Synthesis of a hyperbranched polyamide oligomer containing DOPO for simultaneously enhancing the flame retardance and glass transition temperature of epoxy resin

Abstract

Flame retardants endow epoxy resins (EP) with flame retardance, however, their introduction often lead to the decrease in the glass transition temperature (Tg), which is an important property for EP. Therefore, it is significant to design and synthesize a high‐efficiency flame retardant that enhances flame retardance and Tg of EP. To achieve this goal, a hyperbranched polyamide oligomer containing DOPO (HPD) was successfully synthesized by A4 + B2 polymerization and its structure was confirmed by FTIR, 1H NMR, and 30P NMR spectra and GPC. HPD was used as an additive flame retardant in epoxy resin, and its effect on the flame retardance and thermal properties of epoxy resin was studied. The epoxy resin with 7.5 wt% HPD reached UL‐94V‐0 rating and a higher LOI value of 29.6%, and its Tg was 176.2°C, which is higher than the pure epoxy resin. Moreover, the results of cone calorimetry testing (CCT) and TG‐FTIR analysis suggested that the gas‐phase and condensed‐phase flame‐retarded roles of HPD delayed the time to ignition, and reduced the value of relevant combustion parameters, including the peak of heat release rate, average of heat release rate, total heat release, smoke production rate, and total smoke production. The analysis results of Py‐GC/MS test of HPD further confirmed that HPD was able to play the flame‐retarded role in the gaseous and condensed phases.

From laboratory to industrialization: Eco‐friendly flame retardant endowing epoxy resin with excellent flame retardancy, transparency, and mechanical properties

“…The increase in the residual carbon from 15.8 to 17.9 wt% at 800°C was due to the early degradation of DOPO producing phosphate and polyphosphate, which prevented further decomposition. This conclusion was consistent with other reported results for phosphorus containing flame retardants 11,15,26,36–38 …”

“…For one thing, the rigid aromatic groups in FNU enhanced the intermolecular force. For another, the FNU structure contained NH and OH groups, which formed hydrogen bonds or π–π conjugate enhancement effect with epoxy groups 26,52 …”

“…For another, the FNU structure contained NH and OH groups, which formed hydrogen bonds or π-π conjugate enhancement effect with epoxy groups. 26,52 To further investigated the reasons for the improved mechanical properties, the microstructure of the cross-section of EP thermoset brittle fracture by liquid nitrogen was investigated using SEM, as shown in Figure 12. EP-0 displayed smooth fracture structures and typical brittle fracture characteristics, while EP-1 and EP-2 fracture surfaces contained dense cracks, and were obviously uneven and rough, which could result to the consumption of more energy.…”

“…In this background, a commercial phosphorus‐based flame retardant DOPO is favored by researchers owing to its reaction activity and high flame‐retardant efficiency 25 . The structure of 9,10‐dihydro‐9‐oxo‐10‐phosphofi‐10‐oxide (DOPO) contains P–H active groups, which is used as flame retardant intermediates to synthesize DOPO derivatives with multiple flame retardant elements 26,27 . The incorporation of DOPO derivatives into EP matrix as reactive flame retardants improves the compatibility of DOPO with the matrix without degrading other properties of EP.…”

“…25 The structure of 9,10-dihydro-9-oxo-10-phosphofi-10-oxide (DOPO) contains P-H active groups, which is used as flame retardant intermediates to synthesize DOPO derivatives with multiple flame retardant elements. 26,27 The incorporation of DOPO derivatives into EP matrix as reactive flame retardants improves the compatibility of DOPO with the matrix without degrading other properties of EP. The design and development of DOPO derivative flame retardant in EP has been widely reported.…”