Diverse Properties and Applications

Many of the most accessible commodity polymers have been studied in detail and their applications have been developed extensively. Interest is now focused on the synthesis and study of specialty polymers to meet today's critical applications. Specialty polymers are primarily water- -soluble polymers with functional groups that are pendent to or on the backbone; their global market value currently exceeds 9 billion dollars and continues to grow . They are used extensively for their unique solution properties in various fields of industry, agriculture, medicine, biotechnology, and electronics. Applications of specialty polymers are diverse, including: water treatment, paper processing, mineral sequestering, textile processing, personal care products, pharmaceuticals, drug delivery, petroleum production, enhanced oil recovery, coatings and inks additives, and sensors. Specialty polymers often provide multifunctional properties, i.e., a thickener for a paint may also act as a dispersant for the pigment in the paint. The level of multifunctional properties depends on the type of polymer, the amount used, and interactions with other chemistries in the formulation.

The diverse properties of specialty polymers are capturing the imagination of scientists and engineers worldwide because of their potential applications in many areas of present and future hi-tech and biological applications. Of particular interest is the ability to tailor a polymer to deliver a specified property in response to an external stimuli. This is highly desirable as it enables one to minimize both the amounts of material used and competitive reactions, which is critical in control-release functions, particularly in drug delivery applications. Effective delivery of drugs to a target cell or tissue largely diminishes adverse side effects and increases the pharmacological activity. It is the potential to tailor macromolecules to provide specified properties in an environmentally benign manner that motivates much of the current applied and fundamental research in the field of specialty polymers. These properties are critically needed for many of today's demanding applications.

Material Considerations of Specialty Polymers

There are numerous considerations in determining the appropriate polymer for a given application. In general, for a polymer to be commercially viable it must meet stringent environmental regulations, high performance standards, and be cost effective. The properties of specialty polymers depend on their basic chemical and structural properties, as summarized below.

· Molecular Weight - The molecular weight and molecular weight distribution strongly affect the solution properties of specialty polymers and their applications.

· Hydrophile to Lipophile Balance (HLB) ~ the type and content of hydrophiles and lipophiles significantly impacts specialty polymers inter- and intra-molecular associations.

· Sequence distribution of monomers — block, alternating, or random distribution impacts interaction of monomer groups within the polymer.

· Degree of Branching - a branched polymer frequently has different properties than its linear analog, such as, lower tendency to crystallize, different solution properties and light scattering behavior.

· Hyperbranched materials and dendrimers - offer the synthetic ability to chemically tailor the branches in a step-wise fashion.

· Degree of crosslinking ~ a crosslinked polymer has chemical linkages between chains. In the presence of solvent, it usually swells but does not dissolve. The amount a polymer is swelled by a solvent is inversely proportional to its crosslink density, i.e., the more highly a material is crosslinked, the less it can swell.

· Ionic Character - Many water soluble polymers are polyelectrolytes. Their ionic character depends on the number of charged groups, charge type, and charge distribution.

Ø Polyelectrolytes ~ macromolecules bearing a net charge

1. anionic ~ macromolecules bearing a negative charge.

2. cationic - macromolecules bearing a positive charge.

Ø Polyampholytes ~ macromolecules containing both cationic and anionic repeat units dispersed along the same polymer chain. These polymers may be either neutral, having the same number of cationic as anionic repeat units, or have a net charge of one sign.

1. Polybetaines ~ macromolecules containing both cationic and anionic charges on the same pendent group.

· Degree of Chemical Modification - Synthetic macromolecules and many natural polymers (e.g., polysaccharides) can be chemically modified to adapt their properties to the needs of a particular application. For example, the ionic character of cellulose may be chemically modified from nonionic to anionic through nitration.