Synthesis and properties of aramid dendrimers

Abstract

The synthesis, characterisation and properties of simple low molecular weight aromatic amide dendrimers is described. The insights into the problems inherent in the synthesis of such systems provided by molecular modelling studies are discussed along with possible strategies for circumventing them. Preliminary results concerning blends of aramid dendrimers with poly(hexamethy1eneadipamide) are presented. INTRODUCIlONFollowing the exhortation in the Editors' letter of invitation to contribute; "We would encourage the style of the paper to be of a review type so that it can reach a broad audience", this short paper describes our earliest attempts to prepare and study aramid dendrimers. We have eliminated all but the bare bones of experimental detail, which will be published elsewhere, and present here a general discussion of the origins and objectives of our work, an account of our experiences and how it correlates with what we set out to do and with the reports of earlier workers, and a view about how the theme of aramid dendrimers might be developed. The last fifteen to twenty years have seen the gradual emergence of a distinct area of polymer synthesis concerned with the preparation of macromolecules of exactly defmed size, structure and topology. Many of the topologies explored are relatively unusual including, for example, rods, ribbons, dendrites, rotaxanes, catenanes and well defined networks. This perceptible trend constitutes, of course, only a small part of current research in polymer synthesis, the bulk of which continues to attempt to do better what is already done well. However, this newer development is attractive in that it represents a significant conceptual shift away from the statistical and probabilistic theories which underpin our understanding of established step and chain growth processes for the synthesis of conventional linear, branched and network polymers, and takes us towards the realm of precision and control in synthesis which characterises the traditions and achievements of classical organic chemistry and biochemistry. A fundamental aim of work in this new area is to make and study materials which consist of assemblies of true homostructural monodisperse macromolecules. This category of macromolecule is commonplace in nature where uniquely defined structures give rise to uniquely defined properties and functions; 0 1994 Huthig & Wepf Verlag, Basel

Dendritic aromatic polyamides and polyimides

“…The coupling reaction of the dendrons with a core molecule, such as p ‐phenylenediamine, gave a corresponding dendrimer (Scheme ). Similarly to the case reported by Feast and coworkers,9, 10 the yield of high‐generation dendrimers decreased, probably because of steric hindrance at a focal point. The structure of the polyamide dendrons and dendrimers was confirmed by 1 H NMR, 13 C NMR, and matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI‐TOF MS) measurements.…”

“…Only brief comments on NMR, mass spectrometry, and gel permeation chromatography (GPC) data were described in the text for the polyamide dendrimers ( 1 and 2 ). Feast and coworkers9, 10 reported the synthesis and detailed characterization of aromatic polyamide dendrimers ( 1 , 2 , and 3 ). The peak splitting of aromatic protons derived from inner aromatic rings was observed in an 1 H NMR spectrum for compound 2 , suggesting sterically restricted rotation of inner amide bonds.…”

Novel tetrapodal molecules and reticular polyamides based on tetraphenylmethane

“…The IH NMR spectra of this compound in DMSO-d6 showed split signals of variable, concentration-dependent relative intensity, and revealed intermolecular NOE effects indicating aggregation. Interestingly, split IH NMR signals have been also observed by others for an aramid dendrimer of comparable size in the same solvent; the interpretation, however, has been different [20]. The exact nature of the aggregates formed by 3b was not investigated.…”

Synthesis of cylindrical polyamides from hexakis (4-carboxyphenoxy)cyclotriphosphazene and p-xylyenediamine

“…Such a cylindrical assembly was based on a unique geometry of hexaphenoxycyclotriphosphazene derivatives, in which the phenoxy groups are aligned approximately perpendicular to the nearly planar phosphazene ring [7,8]. So far, studies on synthesis and properties of various polyamides with dendritic or hyperbranched structures have been reported [9][10][11][12]. Our interests lay in extending to the preparation of covalently bonded polymers from self-assembled supramacromolecules with three-dimensional structure.…”