Development of pullulan-based functional materials by graft copolymerization and electrospinning

Abstract

This thesis investigates synthesis and processing strategies to expand the performance envelope of pullulan, a renewable polysaccharide, toward tunable, application-relevant functional materials. The main objective is to understand how pullulan modification governs material structure and properties and enables the formation of water-resilient electrospun membranes. The work is organized into two complementary research paths: a reversible addition-fragmentation chain transfer (RAFT) radical polymerization “grafting from” platform based on pullulan, and a preliminary development of pullulan-derived electrospun membranes. In the first path, 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, yielding pullulan g-poly(N-vinyl caprolactam) (PULL-g-PNVCL) with controlled growth of temperature responsive side chains. Comprehensive characterization, including Gel Permeation Chromatography (GPC) and Proton Nuclear Magnetic Resonance spectroscopy (1H NMR), confirmed successful graft copolymerization. GPC showed molar mass increases from the macro-RAFT precursor to the graft copolymers, with unimodal distributions and dispersities of ~1.74 – 1.78. Dynamic light scattering (DLS) analyses demonstrated a temperature responsive 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. Furthermore, the RAFT platform was extended to xanthate-mediated grafting of acrylic acid, aiming to produce pullulan-g poly(acrylic acid) (PULL-g-PAA). Detailed structural analyses (¹H NMR/DOSY, base catalyzed cleavage, and GPC) showed that acrylic acid polymerization from pullulan-xanthate produces grafted PAA together with a substantial fraction of free PAA, indicating that competing homopolymerization is a dominant side reaction under the investigated conditions. In the second research path, pullulan acetate derivatives with different degrees of substitution (DS ≈ 4, 7, and 8) were synthesized and electrospun to form fibrous membranes. The results demonstrated that DS and the solvent system jointly govern jet solidification and membrane morphology. Water-immersion testing established a DS-dependent transition in aqueous stability: the lower-DS membrane lost its fibrous architecture and collapsed into a film, whereas higher-DS membranes retained a porous fibrous scaffold; importantly, post-spinning water treatment effectively extracted residual spinning solvents. Together, the results of this thesis demonstrate that coupling pullulan architectures with targeted chemical modification provides a coherent route to pullulan-based functional materials with application-relevant performance. Moreover, integrating chemical modifications with polymer design, this research showcases the development of bio-based functional materials aligned with sustainability-driven resource utilization.

Date	31 Mar 2026
Original language	American English
Awarding Institution	École de technologie supérieure
Supervisor	Nicole R. Demarquette (Supervisor), Amilton Martins dos Santos (Co-supervisor) & Milan Bergeron-Brlek (Co-supervisor)