The hierarchical growth of polymeric architectures

In order to arrive at controlled tertiary structures of synthetic polymers it is a prerequisite to design and synthesize mol. fragments that first self-assemble into secondary structures followed by their ordered aggregation. We have used quadruple hydrogen bonding units that form random coil polymers from difunctional monomers in solvents like chloroform. These polymers fold into helical superstructures in apolar solvents, while a preferred handedness of the helix is obtained by the introduction of stereocenters in the side chain. Since the chain length of the polymeric helix can be tuned by the addn. of monofunctional chain stoppers, we are able to connect two or more helixes. By now introducing structure-forming connectors between two chain stoppers, we are able to grow polymeric architectures in a hierarchical way. [on SciFinder (R)

Helical supramolecular aggregates based on ureidopyrimidinone quadruple hydrogen bonding

A series of mono- and bifunctional compds. 2-7, based on the ureido pyrimidinone quadruple hydrogen bonding unit, was prepd. to study the mode of aggregation of these compds. in the bulk and in soln. Compds. 2-7 exhibit thermotropic liq. cryst. properties, as evidenced by differential scanning calorimetry and optical polarization microscopy. The presence of an ordered hexagonal discotic (Dho) phase of 2a was confirmed by X-ray diffraction on an aligned sample. In chloroform, the bifunctional compds. form cyclic dimers at millimolar concns., and these dimers exist in equil. with linear species above a crit. concn., which may be from 6 mM to greater than 260 mM, depending on the structure of the spacer. CD measurements in chloroform did not show a Cotton effect. Dodecane solns. of compds. 3, 4b, and 7b display a Cotton effect at the absorption band of the phenyl-pyrimidinone unit. Amplification of chirality was obsd. in mixts. of 7a and 7b, but not in mixts. of 4a and 4b, indicating that 7a and 7b form mixed polymeric aggregates with a helical architecture in dodecane soln., whereas 4a and 4b do not. The Cotton effect is lost upon increasing the temp. Half of the helicity is lost at 25°C for 3 and at 60°C for 4b, suggesting that 3, bearing the shorters spacer, forms less stable columns than 4b. Compd. 7b losses half of its helicity at 45°C. Compds. 2b, 5, and 6 do not exhibit helical organization, as evidenced by the absence of Cotton effect

Helical supramolecular aggregates based on ureidopyrimidinone quadruple hydrogen bonding

A series of mono- and bifunctional compds. 2-7, based on the ureido pyrimidinone quadruple hydrogen bonding unit, was prepd. to study the mode of aggregation of these compds. in the bulk and in soln. Compds. 2-7 exhibit thermotropic liq. cryst. properties, as evidenced by differential scanning calorimetry and optical polarization microscopy. The presence of an ordered hexagonal discotic (Dho) phase of 2a was confirmed by X-ray diffraction on an aligned sample. In chloroform, the bifunctional compds. form cyclic dimers at millimolar concns., and these dimers exist in equil. with linear species above a crit. concn., which may be from 6 mM to greater than 260 mM, depending on the structure of the spacer. CD measurements in chloroform did not show a Cotton effect. Dodecane solns. of compds. 3, 4b, and 7b display a Cotton effect at the absorption band of the phenyl-pyrimidinone unit. Amplification of chirality was obsd. in mixts. of 7a and 7b, but not in mixts. of 4a and 4b, indicating that 7a and 7b form mixed polymeric aggregates with a helical architecture in dodecane soln., whereas 4a and 4b do not. The Cotton effect is lost upon increasing the temp. Half of the helicity is lost at 25°C for 3 and at 60°C for 4b, suggesting that 3, bearing the shorters spacer, forms less stable columns than 4b. Compd. 7b losses half of its helicity at 45°C. Compds. 2b, 5, and 6 do not exhibit helical organization, as evidenced by the absence of Cotton effect

Ureidotriazine-based supramolecular copolymers

Ureidotriazine-Based supramol. polymers were prepd. from hydroxyterminated poly(ethylene butylene)s by cyanoethylation with acrylonitrile, redn. to the amine-terminated polymer, conversion to the isocyanate with phosgene, and finally reaction with trialkoxyphenyldiaminotriazine. The polymers were characterized for the morphol., discotic liq. cryst. melting temp., and their blends

Hierarchical formation of helical supramolecular polymers via stacking of hydrogen-bonded pairs in water

Bifunctional ureido-s-triazines provided with penta(ethylene oxide) side chains are able to self assemble in water, leading to helical columns via cooperative stacking of the hydrogen-bonded pairs (DADA array). Monofunctional ureido-s-triazines do not form such helical architectures. The presence of a linker, covalently connecting the two ureido-s-triazine units, is essential as it generates a high local concentration of aromatic units, favorable for stacking interactions. This hydrophobic stacking of the aromatic units occurs at concentrations as low as 5(.)10(-6) M and can be visualized by using fluorescence spectroscopy. The stacking generates a hydrophobic microenvironment that allows intermolecular hydrogen bonding to occur at higher concentrations because the hydrogen bonds are shielded from competitive hydrogen bonding with water. This hierarchical process results in the formation of a helical self-assembled polymer in water at concentrations above 10(-4) M. Chiral side chains attached to the ureido-striazine units bias the helicity of these columns as concluded from CD spectroscopy and "Sergeants and Soldiers" experiment

Chiral supramolecular polymers based on multiple hydrogen bonding

A variety of discotic crystalline molecules are studied that form chiral polymeric assemblies in either apolar organic solvents or water. Multiple hydrogen bonds are used to organize the molecules into a well defined helix. A preferred handedness of the helical superstructures is obtained by chiral side chains based on citronellol for assemblies in solvents like dodecane and chiral penta-ethylene glycols for assemblies in water. Sergeants-and-soldiers principles are observed, showing the cooperative character in the chiral superstructures. The stable chiral structures in water of assemblies is used to speculate on the scope and limitations of the folding of chiral synthetic polymers in water using a variety of secondary interactions

Supramolecular polymers in action

Abstract onl