In the present work, innovative polysaccharide-based materials were designed by exploiting synthetic procedures characterized by modular application and high versatility for the controlled modification of the original structure and thus allowing to obtain defined macromolecular architectures.
In this context, Cu(I)-catalyzed azide-alkyne “click” cycloaddition (CuAAC) was investigated as an efficient and versatile tool for the synthesis of complex structures through modification with both low molecular weight species and polymers. In addition, Atom Transfer Radical Polymerization (ATRP) was exploited as a “key” process for the preparation of macromolecules with well defined functionalities and composition. ATRP and “click” cycloaddition, together with other processes, were used singularly or in combination for functionalization, crosslinking or grafting of synthetic phases to polysaccharides. The selection of both the synthetic phase and the reactive strategy to combine them into the final products was carried out by considering the peculiar features of each experimented polysaccharide in terms of structure, functionality, solubility properties and main potential applications.
Four polysaccharides were chemically modified: cellulose, chitosan, glycogen and amylose. They differ in the chemical composition of the repetitive unit or in the configuration of the glycosidic bonds or in the degree of branching.
In particular, in the first part of the research the surface-initiated ATRP grafting “from” approach of acrylate polymers was applied to wood pulp cellulose, particularly aiming to modulate the amount of ATRP initiator covalently bonded to cellulose and thus the chain density, by varying the conditions of the initiator immobilization.
Then, in order to study an innovative route to the C-6 regioselective crosslinking of chitosan, different ways of N3-functionalization and subsequent crosslinking by the Cu(I)-catalyzed azide-alkyne cycloaddition were studied.
The following part of the research interested the modification of glycogen and amylose by periodate oxidation and reductive amination. The actual possibility to control the extent of the oxidation and its regioselectivity was studied, comparing a linear and a highly branched polysaccharide. Moreover, the reductive amination of oxidized glycogen
with low-/high-molecular weight mono-/poly-amines was implemented in the controlled functionalization and crosslinking.
This last approach was also exploited in the synthesis of alkyne-functionalized glycogen and amylose to be used in Cu(I)-catalyzed azide-alkyne dipolar cycloaddition (CuAAC). In particular, these products were used for the synthesis of polysaccharide-based amphiphilic copolymers by grafting “onto”, through CuAAC, of end-N3-functionalized poly(meth)acrylates, which were synthesized by ATRP.
All the experiments that are described and discussed in the present thesis have been carried out aiming to establish various procedures for the efficient and versatile modification of polysaccharides in order to obtain, even in perspective, well-defined polysaccharide-based materials with predictable structures and specific target properties.