for further development of this approach appear to be significant. Environmental considerations here are complex but will almost surely play a key role in defining the impact of biocatalysis in this area.

The direct production of polymers in bacteria and in higher plants is also under active investigation. Commercial development of biodegradable materials based on plant-derived polysaccharides has begun, and fermentation is being used to produce biodegradable polyesters for packaging applications. Recent reports of production of similar materials in higher plants suggest that agricultural routes to these polymers may ultimately prove viable.

A recent development has been the use of genetic engineering to produce polymeric materials. In some cases, this has taken the form of cloning and expression of the genes for natural structural proteins (e.g., spider silk); in others, amino acid copolymers have been designed de novo, encoded into artificial genes, and produced in bacterial hosts via fermentation. This approach offers significant advantages, in that it leads to uniform chain populations of controlled chain length, sequence, and stereochemistry, all the important structural components in polymer synthesis. In addition, the factors that control the secondary structure of proteins can be used to impose three-dimensional structure on the synthetic polymers made by this technique. This approach offers unique possibilities for tailoring the structure of synthetic polymers. The preparation of polymers with useful biological properties is particularly straightforward by this method, and there are promising indications that the scope of the method will be extended beyond the 20 naturally occurring amino acids. This area of research is an excellent point for the interface of the areas of biochemistry and traditional polymer chemistry.

Development of New Polymerization Methods

Even given the synthetic advances described in the preceding sections, there remains an urgent need for the development of new synthetic routes to polymeric materials. To illustrate, one need only consider the striking contrast between the synthetic methods used in the laboratory and in industry on the one hand and in nature on the other. In each case, the process begins with simple feedstocks, that is, with simple carbon compounds derived either from petroleum or from biomass. In industry, such compounds are isolated and then subjected to a series of separate chemical transformations leading to the monomer structure of interest. After rigorous purification to "polymerization grade" material, the monomer is converted in still another step, often at high temperature and pressure, to the polymer. Nature works differently. From mixed feedstocks, nature converts simple carbon compounds to complex polymers directly, without isolation of intermediates and without the assistance of harsh reaction conditions. Until industrial polymer chemistry works with the same degree of process integration and efficiency, there will be room for advances in synthetic methodology.



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