# Effects of Organophosphorus Flame Retardants on the Dissipation Factor of Flame-Retardant Polymers

## TL;DR

This paper studies how a hydroxyl group in flame retardants affects the dielectric loss of polymers, finding that interactions with the polymer matrix are key.

## Contribution

The study reveals the impact of hydroxyl groups and processing temperatures on dielectric losses in flame-retardant polymers.

## Key findings

- DOPO-HM has a lower dissipation factor than DOPO-Me due to hydrogen bonding.
- DOPO-HM is less detrimental to dielectric loss in polystyrene and crosslinked polyphenylene oxide.
- High flame retardant loadings increase dielectric loss in PMMA, with DOPO-HM showing slightly higher loss.

## Abstract

To understand the effect of the hydroxyl group and processing temperatures on dielectric losses of flame retardants and flame-retardant polymers, the performance difference between 6-methyldibenzo[c,e][1,2]oxaphosphinine 6-oxide (DOPO-Me) and 6-(hydroxymethyl)dibenzo[c,e][1,2]oxaphosphinine 6-oxide (DOPO-HM) has been investigated, respectively, in non-polar and polar polymers at 7–20 GHz. DOPO-HM and DOPO-Me differ by only one OH group. The former demonstrates a lower dissipation factor (Df) than the latter, owing to hydrogen bonds. In polystyrene and crosslinked polyphenylene oxide, both flame retardants increase a dielectric loss of flame-retardant polymers, with DOPO-HM being less detrimental because of its higher crystallizability and lower plasticization. In polar poly(methyl methacrylate) (PMMA), conformational changes in PMMA main chains caused by flame retardants and high processing temperatures lead to an early Df drop of PMMA at low loadings of the flame retardants. At high loadings, a change in the physical form of flame retardants from a primitive crystalline state to an amorphous state increases a dielectric loss of flame retardant PMMA, with DOPO-HM resulting in a slightly higher dielectric loss than DOPO-Me. These results prove that the effect of a hydroxyl group in organophosphorus structures on the dielectric loss of flame-retardant polymers is crucially dependent on its interaction with the polymer matrix.