By
Antwi Boniface Yeboah
(M.Phil. Polymer Science and Technology,
Year One.)
Overview.
 Objective
 Background information of dendrimers
 Major Research Contributors
 Architecture of Dendrimers
 Molecular weight of dendrimers
 Properties of Dendrimers
 Synthesis of dendrimers
 Applications of dendrimers
 Conclusion
Objective
To provide an introduction to Dendrimers, their
structure , properties, synthesis and possible
applications.
Background of Dendrimers.
 Dendrimers are large and complex molecules with very well defined
chemical structures. (Suckling ,1982.)
 From polymer chemistry point of view, dendrimers are nearly perfect
monodispersed macromolecules with a regular and highly branched
three-dimensional architecture, (Hyatt, 1978).
 The polymerization of a monomer of the AB2 type had been suggested
decades earlier by Flory,(Flory et al,1952), and much theoretical work
on the possible outcome of this type of reaction had been carried out.
(Maciejewski et al, 1928) and (Gennes et al, 1983).
Background of Dendrimers- Con’t.
 Research
groups
led
by
Tomalia
(Tomalia
et
al,1985.)
and
Denkewalter(Denkewalter et al,1981) devised routes whereby stepwise
'polymerizations' could be performed, giving highly branched polymers with
extremely low polydispersity.
 The polyamidoamine (PAMAM) series that were synthesized by Tomalia
were called 'starburst (The term 'starburst' is a trademark of the Dow
Chemical Company, USA.) dendrimers', after starbranched polymers and the
Greek word „dendron‟ for a tree, and „meros‟ for part, (Murakami,1981).
 The term 'dendrimer' is now used almost universally to describe highly
branched, nearly monodispersed compounds.
Major research Contributors
 He completed his undergraduate chemistry degree at
the University of Michigan, Flint College and obtained
his Ph.D. degree (physical-organic chemistry) from
Michigan State University, (Tomalia, et al 2001).
 He joined the Dow Chemical Company as a synthetic
polymer chemist with a focus on functional monomers
and polymers, (1962–1989) where he discovered
Starburst® dendrimers (Tomalia et al,2001.).
 He is listed as the inventor of over 100 U.S. patents
and authored over 150 papers that focused on the
dendrimer/dendritic polymer field.
Major research Contributors
 Jean M. Fre chet obtained his first degree at the Institut
de Chimie et Physique Industrielles (now CPE) in Lyon,
France, and Ph.D. degrees at SUNY-CESF and Syracuse
University.
 Jean Fre chet is the recipient of both the ACS Awards in
Polymer Chemistry and in Applied Polymer Science,
(Tomalia et al, 2001.).
 His research is concerned with both fundamental and
applied aspects of macromolecular science with
emphasis on functional polymers from their design and
synthesis to their applications, (Tomalia et al, 2001.).
(Watkins et al, 1997)
Architecture of Dendrimers
Dendrimers have a globular configuration with
monomer units branching out from a central core. The
structure is highly defined and organized.
There are three distinct architectural components
(Tomalia, 1985). The
multi-functionalized core
(initiator core) forms the heart of the molecules; all
branches emanate from this core.
Architecture of Dendrimers
The monomers that attach to the core form the
first branches (Tomalia called them the First
Generation).
At the terminating generation, a terminal
functional group is added to the tail of the
monomer.
Components of a dendrimer Chain (eg.PAMA)
Structure of a G5 PAMAM dendrimer.
(From Ref.110, © 2000 Elsevier Science.)
(Watkins et al, 1997)
(Wooley et al, 1997)
Molecular weight of Dendrimers
 Some dendrimers have diameters that are greater than ten nanometers(Dagani, 1996. ).
The molecular weights range from about 50,000 to 200,000 g/mol.
 The number of terminal groups is easily calculated as follows:
Number of terminal groups = Nc (Nr)G
Where Nc is the number of branches at the core (core multiplicity);
Nr is the number of branches on each monomer unit (repeating unit multiplicity);
G is the number of generation.
 The degree of polymerization can be computed using these quantities.
 Degree of Polymerization =
 Similarly, the molecular weight is given as: Mw=
where Mc, Mr, and Mt are the molecular weight of the core, the repeating monomer,
and the terminal group respectively.
Properties of Dendrimers
 Most of the chemical properties of the molecule depend on the
types of terminal groups.
 The physical properties of the molecules, such as solubility and
viscosity are also affected by the terminal groups.
 The voids in the dendrimer consist of channels and cavities.
These unique geometries give the molecule special properties
such
as
adhesiveness
and
molecules(Klushin et al, 1996.).
ability
to
entrap
foreign
Viscosity of Dendrimers
 The
intrinsic
viscosity
of
dendrimers has a peculiar behavior.
It
increases
molecular
with
weight
increasing
(number
of
generations). Contrary to linear
polymers, the viscosity will reach a
maximum value then starts to
decline (Wooley et al,1994).
Synthesis of dendrimers - 1
 Dendrimers are generally prepared using either a divergent method or a convergent
one (Hodge,1993).
 In the divergent methods, dendrimer grows outwards from a multifunctional core
molecule.
 The core molecule reacts with monomer molecules giving the first generation
dendrimer.
 Then the new periphery of the molecule react with more monomers. The process is
repeated for several generations and a dendrimer is built layer after layer, ( Fig 1 A).
 But in this method, problems occur from side reactions and incomplete reactions of
the end groups that lead to structure defects.
Synthesis of Dendrimers - 2
 The convergent methods were developed as a response to the
weaknesses of the divergent synthesis( Hawker et al, 1990)
 In the convergent approach, the dendrimer is constructed
stepwise, starting from the end groups and progressing
inwards.
