Aliphatic polycarbonate-based block copolymers have received considerable attention as carriers for targeted drug and gene delivery because of their biocompatibility and biodegradability. However, there is little understanding of their phase behaviour and physicochemical characterization of the particles made from them. Here, we prepared a series of well-defined poly(trimethylene carbonate) (PTMC)- based copolymers with molar masses of 3-9 kg·mol-1 by metal-free ring-opening polymerization using dihydroxy-terminated poly(ethylene oxide) as a macroinitiator. Micellar nanoparticles self-assembled from copolymers had a size of less than 130 nm. They were degraded by the action of a model lipase from Mucor Miehei at 37 °C, which is of high importance for biodegradability in the living organism. X-ray diffraction and differential scanning calorimetry proved that amorphous copolymers with more than 39 mol% of carbonate units and representative particles were prone to the rearrangement of PTMC chains during storage and to thus undergo post-crystallization. Our findings can contribute to the comprehensive characterization of polycarbonate biomaterials for medical applications.