Synthesis of Macromolecules Containing Phenylalanine and Aliphatic Building Blocks

Abstract

Aiming at developing efficient interfacial agents for fiber-reinforced composite materials, macromolecules are designed to have different components able to stick to the fiber and be compatible with the polymer matrix, respectively. Herein, macromolecules are prepared by solid-phase synthesis considering phenylalanine residues to promote adsorption of the macromolecule on aramid fibers and aliphatic building blocks to interact with a hydrophobic polymer matrix. Using phenylalanine as building block for the preparation of macromolecules by iterative synthesis has been shown to be challenging. Thus, the screening of various parameters for the optimization of the synthesis of these macromolecules is discussed in this communication. A preliminary thermal study by thermal gravimetric analysis is conducted to evaluate their thermal stability.

Direct comparison of solution and solid phase synthesis of sequence-defined macromolecules

“…As it was already demonstrated previously by our group that a large variety of side chains can be introduced to the oligomeric backbone by varying the aldehyde component in the P-3CR, this study was limited to three different aldehydes to generate " [ABC] x "-sequences. 29,30,34,35 Using L1 and L2, a two-step, iterative cycle was developed, consisting of a TAD-based Diels-Alder reaction, followed by the P-3CR (Scheme 1). Both reactions reached quantitative conversions and yields and were carried out both on the solid phase and in solution.…”

“…6,24 A common route towards sequence-defined oligomers, offering full control over each monomer unit, is the iterative synthesis approach. 7,[25][26][27][28][29][30][31][32] This step-by-step growth of the macromolecule is necessary to ensure a perfectly defined sequence as well as monodispersity. Whilst many different approaches exist, the use of multi-component reactions seems to be a logical choice within this area and such reactions have indeed been shown to be highly effective tools for the synthesis of sequence-defined macromolecules.…”

Adsorption of phenylalanine-rich sequence-defined oligomers onto Kevlar fibers for fiber-reinforced polyolefin composite materials

“…The oligomer HOOC-(Fh) 3 Fh-N 3 , where F stands for the phenylalanine unit, h the hexyl chain and  for the triazole group, was prepared by performing four repeating cycles by successive addition of Fmoc-L-Phe-OH (followed by Fmoc removal), 6-azidohexanoic acid, and propargyl amine on a 2-chlorotrityl chloride resin as previously reported. [35] The library of oligomers was first extended to evaluate the influence of the presence of four successive phenylalanine units per repeating cycles affording HOOC-(F 4 h) 3 oligomers obtained with incomplete reaction steps) and PEG (i.e. PEG leakage due to acidic hydrolysis of ester linkage between PEG and polystyrene composing the Tentagel resin).…”

“…The thermal stability of the oligomers synthesized was studied by thermogravimetric analysis. HOOC-(Fh) 3 Fh-N 3 was previously investigated showing at 167 °C a cumulative weight loss of 7 wt% attributed to the loss of the terminal groups, [35] showed an initial degradation temperature between 214 and 230 °C (ESI, Figure S6). The inobservance of earlier degradation for these oligomers could be attributed to their higher molecular weight and thus a contribution of the terminal groups corresponding to 2 wt% that may be difficult to detect.…”

“…poly(propylene-co-ethylene)) matrix using an iterative synthesis on a solid support. [35] Herein, a library of sequence-defined oligomers (Figure 1) were prepared and deposited on Kevlar fibers by dip coating technique to investigate the effect of the number of successive phenylalanine units and the length of the alkyl chains on the coating integrity and quantity adsorbed on the fibers. A comparative study was conducted with model molecules in the attempt to understand which parameters drive the adhesion between Kevlar fibers and the polyolefin matrix.…”