Synthesis, characterisation and properties of novel dendrimers

Abstract

A new family of aliphatic, polyurethane dendritic macromolecules has been designed, synthesised and characterised. The convergent route to dendrimers and the reactions of the selective coupling agent, carbonyl diimidazole (GDI) were employed. The method was successful in the preparation of first, second and third generation dendrimers and dendrons of the first to fourth generations. The structure of the termini of these branched macromolecules was varied to consist of r-butyl, benzhydryl, cyclohexyl or 4-heptyl groups. The dendrons were also coupled to a trifunctional aromatic core unit to create another series of dendrimers with an innermost layer of ester functions. The compounds prepared were soluble in most common organic solvents and insoluble in water. The physical state of the materials ranged from sticky oils to hard, amorphous solids depending on the nature of the end groups and the molecular weight of the macromolecules. The synthesis of the second generation dendrimer with (-butyl end groups was adapted to make a series of six codendrimers with differing arrangements of concentric layers of urethane and carbonate functions as well as the polycarbonate analogue. These second-generation dendrimers varied in their physical state from oils of low viscosity to hard amorphous solids depending on the proportion of carbonate and urethane functions in the molecule. The hydrogen bonding interactions in solution of some of the dendritic compounds were investigated by (^1)H NMR and infrared spectroscopy. From the analysis it was concluded that the hydrogen bonding was intramolecular rather than intermolecular in nature and that the degree of hydrogen bonding was dependent on the generation and the terminal groups of the structures. In addition, the degree of hydrogen bonding of the urethane functions was observed to be dependent on the location of the urethane layers in the second generation poly(urethane-carbonate) codendrimers. The thermal properties of the dendrimers were investigated and the materials observed to have a single glass transition. The glass transition temperatures of the dendritic families with different termini were found to be dependent on the composition of the end group and the molecular weight of the molecule. The glass transition temperatures of the codendrimers were dependent on the proportion of urethane and carbonate links in the structure and also the relative location of the layers. In a preliminary study, it was shown that blends of two different dendrimers were characterised by only one glass transition.