pyrimidinones and benzene-1-3-5-tricarboxamide

The contribution of supramolecular chemistry to polymer science opens new perspectives for the design of polymer materials exhibiting valuable properties and easier processability due to the dynamic nature of non-covalent interactions. Hydrogen bonding polymers can be used as supramolecular units for yielding larger assemblies that possess attractive features, arising from the combination of polymer properties and the responsiveness of hydrogen bonds. The post-polymerization modification of reactive end-groups is the most common procedure for generating such polymers. Examples of polymerizations mediated by hydrogen bonding-functionalized precursors have also recently been reported. This contribution reviews the current synthetic routes toward hydrogen bonding sticker chain-end functionalized polymers.

Topics: Benzamides; Benzoic Acid; Carboxylic Acids; Hydrogen Bonding; Oligopeptides; Peptidomimetics; Polymerization; Polymers; Pyrimidinones; Triazines; Urea; Urethane

We herein report the synthesis and characterization of ABA triblock copolymers that contain two complementary association motifs and fold into single-chain polymeric nanoparticles (SCPNs) via orthogonal self-assembly. The copolymers were prepared using atom-transfer radical polymerization (ATRP) and possess different pendant functional groups in the A and B blocks (alcohols in the A block and acetylenes in the B block). After postfunctionalization, the A block contains o-nitrobenzyl-protected 2-ureidopyrimidinone (UPy) moieties and the B block benzene-1,3,5-tricarboxamide (BTA) moieties. While the protected UPy groups dimerize after photoinduced deprotection of the o-nitrobenzyl group, the BTA moieties self-assemble into helical aggregates when temperature is reduced. In a two-step thermal/photoirradiation treatment under dilute conditions, the ABA block copolymer forms both BTA-based helical aggregates and UPy dimers intramolecularly. The sequential association of the two self-assembling motifs results in single-chain folding of the polymer, affording nanometer-sized particles with a compartmentalized interior. Variable-temperature NMR studies showed that the BTA and UPy self-assembly steps take place orthogonally (i.e., without mutual interference) in dilute solution. In addition, monitoring of the intramolecular self-assembly of BTA moieties into helical aggregates by circular dichroism spectroscopy showed that the stability of the aggregates is almost independent of UPy dimerization. Size-exclusion chromatography (SEC) and small-angle X-ray scattering analysis provided evidence of significant reductions in the hydrodynamic volume and radius of gyration, respectively, after photoinduced deprotection of the UPy groups; a 30-60% reduction in the size of the polymer chains was observed using SEC in CHCl(3). Molecular imaging by atomic force microscopy (AFM) corroborated significant contraction of individual polymer chains due to intramolecular association of the BTA and UPy groups. The stepwise folding process resulting from orthogonal self-assembly-induced supramolecular interactions yields compartmentalized SCPNs comprised of distinct microdomains that mimick two secondary-structuring elements in proteins.

Topics: Benzamides; Models, Molecular; Molecular Structure; Polymerization; Polymers; Pyrimidinones