Plastic ploys

Dendrimers are about to revolutionise the age of polymers

Published: Thursday 30 November 1995

Polymer products. waiting for< (Credit: Arvind Yadav / cse)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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