Synthesis and characterization of pullulan-graft-poly (N-vinyl caprolactam) via RAFT/MADIX polymerization

This study presents a novel synthetic strategy for preparing graft copolymers based on a pullulan backbone. The approach relies on reversible addition-fragmentation chain transfer (RAFT) radical polymerization as the key step. This significant advancement enables the synthesis of the temperature-responsive copolymer pullulan-graft-poly(N-vinyl caprolactam) (PULL-g-PNVCL), leveraging the renewable, biocompatible, and biodegradable nature of pullulan to access this previously challenging target. The synthesis involved partial functionalization of pullulan with bromopropionyl bromide, followed by substitution with a pre-synthesized xanthate-based chain transfer agent, and subsequent polymerization of N-vinyl caprolactam from the pullulan macro-chain transfer agent. Comprehensive characterization, including Gel Permeation Chromatography (GPC) and Proton Nuclear Magnetic Resonance spectroscopy (¹H NMR), confirmed successful graft copolymerization. The results showed decreased thermal stability of PULL-g-PNVCL compared to pullulan. Dynamic light scattering (DLS) analyses demonstrated a thermosensitive behavior, with particle diameter increasing upon surpassing the lower critical solution temperature (LCST) of PULL-g-PNVCL. The LCST was observed to vary as a function of the poly(N-vinyl caprolactam) chain length. The obtained LCST values were lower than physiological temperature, which embeds PULL-g-PNVCL with the potential for expanding pullulan applications, particularly in biomedical fields such as stimuli-responsive drug delivery systems. Integrating chemical principles with polymer design, this research showcases the development of bio-based functional materials, an objective aligned with the sustainable use of industrial crops.