A pathway for marking of polymer chains with radical spin traps during pulsed laser polymerization in free radical polymerization is presented. By introducing a so‐called marker that forms a non‐propagating radical at (or shortly after) the incidence of a laser pulse, a polymer subdistribution is generated by specifically terminating propagating radicals via combination with such a marker radical. The generated polymer subdistribution can subsequently be imaged by modern soft‐ionization mass spectrometry. Herein, the general methodology of the method in which such marker is generated via reaction of an initiating radical with a nitrone is demonstrated on the examples of BA and VAc.
