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Vinyl Polymers
Originally, the vinyl materials were
defined to include any polymeric composition that incorporated ethylene (-CH=CH-) in its synthesis. Later
these came to include any of the double-bonded, alkene monomers like propylene, vinyl chloride, styrene, vinyl acetate,
acrylonitrile, butadiene, and others. These are reactive molecules and are the feedstocks for polyethylene, polypropylene,
styrofoam, and many other very useful plastics. Each of these materials are made via free-radical polymerizations
that require reaction initiators like persulfates, peroxides, or UV light that act to stimulate addition of an electron
to the alkene monomer. This destabilizes the double bond and renders the monomer into the activated,
free-radical form. This, in turn, activates the next monomer, allowing the original residue to be incorporated
as a single-bonded, stable residue. But now there is a free-radical dimer that will activate a third
monomer molecule and so on.
These reactions are often highly exothermic and require built in controls to keep them on track
toward the desired product. There are invariably residuals of unreacted monomers left in the product, often along
with other additives like catalysts and initiators. These can be removed via extra purification steps, but often the
residuals are left in, at least to some extent, owing to the extra effort and costs of producing highly purified products.
The polyacrylates, polyacrylamides, and the copolymers of acrylate and acrylamide
and related polymers are used in many applications that generally call for water-soluble additives. There are three very
large markets that are serviced by these polymers: detergent additives, water treatment chemicals, and superabsorbents.
Detergent Additives Polyacrylate is an additive in detergents, with billions of pounds of annual use. It serves as a dispersant and also a cleansing agent by helping to lift the soil and stains from surfaces such as cloth fibers or dishes and to keep these substances dispersed in the water so that they are removed in the rinse. Water-treatment Chemicals
Copolymers of acrylate and acrylamide are also commoditized for use in water-treatment and sewage treatment, again with billions of pounds of annual use worldwide. In these applications, the copolymers act as water-clarification agents that interact with unwanted solids and emulsified materials in the water, cause them to flocculate into larger agglomerations that can be removed, restoring the water to a clear fluid. There are other designations for these kinds of polymers; some comprise large markets such as thickening agents and "viscosifiers," but water and sewage treatment are the main ones. Superabsorbents
The third of the commodity markets service by polyacrylates is the superabsorbent
market, in particular components of disposable baby diapers. In this application,
crosslinked networks of polyacrylates were formulated as small granules,
added in an amount of 20 to 30 grams in a typical diaper during its construction, and sold under the familiar brand names in the beginning like Pampers and Huggies, and
now including many other brands. The global market for this is also measured in the billions of pounds of annual use.
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