Alkyd resins polyalcohols

Polyester resins are polycondensates prepared in two different forms saturated and unsaturated. Saturated polyesters, alkyd resins, are produced from dicarbox-ylic acids and polyalcohols. Dicarboxylic acids, chiefly phthalic acid or maleic acid, are mainly used in their anhydride forms. Glycerol, pentaerythriol or trimeth-ylolpropane are the most-used polyalcohols. The saturated polyesters synthesized in this way are also named unmodified alkyd resins, which are macromolecules commonly used as plasticizers for other plastic materials. Alkyd resins can be modified by oil-containing fatty acids to be used in water-based paints and surface coatings (Bjorkner 1992 Kanerva et al. i996a,b Tarvainen 1996). 

Polyesters. Polyesters are polymers obtained by reacting monomeric polycarboxylic acid and polyalcohols. They are practically free of fatty acids (oils) and have a much simpler structure than that of alkyd. Polyester resins do not undergo oxidative polymerization (curing) and have a different curing mechanism than an alkyd. 

Commercial electropainting only dates from the early 1960s and the first processes to be introduced used anodic deposition. Some typical paint formulations would contain (i) polycarboxylic acids based on acrylic acid as monomer solubilized by an organic amine, (ii) alkyds, i.e. branched polyesters based on naturally occurring long-chain carboxylic acids and polyalcohols, e.g. glycerol, and (iii) epoxy resins based on phenols, e.g. 

Saturated polyester resins (alkyd or glyptal resins) are made from polyalcohols with a functionality of 3 or more (e.g. glycerol, pentaerythritol (C(CH20H)4), sorbitol) with dicarboxylic acids (e.g. succinic, maleic, phthalic acids). The reaction is allowed to proceed to a viscous oil which can be applied as a coating, adhesive, etc., and then heated or cured to a thermoset. 

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