One‐pot synthesis of octablock copolymers of high‐molecular weight via RAFT emulsion polymerization

Abstract

AbstractMultiblock copolymers (mBCPs) could offer new opportunities to design new nanomaterials with multifunctions or enhanced properties in a cost‐effective way. However, it is still very challenging to obtain high degree of polymerization in each block of mBCPs with large block number using one‐pot synthesis via controlled radical polymerizations. This is due to the accumulation of the dead chains throughout the many step polymerization. In this work, we developed a new highly efficient strategy for preparing mBCPs with large block number using one‐pot reversible addition–fragmentation chain transfer (RAFT) emulsion polymerization, where every polymer block was formed by sequential addition of monomers. We achieved high block degree of polymerizations (~100 per block) for a model system of “octablock” polystyrene (PS) in just 2 hr per block. Experimentally measured molecular weights are in excellent agreement with theoretical predictions. The dead chains generated through the polymerization are negligible due to the low initiator concentration. Yet the polymerization rates are still very fast due to the heterogeneous advantages of emulsion polymerization. We have also applied this strategy to a series of mBCPs from diblock (PS176‐PnBA286)1 to octablock (PS176‐PnBA286)4 (PnBA for poly(n‐butyl acrylate)). The high degree of polymerization in our mBCPs ensures microphase separation even though PS/PnBA system is known for small χ values. We have also found that the tensile properties of our mBCPs increase significantly with increased number of blocks. Our work reveals that the number of blocks is an important molecular variable for tuning the mechanical properties of block copolymers.