3.2.2.2. Effect of chemical architecture
rod–coil block copolymers of tetra(p-phenylene)-poly(ethylene) (PPP-b-PE) exhibited significant structural changes from vesicular micelles for short coil to cylindrical micelles for a twin-rod segment, and then to sphere micelles for a long coil length ( Fig. 14). This demonstrates the ability to regulate the carbohydrate-coated supramolecular structure by a systematic variation in the length of coil and the number of rods [80]. Recently, our group showed the polymer architecture effect on the solution morphology by comparing diblock PF-b-P2VP and triblock P2VP-b-PF-b-P2VP in the THF/methanol mixtures [25]. In such mixed solvent, while the diblock copolymers maintained a spherical micellar aggregates, triblocks were found to aggregate in elongated cylinders. The symmetric P2VP-b-PF-b-P2VP polymer chains could stack together more favorably into cylindrical arrays and provide preferential conditions for π–π interchain stacking compared with the spherical aggregates of PF-b-P2VP ( Fig. 15). H-aggregates were observed in the diblock PF-b-P2VP, but neither with H-type nor J-type aggregation for the P2VP-b-PF-b-P2VP based on their photophysical properties. However, another report suggested that both diblock P3HT-b-PtBuA and triblock PnBuA-b-P3HT-b-PnBuA formed H-aggregates in cyclohexane [68], emphasizing the importance of mixed solvent and solution concentration on the polymer aggregates. Further theoretical and experiment work is needed to understand and predict the packing of conjugated rod segment. Joint microscopic measurements and molecular modeling might be effective in developing a model for chain packing to explain the morphology observations [8].