Direct Biosynthesis of Polymers

Much of the green chemistry enterprise is devoted to the sustainable synthesis of polymers, especially those from biobased materials using biocataly tic syntheses. From the standpoint of green chemistry, it is ideal to have polymers that are made by organisms in a form that is essentially ready to use. Recently, interest has focused on poly(hydroxyalkanoate) compounds, of which the most common are polymers of 3-hydroxybutyric acid  

This compound and some related ones have both a carboxylic acid, -CO2H, group and an alcohol, -OH, group. A carboxylic acid can bond with an alcohol with the elimination of a molecule of H2O, forming an ester linkage (see Chapter 20, Section 20.4). Since hydroxyalkanoates have both functional groups, the molecules can bond with each other to form polymer chains  

Developments in genetic engineering have raised the possibility of producing poly(hydroxyalkanoate) polymers in plants. The plant Arabidopsis thaliana has accepted genes from the bacterial species Alcaligenes eutrophus, which has resulted in plant leaves containing as much as 14% poly(hydroxybutyric acid) on a dry mass basis. Transgenic Arabidopsis thaliana and Brassica napus (canola) have shown production of the copolymer of 3-hydroxybutyrate and 3-hydroxyvalerate. If yields can be raised to acceptable levels, plant-synthesized poly(hydroxyalkanoate) materials would represent a tremendous advance in the biosynthesis of polymers because of the ability of photosynthesis to provide the raw materials used to make the polymers. 

---