Syntheses of Two Dopo-Based Reactive Additives as Flame Retardants and Co-Curing Agents for Epoxy Resins

Article abstract of DOI:10.1080/10426507.2014.884092

Two novel phosphorus-nitrogen-containing flame retardants, 1,1′,2,2′-tetra-hydroxyl-4′′, 4′′′-biphenylene-bis[amino-((10′′′′-O-10′′′′-H-9′′′′-oxa-10′′′′λ⁵-phosphaphenanthrene-10′′′′-yl))-methyl]}-bisphenol (3) and 1,1′,2,2′-tetra-hydroxyl-{4′′,

Full text of DOI:10.1080/10426507.2014.884092

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Phosphorus, Sulfur, and Silicon and the
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Syntheses of Two Dopo-Based Reactive
Additives as Flame Retardants and Co-
Curing Agents for Epoxy Resins
Ling Xiaoa, De-chao Suna, Tian-li Niua & You-wei Yaoa
a Department of Materials Science and Engineering, Graduate School
at Shenzhen, Tsinghua University, Shenzhen 518055, China
Accepted author version posted online: 30 Apr 2014.Published
online: 21 Oct 2014.
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To cite this article: Ling Xiao, De-chao Sun, Tian-li Niu & You-wei Yao (2014) Syntheses of Two Dopo-
Based Reactive Additives as Flame Retardants and Co-Curing Agents for Epoxy Resins, Phosphorus,
Sulfur, and Silicon and the Related Elements, 189:10, 1564-1571, DOI: 10.1080/10426507.2014.884092
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Phosphorus, Sulfur, and Silicon, 189:1564–1571, 2014
Copyright ꢀC Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426507.2014.884092
SYNTHESES OF TWO DOPO-BASED REACTIVE
ADDITIVES AS FLAME RETARDANTS AND CO-CURING
AGENTS FOR EPOXY RESINS
Ling Xiao, De-chao Sun, Tian-li Niu, and You-wei Yao
Department of Materials Science and Engineering, Graduate School at Shenzhen,
Tsinghua University, Shenzhen 518055, China
GRAPHICAL ABSTRACT
Abstract Two novel phosphorus-nitrogen-containing flame retardants, 1,1ꢀ,2,2ꢀ-tetra-
hydroxyl-4ꢀꢀ, 4ꢀꢀꢀ-biphenylene-bis[amino-((10ꢀꢀꢀꢀ-O-10ꢀꢀꢀꢀ-H-9ꢀꢀꢀꢀ-oxa-10ꢀꢀꢀꢀλ5-phosphaphenan
threne-10ꢀꢀꢀꢀ-yl))-methyl]}-bisphenol (3) and 1,1ꢀ,2,2ꢀ-tetra-hydroxyl-{4ꢀꢀ,4ꢀꢀꢀ-phenylene-
bis[amino-((10ꢀꢀꢀꢀ- O-10ꢀꢀꢀꢀ- H-9ꢀꢀꢀꢀ- oxa-10ꢀꢀꢀꢀλ5-phosphaphenanthrene-10ꢀꢀꢀꢀ-yl))-methyl]}-
bis-phenol (4) were synthesized by two steps: 1,1ꢀ,2,2ꢀ-tetra-hydroxyl-{4ꢀꢀ,4ꢀꢀꢀ- bi-phenylene-
bis[amino-methyl]}-bis-phenol, imine (1), was synthesized through condensation reaction
between 3,4-dihydroxybenzaldehyde and 4,4ꢀ-diaminobiphenyl; and, 1,1ꢀ,2,2ꢀ-tetra-hydroxyl-
{4ꢀꢀ,4ꢀꢀꢀ- phenylene-bis[amino-methyl]}-bis-phenol, imine (2) was synthesized by the reaction
of 3,4-dihydroxybenzaldehyde and 1,4-phenylenediamine; then, addition reactions between
9,10-dihydro-9-oxa-10- phosphaphenanthrene-10-oxide and the two imines, the (3) and (4)
were obtained, respectively. (1)–(4) were characterized by FTIR, NMR, and MS. (3) and (4)
reacted with epoxy resins as co-curing agents with 4,4ꢀ-diaminodiphenylmethane. Compared
with control samples, (3) or (4) co-cured epoxy thermosets with phosphorus content of 1.0 wt%
possessed good flame retardant properties with LOI value reaching more than 36.0, higher
char yields. The glass translation temperature (Tg) of thermosets containing (3) or (4) were
characterized with suitable changes by DSC test.
