The role of polymer dynamics on nanocrystal growth in the synthesis of composites is studied with Mg nanocrystal-poly(methyl methacrylate) (PMMA) as a model system by J. J. Urban and co-workers in article number 1602572. The polymer conformation can be controlled by varying the reaction conditions that maneuver in-situ nanocrystal growth in the composite. The concomitant change in functional properties of nanocrystals within polymer matrix shows that the functionality of the composite can be tailored by polymer dynamics.