One monomer wants to make a soft, flexible polymer.
Another wants to make a hard, rigid one.
Butyl acrylate and methyl methacrylate are a classic pair.
A polymer made mainly from butyl acrylate can be soft and rubbery. A polymer rich in methyl methacrylate is much harder. Combine them carefully, and chemists can create a material that bends without cracking but still dries into a strong, durable film.
That balance is especially important in water-based paints and coatings.
As the water evaporates, billions of tiny polymer particles must soften enough to merge into one continuous film. If they're too hard, they won't fuse properly. If they're too soft, the coating may stay sticky.
Global Chemical Database