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 the decreased thermal stability of PULL-g-PNVCL compared to pullulan. Dynamic light scattering (DLS) analyses demonstrated a thermosensitive behavior, with particle diameters increasing above the lower critical solution temperature (LCST) of PULL-g-PNVCL, which was observed to change with the poly(N-vinyl caprolactam) chain length. The LCST values, lower than physiological temperature, highlight the potential of PULL-g-PNVCL for expanding pullulan applications, particularly in biomedical fields such as stimuli-responsive drug delivery systems.