Synthesis of Telechelic Poly(<i>p</i>‑benzamide)s

Well-defined telechelic poly­(benzamide)­s were synthesized by chain-growth polycondensation of phenyl-4-amino benzoate and pentafluorophenyl-4-amino benzoate derivatives with a bifunctional initiator in the presence of LiTMP as base. The polymerization was carried out at −70 °C to prevent self-initiated polymerization. To confirm the control over molecular weight, different defined molecular weight polymers were synthesized and analyzed by GPC. Taking advantage of the labile ester end groups of these poly­(benzamide)­s, we carried out postpolymerization modifications to introduce different end functional groups such as alkyne, amine, alcohol, alkyl halide, and olefin suitable for different types of postpolymerization reactions. Successful end group modification was confirmed by ¹H NMR spectroscopy and isotopically resolved MALDI-ToF mass spectrometry

ROMP Copolymers for Orthogonal Click Functionalizations

The ring-opening metathesis polymerization using ruthenium carbene initiators developed by Grubbs et al. is one of the most functional group tolerant living polymerization methods known. One of the most used postpolymerization functionalization methods used today is the copper-catalyzed 1,3-dipolar cycloaddition between alkynes and organic azides. Organic azides are, however, not tolerated by ruthenium carbene initiators, and nonprotected alkynes have been shown to slow down the propagation reaction or react with the propagating species leading to broad molecular weight distributions. Here we report the copolymer synthesis of three orthogonally functionalizable monomers: one carrying an activated pentafluorophenyl ester, one a maleimide unit, and a third one a trialkylsilyl-protected alkyne. From these monomers, statistical terpolymers as well as diblock copolymers were synthesized with different molecular weights and monomer compositions or block ratios, respectively. Excellent control over molecular weight and molecular weight distribution could be achieved using Grubbs’ first-generation ruthenium carbene initiator. Herein we present the synthesis and orthogonal triple postpolymerization functionalization of these copolymers

Functional Metathesis Catalyst Through Ring Closing Enyne Metathesis: One Pot Protocol for Living Heterotelechelic Polymers

Enyne ring closing metathesis has been used to synthesize functional group carrying metathesis catalysts from a commercial (Ru-benzylidene) Grubbs’ catalysts. The new Grubbs-type ruthenium carbene was used to synthesize living heterotelechelic ROMP polymers without any intermediate purification. Olefin metathesis with a mono substituted alkyne followed by ring closing metathesis with an allylic ether provided efficient access to new functional group carrying metathesis catalysts. Different functional benzylidene and alkylidene derivatives have been investigated in the synthesis of heterotelechelic polymers in one pot

Bis-TEGylated Poly(<i>p</i>‑benzamide)s: Combining Organosolubility with Shape Persistence

The synthesis of perfectly planar, bis-substituted aromatic polyamides is reported herein. With highly flexible triethylene glycol chains attached and conformational restriction through intramolecular, bifurcated hydrogen bonds these are among the most shape-persistent yet organo-soluble polymers to date. Starting from 4-nitrosalicylic acid, our group developed a route to phenyl-2,5-bis-TEGylated aminobenzoate, which could be polymerized by addition of lithium bis­(trimethylsilyl)­amide (LiHMDS). Since this technique has not been applied to step-growth polycondensations of polyaramides so far, the influence of two different solvents and an N-protective group was investigated. Therefore, substituted phenyl aminobenzoate derivatives carrying a free amine or an N-protective group have been polymerized. Additionally, the tendency for self-assembly of the readily soluble bis-TEGylated poly­(<i>p</i>-benzamide) was observed by transmission electron microscopy (TEM) in the dried state. Dynamic light scattering (DLS) measurements of chloroform solutions did not indicate the formation of aggregates. Thus, intermolecular interactions, which other aromatic polyamides typically exhibit, are prevented. The access to bis-substituted, entirely rigid poly­(<i>p</i>-benzamide)­s via this new polycondensation method paves the way for exciting new structures in materials science and supramolecular chemistry

