...without major formulation procedure change. These monomers have been used in a wide range of applications to improve the properties on a variety of substrates. They dramatically improved adhesion as well as other related properties, such as wet scrub resistance and corrosion resistance, for the formulated coatings.

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INTRODUCTION

The ability of a coating to adhere onto different substrates under both dry and wet conditions is critical for many applications. One method of improving adhesion is to incorporate functional groups that promote adhesion into the resins. These functional groups engage in specific interactions with the substrates, and, thus, improve the adhesion.

[ILLUSTRATION OMITTED]

There have been many publications reporting adhesion promotion to metal substrates by phosphorus-containing functional groups. (1-6) The phosphorus-containing functional groups can be incorporated into the polymers during the polymerization or through post-modification of the resins. When these resins are used in coatings or adhesives, the adhesion and anticorrosion performance of the final products are significantly improved. DelDonno (7) discussed the adhesion promotion to metal using polymers with pendant phosphorus groups.

Obviously, incorporating a phosphorus-containing monomer during the radical polymerization is a more direct approach than the post-modification of the resins. However, commercially available phosphonate monomers are generally very expensive and have poor reactivity (for example, vinyl phosphonic acid). On the other hand, there are very few phosphated monomers available on the market. Of these existing monomers, some are not compatible with other common monomer compositions, the polymer formed, and solvents. Moreover, they generally contain a substantial amount of residual phosphoric acid that can be detrimental to the end use properties. This, combined with the usual high dialkyl phosphate content [low ratio of monoalkyl phosphate (MAP) to dialkyl phosphate (DAP)] of these monomers, makes them difficult to use, especially in a solution polymerization process, because dialkyl phosphate has two double bonds and is a crosslinker for polymerization.

Rhodia has developed a proprietary technology that makes it possible to produce phosphate monomers with high MAP/DAP ratio, low acid content, and good compatibility with commonly used monomer compositions or solvents. Three monomers (two methacrylates--Sipomer[R] PAM-100 and Sipomer[R] PAM-200; and one acrylate--Sipomer PAM-300), all made by this technology, are commercially available. All the monomers have the following general structure:

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where R = C[H.sub.3] or H, and [R.sub.1] = alkyl.

The monomers were incorporated into resins by radical polymerization and subsequently formulated into paints. These paint formulations have shown a significant improvement in both wet and dry adhesion as well as other coating properties.

MATERIALS

The phosphate monomers were prepared using Rhodia's proprietary technology. No further purification was performed. They are yellow to brown viscous liquids. Typically the monomers have a MAP/DAP ratio higher than 80:20, and the weight percentage of the residual nonionic compound and phosphoric acid are typically less than 6%.

All other materials were purchased from Aldrich or obtained from other suppliers directly. They were used without further treatment.

RESIN SYNTHESIS

Acrylic latexes were polymerized thermally at 80[degrees]C in a 1.2 liter resin kettle with mechanical agitation using a seeded procedure (Table 1). The phosphate monomers were incorporated at a level of 0-4% based on total monomer (BOTM). While PAM-200 had no impact on the monomer pre-emulsion stability or polymerization, PAM-100...

NOTE: All illustrations and photos have been removed from this article.




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