Diffusion of single molecular and macromolecular probes during the free radical bulk polymerization of MMA

Free radical bulk polymerizations exhibit complex kinetics due to the viscosity increase during the polymerization process. Especially the termination rate constant can be strongly influenced by the mobility of polymer chains in the polymerization mixture. As a consequence an autoacceleration period, the so-called Trommsdorff effect, can be observed often. In order to investigate this behaviour on a nanoscopic scale, we directly visualized the mobility of molecules and macromolecules in polymerizing MMA solutions using a combination of highly sensitive fluorescence correlation spectroscopy and widefield fluorescence microscopy. For this purpose, rather monodisperse PMMA chains were synthesized by RAFT polymerization and fluorescence-labelled with perylenediimide derivatives. The behaviour of the different fluorescent probes could be related to their size and flexibility. Our studies show that diffusional heterogeneities must be accounted for when modeling bulk polymerization.