Proteins are polymers, not lipids since they have long sequences of amino acids. Lipids are known for their single structure made of glycerol and three fatty acids. A polymer is a large molecule made of several monomers. A monomer is a molecule that can attach itself to others to build a more sophisticated structure.
Another example of a polymer is maltose, which is made up of glucose molecules. With polymers, the bonds between the monomers break when exposed to water. This hydrolysis feature is what differentiates polymers from lipids. Lipids are insoluble in water hence not considered true polymers.