One-pot synthesis of bio-based polycarbonates from dimethyl carbonate and isosorbide under metal-free condition†
Synthesis of bioderived high-molecular-weight polycarbonates under metal-free condition is particularly challenging. Here, a green synthetic strategy of bio-based poly(isosorbide carbonate) (PIC) from renewable monomer isosorbide (ISB) and dimethyl carbonate (DMC) was developed by using organo-catalysts, which avoided the use of toxic and metal-containing chemicals. Due to high catalytic activity of the organo-catalysts, the reactivity of ISB and selectivity of carboxymethylated products were improved significantly, resulting in high-molecular-weight PIC. By using 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) as catalyst, an oligomer with [–OC(O)OCH3]/[–OH] ratio of 1.56 and PIC with weight-average molecular weight of 53 200 were obtained, which indicated that both ISB and DMC were effectively activated by TBD according to our proposed bifunctional activation mechanism. Furthermore, one-pot synthesis of copolymeric poly(diol-co-isosorbide carbonate)s from ISB, DMC and various diols was achieved, where the secondary hydroxyl group of ISB and the primary hydroxyl group of diols were dually activated by TBD, which has not been reported to the best of our knowledge.