Ring-Closing Depolymerization: A Powerful Tool for Synthesizing the Allyloxy-Functionalized Six-Membered Aliphatic Carbonate Monomer 2‑Allyloxymethyl-2-ethyltrimethylene Carbonate

Abstract

Ring-closing depolymerization is demonstrated to be a powerful synthetic methodology for the formation of six-membered functional aliphatic carbonate monomers, providing a rapid, straightforward, inexpensive, and green route for obtaining six-membered functional aliphatic carbonate monomers at a scale greater than 100 g. The utility of this technique was observed via the synthesis of the allyloxy-functionalized six-membered cyclic carbonate monomer 2-allyloxymethyl-2-ethyltrimethylene carbonate (AOMEC). The synthesis was performed in a one-pot bulk reaction, starting from trimethylolpropane allyl ether, diethyl carbonate, and NaH, resulting in a final AOMEC yield of 63%. The synthetic methodology is based upon the reversible nature of this class of polymers. The anionic environment produced by NaH was observed to be sufficient to mediate the monomer equilibrium concentration; thus, an additional catalyst is not required to induce depolymerization. 1,5,7-Triazabicyclo[4.4.0]­dec-5-ene (TBD) was demonstrated to be a very active catalyst for the ring-opening polymerization (ROP) of AOMEC, resulting in a rapid (<i>k</i>_p^app = 28.2 s^–1) and controlled polymerization with a low dispersity (<i><i>Đ</i></i> = 1.2). The availability and activity of the functionality of poly­(AOMEC)­s were established through subsequent postpolymerization functionalization via the UV-initiated thiol–ene chemistry of poly­(AOMEC) with 1-dodecanethiol and benzophenone as a radical initiator. The functionalization proceeded with high control and with a linear relation between the molecular weight and conversion of the unsaturation, revealing the high orthogonality of the reaction and the stability of the carbonate backbone. Hence, as a synthetic methodology, depolymerization provides a straightforward and simple approach for the synthesis of the highly versatile functional carbonate AOMEC. In addition, formation of the monomer does not require any solvents, reactive ring-closing reagents, or transition-metal-based depolymerization catalysts, thereby providing a “greener” route for obtaining functional carbonate monomers and polymers