A means to an end: Polyethylene chains obtained by catalyzed chain growth on magnesium and exhibiting molar masses up to 5000 g mol−1 have been end‐functionalized in high yield with iodide, azide, and amine reactive end groups (see scheme). The functionalized polyethylenes can be used to generate a range of reactive polyolefins; for example, the azide‐functionalized chain can undergo “click” reactions to afford macromonomers.

A poly(ethylene oxide)-based macromolecular agent for reversible addition-fragmentation chain transfer (PEO-RAFT, 2 000 g • mol -1 ) was synthesized and used as a stabilizer and a control agent in the miniemulsion polymerization of styrene. Using 2,2′-azobis(isobutyronitrile) as initiator, stable polystyrene (PS) particles sterically stabilized by the PEO segments were obtained with almost complete conversion after 22 h. Molar masses increased linearly with conversion although rather broad molar mass distributions were obtained due to the presence of several populations of PEO-b-PS block copolymers. However, dynamic light scattering analyses showed a significant increase in particle diameter with conversion and the ratio of the number of particles to the number of droplets (N p /N d ) was thus lower than one indicating that the system did not follow a true miniemulsion process. Transmission electron microscopy additionally revealed the presence of holes inside the formed particles suggesting that block copolymer PEO-b-PS could be buried inside the particles during the polymerization. Varying the concentration and the nature of the initiator did not lead to an improvement of the molar mass distribution, while a decrease in polymerization temperature to 40 °C enabled to keep the particle size constant throughout the polymerization with values close to the starting droplet diameter as expected for a true miniemulsion.