Dynamics of Labeled Linear Polystyrenes in Semi‐Dilute Polystyrene Matrices in the Uncross‐Linked and Cross‐Linked States

Linear polystyrene chains that were labeled with a fluorescent dye were enclosed in a semidilute matrix of polystyrene in toluene. The matrix polymers used were suitably functionalized such that they could be photocross‐linked in a stepwise and controlled manner without attachment of the tracer chains. The diffusion coefficient of the tracer chains was determined by fluorescence recovery after photobleaching while the state of the matrix was changing from a semidilute solution to a covalently cross‐linked gel. The progress of the photocross‐linking reaction was macroscopically monitored by rheology. The tracer chains were polystyrenes with molecular weights ranging from 50 000 to 2 000 000 g mol −1 and low polydispersity. They were labeled via polymer analogous reactions with the fluorescent dye 6‐(7‐nitrobenzfurazan‐4‐ylamino) hexanoic acid. The matrix polymers covered a similar molecular weight range. The results of these measurements show that the dependence of the diffusion coefficient on the tracer molecular weight in the gel can be described by a scaling law in the sense of the reptation theory whereas distinct deviations of this scaling behavior appear in the sol state. The ratio of the matrix molecular weight and tracer molecular weight in the initial sol state significantly influences the change of the probe dynamics during the sol‐gel transition.