Synthesis and Self Assembling Properties of Rod-Like, 2-Ureido-4-pyrimidinone-Based Main Chain Supramolecular Dendronized Polymers

A series of G1-G3 supramolecular dendronized polymers 6 bearing dimeric 2-ureido-4-pyrimidinone (UPy) units on the main chain and aliphatic hydrocarbon dendrons as side chain appendages was prepared. Because of the high crystallinity and poor solubility of such rigid rod polymers, only the 03 dendron could confer the resulting polymer 6 (n = 3) with enough solubility to enable its characterization and property studies. It was found that the nature of the dendrons play an important role on the UP.,, binding strength, solubility and self-assembly properties. The reversible nature of the polymerization process was demonstrated in different solvent systems by viscosity studies. A double logarithmic plot of the specific viscosity against concentration revealed a deflection point at 26 mM in CHCl3 at 26 and 40 degrees C. Below this critical concentration a straight line with a slope of 1.5 was obtained, while a slope of 4.0-4.2 was secured above this concentration. The data suggested that the associative interaction between the di-UPy monomer 5 (n = 3) increased nonlinearly with increasing monomer concentration. While the above investigations confirmed that these were main chain supramolecular dendronized polymers, UV-vis spectroscopic study revealed a large bathochromic shift (32 nm) with increasing polymer concentration in CHCl3. This finding was consistent with the formation of J-type aggregates via stair-case stacking between interchain UPy rings. SEM morphological study also confirmed that the resulting polymers appeared as fibrous superbundles with a very high aspect ratio. A model was purposed to rationalize how such bundles could be assembled from the di-UPy dendritic macromonomer 5 via intrachain hydrogen bonding and interchain stacking interactions.