A polymerization reactor having at least three side wall surfaces and a bottom wall surface forming a reservoir and at least one heat exchanger plate in fluid communication with a coolant source, wherein each of the at least one heat exchanger plate is disposed on a lid. The polymerization reactors of the present invention permit large amounts of polymer to be formed in each reactor batch. Preferably, polymers are formed in the polymerization reactor by bulk polymerization. Methods for forming polymers is also disclosed.