Organocatalyzed Synthesis of Aliphatic Polyesters from Ethylene Brassylate: A Cheap and Renewable Macrolactone

The use of organocatalysts for the polymerization of ethylene brassylate, a commercially available, cheap, and renewable macro(di)lactone is reported for the first time. Ethylene brassylate was polymerized by ring-opening polymerization under bulk and solution conditions at 80 °C. Polymerizations were carried out in the presence of several organic catalysts, such as dodecylbenzenesulfonic acid (DBSA), diphenyl phosphate (DPP), p-toluenesulfonic acid (PTSA) and bases, 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD), 1,2,3-tricyclohexylguanidine (TCHG), and 1,2,3-triisopropylguanidine (TIPG), using benzyl alcohol as initiator. Results agreed with a ring opening polymerization process in which the rate of polymerization was accelerated by the catalysts presence in the order of TBD > PTSA > DBSA > DPP > TIPG > TCHG. Complementary computational studies supported the experimental results. The obtained poly(ethylene brassylate) aliphatic polyesters were characterized by NMR, SEC, MALDI-TOF, DSC, and TGA. They showed molecular weights ranging from 2 to 13 kg mol^-1 and polydispersity index between 1.5 and 2. Poly(ethylene brassylate) is a semicrystalline polyester similar to poly(ε-caprolactone) with slightly higher melting and glass transition temperatures (T_m = 69 °C, T_g = -33 °C) and good thermal stability.