Synthesis of an intrinsically flame retardant bio-based benzoxazine resin

Article abstract of DOI:10.1016/j.polymer.2016.05.053

An intrinsically flame retardant bio-based benzoxazine (diphenolic acid pentaerythritol caged phosphate benzoxazine, DPA-PEPA-Boz) monomer was synthesized from bio-based diphenolic acid (DPA) using a four-step process. The monomer of DPA-PEPA-Boz was characterized by FT-IR, ¹H NMR and ¹³C NMR. The curing behavior of DPA-PEPA-boz was studied and compared with those of DPA based benzoxazine (DPA-Boz) and DPA ester derivative (MDP) based benzoxazine (MDP-Boz) without PEPA by means of non-isothermal differential scanning calorimetry. The results indicated that DPA-PEPA-Boz system showed a two-stage curing, assigned to the exothermic opening reactions of oxazine rings and P-O-C ring in PEPA respectively, while the DPA-Boz and MDP-Boz showed a one-stage curing. In addition, the effect of the introduction of PEPA on thermal and inflammable properties of the resin was evaluated. The residual char of the cured DPA-PEPA-Boz (P-DPA-PEPA-Boz) after 400 °C was much higher than those of cured DPA-Boz (P-DPA-Boz) and cured MDP-Boz (P-MDP-Boz) under nitrogen and air atmospheres. Meanwhile, total heat release (THR), peak heat release rate (PHRR) and heat release capacity (HRC) of P-DPA-PEPA-Boz were about half of those of P-DPA-Boz and P-MDP-Boz. P-DPA-PEPA-Boz had a limiting oxygen index (LOI) of 33.5% and achieved V0 rating in UL94 test. P-DPA-PEPA-Boz behaved as a very good intrinsic thermal and flame retardant bio-based benoxazine resin.

Full text of DOI:10.1016/j.polymer.2016.05.053

Accepted Manuscript
Synthesis of an intrinsically flame retardant bio-based benzoxazine resin
Hongqiang Yan, Chuang Sun, Zhengping Fang, Xiaoqing Liu, Jin Zhu, Hao Wang
PII:
S0032-3861(16)30443-8
10.1016/j.polymer.2016.05.053
JPOL 18714
DOI:
Reference:
To appear in: Polymer
Received Date: 28 February 2016
Revised Date: 6 May 2016
Accepted Date: 19 May 2016
Please cite this article as: Yan H, Sun C, Fang Z, Liu X, Zhu J, Wang H, Synthesis of an intrinsically
flame retardant bio-based benzoxazine resin, Polymer (2016), doi: 10.1016/j.polymer.2016.05.053.
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ACCEPTED MANUSCRIPT
Graphic Abstract
An intrinsically flame retardant bio-based benzoxazine (DPA-PEPA-boz) has
been synthesized and behaved as a very good intrinsic thermal stable and flame
retardant bio-based benzoxazine resin.

ACCEPTED MANUSCRIPT
Synthesis of an intrinsically flame retardant bio-based
benzoxazine resin
a
∗
a
a
b
b
Hongqiang Yan , Chuang Sun , Zhengping Fang , Xiaoqing Liu , Jin Zhu , Hao
c
Wang
a
Lab of Polymer Material and Engineering, Ningbo Institute of Technology, Zhejiang
University, Ningbo Zhejiang 315100, China.
b
Ningbo Key Laboratory of Polymer Materials, Ningbo Institute of Materials
Technology and Engineering, Chinese Academy of Sciences Institution, Ningbo,
Zhejiang 315201, China.
c
Centre of Excellence in Engineered Fibre Composites (CEEFC), University of
Southern Queensland, Toowoomba, Queensland 4350, Australia.
ABSTRACT: An intrinsically flame retardant bio-based benzoxazine (diphenolic
acid pentaerythritol caged phosphate benzoxazine, DPA-PEPA-Boz) monomer was
synthesized from bio-based diphenolic acid (DPA) using a four-step process. The
1
13
monomer of DPA-PEPA-Boz was characterized by FT-IR, H NMR and C NMR.
The curing behavior of DPA-PEPA-boz was studied and compared with those of DPA
based benzoxazine (DPA-Boz) and DPA ester derivative (MDP) based benzoxazine
(MDP-Boz) without PEPA by means of non-isothermal differential scanning
calorimetry. The results indicated that DPA-PEPA-Boz system showed a two-stage
curing, assigned to the exothermic opening reactions of oxazine rings and P-O-C ring
in PEPA respectively, while the DPA-Boz and MDP-Boz showed an one-stage curing.
∗
Corresponding author: Tel(Fax):+86 574 88130140. E-mail address: yanhongqiang@nit.net.cn (HQ Yan).

