FR, hexa(phosphazene aminophenoxyl)cyclotriphosphozene (HPAPC) was synthesized, which contains phosphazene combined with DOPO, and it showed efficient FR activity. Polylactide (PLA) FR composites were prepared by melt blending
with different percentages of HPAPC and their thermo-mechanical, FR, and other
properties were evaluated [110]. It was observed that even at low weight percentages (5%), PLA FRs showed high FR activity with high LOI values and V-0
rating in the UL-94 test. Reactive phosphazene-containing epoxy FR resins
(PPCPT) were prepared and cured with different amine compounds, including 4,4′diaminodiphenylsulfone (DDS); dicyanodiamide (DICY); 3,4′-oxydianiline (ODA);
4,4′-diaminodiphenylmethane (DDM). The LOI values of 4-diethoxyphosphoryloxyphenoxy)(4-glycidoxyphenoxy)cyclotriphosphazene (PPCPT) with DICY were
found to be high, owing to the synergetic effect of P and N in DICY and PPCPT
[111]. DOPO-based triazole (DTA) was synthesized and used to prepare FR epoxy
polymers and it was observed that even at low weight percentages (4 wt%), the
DTA-containing epoxy resins showed a high LOI value of 34.8% and achieved
a V-0 rating in the UL-94 test [74]. Because of the blowing-out effect, the addition of DTA drastically changed the combustion behavior of the resins; flame
dripping disappeared completely, the ignition time decreased, and the resins
exhibited self-extinguishing ability, as illustrated in Chap. 6. Yang et al. [112]
synthesized rigid PU foams using reactive HPHPCP (hexa (phosphite-hydroxylmethyl-phenoxyl) cyclotriphosphazene) as a FR additive and they observed a great
improvement in the FR and thermal properties of the resultant foams. Because
HPHPCR contains a large number of functional groups, it increases the crosslinking
density and hence the FR activity. Liu et al. [113] prepared DGEBA/PN-EPC
thermosets cured with different FR hardeners, such as DDM, DICY, and MeTHPA.
In the presence of DICY, the epoxy resins showed high FR activity compared to
other systems due to a possible synergetic effect. Melt behavior and crystallinity
also play important roles in controlling the char formation and dripping. Similarly,
in the presence of PN6 and PPPMS, poly(ethylene terephthalate) (PET) showed
improved melt viscosity, char yield, and anti-dripping nature during combustion
[114]. Mathew et al. [101] synthesized different cyanato derivatives from hydroxyl
phenyl cyclotriphosphazenes and further used them to prepare cross-linked polymer
networks with varying percentages of phosphazene and triazine. The resulting
polymers showed high FR activity with increasing crosslink density and char
residue in the condensed phase. Huang et al. [115] synthesized NHPE from hexachloro phosphazene and HEMA and prepared FR-PU coatings using a UV-curable
technique; these coatings exhibited high thermal stability and FR activity.
4.3.4 Phosphorus-Based Spiro Cyclic FRs
Pentaerythritol (PER) is considered as one of the best char-forming agents and it
has been used in the synthesis of P-based caged bicyclic compounds, as shown in
Scheme 4.11; these compounds are later used in the synthesis of FR-PUs. Because
4.3 Phosphorus-Based FRs
31
with different percentages of HPAPC and their thermo-mechanical, FR, and other
properties were evaluated [110]. It was observed that even at low weight percentages (5%), PLA FRs showed high FR activity with high LOI values and V-0
rating in the UL-94 test. Reactive phosphazene-containing epoxy FR resins
(PPCPT) were prepared and cured with different amine compounds, including 4,4′diaminodiphenylsulfone (DDS); dicyanodiamide (DICY); 3,4′-oxydianiline (ODA);
4,4′-diaminodiphenylmethane (DDM). The LOI values of 4-diethoxyphosphoryloxyphenoxy)(4-glycidoxyphenoxy)cyclotriphosphazene (PPCPT) with DICY were
found to be high, owing to the synergetic effect of P and N in DICY and PPCPT
[111]. DOPO-based triazole (DTA) was synthesized and used to prepare FR epoxy
polymers and it was observed that even at low weight percentages (4 wt%), the
DTA-containing epoxy resins showed a high LOI value of 34.8% and achieved
a V-0 rating in the UL-94 test [74]. Because of the blowing-out effect, the addition of DTA drastically changed the combustion behavior of the resins; flame
dripping disappeared completely, the ignition time decreased, and the resins
exhibited self-extinguishing ability, as illustrated in Chap. 6. Yang et al. [112]
synthesized rigid PU foams using reactive HPHPCP (hexa (phosphite-hydroxylmethyl-phenoxyl) cyclotriphosphazene) as a FR additive and they observed a great
improvement in the FR and thermal properties of the resultant foams. Because
HPHPCR contains a large number of functional groups, it increases the crosslinking
density and hence the FR activity. Liu et al. [113] prepared DGEBA/PN-EPC
thermosets cured with different FR hardeners, such as DDM, DICY, and MeTHPA.
In the presence of DICY, the epoxy resins showed high FR activity compared to
other systems due to a possible synergetic effect. Melt behavior and crystallinity
also play important roles in controlling the char formation and dripping. Similarly,
in the presence of PN6 and PPPMS, poly(ethylene terephthalate) (PET) showed
improved melt viscosity, char yield, and anti-dripping nature during combustion
[114]. Mathew et al. [101] synthesized different cyanato derivatives from hydroxyl
phenyl cyclotriphosphazenes and further used them to prepare cross-linked polymer
networks with varying percentages of phosphazene and triazine. The resulting
polymers showed high FR activity with increasing crosslink density and char
residue in the condensed phase. Huang et al. [115] synthesized NHPE from hexachloro phosphazene and HEMA and prepared FR-PU coatings using a UV-curable
technique; these coatings exhibited high thermal stability and FR activity.
4.3.4 Phosphorus-Based Spiro Cyclic FRs
Pentaerythritol (PER) is considered as one of the best char-forming agents and it
has been used in the synthesis of P-based caged bicyclic compounds, as shown in
Scheme 4.11; these compounds are later used in the synthesis of FR-PUs. Because
4.3 Phosphorus-Based FRs
31