AAEMA (Acetoacetoxyethyl Methacrylate, CAS No. 021282-97-3), also known as AAEM, is an acetoacetyl intermediate chemistry widely used as an acrylic monomer to make resins for paints and coatings applications. AAEMA is particularly well suited for resins that require higher nonvolatile content, cross-linking versatility, or lower glass transition temperatures (Tg).
AAEMA has two reactive sites useful for cross-linking – an active methylene group and ketone carbonyl group. These two acetoacetyl side groups improve chain separation and free volume, which lowers polymer solution viscosity and the glass transition temperature, and allow for cross-linking and polymer modification.
Lower Solution Viscosity
A lower solution viscosity is necessary to develop high-solids coatings. The long, bulky side chain in AAEMA increases the separation between polymer chains. AAMEA also has no hydroxyl groups which helps minimizes hydrogen bonding between polymer chains. The increased chain separation results in a decreased solution viscosity.
Lower Glass Transition Temperature
The same chain separation that results in decreased solution viscosity also lowers the polymer glass transition temperature. A low polymer Tg is important for paint and good film formation.
A variety of cross-linking reactions or further polymer modification can be done from the acetoacetyl groups on the polymer chain of AAEMA. This cross-linking versatility allows for innovative cross-linking pathways, and has gained considerable attention from coating resin manufacturers. Acetoacetylated polymers can be made by polymerizing AAEMA into the polymer chain, or by acetoacetylating the polymer post synthesis. There are two active sites on the acetoacetyl group used for cross-linking: the active methylene group (CH2) and the ketone carbonyl group (C = O). Below we explore common reactions for cross-linking or modifying AAEMA polymers.
Methylene Group (CH2) Cross-Linking Reactions:
The active methylene group will react with melamines under certain conditions to form a carbon-carbon bond.
The active methylene group will react with free isocyanates at room temperature and blocked isocyanates at high temperatures.
The active methylene group rapidly reacts with aldehydes, especially formaldehyde, to form bridges between methylene groups and cross-link linear polymers into thermoset materials.
The Michael reaction can be used to cross-link AAEMA, whereby the methylene group is deprotonated in the presence of a strong base, and then reacted with an electron-deficient olefin. The methylene group can also be alkylated with an alkyl halide in a strong base.
Ketone Carbonyl Group (C = O) Reactions:
Enamines can be formed by reacting amines with carbonyl groups. Diamines can then be reacted to cross-link AAEMA polymers.
The carbonyl group of AAEMA can be chelated with metals, including tin, aluminum, zinc, lead, copper, and zirconium. Metal chelation provides resins with increased adhesion and corrosion resistance properties for metal coatings applications.
Benefits of Using AAEMA for Acrylic Resins:
Can be used in both solution (solvent) and emulsion (water) polymerization
Reacts readily with other acrylic and methacrylic monomers
Low solution viscosity
Good acrylic reactivity
Low polymer Tg
Excellent cross-linking versatility via multiple reaction pathways
Improved adhesion, flexibility, and corrosion resistance via metal chelation