Abstract
The current trend for future flame retardants (FRs) goes to novel efficient halogen-free materials, due to the ban of several halogenated FRs. Among the most promising alternatives are phosphorus-based FRs, and of those, polymeric materials with complex shape have been recently reported. Herein, we present novel halogen-free aromatic and aliphatic hyperbranched polyphosphoesters (hbPPEs), which were synthesized by olefin metathesis polymerization and investigated them as a FR in epoxy resins. We compare their efficiency (aliphatic vs. aromatic) and further assess the differences between the monomeric compounds and the hbPPEs. The decomposition and vaporizing behavior of a compound is an important factor in its flame-retardant behavior, but also the interaction with the pyrolyzing matrix has a significant influence on the performance. Therefore, the challenge in designing a FR is to optimize the chemical structure and its decomposition pathway to the matrix, with regards to time and temperature. This behavior becomes obvious in this study, and explains the superior gas phase activity of the aliphatic FRs.
Highlights
The overlap of the decomposition temperatures of a flame retardant (FR) and its polymer matrix is essential for its effectiveness in the case of fire [1,2,3,4]
Acyclic diene metathesis polymerization (ADMET) is a versatile technique to prepare a broad range of linear functional polymers [26,27,28,29,30]
In all cases, the addition of aliphatic FRs 2 and poly-2 resulted in a higher or equivalent decrease of Tg compared to the aromatic FRs
Summary
The overlap of the decomposition temperatures of a flame retardant (FR) and its polymer matrix is essential for its effectiveness in the case of fire [1,2,3,4]. Aromatic polymers typically have higher thermal stability than aliphatic polymers. In the case of a FR, this higher thermal stability influences at which temperatures the active species are available in the gas phase. An important example of this behavior was reported for brominated aromatic and aliphatic FRs in polypropylene. The thermal decomposition of aliphatic FRs starts below the thermal decomposition of polypropylene, which leads to a good performance in this matrix. Aromatic FRs decompose after polypropylene and at the decomposition temperature of polypropylene, no optimal debromination is achieved, resulting in mediocre performance [5]
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