Organic base-catalyzed polymerization of γ-n-Butoxyl-ε-caprolactone and its one-pot block copolymerization with N-Boc-Proline lactone

The current study explores the organocatalytic ring-opening polymerization (ROP) of γ - n -butoxyl- ε -caprolactone (BCL) and its one-pot block copolymerization with a strained bridged ester N -Boc-substituted proline lactone (N Boc PL), using 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) as the catalyst. The TBD-catalyzed ROP of BCL in toluene demonstrates the first-order polymerization kinetics and exhibits living polymer characteristics within moderate monomer conversion. It effectively suppresses inter- and intramolecular transesterification side reactions to the minimum, which are commonly observed in base-promoted ROP of lactone monomers. It provides acceptable control over the molecular weight of poly( γ - n -butoxyl- ε -caprolactone) (PBCL) by simply tuning the initial monomer-to-initiator molar ratio and controlling the monomer conversion. For instance, the polymerization using bifunctional 1,4-butanediol as the initiator can produce narrowly distributed PBCL with M n,SEC up to 34.5 kg mol −1 and M w / M n of less than 1.20. The TBD-catalyzed copolymerization of BCL with N Boc PL is successful to synthesize block copolymers. Notably, the one-pot copolymerization of the two monomers demonstrates a strictly sequential monomer consumption with N Boc PL polymerizing first followed by BCL. This unique copolymerization behavior enables the synthesis of block copolymers via a one-pot procedure, and tri-, penta-, and heptablock copolymers are accordingly synthesized by introducing monomers simultaneously or in multiple steps. The polymer structures are characterized using NMR, FT-IR spectroscopy, MALDI-TOF MS, and SEC. The thermal characteristics and self-assembly behavior of the polymers in aqueous solutions are further evaluated using TGA, DSC, and DLS. Additionally, the cytotoxicity of the Boc-deprotected triblock copolymers towards mouse fibroblasts (3T3 cells) and their hemolytic effects on rat red blood cells are further investigated, with the detailed results presented in subsequent sections.