Phosphazene/silsesquioxane-polycondensates for flame retardancy applications

Gómez, Debra Carolina Cortés; Möller, Martin (Thesis advisor); Pich, Andrij (Thesis advisor)

Aachen : RWTH Aachen University (2021, 2022)
Dissertation / PhD Thesis

Dissertation, RWTH Aachen University, 2021

Abstract

Poly(organo)phosphazenes are macromolecules with alternating phosphorous-nitrogen atoms in their skeleton -with linear (chains) or cyclic (rings) structure- and organic side groups. This thesis investigates the synthesis and properties of cyclomatrixtype polyphosphazenes, starting from hexachlorocyclotriphosphazene N3P3Cl6 (HCCP) or partially substituted HCCP with methoxy-groupsN3P3Cl6-n(OMe)n, and amine functionalized silsesquioxanes. The polycondensation of HCCP with multifunctional amines results in a three dimensional network with high crosslink density. As such, they have found little interest because their intractability and poor solubility [1, 67]. The reduction of reactive chlorine in HCCP via partial substitution by inert groups, provides access to monomers with reduced functionality, suitable for the formation of less branched or even linear cyclomatrix polymers. In this way, novel soluble and tractable partially substituted HCCP with methoxy-groupsN3P3Cl6-n(OMe)n are synthesized by a simple and robust synthesis in Chapter 3.Because in the course of the years strict regulations have emerged regarding the toxicity of flame retardants, halogen-free alternatives have been intensively explored by the scientific community. In the last years, particular interest has raised for polyphosphazenes, due to its hybrid inorganic-organic backbone with high amount of phosphorous and nitrogen-atoms [9, 128] and their flame inhibition properties. Inspired by the actual needs, high thermally stable cyclomatrix poly-(organo)phosphazenes made by precipitation polymerization of N3P3Cl6 or N3P3Cl6-n(OMe)n and silsesquioxane building blockshave been synthesized in Chapter 4.Our contact to textiles is almost everywhere, in clothing, at our living- and working-spaces as well as in transportation. The high specific surface area of synthetic and natural fibers make these materials easy to ignite due to the overall-contact to atmospheric oxygen [63]. Thermal stable polyphosphazene-silsesquioxane cyclo-matrix polymers presented in Chapter 5, retard or completely inhibit cellulose-degradation, due to a synergism between phosphorous and nitrogen as well as the formation of a protective carbonaceous-silica char. The polymers are easily applicable as nanocoatings on cotton fibers in a finishing process and relatively small amounts are needed to induce flame retardation. Chapter 6 summarizes conclusions and gives insights in new properties of organo(cyclo)phosphazenes which have been briefly evaluated within the scope of this work. Furthermore an outlook for future research is presented.