Keywords Flame retardant; epoxy resin; thermal stability; phosphorus
Received 19 August 2013; accepted 26 November 2013.
Address correspondence to You-wei Yao, Department of Materials Science and Engineering, Graduate
School at Shenzhen, Tsinghua University, Shenzhen 518055, China. E-mail: yaoyw@mail.tsinghua.edu.cn
Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/gpss.
1564

SYNTHESES OF TWO DOPO-BASED REACTIVE ADDITIVES
1565
INTRODUCTION
Epoxy resins are widely used in lamination, adhesive, coating application, electronic
insulation, because of their excellent performance, such as favorable chemical and electri-
cal resistance, outstanding mechanical properties, moisture, and remarkable toughness.1–3
However, epoxy resins have a flaw, inflammability, which limits their application severely.
It is an exigent task to improve their thermal and flame resistance.4,5 It has been reported that
phosphorus-containing compounds able to molecularly incorporate in the resin network are
expected to exhibit better flame retardancy.6–10 As a typical flame retardant (FR) with active
phenolic OH groups, 2-(6-oxid-6H-dibenz[c,e][1,2]-oxaphosphorin-6-yl)-1,4-benzenediol
embody this incorporation strategy.11 Another approach to realize this strategy is based on
the addition reactions of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO)
and imines, whose products are characteristic of binary functionality of FR and co-curing
agent.12–14
In this paper, FRs, 1,1ꢀ,2,2ꢀ-tetra-hydroxyl-{4ꢀꢀ, 4ꢀꢀꢀꢀ-biphenylene-bis[amino-((10ꢀꢀꢀꢀ
-
O-10ꢀꢀꢀꢀ-H-9ꢀꢀꢀꢀ-oxa-10ꢀꢀꢀꢀλ5- phosphaphenanthrene -10ꢀꢀꢀꢀ-yl))-methyl]}-bisphenol (3)
and
1,1ꢀ,2,2ꢀ-tetra-hydroxyl-{4ꢀꢀ,4ꢀꢀꢀꢀ-phenylene-bis[amino-((10ꢀꢀꢀꢀ-O-10ꢀꢀꢀꢀ-H-9ꢀꢀꢀꢀ-oxa-
10ꢀꢀꢀꢀλ5- phosphaphenanthrene -10ꢀꢀꢀꢀ-yl))-methyl]}-bis-phenol (4) with active phenolic
OHgroups in each of molecular structures are reported. Through the LOI and UL-94
vertical flame retardancy tests, (3) with building unit of biphenyl possesses better flame
retardancy than that of (4) with building unit of phenyl. Thus, (3) and (4) display design of
FR for epoxy resin based on modification of carbon-containing framework.
RESULTS AND DISCUSSION
Syntheses and Characterization of (1) and (2)
The syntheses of the imine compounds, 1,1ꢀ,2,2ꢀ-tetra-hydroxyl-{4ꢀꢀ,4ꢀꢀꢀ- bi-
phenylene-bis[amino-methyl]}-bis-phenol (1), and 1,1ꢀ,2,2ꢀ-tetra-hydroxyl-{4ꢀꢀ,4ꢀꢀꢀ-
phenylene-bis[amino-methyl]}-bis-phenol (2) were performed by the reaction of
3,4-dihydroxybenzaldehyde with 4,4ꢀ-diaminobiphenyl and 1,4-phenylenediamine,
1
respectively, as described in Scheme 1. The H NMR data displayed that the chemical
shifts of amine hydrogen at 8.46 ppm in (1) and 8.43 ppm in (2) corresponded to the
existence of imide structure. 13C NMR data revealed that the chemical shifts of proton
C7 at about 149.8 ppm in (1) and 149.1 ppm in (2) identified the emergence of C
N
bond. Furthermore, according to the FTIR signals of the intermediates (1) and (2), the
representative and strong absorptions of the C N bond at 1647, 1625 cm−1, respectively,
stated the imide group present in compounds (1) and (2).
