Synthesis and characterization of dendritic macromolecules based on 2,2-bis(hydroxymethyl)propionic acid

Abstract: Dendrimers are a relatively new type of macromolecules characterized by a well-defined, highly branthed, layered structure with a multitude of chain ends, adopting a globular shape at higher molar masses. Dendrimers are usually constructed from ABx type of monomers in either one of the two step-wise approaches known as thedivergentor theconvergent growth approach. In this thesis, two different synthetic routes are described for the synthesis of aliphatic polyester dendrimers based on 2,2 bis(hydroxymethyl)propionic acid (bis-MPA). Examples are also given where dendrimers based on bis-MPA are used as scaffolds in the synthesis of chiral and ferrolelectric dendrimers, and as initiators for ring-opening polymerization.Acetate terminated dendrimers, up to generation four, were synthesized in a convergent approach by acid chloride couplirigs. These dendrimers were not only characterized by traditional techniques like SEC, elemental analysis, 1H- and 13C-NMR, verifying their high purity, but also by self-diffusion 1H-NMR studies allowing the hydrodynamic size of these dendrimers to be estimated.In a more versatile route, the acetonide-terminated fourth generation dendrimer was synthesized by DCC coupling according to a double stage convergent approach. After deprotection of the terminal acetonide groups, the corresponding hydroxyl functional dendrimer, possesing 48 terminal hydroxyl groups, was generated and subjected to a number of surface modifications by reaction with different acid chlorides.By appropriate choice of acid chloride, different physical properties, such as thermal and solubility behavior, could be tuned. For instance, the glass transition temperature (Tg) could be altered from + 57° to - 38°C merely by end-capping the hydroxyl functional dendrimer with octanoate functional groups.Chiral dendritic block copolymers, from the pseudo-first to the pseudo-fifth generation, were also synthesized by end-capping hydroxyl functional dendrimers with a derivative of (S)-(-) malic acid. The optical rotation of these dendrimers was found to be constant and independent of the generation munber.It was also demonstrated that hydroxyl functional dendrons and dendrimers based on bis-MPA could be used as initiators yielding narrow polydispersity branthed polyesters by ring-opening polymerization of E- caprolactone.A ferroelectric liquid crystalline dendrimer was also synthesized using the third generation hydroxyl functional dendrimer as a scaffold. Interesting electro-optical properties, such as a pronounced electroclinic effect, were observed.