Dendrimers are about to revolutionise the age of polymers
POLYMERs are probably the most
easily visible materials in our lives.
From bottles to toys and from
crates to packaging materials -
they are omnipresent.
Polymers are basically chemical
compounds of high molecular
weights consisting of a number of
structural units - called
monomers - which are linked
together by covalent bonds. The
chemical, physical and other properties of the material is closely
related to the nature and degree of
branching of the polymer chains.
For instance-, polyethylene can be
made into high-density polyethyl-
ene (HDPE) when it is completely
linear. HDPE has a high melting
point and is used for making
houseware, bottles and toys.
On the other hand, a slightly
branched version of polyethylene is
low-density polyethylene (LDPE), which
has a lower melting point and is used
where toughness and flexibility is crucial - like in packaging.
Recently, a new class of polymers
called dendrimers has been developed.
These are highly branched polymers
which emanate from a central core.
Their revolutionary applications
range from nanometer scale building
blocks for new materials to specialised drug delivery vehicles. The
three-dimensional structure of these
materials has been studied extensively
by researchers. The problem, however,
has been the process for manufacturing these materials: a tedious
method which involves a multi-step
synthesis with expensive reagents. This
kas proved to be the hurdle in the
development of new applications for
materials.
Now J M J Frechet and his team at
Cornell University, New York (us), have
developed a cheaper and easier method
of making dendritic 'materials. Termed
the 'self-condensing' vinyl polymerisation method, it involves the activation
of a vinyl monomer by an external stimulus (in this case a Lewis acid), which
results in the self- condensation. A
hyperbranched dendritic polymer is
made which can lead to a highly branched polymer by subsequent condensations and additions of vinyl monomers
(Science, Vol 269, August 25, 1995).
The method is cheap and uses
commercially available vinyl monomers
and their derivatives. With the developmerit of this method, researchers can
now focus on the production of new
materials like dendritic perflouropolymers and liquid crystalline polymers,
opening up new markets and domains
of applications.
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