Rapid, controlled ring-opening polymerization of salicylic acid o-carboxyanhydride for poly(salicylate) synthesis

Abstract

Salicylic acid (SA), derived from plants such as willow bark (Latin: Salix), is one of the most widely used antipain agents. Beyond this classic use, salicylate-based macromolecules with particular properties have attracted great interest. In this work, we describe a simple and rapid synthesis pathway of poly(salicylate) homopolymers. Based on the preparation of pure six-member cyclic SAOCA monomers, organocatalysts, such as DBU, initiate a fast SAOCA polymerization process, in which the full conversion of SAOCA is completed within 40 seconds for a monomer-to-DBU-to-benzyl alcohol ratio of 50/1/1 at ambient temperature. Homopolymer poly(salicylate)s with variable chain lengths (3.8–13.9 kDa) and a narrow molecular weight distribution (Đ < 1.28) were readily prepared without any metallic residues. The computational studies verify the different functions of DBU during the ROP of SAOCA: the nucleophilic attack of DBU on SAOCA at the initiation stage and the promotion of the terminal activity of the propagation chain by H-bonding at the polymerization stage. The poly(salicylate)s obtained exhibit striking thermal properties, particularly T_g above 100 °C. This simple pathway provides a great method to synthesize versatile poly(salicylate)-based polymers via ring-opening copolymerization with other cyclic monomers for further broadening the application of poly(salicylate)s.