In this article, we reported the synthesis of thermoresponsive palladium nanoparticles, stabilized by polymer‐tagged N‐heterocyclic carbenes (NHCs), using two different approaches. In one case, the nanoparticles were synthesized from the NHC–palladium complex, while in other cases, palladium nanoparticles and NHC were synthesized simultaneously for the in situ cappings of the nanomaterial. While the thermoresponsive nature of the nanomaterials was observed in both cases, differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) analyses showed distinct characteristics in the thermal behavior of those materials. High‐resolution transmission electron microscopic (HRTEM) and scanning electron microscopic studies separately revealed temperature‐dependent aggregation in both cases although separate patterns were observed when the nanomaterials were synthesized using different approaches. Finally, both the nanomaterials were successfully used as a recyclable catalyst for Suzuki reactions in an aqueous medium, with slightly different catalytic activity, plausibly due to variations in the size of the nanoparticles.
Recently, bacterial cellulose and related materials attracted significant attention for applications such as leather-like materials, wound healing materials, etc., due to their abundance in pure form and excellent biocompatibility. Chemical modification of bacterial cellulose further helps to improve specific properties for practical utility and economic viability. However, in most cases, chemical modification of cellulose materials involves harsh experimental conditions such as higher temperatures or organic solvents, which may destroy the 3-dimensional network of bacterial cellulose, thereby altering its characteristic properties. Hence, in this work, we have adopted the Suzuki coupling methodology, which is relatively unexplored for chemically modifying cellulose materials. As the Suzuki coupling reaction is tolerable against air and water, modification can be done under mild conditions so that the covalently modified cellulose materials remain intact without destroying their 3dimensional form. We performed Suzuki coupling reactions on cellulose surfaces using a recently developed thermoresponsive catalyst consisting of poly(N-isopropylacrylamide) (PNIPAM)-tagged N-heterocyclic carbene (NHC)-based palladium(II) complex. The thermoresponsive nature of the catalyst particularly helped to perform reactions in a water medium under mild conditions considering the biological nature of the substrates, where separation of the catalyst can be easily achieved by tuning temperature. The boronic acid derivatives have been chosen to alter the wettability behavior of bacterial cellulose. Bacterial cellulose (BC) obtained from fermentation on a lab scale using a cellulose-producing bacterium called Gluconacetobacter kombuchae (MTCC 6913) under Hestrin-Schramm (HS) medium, or kombucha-derived bacterial cellulose (KBC) obtained from kombucha available in the market or cotton-cellulose (CC) was chosen for the surface functionalization to find the methodology's diversity. Movie files in the Supporting Information and figures in the manuscript demonstrated the utility of the methodology for fluorescent labeling of bacterial cellulose and related materials. Finally, contact angle analysis of the surfaces showed the hydrophobic natures of some functionalized BC-based materials, which are important for the practical use of biomaterials in wet climatic conditions.
Herein we have reported the effective use of palladium‐based systems which contain modified N‐Heterocyclic carbene (NHC) tagged with poly(N‐isopropylacrylamide) (PNIPAM) moiety as an organometallic catalyst. This report involves a comparative study between two catalysts, PNIPAM‐NHC‐Pd (II) complex (catalyst A) and PNIPAM‐NHC‐Pd (0) nanoparticles (catalyst B), to participate in the degradation of poly(ethylene terephthalate) (PET) into its monomer, bis(2‐hydroxyethyl terephthalate) (BHET) through glycolysis with ethylene glycol (EG). Glycolysis of the PET was carried out at different temperatures (170, 175, 180, 185, and 190°C) and times (6 and 24 h) where optimum results were obtained while glycolysis was performed at 180°C for 24 h using catalyst B. The investigation of the glycolysis product through NMR, ATR‐IR, TGA, and DSC proved the formation of BHET as the main product. To ensure the effective recycling of the PET and further value additions, the obtained glycolysis product, BHET was further transformed into its dibenzoylated derivative, bis(2‐([4‐Butoxy benzoyl]oxy)ethyl) terephthalate (BBET) by successive benzoylation using 4‐butoxybenzoyl chloride. The obtained BBET was used as an additive along with the commercial polyurethane‐based adhesive (CPU), and its effect on the properties of CPU was investigated using differential scanning calorimetry (DSC) studies.
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