Syntheses and Characterization of (3) and (4)
Scheme 1 showed that phosphorus-containing flame retardants, 1,1ꢀ,2,2ꢀ-tetra-
hydroxyl-{4ꢀꢀ, 4ꢀꢀꢀ-biphenylene-bis[amino-((10ꢀꢀꢀꢀ-O-10ꢀꢀꢀꢀ-H-9ꢀꢀꢀꢀ-oxa-10ꢀꢀꢀꢀλ5-phosphap-
henanthrene-10ꢀꢀꢀꢀ-yl))-methyl]}-bisphenol (3) and 1,1ꢀ,2,2ꢀ-tetra-hydroxyl-{4ꢀꢀ,4ꢀꢀꢀ-
phenylene-bis[amino-((10ꢀꢀꢀꢀ-O-10ꢀꢀꢀꢀ-H-9ꢀꢀꢀꢀ-oxa-10ꢀꢀꢀꢀλ5-phosphaphenanthrene-10ꢀꢀꢀꢀ-yl)-
methyl]}-bis-phenol (4) were obtained by the addition of DOPO with (1) and (2),
respectively. In view of 1H NMR data, the specific peaks of four OH groups in the range of
ꢀ
8.74–8.93 ppm, H7, H7 with the range 4.37–4.82 ppm, it can prove the addition reactions
between the DOPO and the imide compounds, respectively. Other peaks of NH and NHꢀ

1566
L. XIAO ET AL.
Scheme 1 Syntheses of (3) and (4).
at 6.61–6.64 ppm in (3), 5.66–5.73 ppm in (4) also confirmed the conclusion. According
to the 13C NMR, the chemical shifts of polymers (3) and (4), respectively, changed from
ꢀ
the range of 149.7–149.8 ppm in (1) and 149.1 ppm in (2) to 55.3–56.7 ppm (C7, C7 ),
ꢀ
and 55.9–56.1 ppm (C7, C7 ), suggesting the reaction of DOPO and the imide compounds.
Moreover, from 31P NMR data, the chemical shifts at 34.1, 31.3 ppm in (3) and 34.7,
31.3 ppm in (4) revealed that incorporating phosphorus to the imines (1) and (2) was
successful. The typical absorptions of P – Ph bond at 1611, 1610 cm−1, C – N bond at
1282, 1275 cm−1, P O bond at 1234, 1275 cm−1, and N – H bond at 3503, 3556 cm−1
,
respectively, potentially further proved the formation of (3) and (4). MS demonstrated
results in consistency to the NMR and FTIR analyses.
DSC Analysis
As shown in Table 1, compared with Tg value of diglycidyl ether of bisphe-
nol(DGEBA)/DDM, Tg values of the epoxy thermosets (3)/DDM and (4)/DDM decreased,
which suggests that the addition of (3) and (4) decreases the cross-linking density of the
epoxy thermosets. In addition, with the increasing contents of (3) and (4), Tg values of
the epoxy thermosets reduced. Tg value of (3)/DDM was closer to that of DGEBA/DDM,
probably indicating that (3) is suitable for moderate change of Tg values. With the identical
phosphorus content, Tg values of (3)/DDM were much higher than that of (4)/DDM sys-
tem, which probably attributed to that the cross-linking density of (3) with building unit of
biphenyl was higher than that of (4) with building unit of phenyl.

SYNTHESES OF TWO DOPO-BASED REACTIVE ADDITIVES
1567
Table 1 Thermal and flame-retardant properties of the epoxy thermosets (3) and (4)
Thermoset ID
P (wt%)a
N (wt%)b
Tg (◦C)c
Td (◦C)d
Char yielde
UL-94 rating
LOI
DGEBA/DDM
(3–0.75)/DDM
(3–1.00)/DDM
(3–1.25)/DDM
(3–1.50)/DDM
(4–0.75)/DDM
(4–1.00)/DDM
(4–1.25)/DDM
(4–1.50)/DDM
0
2.83
2.49
2.37
2.25
2.13
2.51
2.40
2.29
2.18
160
157
150
149
148
142
140
137
135
378
351
350
346
343
348
344
341
340
15.97
23.20
24.69
24.91
25.54
22.27
23.08
23.69
23.71
Burning
V-1
V-0
V-0
V-0
V-1
V-0
V-0
V-0
25.1
36.8
37.0
37.1
37.2
36.0
36.2
36.7
36.9
0.75
1.00
1.25
1.50
0.75
1.00
1.25
1.50
aPhosphorus content; bNitrogen content; cThe glass transition temperature; dThermal decomposition tempera-
ture of 5% weight loss; e(wt%) Residual weight percentage at 800◦C.
