Toward large tubular helices based on the polymerization of tri(benzamide)s

Abstract

Herein we present the synthesis and polycondensation of mono-and di-N-protected, bis-substituted tri(benzamide)s with the aim to create large, tubular helices. We synthesized 2,4-dimethoxy and 2,5-bis-TEGylated aminobenzoic acid derivatives as bent and linear monomers and introduced p-methoxybenzyl (PMB) amide protecting groups to the oligobenzamide backbone. An iterative coupling strategy allowed for sequence control, giving rise to oligomers consisting of one bent and two linear monomers. The resulting meta-parapara-linked aromatic trimers carried either one or two PMBprotecting groups. With high organosolubility and flexibility, this synthetic strategy generated suitable precursors for subsequent polycondensation reactions. After polymerization, treatment with acid triggered the cleavage of the N-protecting groups. We hypothesize that the hydrogen bonding pattern generated along the polyaramide backbone could lead to the formation of a helical polymer. A drastic change in hydrodynamic volume was observed by gel permeation chromatography and dissolution in a chiral solvent lead to the observation of a circular dichroism signal for this polymer. The results of the polycondensations of N-protected oligobenzamides are reported herein. The formation of macrocycles as well as polymers could also be observed, giving a highly interesting insight into the underlying mechanism of the polycondensation of flexible, oligobenzamide-based oligomers.

Analysis using size exclusion chromatography of poly( N -isopropyl acrylamide) using methanol as an eluent

“…Analysis of samples is restricted by the requirement that the mobile phase must be compatible with both the analyte and the stationary phase. Common mobile phases in SEC are tetrahydrofuran (THF) [2] , [3] , [4] , [5] , [6] , dimethyl formamide (DMF) [5] , [7] , [8] , [9] , [10] , [11] , [12] , [13] , [14] , Chloroform [4] and water [9] and common calibration standards used include polystyrene [2] , [3] , [4] , [5] , [7] , polyethylene oxide [8] or polymethyl methacrylate [5] , [6] , [10] , although many variations and alternatives have been reported [15] . However SEC measurements in eluent blends including alcohols have only been reported rarely [16] , [17] and there appears to be only one recent report on the use of methanol or ethanol as the sole component of the eluent, in an ultra high pressure SEC system [1] .…”

Synthesis of Telechelic Poly(p-benzamide)s

“…For monomers carrying N-protected secondary amine groups this method represents a facile route to end-functional shape-persistent building blocks for the construction of supramolecular architectures. For alkyl chain N-substituted amine monomers this method opens a pathway to soluble macromonomers that can be utilized in subsequent step-growth polymerization processes. − These end-functional polymers are currently investigated as macromonomers in step-growth polymerizations in our group.…”

Synthesis of High Molecular Weight Poly(p-benzamide)s

“…In order to investigate potential side reactions during the Yokozawa-type polycondensation of our previously reported oligomers, we designed a monomer ( M1 ) exhibiting the important features of the oligomers reported earlier Figure .…”

“…21 M1 was synthesized in seven straightforward steps as shown in Figure 1. 2-Hydroxy-4-nitrobenzoic acid was converted into 2,5-bishydroxy-4-nitrobenzoic acid (1, 39%) using Elbs persulfate oxidation. 23 A Fischer esterification gave the methyl ester (2, 60%) followed by a Williamson ether synthesis using 2-ethylhexyl bromide provided the highly organo soluble methyl 2,5-bis((2-ethylhexyl)oxy)-4-nitrobenzoate (3, 59%).…”

“…18,19 We recently reported the polymerization of trimers of derivatives of 4-aminobenzoic acid using Yokozawa's polymerization method in a step-growth polymerization context. 20,21 However, we were not able to synthesize high molecular weight polymers.…”