Issue 27, 2023

Flame retardant phosphonate-functionalised polyethylenes


The two-step synthesis of phosphonate-functionalised polyethylenes with enhanced thermal and flame-retardant properties has been described. Solution phase copolymerisation of ethylene and 11-bromo-1-undecene using the commercially available early transition metal catalyst, rac-ethylenebis(indenyl)zirconium dichloride, produced poly(ethylene)-co-(11-bromo-1-undecene) with comonomer incorporation levels up to 6.10 mol%. Solvent-free post-polymerisation modification of the poly(ethylene)-co-(11-bromo-1-undecene) with the phosphite esters, P(OiPr)3 and P(OPh)3 successfully converted the bromide group into the corresponding phosphonate group on polyethylene (PE–PO(OR)2). The phosphonate-functionalised polyethylene was characterised by NMR and IR spectroscopy, GPC and DSC. Higher thermal stability (higher T10%, T50%, Tmax and % residue at 700 °C) was determined by TGA with respect to pure LDPE. Microscale combustion calorimetry (MCC) tests indicate significant lower values of heat release capacity (HRC), peak heat release rate (pHRR) and total heat release (THR) compared to those of LDPE, indicating an enhanced flame retardancy. Importantly, blends of LDPE and PE–PO(OR)2 with weight ratios of 90 : 10, 95 : 5 and 99 : 1 demonstrate higher thermal stability compared to LDPE despite the low concentration of the phosphonate group. Additional incorporation of traditional inorganic flame retardant additives (aluminium hydroxide, ATH), LDPE : ATH : PE–PO(OR)2 with 80 : 10 : 10 wt%, presents higher thermal stability than pure LDPE or blended LDPE with PE–PO(OR)2 due to a synergistic effect from the combination of the phosphonate group and ATH.

Graphical abstract: Flame retardant phosphonate-functionalised polyethylenes

Supplementary files

Article information

Article type
07 Feb 2023
15 Jun 2023
First published
15 Jun 2023
This article is Open Access
Creative Commons BY license

Polym. Chem., 2023,14, 3175-3185

Flame retardant phosphonate-functionalised polyethylenes

N. Blake, Z. R. Turner, J. Buffet and D. O'Hare, Polym. Chem., 2023, 14, 3175 DOI: 10.1039/D3PY00143A

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