TGA Analysis
The thermal decomposition temperature of 5% weight loss (Td) and the char yields of
the epoxy thermosets (3)/DDM and (4)/DDM were obtained from TGA curves, as showed
in Figure 1, respectively. Td values of the epoxy systems (3)/DDM and (4)/DDM are in
the range of 340–351◦C, lower than that of DEGBA/DDM. With increasing of (3) and
(4), Td values of the epoxy thermosets decreased gradually. Td values of (3)/DDM were
higher than that of (4)/DDM with the same phosphorus content. Compared with 15.97 wt%
char yield of DGEBA/DDM, char yields of (3)/DDM and (4)/DDM are in the range of
22.27–25.54 wt%, significantly increased. With the addition of phosphorus contents, the
char yields increased gradually, as is in accordance with the some phosphorus-containing
FRs.15 Also, it can be clearly observed that the char yields of (3)/DDM were higher than that
of (4)/DDM with identical phosphorus content. It was probably attributed to the reason that
the polymer with a high content of aromatic possessed better fire retardancy and thermal
stability.13,15,16
Analysis of Flame-Retardant Properties
The UL-94 flammability ratings and the LOI values of the epoxy thermosets were
listed in Table 1. UL-94 V-1 rating was obtained with the phosphorus content of 0.75 wt%.
DGEBA/DDM
-0.75)/DDM
100
80
60
40
20
0
100
80
60
40
20
0
DGEBA/DDM
(
3
(
(
(
(
4-0.75)/DDM
4-1.00)/DDM
4-1.25)/DDM
4-1.50)/DDM
(
(
(
3
3
3
-1.00)/DDM
-1.25)/DDM
-1.50)/DDM
0
100
200
300
400
500
600
700
800
0
100
200
300
400
500
600
700
800
Temperature
(
OC
)
Temperature(oC)
Figure 1 TGA thermograms of (3)/DDM thermosets and (4)/DDM thermosets.

1568
L. XIAO ET AL.
And with increasing of phosphorus content, the UL-94 V-0 ratings were achieved. In ad-
dition, compared with the LOI value of 25.1 of DGEBA/DDM system, the LOI values of
phosphorus-containing epoxy thermosets increased markedly from 36.0 to 37.2. And the
LOI values of (3)/DDM were higher than that of (4)/DDM with identical phosphorus con-
tents. Therefore, the UL-94 flammability ratings and the LOI values clearly demonstrated
that the flame retardancy can be enhanced significantly by increasing the phosphorus con-
tent in epoxy systems, which was in excellent agreement with the consequence from the
char yield.
CONCLUSION
Two novel phosphorus–nitrogen-containing FRs (3) and (4) with four OH groups
were synthesized, and were used as co-curing agent for epoxy system. The Tg values, Td
values, char yields, and the LOI values of (3)/DDM were relatively higher than that of
(4)/DDM system with same phosphorus contents.
EXPERIMENTAL
Materials
DGEBA(E51, epoxy equivalent = 0.51 mol/100 g) was provided by Guangzhou
Dute Chemical Co., Ltd., China. DOPO was supplied by Huizhou Shengshida Technology
Co., Ltd., China. 4,4ꢀ-diaminodiphenylmethane (DDM), 4,4ꢀ-diaminobiphenyl, and 1,4-
phenylenediamine were all obtained from Shanghai Aladdin Reagent Co., Ltd., China.
3,4-dihydroxybenzaldehyde was received from Shanghai Energy Chemical, China. Ethanol
was acquired from Tianjin Damao Chemical Reagent Factory, China. The Supplemental
Materials (Figures S1–S16) contain extensive spectroscopic characterization of the novel
compounds 1–4.
