In this month’s column, I will be discussing alkyd resins. I will start with a history of solvent-based alkyds and cover other topics in future columns. There is the old expression that history repeats itself, and alkyds are the perfect example. Drying oils such as linseed oil and tung oil have been used for centuries, and pigment / oil combinations were used in cave art thousands of years ago. The big breakthrough came when it was discovered that if you react an acid and alcohol, you get a polyester. In fact, the term alkyd comes from the combination of alcohol and acid to form alcid.
Traditionally, solvent-based alkyds were made from fatty alcohols reacted with an anhydride such as phthalic anhydride. The original polyester for alkyds was discovered by Watson Smith in 1901 and was the reaction of glycerol and phthalic anhydride to form a polyester (Figure 1).