Efficient Amine End-Functionalization of Living Ring-Opening Metathesis Polymers

An efficient strategy for the synthesis of monoamine end-functionalized living polymers using ring-opening metathesis polymerization with ruthenium initiators is reported. A new end-capping agent for this purpose was synthesized, and its efficiency for end-functionalization was evaluated using two common ruthenium-based initiators. Finally, terminal cross-metathesis was also explored as another alternative toward the synthesis of amine end-functionalized polymers, and the comparison between the two techniques is presented

La naissance des jeux olympiques et le sport dans l'antiquité

The ultrasound-induced cleavage of macromolecules has become a routine experiment in the emerging field of polymer mechanochemistry. To date, it has not been conclusively proven whether the molecular weight of a polymer or its contour length is the determining factor for chain scission upon ultrasonication. Here we report comparative experiments that confirm unequivocally that the contour length is the decisive parameter. We utilized postpolymerization modifications of specifically designed precursor polymers to create polymers with identical chain length but different molecular mass. To demonstrate the universality of the findings, two different polymer backbones were utilizedpoly­(styrene) and poly­(norbornene imide alkyne)whose molecular weights were altered by bromination and removal of pendant triisopropylsilyl protecting groups, respectively. Solutions of the respective polymer pairs were subjected to pulsed ultrasound at 20 kHz and 10.4 W/cm² in order to investigate the chain scission trends. The effects of cleavage and sonochemical treatments were monitored by size exclusion chromatography. In both series, experimental data and calculations show that the molecular weight reduction upon sonication is the same for polymers with the same contour length

One-Pot Synthesis and AFM Imaging of a Triangular Aramide Macrocycle

Macrocyclizations in exceptionally good yields were observed during the self-condensation of <i>N</i>-benzylated phenyl <i>p</i>-aminobenzoates in the presence of LiHMDS to yield three-membered cyclic aramides that adopt a triangular shape. An <i>ortho</i>-alkyloxy side chain on the <i>N</i>-benzyl protecting group is necessary for the macrocyclization to occur. Linear polymers are formed exclusively in the absence of this Li-chelating group. A model that explains the lack of formation of other cyclic congeners and the demand for an <i>N-</i>(<i>o</i>-alkoxybenzyl) protecting group is provided on the basis of DFT calculations. High-resolution AFM imaging of the prepared molecular triangles on a calcite(10.4) surface shows individual molecules arranged in groups of four due to strong surface templating effects and hydrogen bonding between the molecular triangles

Controlling Molecular Self-Assembly on an Insulating Surface by Rationally Designing an Efficient Anchor Functionality That Maintains Structural Flexibility

Molecular self-assembly on surfaces is dictated by the delicate balance between intermolecular and molecule–surface interactions. For many insulating surfaces, however, the molecule–surface interactions are weak and rather unspecific. Enhancing these interactions, on the other hand, often puts a severe limit on the achievable structural variety. To grasp the full potential of molecular self-assembly on these application-relevant substrates, therefore, requires strategies for anchoring the molecular building blocks toward the surface in a way that maintains flexibility in terms of intermolecular interaction and relative molecule orientation. Here, we report the design of a site-specific anchor functionality that provides strong anchoring toward the surface, resulting in a well-defined adsorption position. At the same time, the anchor does not significantly interfere with the intermolecular interaction, ensuring structural flexibility. We demonstrate the success of this approach with three molecules from the class of shape-persistent oligo(<i>p</i>-benzamide)s adsorbed onto the calcite(10.4) surface. These molecules have the same aromatic backbone with iodine substituents, providing the same basic adsorption mechanism to the surface calcium cations. The backbone is equipped with different functional groups. These have a negligible influence on the molecular adsorption on the surface but significantly change the intermolecular interaction. We show that distinctly different molecular structures are obtained that wet the surface due to the strong linker while maintaining variability in the relative molecular orientation. With this study, we thus provide a versatile strategy for increasing the structural richness in molecular self-assembly on insulating substrates