Disklike Micelles in Water from Polyethylene-Containing Diblock Copolymers

Poly(N,N-dimethylacrylamide)-polyethylene (AE) diblock copolymers were synthesized by the combination of living anionic and reversible addition-fragmentation transfer (RAFT) polymerizations. By direct dispersion of the copolymers into water above the melting transition of polyethylene and cooling to 25 degrees C, disklike micelles were obtained and visualized by cryogenic transmission electron microscopy (cryo-TEM). Spherical micelles were formed from a control noncrystalline poly(N,N-dimethylacrylamide)-poly(ethylene-alt-propylene) (AP) sample with similar composition and overall molecular weight. In combination with differential scanning calorimetry (DSC) and wide-angle X-ray scattering (WAXS), the disklike morphology in AE micelles was ascribed to the crystallization of polyethylene, driving the formation of disklike structures in this stepwise micellization-crystallization protocol. Further, as evidenced by small-angle neutron scattering (SANS), chain exchange between micelles was absent at elevated temperature, and thus the crystallization upon cooling was confined within each frozen micelle.