Ring-opening polymerization of l-lactide catalyzed by food sweetener saccharin with organic base mediated: A computational study

Abstract

The mechanisms of ring-opening polymerization (ROP) of l-lactide (L-LA) and trimethylene carbonate (TMC) by DMAP/Sac (saccharin) were disclosed by DFT calculations. The DMAP/Sac as a bifunctional catalyst can simultaneously activate monomer and initiator/chain-end in the ROPs of L-LA and TMC, respectively. And, two possible intramolecular H-bond rearrangements and two ring-opening modes were found. In addition, we computationally designed a novel two-component organocatalyst Adenine/Sac and assessed its catalytic performance. It was found that the energy barriers of rate-controlling step (ring-opening of L-LA and TMC) by Adenine/Sac apparently decrease, thus suggesting higher catalytic activity. Further analysis confirmed that the natural atomic orbital energy of N atom (E(NAO)N) in protonated Adenine is lower than that in DMAPH+, which makes the proton transfer between the protonated Adenine and monomers easier. Therefore, the present work could provide some valuable information for designing new two-component organocatalysts for ROP of cyclic esters.