Problem of polymerization?

Hi! I just don't remember anything from my chemistry courses... I have a protein that is completly monomeric at low concentration and completly polymeric at high concentration. Is it standard for polymers? Or is there normally an equilibirum between monomer and polymer that would change with initial concentration? Is there a mathematical formalism for that? Do other biological polymers like actin or microtubules behave like that? Any good reference for that? Thanks in advance!