AAEM is a specialty methacrylic monomer used to formulate one-pack (1K) self crosslinkable, ambient temperature cure acrylic emulsions, especially for high performance paints and coatings. AAEM readily polymerizes with other acrylic and methacrylic monomers. The acetoacetoxy moiety on AAEM react with dihydrazides and diamines, making it ideal for self-crosslinkable, room temperature cure acrylic emulsions. This technology is call keto-hydrazide crosslinking. AAEM also finds use in acetoacetoxy copolymers crosslinked through chelation with metal ions, such as zinc and aluminum. The chemistry of AAEM provides the formulator with new options for the design of acrylic copolymer systems.
Keto-hydrazide crosslinking technology is based on keto-functional monomers like AAEM, DAAM (Diacetone Acrylamide) and crosslinking agents like ADH (adipic acid dihydrazide) or hexamethylenediamine (HMDA). These systems represent the most advanced stage of technology for acrylic emulsion crosslinking chemistry. AAEM is used at levels up to 5 weight percent in the acrylic copolymers, with levels of about 3-4 weight percent being optimum.
Formulators can optimize the polymer properties, “in-can” emulsion stability, film coalescence, and dried film performance by adjusting the levels and ratios of AAEM and ADH in the final emulsion.
In addition to both safe and convenient handling, this ambient temperature crosslinking technology enhances film mechanical properties, resistance to staining, scrubbing, abrasion and dirt pick-up, water, chemical, and block resistance, toughness, impact strength, adhesive properties, and more for multiple applications. This range of attributes is a result of the attaining high gel fractions (crosslinked polymer chains), but only after emulsion particle coalescence and the beginning of polymer-chain interdiffusion.
The preferred keto-functional monomers are acetoacetoxyethyl methacrylate (AAEM) and diacetone acrylamide (DAAM). The chemical structures of both are provided below.
Both AAEM and DAAM contain a ketone moiety as exhibited above. Having the bulky pendant acetoacetoxyethyl group in AAEM increases separation from the main chain and decreases
chain packing (increased free volume), thereby reducing the polymer solution viscosity. The lower viscosities facilitate achieving higher solids in an emulsion.
Some characteristics of the two monomers are revealed in the table below.
|Appearance||clear, light yellow liquid||white to yellow crystalline solid|
|Flash Point, OC, °C||139||126|
|Homopolymer Tg, °C||+3||+85|
R1 = MMA
R1 = 0.90; R2 = 0.95
|R1 = 0.57 R2 = 1.68|
|R1 = Styrene||R1 = 0.70; R2 = 0.60
||R1 = 0.49; R2 = 1.77|
AAEM exhibits very good toxicology characteristics. DAAM also shows good toxicity characteristics, but there can be concern regarding trace residual content of the starting raw material, acrylamide (AA). Both monomers are formaldehyde free. DAAM shows better hydrolytic stability than AAEM at low pH values and elevated temperatures in an emulsion. It is better to add AAEM in the latter stages of an emulsion copolymerization and maintain emulsion copolymers at ambient temperatures. To reduce yellowing that can occur at high levels of AAEM in a copolymer, avoid contamination with iron and avoid low pH values.
The reactivity ratio comparisons in the above table show that AAEM affords more random copolymerization with MMA and styrene. The reactivity ratio for a pair of monomers is the reaction rate constant for propagation of the first monomer in a growing polymer chain to itself versus addition to the second monomer. When the reactivity ratios of comonomer pairs are similar, random copolymerization is observed.
The chelation characteristics of the acetoacetoxy group adds additional innovative dimensions to the applications for AAEM copolymers. With ADH as a crosslinking agent, both AAEM and DAAM exhibit excellent outdoor weathering durability and lifespans in acrylic polymers. AAEM containing polymers can be crosslinked using multivalent cations like Cu ++ , Zn ++ , Zr +++ and Al +++ . Metal chelation pathways also offer options to improve adhesion to metal surfaces and to afford corrosion protection.
In 1K acrylic emulsions, using ADH or HMDA as a crosslinking agent, AAEM containing acrylic polymers are used in both indoor and outdoor, durable architectural, industrial and maintenance paints and coatings for wood, metal, concrete, and other surfaces. Acrylic emulsions containing AAEM as a crosslinking monomer and adhesion promoter are also used in inks, adhesives, sealants, and water repellent coatings. AAEM copolymerizes well with vinyl acetate monomer (VAM), where it is used in adhesives, also containing vinyl neodecanoate comonomer.
Urethane/acrylic hybrid dispersions have been developed using AAEM-acrylic emulsions and polyurethane dispersions (PUDs), cured with ADH. Clear urethane/acrylic hybrid films have been produced with high tensile properties and elongations.
Like many acrylic monomers, AAEM hazards include skin sensitization, flammability, and the potential for uncontrolled and rapid polymerization. The chemical industry continues to handle AAEM safely.
The following principles promote the safe handling and polymerization of AAEM. Use and maintain proper inhibitor levels, as inhibitors are consumed over time.
We encourage our customers to have a comprehensive understanding of the EH&S information and safe product handling procedures when working with any acrylate monomers. Gantrade can supply a GHS compliant SDS for AAEM. Fill out the form below:
If you are looking to purchase high-purity AAEM, Gantrade Corporation markets this monomer in 200 Kg. (441 lbs.) factory-sealed drums and 1 MT IBCs for industrial use only. Sample quantities are available.
The purity of our AAEM is greater than 95 percent with the impurities being HEMA and MAA. Gantrade’s AAEM contains ~300 ppm of BHT inhibitor.
To explore how our range of acrylic and vinyl monomers, and crosslinking chemistries can address your unique applications, partner with Gantrade Corporation. Our expert teams, armed with a wealth of technical knowledge and experience, can guide you to the best solutions for your applications. Contact Gantrade today to get started.