The challenges of defining structures in a new, unprecedented polymer architecture

Characterization methodologies are a critical component for all the natural sciences. Appropriate protocols are required that both identify as well as define new entities within specific systems under investigation. Staudinger originally introduced the concept of polymers as covalent macromolecules [1, 2]. Shortly after his concept gained acceptance the important and seminal question arose: How does one characterize these new polymer entities? Traditional polymers at their inception were viewed as completely new classes of chemical structure and material. Unlike simple, monodisperse structures normally associated with traditional low molecular weight organic and inorganic compounds, these polymers were accessible only as polydisperse mixtures of macromolecular structures. Many traditional analytical/characterization methods developed for small molecules were of very limited use for these new materials. Polymers do not have boiling points. In many cases they were amorphous, not crystalline and were produced with variable compositions that were often dependent on the way they were synthesized. As a consequence, traditional characterization and elemental analyses were often meaningless. Methods developed for characterization of polymers not only reflected the fact that polymers are polydisperse mixtures of covalent compounds, but also that they are large molecules of unprecedented nanoscale dimensions.

In this context, both dendrimers and dendrons may be thought of as well-defined macromolecular compounds that exhibit features reminiscent of both small molecule and macromolecular regimes. More specifically, they are well-defined, quantized molecules in the classical sense of organic chemistry, yet they are also large polymeric, molecules of nanoscale dimensions. As a consequence, both small molecule and large molecule techniques are generally used in a convergent and collective fashion in order to characterize and define all dendrimers and dendrons. In the early, emerging days of the dendritic polymer field, substantial rejection was encountered concerning the very existence of these dendrimer and dendron structures.