| Dendritic macromolecules have been prepared by the convergent growth approach, with control over the entire macromolecular architecture. The synthesis and characterization of a number of types of dendritic macromolecules is described.; By using monomer units of differing spacer length and flexibility, the branching density was adjusted to allow for the preparation of dendritic structures having molecular weights of up to 84,000 a.m.u. This was accomplished through the double-stage convergent growth process involving initial preparation of a dendritic, highly functionalized and flexible core molecule (hypercore), followed by attachment of several dendritic fragments to give the final structure.; Because the convergent growth approach begins with the chain ends of the final dendrimer, the number and placement of functionalities at the chain ends was readily controlled. This then allowed for the preparation of dendritic macromolecules possessing large dipole moments, through placement of electron-withdrawing and electron-donating substituents at opposing segments of the dendritic globule.; The thermal behavior of dendritic macromolecules based on variation in molecular weight, chain-end composition, and macromolecular composition was studied, and was found to be greatly dependent upon the chain end and internal monomeric groups. The chain end free volume theory derived for linear polymers was modified to account for the dendritic structure.; The characteristic single focal point group present in the growing dendritic fragments provided a single attachment site for the creation of a number of hybrid structures between dendrimers and fullerenes or between dendrimers and linear polymers. Dendritic macromolecules designed as cores for star polymer formation were prepared, and initial attempts were made for attachment of multiple linear polymer "arms". A macromonomer composed of a dendrimer containing a polymerizable methacrylate group at the focal point were also synthesized for incorporation of dendritic units along a linear polymer chain.; The one-step polymerization of an AB{dollar}sb2{dollar} monomer, 3,5-bis(trimethylsiloxy)benzoyl chloride, was employed to afford a hyperbranched aromatic polyester with a degree of branching of ca. 60%. The resulting phenolic chain ends were completely modified in homogeneous solution, however, did not undergo hydrogenolysis on a Pd/C surface. Whereas, modification of the chain end groups after construction of the dendrimers was possible with both homogeneous and heterogeneous reagents. |
