Efficient Synthesis of High-Molecular-Weight Biobased Polycarbonates by Lithium Lactate

Abstract

Biobased polycarbonates have attracted a wide range of interest due to sustainable resources; however, the synthesis of biobased polycarbonates with a high molecular weight remains a great challenge on account of the influence of catalysts. Herein, biobased poly(isosorbide carbonate) (PIC) with a high molecular weight of 105.0 kDa and excellent light transparency was synthesized via melt polycondensation of isosorbide and diphenyl carbonate by an efficient lithium lactate catalyst under mild conditions, including a short transesterification time of 0.5 h at a low reaction temperature of 150 °C, followed by polycondensation at 200 °C for 1 h. Furthermore, the structures of reaction intermediates and polymers were characterized, and the catalytic mechanism was elucidated by density functional theory calculations. Such a low-cost commercial catalyst would have a broad application prospect in the industrial production of PIC.

Alkali Metal/Quaternary Ammonium Salt Synergistic Catalytic System for the Efficient Synthesis of Biobased Poly(Isosorbide Carbonate)

“…The conversions of DPC catalyzed by NaOH and Cs 2 CO 3 in the transesterification stage were high enough. However, high molar mass products were not obtained under the conditions, which might be attributed to the strong alkalinity of catalysts, resulting in a high degree of degradation or hydrolyzation of the polymer chain . In addition, the products were dark in color and unsuitable for applications (shown in Figure ).…”

“…30 Several catalysts with alkali metal cation and organic acid anion were selected by Wang et al to synthesize PICs. 37 They found that lithium lactate showed the highest catalytic reactivity, and metal cations and acid anions might have interactions with the oxygen and hydrogen atom in the hydroxyl groups of ISB, respectively. It is noteworthy that high reactivity of alkali metal catalysts usually results in the coloration of PIC products.…”

“…However, high molar mass products were not obtained under the conditions, which might be attributed to the strong alkalinity of catalysts, resulting in a high degree of degradation or hydrolyzation of the polymer chain. 37 In addition, the products were dark in color and unsuitable for applications (shown in Figure 1). LiAcac and LiCl demonstrated better catalytic efficiency with M η values of 18,200 and 25,800 g/mol, respectively.…”

“…The excess of catalyst affected the competition between polymerization and side reactions, and accelerated the decomposition reaction. 37 Therefore, the optimized amount of the catalysts was 0.05 mol %. The effect of the ratio of the dual catalysts was investigated as well (Figure 4b).…”

“…Li et al found that lithium acetylacetonate was an efficient catalyst for the transesterification of ISB and dimethyl carbonate, and the conversion of ISB reached 95.2% . Several catalysts with alkali metal cation and organic acid anion were selected by Wang et al to synthesize PICs . They found that lithium lactate showed the highest catalytic reactivity, and metal cations and acid anions might have interactions with the oxygen and hydrogen atom in the hydroxyl groups of ISB, respectively.…”