Acrylic acid isocyanate-hydroxyl reactions

Chemical reactions with alkyd resins can take place via their hydroxyl or carboxyl groups as well as via the double bonds of the unsaturated fatty acids. Isocyanates, epoxy resins, or colophony, for example, may be reacted with the hydroxyl groups. The carboxyl groups can be reacted with polyamidoamines (reaction products formed from dimerized linoleic acid and ethylenediamine) to form thixotropic resins, or can react with hydroxy-functional silicone precondensates. The double bonds of the unsaturated fatty acids permit copolymerization with vinyl compounds [e.g., styrene or (meth)acrylic acid derivatives]. 

A series of patents issued to Asahi Chemical Industry Co., deal with the modification of hexamethylenediamine by reaction with (meth)acrylic-, glycidyl ether-, hydroxyl-, amino-, amido-, or carboxy-substituted vinyl compounds, isocyanate, and amino acid compounds (Table IV). These modified amine curing agents are active at low temperatures and, in some cases, on wet substrates. Amine-substituted resole phenolics have also been described as useful epoxy curing agents." " Preparation of these curing agents is via condensation of the phenol, formaldehyde, and polyamine (Eq. 8). 

Thermosetting acrylic binder systems utilize copolymers of functional and nonfunctional acrylic (or similar) monomers. The functional monomers are incorporated for reactivity with crosslinkers. The most common functional monomer for reactions is the hydroxyl group. The hydroxyl groups on the acrylic copolymers react with melamine and urea resins (amino resins) and with polyisocyanates. These reactions are shown in Figure 11. The reaction of hydroxy functional polymers with amino resins require acid catalysis and heat. The reaction with polyisocyanates can occur at room temperature as well as at higher temperatures. A number of materials will catalyze the hydroxyl/isocyanate reaction (organotin compounds, acids, amines, metal salts, etc.)(9). 

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