Preparation of 1,1ꢀ,2,2ꢀ-tetra-hydroxyl-{4ꢀꢀ,4ꢀꢀꢀ- bi-phenylene-bis[amino-methyl]}-
bis-phenol (1)
To a 500 mL three-neck and round-bottom glass flask equipped with a condenser and
a stirrer was added 4,4ꢀ-diaminobiphenyl (9.212 g, 0.05 mol), 3,4-dihydroxybenzaldehyde
(13.812 g, 0.1 mol), and ethanol (200 mL). The reaction mixture was stirred at the tem-
perature of 50◦C for 2 h. After cooling down to room temperature, the precipitate was
filtered and washed three times with ethanol. The deep orange-red powder (19.102 g, 90%
yield) was collected after drying for more than 8 h in a vacuum oven. The structure of
1
(1) was shown in Scheme 1. H NMR (DMSO-d6, ppm): δ = 9.35–10.13 (meta-position
ꢀ
ꢀ
ꢀ
ꢀ
OH, OH , para-position OH, OH ), 8.46 (H7), 7.70–7.72 (H3, H3 ), 7.56 (H7 ), 7.38–7.45
(H5, H5 , H9), 7.24–7.31 (H9 , H10), 6.87–6.93 (H6, H6 ), 6.67 (H10 ). 13C NMR (DMSO-d6,
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ppm): δ = 160.4 (C1), 159.6 (C1 ), 152.6 (C2), 151.4 (C2 ), 149.8 (C7), 149.7 (C7 ), 148.6
ꢀ
ꢀ
ꢀ
ꢀ
(C3), 147.0 (C3 ), 146.4 (C8), 146.1 (C8 ), 138.4 (C4), 137.2 (C4 ), 129.4 (C5), 128.6 (C5 ),
ꢀ
ꢀ
127.4–127.6 (C9), 126.4–126.5 (C9 ), 125.0 (C11), 123.0 (C11 ), 121.9–122.0 (C10), 116.0
(C10 ), 114.6–115.0 (C6, C6 ). FTIR absorption (KBr, cm−1): 1647 (C N), 3347 (OH).
ꢀ
ꢀ
MS: m/z = 423.1334 [M−H]−.
Preparation of 4,4ꢀ-diaminobiphenyl and, 1,1ꢀ,2,2ꢀ-tetra-hydroxyl-{4ꢀꢀ,4ꢀꢀꢀ-
phenylene-bis[amino-methyl]}-bis-phenol (2).
Compound (2) was acquired in a similar synthetic procedure to compound (1).
The deep yellow powder (27.870 g, 80% yield) was collected after the reaction of 1,4-
phenylenediamine (10.814 g, 0.1 mol) and 3,4-dihydroxybenzaldehyde (27.624 g, 0.2 mol),

SYNTHESES OF TWO DOPO-BASED REACTIVE ADDITIVES
1569
as Scheme 1 shown the structure of (2). 1H NMR (DMSO-d6, ppm): δ = 9.32–9.60 (meta-
position OH, para-position OH), 8.43 (H7), 7.41 (H3), 7.25 (H9), 7.18–7.21 (H5), 6.83–6.85
(H6). 13C NMR (DMSO-d6, ppm): δ = 159.2 (C1), 149.2 (C2), 149.1 (C7), 145.5 (C8), 128.1
(C3), 122.3 (C5), 121.6 (C9), 115.4 (C4), 114.1 (C6). FTIR absorption (KBr, cm−1): 1625
(C N), 3479 (OH). MS: m/z = 347.1040 [M−H]−.
Preparation of 1,1ꢀ,2,2ꢀ-tetra-hydroxyl-{4ꢀꢀ, 4ꢀꢀꢀ-biphenylene-bis[amino-((10ꢀꢀꢀꢀ-O-
10ꢀꢀꢀꢀ-H-9ꢀꢀꢀꢀ-oxa-10ꢀꢀꢀꢀλ5-phosphaphenanthrene -10ꢀꢀꢀꢀ-yl))-methyl]}-bisphenol (3).
To a 500 mL three-neck and round-bottom glass flask equipped with a condenser
and a stirrer was added (1) (21.224 g, 0.05 mol), DOPO (21.600 g, 0.1 mol) and ethanol
(300 mL), the reaction mixture was stirred at 50◦C for 10 h. After cooling down to room
temperature, the precipitate was filtered and washed three times with ethanol. The terreous
powder (3) [36.400 g, 85% yield; mp (DSC): 183◦C; Td = 268◦C (TGA)] was collected
after drying for more than 8 h in a vacuum oven. Scheme 1 described the structure of (3).
