ACS Applied Polymer Materials

Synthesis of Aromatic–Aliphatic Polyesters by Enzymatic Ring Opening Polymerization of Cyclic Oligoesters and their Cyclodepolymerization for a Circular Economy

Cyclic oligomers of hexamethylene furanoate and hexamethylene terephthalate were obtained from 1,6-hexanediol and the corresponding methyl esters using Candida antarctica lipase B (CALB) enzyme catalyst. HPLC, MALDI-TOF MS, and NMR analyses showed that mixtures composed from cyclic dimer up to heptamer were obtained almost quantitatively. Subsequently, these cycles were polymerized by ring opening polymerization (ROP) mediated by CALB to obtain semicrystalline polymers. In addition, we demonstrated that the polymers obtained from the ROP process could be transformed into cyclic oligomers in high yields using enzymatic cyclodepolymerization, thereby recycling the polymer in a circular biosynthetic path.

Recyclable and Degradable Vinylogous Urethane Epoxy Thermosets with Tunable Mechanical Properties from Isosorbide and Vanillic Acid

Conventional epoxy resins derived from unsustainable petroleum resources are unrecyclable and nondegradable. Herein, we facilely synthesized biobased vinylogous urethane epoxy thermosets (VUEs) using sustainable isosorbide and vanillic acid via a post-crosslinking method. Isosorbide was directly functionalized to isosorbide-bis-acetoacetate, which could be reacted with primary amines provided by triethylenetetramine and diamine to generate linear prepolymers with vinylogous urethane bonds. Then, VUEs were constructed, in which permanent covalent crosslinkers were generated by ring opening of the epoxy group in vanillin acid with the secondary amine already present in the linear prepolymer. By integrating different types of diamines, the obtained biobased VUEs display tunable mechanical properties; specifically, the tensile strength varies from 31.5 to 114.6 MPa and the elongation at break ranges from 9.5 to 150.0%. The VUE using ethylenediamine (TT-VUE) is comparable to that of bisphenol-A epoxy in terms of its mechanical qualities. The incorporation of vinylogous urethane bonds confers recyclable capability on VUEs, and the recycled VUEs show a lap shear strength of 7.39 MPa, indicating their potential application in adhesives. We envisaged that biobased VUEs with desirable tunable mechanical properties would be excellent replacements for petroleum-based epoxy resins.

Piperazine-Linked Covalent Triazine Polymer as an Efficient Platform for the Removal of Toxic Mercury(II) Ions from Wastewater

A piperazine-linked robust N-rich covalent organic polymer (COP), SMCOP-1, was synthesized by a catalyst-free method and characterized by Fourier transform infrared (FTIR), 13C CP/MAS, X-ray photoelectron spectroscopy (XPS), and powder X-ray diffraction (PXRD). This polymeric material can work as an efficient platform for removing toxic Hg2+ from wastewater. This system showed >97% Hg2+ removal, as confirmed by inductively coupled plasma atomic emission spectroscopy (ICP-AES), with a maximum uptake capacity of 1329 mg g–1. Hg2+ incorporation inside SMCOP-1 was confirmed by XPS, energy-dispersive spectrometry (EDS), and elemental mapping of field emission scanning electron microscopy (FE-SEM). The high Hg2+ removal capacity of SMCOP-1 can be attributed to the strong noncovalent interaction between the Hg2+ ion and the binding sites of the covalent organic polymer, as suggested by density functional theory (DFT) calculations, noncovalent interaction (NCI) analysis, and the electrostatic potential (ESP) map. The material’s recyclability was studied for up to four consecutive cycles, and it was observed that it retained a high removal capacity without any change in the structure and morphology, as confirmed by FTIR and FE-SEM.

Water-Soluble Napthalimide-Conjugated N-Nitrosamine-Based Block Copolymers for Photoinduced Nitric Oxide Delivery and Cell Imaging

N-Nitrosamine-derived nitric oxide (NO) delivery agents find widespread use in diverse biomedical applications, including cancer therapy. To understand how NO is released from these compounds and acts within cells, herein, we report a facile approach to synthesize N-nitrosamine-bound water-soluble napthalimide-based block copolymers (BCPx-NO) with improved regulation over their molecular weight and aqueous solution self-assembly. These polymers exhibit a fluorescence “turn-on” response upon photostimulated (365 nm, 3.71 mW/cm2) NO release, delivering 47–53 μM of NO within 10 h, while their concentration varied from 0.26 to 0.60 mg/mL. This accounts for approximately 67–75% of the theoretically bound NO within the polymers. The fluorescence “turn-on” response is characteristic of the small-molecule NO donor (NOD), although the emission time has a longer half-life in the polymers. The type of NO released from the NOD is a nitric oxide radical (•NO), as per the electron paramagnetic resonance spectroscopy results. The in vitro NO release in response to the photoirradiation and the consequent acquired fluorescence are corroborated using flow cytometry and confocal imaging studies. It was also manifested that these NO conjugated polymers can physically encapsulate doxorubicin (DOX) in aqueous environment, and the synergistic effect of DOX and NO is reflected in the exhibited cytotoxicity against the MCF-7 (human breast adenocarcinoma) cells. The spatiotemporally modulated NO release steered fluorescence “turn-on” may find abundant biomedical applications.

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