Challenging commercial polycarbonate: Suzuki polycondensation afforded a high‐molar‐mass poly(meta‐phenylene) (see structure) which displays not only outstanding toughness, convenient processability, and a high glass‐transition temperature, but also considerable resistance against environmental stress‐cracking; thus, it rivals high‐performance polycarbonate in its fundamental properties.
This paper describes the successful application of the Suzuki polycondensation (SPC) to the synthesis of high molecular weight polyphenylenes using aryl dichloride monomers. From readily available starting material, two meta‐dichloromonomers (2b and 2c) were prepared and subjected to SPC with benzene 1,4‐diboronic acid ester to produce reasonably high molar mass poly(para‐meta‐phenylene)s 4a and 4b, respectively, if freshly prepared Pd‐catalyst, Buchwald ligand and the base K3PO4 were used. The polymer with butoxy substituent (4a) was compared regarding GPC molar mass and glass transition temperature with its exact same congener which had been synthesized in a previous work starting from a meta‐dibromo monomer. This comparison unequivocally confirms the molar masses achieved and, thus, establishes the first reported case of a SPC using aryl chloride monomers, instead of the more expensive and less amply available aryl bromides which had to be used otherwise.
The synthesis of "designer" dendrimers and dendrons with sulfonimide units at every branching point is reported. The synthesis is based on a series of (regio)selective functionalization reactions of amines and sulfonamides allowing precise control of the dendrimers' shape, the number of branches in each generation, and their peripheral decoration with functional groups. In principle, structurally different branches can be incorporated at any position within the dendrimer structure at will. Structurally perfect symmetrical and two-faced "Janus"-type dendrimers, as well as dendrimers and dendrons with intended interstices were synthesized on a preparative scale and fully characterized. Oligosulfonimide dendrons of various generations bearing an aryl bromide functional group at their focal points were attached to a p-phenylene core with the aid of Suzuki cross-coupling reactions resulting in dendrimers with photoactive terphenyl cores. The structure and the high purity of all dendritic sulfonimides were confirmed by means of (1)H and (13)C NMR, electrospray ionization mass spectrometry (ESI-MS), and elemental analysis. The utility of MALDI-TOF mass spectrometry for the analytical characterization of these dendrimers was evaluated in comparison to electrospray ionization. Two model branched oligosulfonimides were characterized in the solid state by single-crystal X-ray analysis. Reaction selectivities and conformation of sulfonimide branching points were rationalized by DFT calculations.
The photophysical properties of three dendrimers containing a p-terphenyl core with appended sulfonimide branches of different size and n-octyl chains have been investigated in dichloromethane solution. In the dendrimer absorption spectra contributions from both the branches and the core are clearly identified. The fluorescence spectra show only the characteristic fluorescence of the terphenyl unit. Energy transfer from the appended chromophoric groups to the core does not occur. In the dendrimers, the terphenyl core exhibits a very high fluorescence quantum yield (ca. 0.75) and a short emission lifetime (0.8 ns). These properties allowed investigations of the fluorescence depolarization caused by rotation of the dendrimers. The dendrimers show a very high steady-state anisotropy in dichloromethane solution at room temperature (0.24 for the largest one), compared to that of the parent terphenyl under the same experimental conditions (<0.01) and in rigid matrix (0.33). Both the n-octyl chains and the sulfonimide branches play important roles to slow down the molecular rotation.
Summary: Four different 1,4‐ and 1,3‐dibromobenzenes carrying nonpolar dodecyloxy and linear as well as branched polar oligo(ethylene glycol) side chains were subjected to Suzuki polycondensation (SPC) with benzene‐1,4‐bisboronic acid ester to produce high‐molecular‐weight amphiphilic polyphenylenes, three of which are all‐para and one is meta linked. Molecular weights were determined by size exclusion chromatography with conventional polystyrene calibration and, for two selected samples, with universal calibration. Polymerization under SPC conditions of one of the 1,4‐dibromo monomers is compared to that of the direct 1,4‐diiodo analog.Polyphenylenes prepared in this study.imagePolyphenylenes prepared in this study.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.