1H NMR (DMSO-d6, ppm): δ = 8.81–8.93 (meta-position OH, OHꢀ, para-position
OH, OHꢀ), 8.04–8.17 (H11, H11 , H17, H17 , H14), 7.73–7.74 (H14 , H12, H12 ), 7.55 (H13,
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
H13 ), 7.50 (H19, H19 ), 7.45 (H18, H18 ), 7.20 (H3),ꢀ7.05 (H3 , H5, H5 , H6, H6 ), 6.82–6.87
ꢀ
ꢀ
ꢀ
ꢀ
(H20, H20 ), 6.61–6.64 (H9, H9 , H22, H22 , NH, NH ), 4.82 (H7), 4.37 (H7 ).
13
ꢀ
ꢀ
C NMR (DMSO-d6, ppm): δ = 149.4 (C1), 149.3 (C1 ), 146.0 (C2), 145.8 (C2 ),
ꢀ
ꢀ
ꢀ
145.5 (C21), 145.4 (C21 ), 135.8 (C8), 135.7 (C8 ), 134.1 (C16), 134.0 (C16 ), 132.2 (C12),
ꢀ
ꢀ
ꢀ
ꢀ
132.1 (C12 ), 131.3 (C14), 131.1 (C14 ), 130.2 (C19), 130.1 (C19 ), 128.9 (C13), 128.8 (C13 ),
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
126.2–126.4 (C3, C3 , C5, C5 , C17, C17 ), 126.0 (C4), 125.9 (C4 ), 125.2 (C23, C23 ), 125.1
ꢀ
ꢀ
ꢀ
(C18), 124.9 (C18 ), 124.5 (C11), 124.4 (C11 ), 123.8 (C10), 123.7 (C10 ), 122.3 (C15), 122.2
ꢀ
ꢀ
ꢀ
ꢀ
(C15 ), 120.6 (C20), 120.5 (C20 ), 120.1 (C6), 120.0 (C6 ), 116.3–116.4 (C9), 115.6 (C9 ),
ꢀ
ꢀ
114.4 (C22, C22 ), 55.3–56.7 (C7, C7 ).
31P NMR (DMSO-d6, ppm): δ = 34.1, 31.3.
FTIR absorption (KBr, cm−1): 3503 (N–H), 3275 (OH), 1611 (P – Ph), 1282 (C – N),
1234 (P O). MS: m/z = 855.2029 [M−H]−.
Preparation of
1,1ꢀ,2,2ꢀ-tetra-hydroxyl-{4ꢀꢀ,4ꢀꢀꢀ-phenylene-bis[amino-((10ꢀꢀꢀꢀ
-
O-10ꢀꢀꢀꢀ- H-9ꢀꢀꢀꢀ- oxa-10ꢀꢀꢀꢀλ5-phosphaphenanthrene-10ꢀꢀꢀꢀ-yl))-methyl]}-bis-phenol (4).
(4) was obtained in a similar synthetic procedure to compound (3). The shallow
terreous powder (4) [31.215 g, 80% yield; mp (DSC): 204◦C; Td = 275◦C (TGA)] was
collected after the reaction of (2) (17.419 g, 0.05 mol) and DOPO (21.600 g, 0.1 mol). The
structure of (4) was depicted in Scheme 1.
1H NMR (DMSO-d6, ppm): δ = 8.74–8.88 (meta-position OH, OHꢀ, para-position
OH, OHꢀ), 813–8.16 (H11, H11 , H17, H17 ), 7.95–7.80 (H14, H14 ), 7.70–7.74 (H12, H12 ),
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
7.50–7.52 (H13, H13 ), 7.39–7.43 (H19, H19 ), 7.28–7.32 (H18, H18 ), 6.98–7.02 (H3, H3 ),
ꢀ
ꢀ
ꢀ
ꢀ
6.72–6.75 (H20, H2ꢀ0 ), 6.59–6.61 (H5, H5 ), 6.53–6.54 (H6, H6 ), 6.25–6.31 (H9, H9 ),
ꢀ
5.66–5.73 (NH, NH ), 4.46–4.63 (H7, H7 ).
