The invention is generally related to a process for producing a relatively high molecular weight poly(methacrylic acid) (“PMAA”) in a water-based system. The process of the invention comprises polymerization of from about 1% to about 20% by weight of methacrylic acid in water or a water-based system in the presence of thiol compound and an azo radical initiator under controlled reaction and process conditions. A process of the invention can be easily scaled up into the pilot scale for producing large quantities of high molecular weight PMAAs. The invention is also related to high molecular weight poly(methacrylic acid)s obtained according to a process of the invention.