The Emergence of a New Macromolecular Architecture: “The Dendritic State”
This chapter discusses the emergence of the dendritic state as a new macromolecular architecture. The dendritic structures as intermediary architectures between thermoplastics and thermosets are discussed. This new architectural polymer class consists of four major subsets, namely: (a) random hyperbranched, (b) dendrigrafts, (c) dendrons, and (d) dendrimers. In general, dendrimer synthesis involves divergent or convergent hierarchical assembly strategies that require the construction components. In addition, the features and shape changes of dendrimer are discussed. Several significant physical property differences between the linear and dendritic topologies related to conformations, crystallinity, solubilities, intrinsic viscosities, entanglement, diffusion/mobility, and electronic conductivity are compared. The first two major domains defined in polymer science were associated with certain distinguishing properties and architecture. One domain included linear, random coil thermoplastic polymers such as poly(styrenes) or poly(acrylates). The second domain of "thermoset polymers" included cross-linked architectures such as vulcanized rubber, epoxies, and melamine resins all of which were recognized as insoluble macromolecules. A new class of regio-specifically cross-linked dendrimers is megamers which is described. Dendritic polymers, especially dendrons and dendrimers, are expected to fulfill an important role as fundamental modules for nanoscale synthesis.