-Loop Recyclability from A New Chemically Reversible Alternating Copolymerization

Polyesters with both cyclic topology and chemical recyclability are attractive. Here, the alternating copolymerization of cyclic anhydride and o-phthalaldehyde to synthesize a series of cyclic and recyclable polyesters are reported for the first time. Besides readily available monomers, the copolymerization is carried out at 25 °C, uses common Lewis/Brønsted acids as catalysts, and achieves high yields within 1 h. The resulting polyesters possess well-defined alternating sequences, high-purity cyclic topology, and tunable structures using distinct two monomer sets. Of interest, the copolymerization manifests obvious chemical reversibility as revealed by kinetic and thermodynamic studies, making the unprecedented polyesters easy to recycle to their distinct two monomers in a closed loop at high temperatures. This work furnishes a facile and efficient method to synthesize cyclic polyesters with closed-loop recyclability.

Mechanochemically accessing a challenging-to-synthesize depolymerizable polymer

Polymers with low ceiling temperatures (T_c) are highly desirable as they can depolymerize under mild conditions, but they typically suffer from demanding synthetic conditions and poor stability. We envision that this challenge can be addressed by developing high-T_c polymers that can be converted into low-T_c polymers on demand. Here, we demonstrate the mechanochemical generation of a low-T_c polymer, poly(2,5-dihydrofuran) (PDHF), from an unsaturated polyether that contains cyclobutane-fused THF in each repeat unit. Upon mechanically induced cycloreversion of cyclobutane, each repeat unit generates three repeat units of PDHF. The resulting PDHF completely depolymerizes into 2,5-dihydrofuran in the presence of a ruthenium catalyst. The mechanochemical generation of the otherwise difficult-to-synthesize PDHF highlights the power of polymer mechanochemistry in accessing elusive structures. The concept of mechanochemically regulating the T_c of polymers can be applied to develop next-generation sustainable plastics.

Modular Synthesis of Phthalaldehyde Derivatives Enabling Access to Photoacid Generator-Bound Self-Immolative Polymer Resists with Next-Generation Photolithographic Properties

The resolution, line edge roughness, and sensitivity (RLS) trade-off has fundamentally limited the lithographic performance of chemically amplified resists. Production of next-generation transistors using extreme ultraviolet (EUV) lithography depends on a solution to this problem. A resist that simultaneously increases the effective reaction radius of its photogenerated acids while limiting their diffusion radius should provide an elegant solution to the RLS barrier. Here, we describe a generalized synthetic approach to phthalaldehyde derivatives using sulfur(VI) fluoride exchange click chemistry that dramatically expands usable chemical space by enabling virtually any non-ionic photoacid generator (PAG) to be tethered to phthalaldehyde. The resulting polymers represent the first ever PAG-tethered self-immolative resists in an architecture that simultaneously displays high contrast, extraordinary sensitivity, and low roughness under EUV exposure. We believe this class of resists will ultimately enable researchers to overcome the RLS trade-off.

Synthesis of End-Cap Enabled Self-Immolative Photoresists For Extreme Ultraviolet Lithography

Conventional chemically amplified resists (CARs) rely on the usage of photoacid generators to serve as the source of chemical amplification. However, acid diffusion inevitably accompanies CARs and has led to the resolution, line edge roughness, and sensitivity (RLS) trade-off, which is the most challenging technical problem for modern photoresists. Herein, we take advantage of the self-immolative property of polyphthalaldehyde (PPA) derivatives to create end-cap enabled chain scissionable resists for extreme ultraviolet (EUV) lithography. The feasibility of this strategy was demonstrated under UV photodegradation experiments. The dose-to-clear (DTC) under EUV radiation was 90 mJ/cm² for the most promising resist, representing more than a 100-fold improvement over previous PPA resists. Density functional theory (DFT) calculations were conducted to understand the structural origin of end-cap EUV sensitivity.

Direct Heat-Induced Patterning of Inorganic Nanomaterials

Patterning functional inorganic nanomaterials is an important process for advanced manufacturing of quantum dot (QD) electronic and optoelectronic devices. This is typically achieved by inkjet printing, microcontact printing, and photo- and e-beam lithography. Here, we investigate a different patterning approach that utilizes local heating, which can be generated by various sources, such as UV-, visible-, and IR-illumination, or by proximity heat transfer. This direct thermal lithography method, termed here heat-induced patterning of inorganic nanomaterials (HIPIN), uses colloidal nanomaterials with thermally unstable surface ligands. We designed several families of such ligands and investigated their chemical and physical transformations responsible for heat-induced changes of nanocrystal solubility. Compared to traditional photolithography using photochemical surface reactions, HIPIN extends the scope of direct optical lithography toward longer wavelengths of visible (532 nm) and infrared (10.6 μm) radiation, which is necessary for patterning optically thick layers (e.g., 1.2 μm) of light-absorbing nanomaterials. HIPIN enables patterning of features defined by the diffraction-limited beam size. Our approach can be used for direct patterning of metal, semiconductor, and dielectric nanomaterials. Patterned semiconductor QDs retain the majority of their as-synthesized photoluminescence quantum yield. This work demonstrates the generality of thermal patterning of nanomaterials and provides a new path for additive device manufacturing using diverse colloidal nanoscale building blocks.