13
ꢀ
ꢀ
C NMR (DMSO-d6, ppm): δ = 162.2 (C1), 162.1 (C1 ), 148.8 (C2), 148.7 (C2 ),
ꢀ
ꢀ
ꢀ
144.8 (C21), 144.7 (C21 ), 138.8 (C8), 138.6 (C8 ), 135.1 (C16), 135.0 (C16 ), 133.3 (C12),
ꢀ
ꢀ
ꢀ
ꢀ
133.2 (C12 ), 131.6 (C14), 131.5 (C14 ), 130.7 (C19), 130.6 (C19 ), 128.2 (C13), 128.1 (C13 ),
ꢀ
ꢀ
ꢀ
ꢀ
125.6 (C3, C3 ), 125.4 (C5), 125.3 (C5 ), 124.6 (C17), 124.5 (C17 ), 123.9 (C4), 123.8 (C4 ),
ꢀ
ꢀ
ꢀ
123.6 (C18), 123.4 (C18 ), 121.8 (C11), 121.7 (C11 ), 120.0 (C10), 119.9 (C10 ), 119.5 (C15),
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
119.4 (C15 ), 115.9 (C20), 115.8 (C20 ), 115.0 (C6, C6 ), 114.8 (C9, C9 ), 55.9–56.1 (C7, C7 ).
31P NMR (DMSO-d6, ppm): δ = 34.7, 31.3.
FTIR absorption (KBr, cm−1): 3556 (N–H), 3278 (OH), 1610 (P – Ph), 1275 (C – N),
1229 (P O). MS: m/z = 779.1730 [M−H]−.

1570
L. XIAO ET AL.
Preparation of the Epoxy Thermosets
Taking the active proton numbers of amino and phenol groups in (3), (4), and DDM
into account, the DDM, (3), and (4) with an equivalent ratio to epoxy resins of 1:1 were
mixed. The resins were cured in a mold at 140◦C for 2 h, 180◦C for 2 h, respectively. Finally,
epoxy thermosets were cooled down gradually to room temperature to avoid cracking. The
phosphorus contents of the epoxy thermosets were 0.75, 1.00, 1.25, and 1.50 wt%. And the
epoxy thermosets were labeled as (n-m)/DDM (n stands for the (3) or (4), and m for the
percentage content of phosphorous in thermosets) and listed in Table 1.
Characterization
Fourier transform infrared (FTIR) spectra were recorded on a Bruker Vertex 70
infrared spectrophotometer by KBr disc method with the optical range of 400–4000 cm−1
.
1H NMR, 13C NMR, and 31P NMR spectra were registered with a Bruker spectrometer by
using DMSO-d6 as a solvent. Mass spectra were performed on a Waters Quattro X Premier
mass spectrometer. DSC scans were obtained in the way that samples of approximately
5–10 mg were scanned in the range of 25–300◦C under argon atmosphere at a heating rate of
10◦C/min by using a Mettler-Toledo DSC 823e. And the glass transition temperature (Tg)
was taken as midpoint of enthalpy transitions along the thermal analysis curve. Thermal
gravimetric analyses (TGA) of samples were carried out with Mettler-Toledo TGA/DSC1
from 50 to 800◦C under argon atmosphere at a heating rate of 10◦C/min. The UL-94 test was
measured according to the testing procedure of vertical burning test with the dimensions
127 × 13 × 3 mm3 of each sample. During the test, five samples hung vertically were
ignited for two 10 s. After the first ignition, the time for the polymer to self-extinguish (t1)
was gained when the flame removed. Cotton ignition would be noted if polymer dripping
occurred during the test. After cooling, a second ignition was performed on the same
sample, and the self-extinguish time (t2) and dripping characteristics were also recorded.
The polymer would achieve the UL-94 V-0 flammability rating if t1 + t2 of each sample
did not exceed 10 s without any dropping. If t1 + t2 was in the range of 10–30 s without
any dropping, the polymer would reach the UL-94 V-1 flammability rating. The LOI test
was performed according to the testing procedure of GB/T 2406–2009 with the dimensions
(70–150) × 6.5 × 3 mm3 of each sample.
SUPPLEMENTAL MATERIAL
Supplementary data for this article can be accessed on the publisher’s website,
www.tandfonline.com/gpss
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