One-pot synthesis of PLA-b-PHEA via sequential ROP and RAFT polymerizations

Abstract

A block copolymer library of polylactide (PLA) and poly(2-hydroxyethyl acrylate) (PHEA) was prepared via sequential ring opening polymerization (ROP) and reversible addition fragmentation chain transfer (RAFT) polymerization in a one-pot approach. The whole process was conducted at room temperature in THF without employing any protection chemistry or intermediate purification steps. The ROP of L-lactide was performed via in situ calcium alkoxide formation by using 4-cyano-4-[(dodecylsulfanylthiocarbonyl)sulfanyl]pentanol (CDP) and [(THF)₂Ca{N(SiMe₃)₂}₂]. The PLA based macro chain transfer agent (CTA) (M_n = 2550 g mol⁻¹, Đ = 1.18) was characterized in-depth by (tandem) mass spectrometry and proved to be suitable to obtain PHEA blocks with M_n values up to 10 000 g mol⁻¹ (Đ ≤ 1.28). Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) measurements indicated an increased miscibility between both blocks in bulk as the length of the PHEA unit increases. The amphiphilic block copolymers self-assembled into micellar structures in aqueous media, which were studied by dynamic light scattering (DLS) and cryo-transmission electron microscopy (cryo-TEM).