This perspective addresses efficiency and selectivity of high-temperature lignin liquefaction processes conducted in various reaction media as sub-and supercritical fluids. The challenges in efficient and selective production of high-value organic monomers from lignin are reviewed critically, along with analytical protocols essential for their accurate recovery after lignin degradation. The current approaches targeting the formation of phenolic monomers from lignin are discussed in terms of their repolymerization, a process that decreases the reaction selectivity and yield of the dominant phenolic monomers. The potential to solve this grand challenge is analyzed in terms of acid and/or protic cosolvent application, reduction of the reaction temperature, "quenching" of the reactive lignin depolymerization intermediates, and presence of heterogeneous catalysts, such as zeolites, metals, and metal oxides, sulfides, and phosphides.

Recently, polycarbonates have attracted considerable research interest because of their potential biodegradability and sustainability. Here, we present a direct route for the synthesis of polycarbonates and poly(ether carbonate)s from carbon dioxide (CO 2 ) and diols, promoted by Cs 2 CO 3 and CH 2 Cl 2 under 1 atm of CO 2 . Quantitative conversion of diols and polymers with up to 11 kg/mol molecular weight could be obtained. While benzylic diols lead to predominantly carbonate linkage, aliphatic diols result in the incorporation of the methylene unit of CH 2 Cl 2 that produces poly(ether carbonate)s. Both primary and secondary diols have been successfully incorporated into the polymer chain.

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