Chemical Pathways for Galactoglucomannan-based Materials

Sammanfattning: Polysaccharides are an important resource for a variety of products, from food via fuel supply to functional materials of every kind. Due to their natural diversity they can be found in many special applications, e.g. in the biomedical sector and are the major renewable resource for materials of many kinds.Recently, a fairly unused group of polysaccharides, so calledhemicelluloses, have attracted increasing attention due to their high availability and promising properties in combination with renewability and a potentially low price.This thesis presents pathways for the chemical modification of the water-soluble hemicelluloseacetylated galactoglucomannan (AcGGM), enabling this raw material to be utilized in the synthetic design of new classes of materials.Based on the chemical modification of the hydroxyl groups with crosslinkable groups in combination with the naturally high hydrophilicity, synthetic pathways for the production of functional hydrogels are presented. Thanks to the great availability and the native properties of AcGGM, this material was found to be an outstanding candidate in this respect and was adjudged to be a cheap and green resource for hydrogel design.For this purpose, a three-step method was devised consisting of (1) the carbonyldiimidazole activation of primary hydroxylated vinylic compounds, (2) the substitution of hydroxyl groups of the AcGGM backbone with vinylic functions, and (3) radical crosslinking yielding a hydrophilic three-dimensional network – a hydrogel.Crosslinking strategies were varied from photo-crosslinking in dimethyl sulfoxide (DMSO) to redox-initiated crosslinking in H2O, with the objective of adapting the synthesis to benign conditions. Varying the crosslinking species as well as the medium was found to have a significant influence on the resulting gels’ properties, such as swelling capacity and G-modulus. Swelling capacity could be varied between ~0.6 and ~23 times the gel’s own weight and the G-modulus ranged from 0.4 to 145 kPa.AcGGM and 2-hydroxy ethyl methacrylate (HEMA) gels were studied further and evaluated for their suitability as drug delivery systems for two model drugs (caffeine and Vitasyn Blue) varying size, polarity, and hydrophilicity of the drug to be IIreleased. It was found that the gels composition as well as a second modification with maleic acid anhydride affects the release properties.Taking well-studied polysaccharide modification chemistry one step further and combining it with state of the art polymer synthesis, graft-copolymers of AcGGM were successfully synthesized via single-electron-transfer living-radical polymerization (SET-LRP). For this purpose, a macroinitiator was derived from AcGGM to enable a grafting of diverse hydrophilic and hydrophobic monomers from the AcGGM under benign conditions. Hybrid materials of the natural polymer AcGGM as a backbone with synthetic poly(methyl acrylate), poly(methyl methacrylate), poly(acrylamide), and poly(N-isopropyl acrylamide) graft-copolymers with a brush-like architecture were successfully synthesized, yielding molecular weights of up to 240∙10³ g ∙ mol-1. As expected, the solubility and thermal properties were significantly altered, opening a wider range of potential applications.We conclude that the presented chemical pathways are important steps towards a promising future for hemicelluloses as raw materials and their derivatives as shown for the resource AcGGM.