ACCEPTED MANUSCRIPT
In addition, the effect of the introduction of PEPA on thermal and inflammable
properties of the resin was evaluated. The residual char of the cured DPA-PEPA-Boz
o
(
P-DPA-PEPA-Boz) after 400 C was much higher than those of cured DPA-Boz
(P-DPA-Boz) and cured MDP-Boz (P-MDP-Boz) under nitrogen and air atmospheres.
Meanwhile, total heat release (THR), peak heat release rate (PHRR) and heat release
capacity (HRC) of P-DPA-PEPA-Boz were about half of those of P-DPA-Boz and
P-MDP-Boz. P-DPA-PEPA-Boz had a limiting oxygen index (LOI) of 33.5 % and
achieved V0 rating in UL94 test. P-DPA-PEPA-Boz behaved as a very good intrinsic
thermal and flame retardant bio-based benoxazine resin.
Keywords: diphenolic acid, bio-based polymer, benzoxazine, intrinsically flame
retardant, synthesis
1
. Introduction
The development of environmentally friendly polymers from bio-based materials
and compounds is one of the current challenges and also opportunities for polymer
chemistry. Many new bio-based compounds have been developed and commercialized
for the production of bio-based polymers, which have the potential of significant
economic and environmental benefits to the society and creating new property
profiles that the traditional nonrenewable polymers do not exhibit[1,2]. Up to now,
much effort has been made to synthesize polylactic acid, polycarbonates, polyesters,
epoxy resin and benzoxazine resin from renewable feedstock, such as rosin,
cyclodextrins, soybean oil, diphenolic acid, itaconic acid, etc[3-10].
Benzoxazine resins (Bozs) have attracted increasing attention in the past decade

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due to their excellent high temperature stability, low water absorption, good dielectric
properties and structure-design flexibility, in addition to their zero shrinkage or a
slight expansion upon curing[11-14]. These good properties give them a huge
potential in industrial applications, such as high-speed printed circuit boards,
aerospace structural composites, etc[15-19]. The bisphenol A (BPA) based Boz
(
BPA-Boz) stands out from many types of Bozs due to its high structural integrity and
superior properties[20]. Diphenolic acid (DPA), which has a structure similar to BPA
Fig. 1), can be prepared from low-grade lignin and cellulose biomass resources[21].
(
Through plant photosynthesis to synthesize cellulose, it is a renewable material that
can alleviate our current large dependence on petroleum for chemicals, preserve the
planet nature resources, and obtain good environmental and economic benefits[22].
DPA is commercially available and much cheaper than BPA and has the ability to
introduce functional carboxyl group into the polymer structure. Therefore DPA is
believed to be a cheap bio-based compound in large scale and can be used as a BPA
alternative to synthesize new polymers. In the last decade, DPA has attracted much
attention from researchers to replace BPA for synthesizing new polyesters,
polycarbonates and Bozs[7, 23-27].
COOH
CH
CH
C
2
CH
C
3
2
HO
OH
HO
OH
CH
3
CH
3
BPA
DPA
Fig.1 The structure comparison between BPA and DPA.
With the rapid development of aerospace, microelectronics and energy industries,
there is an urgent requirement to further improve the properties of Bozs, such as heat

