"Shaping" the Future of Molecular Weight Distributions in Anionic Polymerization.

Varying molecular weight distributions (MWDs) have the potential to precisely tune polymer properties, but this approach remains relatively unexplored owing to a lack of synthetic methods that provide control over the exact makeup of a distribution. Herein, we report a simple and highly efficient strategy for addressing this challenge through temporal regulation of initiation in the anionic polymerization of styrene. This method yields unprecedented control over the shape of the polymer MWD and facilitates the synthesis of diblock copolymers with controlled MWD compositions. Importantly, we show that the MWD symmetry has a marked influence on the stiffness of poly(styrene--isoprene) copolymers, which demonstrates that varying MWD shape is an effective method for altering polymer properties.