Clip Chemistry: Diverse (Bio)(macro)molecular and Material Function through Breaking Covalent Bonds

In the two decades since the introduction of the "click chemistry" concept, the toolbox of "click reactions" has continually expanded, enabling chemists, materials scientists, and biologists to rapidly and selectively build complexity for their applications of interest. Similarly, selective and efficient covalent bond breaking reactions have provided and will continue to provide transformative advances. Here, we review key examples and applications of efficient, selective covalent bond cleavage reactions, which we refer to herein as "clip reactions." The strategic application of clip reactions offers opportunities to tailor the compositions and structures of complex (bio)(macro)molecular systems with exquisite control. Working in concert, click chemistry and clip chemistry offer scientists and engineers powerful methods to address next-generation challenges across the chemical sciences.

Coordination-induced polymerization of P═C bonds leads to regular (P─C) n polycarbophosphanes

The replacement of carbon in (C─C) n chains of polyolefins by phosphorus leads to polycarbophosphanes (P─C) n , which may possess unique chemical and physical properties. However, macromolecules with a regular (P─C) n chain have never been unambiguously identified. Here, we demonstrate that addition polymerization, a general concept to polymerize olefins, can be extended to P═C double bonds. The polymerization of monomeric 2-phosphanaphthalenes is mediated by copper(I) halides and leads to polycarbophosphanes with an M n of 14 to 34 kDa. Each phosphorus is coordinated to Cu(I), which can be easily removed. Unlike long-term durable polyolefins, the metal-free polymers depolymerize rapidly back to monomers under sunlight or ultraviolet irradiation at λ = 365 nm. The monomers can be recycled for repolymerization, demonstrating a cradle-to-cradle life cycle for polycarbophosphanes.

Maskless Device Fabrication and Laser-Induced Doping in MoS2 Field Effect Transistors Using a Thermally Activated Cyclic Polyphthalaldehyde Resist

We present a novel maskless device fabrication technique for rapid prototyping of two-dimensional (2D)-based electronic materials. The technique is based on a thermally activated and self-developed cyclic polyphthalaldehyde (c-PPA) resist using a commercial Raman system and 532 nm laser illumination. Following the successful customization of electrodes to form field effect transistors based on MoS₂ monolayers, the laser-induced electronic doping of areas beneath the metal contacts that were exposed during lithography was investigated using both surface potential mapping and device characterization. An effective change in the doping level was introduced depending on the laser intensity, i.e., low laser powers resulted in p-doping, while high laser powers resulted in n-doping. Fabricated devices present a low contact resistance down to 10 kΩ·μm at a back-gate voltage of V_G = 80 V, which is attributed to the laser-induced n-type doping at the metal contact regions.

Self-immolative polymers in biomedicine

Biomedical use cases for self-immolative polymers.

Exceptional copolymerizability of o-phthalaldehyde in cationic copolymerization with vinyl monomers

o-Phthalaldehyde is copolymerized via the unique active species, which allows the controlled copolymerization with alkyl vinyl ethers, alternating copolymerization, and copolymerization with sterically hindered nonhomopolymerizable vinyl monomers.

Cyclopolymerizations: Synthetic Tools for the Precision Synthesis of Macromolecular Architectures

Monomers possessing two functionalities suitable for polymerization are often designed and utilized in syntheses directed to the formation of cross-linked macromolecules. In this review, we give an account of recent developments related to the use of such monomers in cyclopolymerization processes, in order to form linear, soluble macromolecules. These processes can be activated by means of radical, ionic, or transition-metal mediated chain-growth polymerization mechanisms, to achieve cyclic moieties of variable ring size which are embedded within the polymer backbone, driving and tuning peculiar physical properties of the resulting macromolecules. The two functionalities are covalently linked by a "tether", which can be appropriately designed in order to "imprint" elements of chemical information into the polymer backbone during the synthesis and, in some cases, be removed by postpolymerization reactions. The two functionalities can possess identical or even very different reactivities toward the polymerization mechanism involved; in the latter case, consequences and outcomes related to the sequence-controlled, precision synthesis of macromolecules have been demonstrated. Recent advances in new initiating systems and polymerization catalysts enabled the precision syntheses of polymers with regulated cyclic structures by highly regio- and/or stereoselective cyclopolymerization. Cyclopolymerizations involving double cyclization, ring-opening, or isomerization have been also developed, generating unique repeating structures, which can hardly be obtained by conventional polymerization methods.