Methods for making P4HB polymers and copolymers thereof that are useful for preparing controlled release systems, medical devices and as intermediates in chemical synthesis, have been developed. These methods avoid the use of organic solvents, and basic conditions that can cause transesterification reactions with polymer terminal end groups or elimination reactions. A preferred embodiment is a method for producing polymers of P4HB with weight average molecular weight less than 250,000, and more preferably, less than 100,000, and a Pd of less than 3, which are useful in controlled release. A particularly preferred embodiment utilizes aqueous acetic acid to hydrolyze pellets of P4HB polymers and copolymers while in suspension.
