Yttrium-mediated ring-opening polymerization of functionalizable dihydrocarvide: tunable terpene-based polyesters using grafting from and block copolymerization strategies

Abstract

Poly(dihydrocarvide) (PDHC) is synthesized through ring-opening polymerization (ROP) of terpene-based 7-membered lactone dihydrocarvide (DHC) using an amino-alkoxy-bis(phenolate) yttrium amido catalyst and isopropanol (iPrOH) as a chain transfer agent while retaining the pendant-group double bond in the monomer unit. Polymerization under conditions found to be favorable (60 °C, 1 eq. iPrOH) yielding PDHC with tunable molecular weights and low to moderate polydispersities (Ð = 1.2-1.5). Crystalline fractions are introduced into amorphous PDHC by producing block copolymers with 16-membered ω-pentadecalactone (PDL) or 4-membered racemic β-butyrolactone (BBL) via sequential addition following the coordination strength hierarchy (PDL ˂ DHC ˂ BBL). This resulted in semi-crystalline renewable block copolymers P(PDL-b-DHC) and P(DHC-b-PHB) that were further analyzed by PXRD and SAXS measurements. Additionally, PDHC is functionalized via thiol-ene reaction with 2-mercaptoethanol, introducing hydroxyl functionality and opening up a multitude of functionalization possibilities. As one example, atom transfer radical polymerization (ATRP) initiators are attached, and SARA and ARGET ATRP techniques are employed to graft poly(ethyl acrylate) (PEA) as model compound, forming PDHC-g-PEA brush polymers. The TPMA^NMe2-based ARGET ATRP system demonstrates superior control over molecular weight and polydispersity compared to SARA ATRP, though both methods yield well-defined polymer brushes with molecular weight growth correlating with the initial amount of ethyl acrylate. This approach demonstrates the potential of PDHC for constructing diverse polymer architectures from different types of lactones or vinyl monomers by combining ROP and ATRP.