Method for preparing microparticles having a selected polymer molecular weight

A method of preparing microparticles having a selected microparticle polymer molecular weight, comprising:

• (a) preparing a first phase, the first phase comprising a nucleophilic active agent, a polymer having a starting molecular weight, and a solvent for the polymer;
• (b) combining the first phase with a second phase in a static mixer to form an emulsion;
• (c) extracting solvent from the emulsion, thereby forming microparticles;
• and
• (d) maintaining the first phase at a hold temperature for a hold period prior to step (b), the hold period of sufficient duration to allow the starting molecular weight of the polymer to reduce so that the selected microparticle polymer molecular weight is achieved.