What are Dendrimers
Dendrimers are tree-like polymers. They are highly branched, mono-disperse macromolecules composed of core, branching and terminal units.They also have internal voids and modifiable surface functionalities. As consequence of their unique architecture dendrimers have well defined and monodisperse size. Furthermore, the chemical and architectural flexibility of dendrimers allows dendrimers to have a myriad of industrial, commercial, and medical applications. Applications fuelling interest include light-harvesting, sensing, catalysis and composite material fabrication. Dendrimers are also investigated in the biomedical field for drug delivery and gene therapy and as imaging contrast.
 |
| Figure 01 - Computationally created model image of Dendrimers |
agents.
Stucture of Dendrimers
Dendrimers are branching molecules with branching beginning at the "core". Core is the center of the Dendrimer and molecular layers are formed symmetrically around the core using a repeating molecular unit. Dendrimers which have a finite and well-defined structure fall on to a special class of hyperbranched polymers which refers to polymer structures which are achieved by incoherent polymerization of ABn (n≥2).
 |
| Figure 02 -Evolution of polymers towards dendritic structures |
"Dendrigrafts" are class of dendritic polymers like dendrimers that can be constructed with a well-defined molecular structure but when comparing to dendrimers, dendrigrafts are centered around a linear polymer chain and branches consisting of copolymer chains are attached to that.
"Dendrons" is referred to a dendritic wedge without a core, the dendrimer can be prepared from assembling two or more dendrons
 |
| Figure 03 - Schematic diagram of structure of a G4-dendrimer |
"Dendrons" is referred to a dendritic wedge without a core, the dendrimer can be prepared from assembling two or more dendrons. The hyperbranching when going from the center of the dendrimer towards the periphery, resulting in homostructural layers between the branching points (Focal points). The number of focal points when going from the core towards the dendrimer surface is the "generation" number of a Dendrimer. As an example, If a dendrimer having five focal points when going from the centre to the periphery is defined as a 5th generation dendrimer. It can be abbreviated as "G5-dendrimer".
Some of the Applications
In contrast with linear polymers, dendrimers are monodisperse macromolecules. The classical polymerization process which used in the synthesis of The linear polymers which are synthesised by classical polymerization process usually random in nature and produces molecules of different sizes. But size and molecular mass of dendrimers can be specifically controlled during synthesis. Dendrimers show some significantly improved physical and chemical properties as a result of their molecular architecture, when compared with traditional linear polymers.Linear chains exist as flexible coils In a solution but dendrimers form a tightly packed ball. This has a huge impact on their rheological properties. In contrast with linier polymers , dendrimer solutions have significantly lower viscosity. When the molecular mass of a dendrimer increases, their intrinsic viscosity increases up to a maximum at the fourth generation and then begins to decrease. Such behaviour is not shown in linear polymers. In classical polymers the intrinsic viscosity increases continuously with molecular mass. As a result of large number of chain-ends, dendrimers show higher solubility, higher miscibility and higher reactivity. Solubility of a dendrimer is controlled strongly by the nature of surface groups. Dendrimers with hydrophilic terminal groups are soluble in polar solvents, while dendrimers with hydrophobic terminal groups are soluble in nonpolar solvents.One of the most important properties of dendrimers is the possibility to encapsulate guest molecules in the macromolecule interior as a result of having internal cavities.Meijer and co-workers trapped small molecules like rose bengal or p-nitrobenzoic acid inside the ‘dendritic box’ of PPI dendrimer with 64 branches on the periphery. Then a shell was formed on the surface of the dendrimer by reacting the terminal amines with an amino acid (L-phenylalanine) and guest molecules were stably encapsulated inside the box (Figure 08). Guest molecules could be removed by hydrolysing the outer shell .The number of guest molecules that can be entrapped depend on the shape of the guest and the architecture of the box and its cavities
