Dilute Solution Properties of a Polystyrene-Poly(methyl methacrylate) Graft Copolymer Studied with the Emission Probe Technique

Transition phenomena in the aggregation processes of a graft polystyrene (PS)-poly(methyl methacrylate) (PMMA) copolymer in dilute solution were studied with the emission probe technique; 2-vinylfluorene is copolymerized at an appropriate number in the backbone PS chain and pyrene is introduced at the grafted PMMA chain endings as emission probes. The binary solvent mixtures consisting of various compositions of tetrahydrofuran (THF; a good solvent for both PS and PMMA) and acetonitrile (AN; a nonsolvent for PS) or of THF and cyclohexane (CH; a nonsolvent for PMMA) were used as solvents. The efficiency of the nonradiative energy transfer from fluorene to pyrene in a poor solvent system abruptly increased at a certain graft copolymer concentration and then leveled off with an increase in the copolymer concentration. This suggests the multimolecular micelle formation and this phenomenon took place at copolymer concentrations lower than 10^-5 g/mL. The multimolecular micelle formation at the concentration where the efficiency of nonradiative energy transfer reached a plateau was confirmed by low-angle light scattering. A similar dependence of aggregation upon the composition of mixed solvents was observed by the emission probe technique and by the low-angle light scattering method.