Main-chain, stimuli-degradable polymers possess important advantages in polymer waste management and biomedical applications, allowing the on-demand main-chain polymer degradation using certain external stimuli. Among the different triggers proposed to cleave the polymer bonds, light has emerged as a particularly attractive stimulus to induce a photo-mediated main chain polymer degradation, because of its spatiotemporal control, tunable intensity and wavelength, and noninvasive nature [1]. Herein, two novel, main-chain, stimuli-degradable polymer families as proof-of-concept studies to improve polymer sustainability, are presented. First, soft, transparent, photodegradable, and thermo-reversible polymer gels, comprising PEG as the elastic strands, that undergo degradation upon exposure to light, will be discussed [2]. Mechanistic studies revealed a chemical recycling process to obtain the initial reagents as the main photoproducts, enlightening the mechanism of network reformation upon heating the system at mild temperatures, as verified by shear rheology experiments. The hydrogels successfully underwent reversible photodegradation and reformation upon heating, restoring the initial mechanical properties of the polymer network and thus revealing the re-processability of the system. In the second part, photo- and acid-degradable poly(acylhydrazones) synthesized via a step-growth reaction of dicarbonyl and diacylhydrazide comonomers is presented [3]. The photo-sensitivity of the synthesized polymers to light was verified by irradiation studies in aqueous solution, while a mechanistic study shed light on the photodegradation mechanism and the produced photoproducts.

Acknowledgments
The research project was supported by the Hellenic Foundation for Research and Innovation (H.F.R.I.) under the “2nd Call for H.F.R.I. Research Projects to support Faculty Members & Researchers” (Project Number: HFRI-FM17-3346).

Two furan-based monomers were derived starting from 5-bromofurfural, a furfural derivative, and sodium sulfide. Subsequent reaction steps gave the sulfide and sulfone containing monomers as dimethyl esters. Polyesters were then derived from various alkyl diols e.g., ethylene glycol, 1,4-butanediol, and diethylene glycol, in melt polycondensation reactions catalyzed by a titanium catalyst. The polyesters were processed into films via melt-pressing for further characterization. The sulfide bridge appeared especially beneficial for realizing films with low oxygen gas permeability while the sulfone bridge gave somewhat increased permeability. The polyesters derived from the sulfone containing monomer gave much higher glass transition temperatures (ca. 40 degrees higher) than those from the corresponding sulfide monomer. Interestingly, 1,3-propanediol appeared to give polyesters with the highest tendency to crystallize with both the sulfide or sulfone monomer, with other diols giving polyesters with largely amorphous character.

Recyclability was studied with both the sulfide and sulfone monomers with 1,5-pentanediol or diethylene glycol as the diol components. Free-standing films of all four polyesters could be chemically recycled back into monomers in a facile manner using methanol in the presence of catalytic potassium carbonate. Notably, diethylene glycol endowed the polyesters with room-temperature recyclability in methanol, providing yields >89% of the original sulfide and sulfone monomers with excellent purity.

As the global energy transition shifts towards renewable sources like solar, wind, and geothermal power, it is crucial to consider not only the performance of materials but also the sustainability of their production and end-of-life management. Conventional materials, while efficient, often neglect the environmental impact of their manufacturing processes and recyclability. This work focuses on developing green polymer materials and processes for organic photovoltaics (OPV), with an emphasis on enhancing the sustainability of electro- and photoactive π-conjugated polymers.(i) By incorporating biobased synthons into polymer synthesis, this approach aims to improve both the efficiency and environmental footprint of OPVs, addressing challenges related to biodegradability and recycling. This study specifically explores the use of furan-based monomers and polymers in OPVs, synthesized through microwave-assisted methods and electro-polymerization. These innovative techniques offer faster, more energy-efficient routes compared to traditional methods. Furan-based materials, with their inherent electronic properties, have shown promise as hole transport layers in organic solar cells, potentially enhancing device performance while reducing reliance on fossil-derived chemicals. By advancing sustainable polymer synthesis for OPVs, this research not only contributes to more eco-friendly energy solutions but also aligns with broader goals of circular economy and material sustainability in the renewable energy sector.

Over the last decade, the issue of plastic pollution has prompted a shift towards bioplastics and paper-based materials over fossil-derived plastics, highlighting cellulose as a promising alternative as it is the most abundant organic polymer in nature [1]. However, cellulose's susceptibility to moisture significantly limits its mechanical performance and so its widespread application. To increase paper's mechanical strength in humid environments, wet-strength agents are employed, traditionally synthetic polymers like polyaminoamide-epichlorohydrin (PAE) and melamine-formaldehyde (MF) resin, which pose health risks due to carcinogenic compounds and hinder recyclability of final products. Consequently, research is directed towards natural alternatives to enhance process circularity [2].
This study focuses on developing a novel wet-strength agent derived from eugenol through a facile, economical, one-pot polymerization. Eugenol, obtainable from cloves or synthesized from lignin derivatives, is widely employed in the cosmetic and pharmaceutical sectors [3].
This approach aims to overcome the performance limitations of existing biopolymer-based agents. The resulting polymer (PEU) when impregnated into cellulose, imparts significant hydrophobic properties, demonstrated by water-contact angles exceeding 100°, and substantially enhances mechanical strength, evidenced by enhancement in Young's Modulus and resilience, even in humid conditions. These enhancements are achieved with low concentrations of PEU, attributable to its effective coverage of cellulose fibers, mimicking lignin's protective function. This natural, eugenol-derived polymer offers a sustainable solution, mitigating the drawbacks of synthetic wet-strength agents and advancing the development of high-performance, recyclable paper products.