 When the growing branched polymeric arms, called dendrons,
are large enough, they are attached to a multifunctional core
molecule, (Fig. 1B).
Representation of dendrimer growth by
the divergent and convergent methods.
EXAMPLE OF THE SYNTHESIS MECHANISM ( divergent method)
Poly (propyleneimine) dendrimer.
It is based on a skeleton of poly
alkylamines, where each nitrogen atom
serves as a branching point.
The basic operations consist of repeated
double alkylation of the amines with
acrylonitrile by “Michael addition” results
in a branched alkyl chain structure.
Subsequent reduction yields a new set of
primary amines, which may then be
double
alkylated
to
provide
further
branching etc. (Francavilla, et al,1999)
Polyamidoamine (PAMAM) series that was synthesized by
Tomalia.
PAMAM dendrimer is
based on a
dendritic mixed structure of tertiary
alkylamines as branching points.
The secondary amides being the
chain extension points was synthesized
by Michael alkylation of the amine
with acrylic acid methyl ester to
yield a tertiary amine as the branching
point.
It was then followed by aminolysis of
the resulting
methyl ester by ethylene diamine.
(Francavilla, et al,1999)
Applications of dendrimers - 1
Medical Applications.
 Dendrimers are “stealth molecules” that have many potential applications, including
diagnostic and therapeutic applications.
 Frechet‟s group at Cornell worked on a dendrimer for chemotherapy,(Freemantle, 1999).
 A chemotherapeutic drug is weakly bonded to the periphery of a dendrimer. Other
functional groups add to the dendrimer to increase water solubility. Once the dendrimer
reaches its target, the bond between the drug and the dendrimer is cleaved (enzymatically
or photochemically). Since dendrimers are inert and stable, they are nontoxic to human.
 It was shown that dendrimers could eliminate through the kidneys as urine,(Freemantle,
1999).
Applications of dendrimers-2
Industry Applications.
 Dendrimer films also serve as anti-corrosive coating on metal surfaces. The film is able
to trap corrosive agent in the dendritic cavities, preventing any diffusion to the surface of
the metal,(Wells et al,1996).
 Poly(amidoamine) dendrimers (Diallo et al. 2004), can effectively remove various
organic molecules from water.
 Dendrimers have been found to have a significant effect on the degrees of
polymerization and polydispersities of the polymers. It is believed that the growing tip
of the polymer chain resides inside the cavity of a dendrimer, avoiding termination by
reaction with another chain. Monomer molecules diffuse into the dendrimer, allowing
the polymerisation to continue,(Buhleier et al, 1978.).
Conclusion
 “Dendritic polymers, more specifically dendrimers, are
expected to play a key role as an “enabling technology”
during the next century. Just as the first three traditional,
synthetic polymer architectures have so successfully
fulfilled the critical material and functional needs for
society during the past half century, it is appropriate to be
optimistic about such a role for the dendritic state”
(Tomalia,2001.)
–
REFERENCES
 Buhleier E. , W. Wehner, F. Vögtle (1978) , Synthesis,
Chem. Int. Ed.
Engl.,155-158.
 C. J. Suckling (1982), Dendrimers Designed for Functions: From Physical,
Photophysical, and Supramolecular Properties to Applications in Sensing,
Catalysis, Molecular Electronics, Photonics, and Nanomedicine, J. Chem.
Soc.,V12, 661-662.
 Dagani R., (1996), Dendrimer Overview, J. Am. Chem. Soc., V120, 4644-
4651.
 Denkewalter R. G., Kolc J., Lukasavage W. J., (1981), Molecular-size
Nanocage For Catalysis: Shell Cross-linked Carbamate, J. Am. Chem. Soc.,
V4, 289-872.
REFERENCES
 Diallo M.S., , Swaminathan S. , Johnson P., and Goddard, (2005), Dendrimer-
enhanced ultrafiltration. 1. Recovery of Cu(II) from aqueoussolutions using Gx–
NH2PAMAM dendrimers with ethylene diamine core., J. Environ. Sci.
Technology, V39, 1366–1377.
 Gennes de P. G., Hervet, H. , (1983), Dendrimers and Nanotechnology: A Patent
Explosion., J. Macromolecules,V12, 351-360.
 Hyatt J. A., Vögtle F., Weber E., (1978), Dendrimers: Design, Synthesis and
Chemical Properties, J. Org. Chem., Int. Ed. Engl., 1974, 13, 814-815
 Klushin L.I., and Mnsfield, M.L., (1996), Dendritic Architectures, J.
Macromolecular. Science, V 12, 1278-1285.
 Maciejewski, Burchard K., (1982), Dendrimers as Macroscopic Building Blocks,
J. Macromolecular Science, V17, 689-703.
REFERENCES
 Murakami Y., Nakano A., Akiyoshi K., Fukuya K., (1981), The Construction of
Dendrimers, J. Chem. Soc.,V10, 2800-2808.
 Tomalia D. A., (1985), Macromolecules, J. Polymer. Sci., V17, Am., 138-175.
 Tomalia, D. A.; Fre chet J. ,(2001), A Brief Historical Perspective in Dendrimers
and Other Dendritic Polymers; In. Eds. ; © John Wiley & Sons and Wells, 3988-
3989.
 Watkins D.M., Sweet, Kimash Y.S., and Tomalia, D.A., Langmuir, (1997),
Emerging Nanotechnologies For Water Treatment, J. Pure Appl. Chem ,V19,
3136-3141.
 Wooley K.L., Hawker C.J., and Frechet J.M.,(1994), Nanotechnology In The
Water Industry, J. Pure Appl. Chem.,V13,1627-1645.
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