RAFT mediated polysaccharide copolymers

[摘要] Cellulose, one of the most abundant organic substances on earth, is a linear polymerof D-glucose units joined through 1,4-β-linkages. Cellulose is however not easilyprocessed without chemical modification. A number of techniques exist for themodification of cellulose, of which the viscose process is one of the most widelyapplied. Grafting of synthetic polymeric chains onto or from cellulosic materials is anuseful technique that can be used to combine the strengths of synthetic and naturalpolymers dramatically, so changing the properties of cellulosic materials (pulp,regenerated cellulose, cellulose derivatives).In this study five model xanthate (Reversible Addition-Fragmentation chain Transfer(RAFT)/Macromolecular Design through Interchange of Xanthates (MADIX)) agents,namely, monofunctional, difunctional, trifunctional and tetrafunctional species of theform S=C(O-Z)-S-R, with different leaving groups and different activating moieties,were prepared and then studied to determine the feasibility of cellulose modificationvia addition fragmentation processes. These agents were characterized by NuclearMagnetic Resonance spectroscopy (NMR), Fourier Transform Infrared spectroscopy(FT-IR) and Ultraviolet spectroscopy (UV). Polyvinyl acetates (PVAc) in the form oflinear, three armed and four armed star shaped polymers were then successfullysynthesized in reactions mediated by these xanthate RAFT/MADIX agentsXanthates were applied to polysaccharide materials using the viscose process(xanthate esters were formed directly on a cellulosic substrate, with subsequentalkylation) Grafting reactions were then conducted with the polysaccharides; cellulosewas modified with vinyl acetate, [this is an example of a surface modification ofnatural polymers that is of interest in various industries, such as textiles and papermanufacture].Analysis of the graft copolymers was conducted via Size Exclusion Chromatography(SEC), Liquid Adsorption Chromatography (LAC), Thermogravimetric Analysis(TGA), and FT-IR.Polyvinyl acetate was successfully grafted onto three polysaccharides (cellulosicmaterials), namely Hydroxyl Propyl Cellulose (HPC), Methyl Cellulose (MC) andcellulose. The study showed that the modification of cellulosic substrates with definedgrafts of vinyl acetate can be easily achieved through minor modifications to existingindustrial techniques.

[发布机构] Stellenbosch University