COMMUNICATION | doi:10.20944/preprints202105.0397.v1
Subject: Chemistry And Materials Science, Analytical Chemistry Keywords: phosphazenes; cyclization; controlled cycle size; living cationic polymerization; hexamethyldisilazane
Online: 17 May 2021 (17:02:38 CEST)
Despite a significant number of investigations in the field of phosphazene chemistry, the mechanism of this class cyclic compounds formation is still poorly studied. At the same time, a thorough understanding of this process is necessary both for the direct production of phosphazene rings with a given size, and for the controlled cyclization reaction when it is secondary and undesirable. Here we have synthesized a series of short linear phosphazene oligomers with the general formula Cl[PCl2=N]n–PCl3+PCl6– and studied their tendency to form cyclic structures under the influence of elevated temperature or in the presence of nitrogen-containing agents, such as hexamethyldisilazane (HMDS) or ammonium chloride. It was established that linear oligophosphazenes are inert when heated in the absence of the mentioned cyclization agents, and the formation of cyclic products occurs only when these agents are involved in the process. It is for the first time shown the ability to obtain the desired size phosphazene cycle from corresponding linear chain. Known obstacles like side interaction with the PCl6– counterion and a tendency of longer chains to undergo crosslinking elongation instead of cyclization are still relevant and ways to overcome them are being discussed.
ARTICLE | doi:10.20944/preprints202012.0665.v1
Subject: Chemistry And Materials Science, Biomaterials Keywords: benzoxazines; phosphazenes; curing kinetics; flammability; flame retardant; catalysis; m-toluidine
Online: 25 December 2020 (13:34:05 CET)
A novel type of phosphazene containing additive that act both as catalyst and as flame retardant for benzoxazine binders is presented in this study. The synthesis of a derivative of hexachlorocyclotriphosphazene (HCP) and meta-toluidine was carried out in the medium of the latter, which made it possible to achieve complete substitution of chlorine atoms in the initial HCP. Thermal and flammability characteristics of modified compositions are revealed. The modifier catalyzes the process of curing and shifts the beginning of reaction from 222.0 C for pure benzoxazine to 205.9 C for composition with 10 phr of modifier. The additive decreases the glass transition temperature of compositions. Achievement of the highest category of flame resistance (V-0 in accordance with UL-94) is ensured both by increasing the content of phenyl residues in the composition and by the synergistic effect of phosphorus and nitrogen. Brief research of the curing kinetics disclosed the complex nature of the reaction. An accurate two-step model is obtained using extended Prout-Tompkins equation for both steps.
ARTICLE | doi:10.20944/preprints202101.0268.v1
Subject: Chemistry And Materials Science, Analytical Chemistry Keywords: phosphazenes; cross-linked; hydrosilylation; Piers–Rubinsztajn reaction; eugenol; siloxanes; model compounds; siloxane-phosphazene
Online: 14 January 2021 (13:12:12 CET)
Finding new ways for the preparation of cross-linked structures is a significant problem in terms of materials for biomedical application, lithium batteries electrolytes, and etc. Within this work we have studied the possibility to utilize hydrosilylation and Piers-Rubinsztajn reactions to obtain cross-linked model phosphazene compounds, containing eugenoxy and guaiacoxy groups. It was shown that Piers-Rubinsztajn reaction cannot be efficiently used to prepare tailored polymer-matrix, due to the catalyst deactivation by nitrogen atoms of phosphazene units. A number of cross-linked phosphazene-based materials was obtained with the use of hydrosilylation reaction and their properties were studied by NMR spectroscopy, FTIR, DSC, and TGA. This work showed a perspective for the use of eugenoxy functional groups for the preparation of three-dimensional hybrid phosphazene/siloxane-based materials for various applications.