Self-Assembling Polycondensation of 4-Aminobenzaldehyde. Preparation of Star-Like Aggregates of Cone-Shaped Poly(azomethine) Crystals

Abstract

KEY WORDSSelf-Assembling / Polycondensation / Poly(azomethine) / Crystallization / Morphology / Aromatic poly(azomethine)s belong to a class of high performance materials that are known because of their excellent thermal stability, good mechanical properties and environmental resistance, 1-4 but more particularly as promising materials with optoelectrical, photonic and magnetic application. [5][6][7][8] Numerous types of aromatic poly(azomethine)s have been synthesized by the condensation between aromatic dialdehydes and diamines. However, their high melting points and low solubility usually make them inaccessible for processing by conventional techniques. In order to improve their intractability, several approaches such as the introduction into the main chain of flexible aliphatic segments, bulky lateral substituents or fluorine groups have been attempted so far. [9][10][11][12] We have been studying on the morphology control of intractable polymers during solution polymerization, and succeeded in preparing the whiskers of poly(poxybenzoyl) and other aromatic polyesters by polymerization in liquid paraffin (LPF). [13][14][15][16][17][18] These whiskers are formed by the reaction-induced crystallization of oligomers during solution polymerization. The polymer chains are aligned along the long axis of the whiskers and they show single crystal nature. This morphology and the chain alignment are desirable to endow the essential properties for industrial materials such as organic reinforcements. The formation mechanism of these whiskers contains the following three steps: (1) When the degree of polymerization of the oligomers exceed a critical value, they are precipitated from the solution to form lamellae. (2) The lamellae pile up in the form of needle-like crystals with spiral growth.(3) Post-polymerization occurs topochemically in the needle-like crystals, and the whiskers consisting of high molecular weight extended polymer chains are eventually formed. 14 The preparation method of the whisker can be recognized as the self-assembling polycondensation accompanied by the reaction-induced crystallization of oligomers, and it is a very valuable method for the morphology control of intractable polymers to overcome the antagonistic problem between intractability and properties.In many reports it has been very difficult to obtain the high molecular weight poly(azomethine) (PAZM). One of reasons is that aromatic poly(azomethine)s are precipitated in the solution during polycondensation because of the low solubility. 12 Much effort was devoted recently to preparing soluble and fusible aromatic poly(azomethine)s in many different ways. [19][20][21] However, the modification of polymer chain structures sacrifices their essential properties derived from their straight rigid-rod structures. Precipitation during polymerization is of advantage to control the morphology by means of the reaction-induced crystallization of oligomers as described before. In this study, we report the morphology of PAZM crystals prepared by the self...

Catalytic Deoxygenation of Nitroarenes Mediated by High-Valent Molybdenum(VI)–NHC Complexes

“…We assume that due to the high temperature necessary for the reaction to proceed, the aldehyde condensates directly with the formed amine to (polymeric) imines. Polymerization of amino-benzaldehydes has also been seen previously in the literature . Turning to more electron-withdrawing substituents such as fluorides and esters, we have also observed moderate to good conversions of the corresponding nitroarenes.…”

“…Polymerization of aminobenzaldehydes has also been seen previously in the literature. 97 Turning to more electron-withdrawing substituents such as fluorides and esters, we have also observed moderate to good conversions of the corresponding nitroarenes. However, this indicates that for strongly electron-withdrawing substituents the higher catalyst loadings might be necessary to reach full conversion of the substrates.…”

Morphology Control of Aromatic Polymers in Concert with Polymerization

“…56 Polymerization proceeds with eliminating water and the crystals were formed by the crystallization of oligomers. The obtained crystals exhibited cone-shape morphology, and the average length was 0.5-0.6 mm and the average width was 0.1 mm.…”

Predictors of morbidity following free flap reconstruction for cancer of the head and neck

“…The POB whiskers, in which the polymer chains are aligned along the long axis of the whiskers, are formed by the reaction‐induced crystallization of oligomers with the spiral growth of oligomer lamellae and the subsequent solid‐state polymerization in the crystals. Many other aromatic polymer whiskers have been prepared by this method 4–12. In contrast to the POB whisker, we have prepared poly( p ‐oxycinnamoyl) (POC) microspheres by the solution polymerization of 4‐acetocycinnamic acid 13.…”