Abstract
A crosslinked network was used to restrain undesired interchain aggregation of fluorescent polymers in this study. Primarily, solutions of poly(9,9โdihexylfluorene) (PF) in toluene and in curable liquid monomer mixtures of methyl methacrylate (MMA) and ditrimethylolproane tetracrylate (DTTPT) were compared to study the effect of concentration on absorption and emission behaviors. Results from ultravioletโvisible absorption, photoluminescence (PL) emission, and PL excitation reveal that the degree of aggregation depended strongly on the concentration and was correlated to the size of the polymer coil as determined from light scattering. Solutions of known PF content in MMA/DTTPT were then photoirradiated to yield PF/crosslinked poly(methyl methacrylate) (XโPMMA) composite films. Comparison among the pure PF, PF/MMA/DTTPT mother liquid, and PF/XโPMMA solid composites were then conducted to evaluate the effect of crosslinking on the degree of aggregation. With small amounts of imbedded PF (0.0015 wt %), the PF/XโPMMA composite had a PL quantum yield (0.70) higher than the pure PF (0.65) itself. Most notably, the PF/XโPMMA composites after annealing at 120 and 200ยฐC for 5 h still retained a reasonable emission efficiency (with related PL quantum yields of 0.61 and 0.43), in contrast to the large PL quantum yield reductions to 0.32 and 0.19 for the annealed PFs after the same treatment. Suggestively, interchain aggregation during a highโtemperature annealing process can be largely inhibited by the surrounding crosslinked network matrix. ยฉ 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007