Modelling Polymerization-Induced Self Assembly (PISA)

In this work we studied polymerization-induced self-assembly by means of computer simulations. Using this model, phase diagrams of the micelle states were constructed depending on the polymer concentration and the asymmetry of the composition for various reaction conditions. We found that if the reaction is ideal controlled radical polymerization (the initiation speed is much larger than the propagation speed and there are no side reactions such as termination or chain transfer), the phase diagram is no different from that obtained for pre-synthesized monodisperse diblock-copolymers with one insoluble block. Next, we studied two cases of slow initiation. We found that the phase diagram change dramatically: upon decreasing the initiation speed, the regions of spherical and cylindrical micelles shrink, while the region of vesicles/lamellae expands. This happens because at small initiation speed there is a significant amount of chains with a very short non-soluble block (and even without such block altogether), which do not participate in the formation of micelles. Therefore, decreasing the initiation speed essentially remaps the phase diagram coordinates by making the effective concentration lower (by decreasing the number of active chains) and the effective block length ratio higher (again, because the number of active chains gets higher, while the number of monomers remains the same).