The following sections of this BookRags Literature Study Guide is offprint from Gale's For Students Series: Presenting Analysis, Context, and Criticism on Commonly Studied Works: Introduction, Author Biography, Plot Summary, Characters, Themes, Style, Historical Context, Critical Overview, Criticism and Critical Essays, Media Adaptations, Topics for Further Study, Compare & Contrast, What Do I Read Next?, For Further Study, and Sources.
(c)1998-2002; (c)2002 by Gale. Gale is an imprint of The Gale Group, Inc., a division of Thomson Learning, Inc. Gale and Design and Thomson Learning are trademarks used herein under license.
The following sections, if they exist, are offprint from Beacham's Encyclopedia of Popular Fiction: "Social Concerns", "Thematic Overview", "Techniques", "Literary Precedents", "Key Questions", "Related Titles", "Adaptations", "Related Web Sites". (c)1994-2005, by Walton Beacham.
The following sections, if they exist, are offprint from Beacham's Guide to Literature for Young Adults: "About the Author", "Overview", "Setting", "Literary Qualities", "Social Sensitivity", "Topics for Discussion", "Ideas for Reports and Papers". (c)1994-2005, by Walton Beacham.
All other sections in this Literature Study Guide are owned and copyrighted by BookRags, Inc.
Traditionally, polymers are long chains of monomers, repeated over and over until a specific size range is achieved. Essentially, this process results in a "one dimensional" molecule having length but little breadth or width. In addition, each chain is individual grown and the reactions are concurrent, which results in limited control of the exact molecular weight and dimensions of the product.
An alternative approach is to grow the polymer in three dimensions to produce tree like structures and this is exactly what chemist Donald A. Tomalia and co-workers accomplished in the late 1970s. They called these compounds "dendrimers" which comes for "dendron", Greek for tree, and polymers. Retaining the allusion to trees, some chemists have adopted the name "arborols" although dendrimer is the preferred name.
In essence, these molecules start with a three dimensional core and, by adding successive layers, rapidly blossom into high molecular weight molecules. They are a molecular example of the doubling process. For example, starting with 1,4-diaminobutane as the core, four acrylonitriles can be added by a conjugate addition of the amine alkene of the acrylonitrile. After hydrogenation, each of the four new amines on the ends of the molecule can react with acrylonitrile, resulting in eight new ends. The next generation involves sixteen acrylonitriles and the next 32. The molecule quickly blossoms in size and, because of steric crowding, it adopts a three dimensional or spherical shape. With each generation a separate reaction, control of the domains in the polymer is significantly and exquisitely enhanced.
Probably one of the most exciting aspects of dendrimers is their demonstrated capacity to encapsulate small molecules for controlled release. This property will eventually allow these polymers to act as drug delivery agents at the molecular level. The specificity of the release mechanism will ultimately may allow site specific delivery which will benefit patients undergoing chemotherapy for cancer.