Abstract: The invention pertains to a process for preparing resorbable polyesters by bulk polymerization, wherein the reaction components are melted and homogenized in a reactor, the reaction mixture is then transferred into a polymerization reactor having a lumen defined by a reaction wall, wherein said reactor wall comprises at least two components which are releasably fitted to each other and wherein the shortest distance of any point within said lumen to the reaction wall is less than 8 cm, the reaction mixture is polymerized and the resulting polymer is removed from the polymerization reactor by releasing the components of the reactor wall exposing the resulting polymer lengthwise. The invention further relates to a polymerization reactor having a lumen defined by a reaction wall for performing said process.