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resistance, flame retardancy, toughness, low dielectric constant, etc[28]. The flame
retardancy of BPA-Boz cannot meet the more demanding requirement. Challenges
also exist for the diphenolic acid based Boz (DPA-boz) in this regard. For example,
DPA-Boz has been modified using DOPO or DOPO-2Me to prepare Boz foams[27].
But the choice of flame retardant is limited due to the poor compatibility between
flame retardant and Boz. Fortunately, with the carboxyl group in the DPA-boz
structure, it is possible to introduce flame retardant moieties to improve its flame
retardancy. Common flame retardants contain N, P, Si and halogen elements.
Researchers pay more attention to P containing flame retardants because of their
better flame retardant effect, less smoke, and lower emissions of harmful substances.
A
representative
P
containing
flame
retardant
is
4
-(hydroxymethyl)-1-oxido-2,6,7-trioxa-1-phosphabicyclo[2.2.2]octane
(PEPA),
which was synthesized by Verkade for the first time in the 1960s[29]. It has aroused
people's great interest due to the highly symmetrical cage structure in its molecule.
PEPA can be used as intumescent type flame retardant because its molecule contains
acid source and carbonization agent, which resulting in characteristics of good
char-forming ability and excellent thermal stability. Synthesis of cage phosphate ester
compounds and their application in flame retardant materials have received wide
attention in recent years[30-33].
In this study, an intrinsically flame retardant bio-based Boz (DPA-PEPA-boz) was
synthesized from renewable diphenolic acid. The material was characterized by
1
13
fourier transform infrared (FTIR) spectrophotometer, H and C nuclear magnetic

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resonance (NMR). Its curing behavior, thermal and inflammable properties were
evaluated and compared with DPA based Boz (DPA-boz) and DPA ester derivative
(MDP) based Boz (MDP-boz).
2
. Experimental
2
.1. Materials
The following chemicals were analytical purity, obtained from Aladdin Industrial
Corporation: diphenolic acid (98%), paraformaldehyde (95%), aniline (99.5%),
pentaerythritol (98%), p-toluene sulfonic acid (99%), toluene (99%), phosphorus
o
oxychloride (98%), ethyl acetate (99.5%), petroleum ether (boiling range: 60~90 C),
sodium sulfate (99%), sodium hydrogen carbonate (99%), sodium chloride (99.5%),
acetonitrile (99%), chloroform (99%), sodium hydroxide (96%), hydrochloric acid
(38%), diethyl ether (99.5%), hexane (95%), 1,4-dioxane (99.5%), methanol (99.5%).
All solvents were purified by standard procedures.
2
.2. Synthesis of DPA-Boz monomer
The synthesis pathway of DPA-Boz was as follows (Scheme 1):
NH
2
2
NHCH OH
N
3
n
3
(CH
2
O)
n
3n
n
N
N
1
,3,5-Triphenylhexahydro-1,3,5-triazine
OH
O
OH
O
3
6(CH
2
O)
n
2
N
3
O
N
O
N
2
6H O
N
N
HO
OH
Diphenolic acid based benzoxazine (DPA-Boz)
Scheme 1 Schematic pathway of synthesis of DPA-Boz.

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Synthesis of 1,3,5-triphenylhexahydro-1,3,5-triazine[34]: Paraformaldehyde
o
(
0.02 mol) and aniline (0.01 mol) were mixed for 35 min at 70 C. The product was
dissolved in chloroform, washed with a 1 mol/L sodium hydroxide aqueous solution
and recrystallized from diethyl ether. White crystals were obtained with a yield of
7
0.2 %. Characterization of the crystal was summarized as follows:
-1
IR (v/cm ): 1599, 1499, 755 and 689 (monosubstituted benzene, v); 1334 (C-N-C, as);
1
203 ( C-N-C, s); 1163 ( C-N-C, γ ).
1
H NMR (ppm, CDCl ): 4.88 (d, N-CH -N, 6H); 6.76, 7.06 and 7.16 (q, -Ar-H, 15H).
3
2
1
3
C NMR (ppm, CDCl ): 67.35 (-N-CH -N-, 3C); 120.58, 129.60, 117.52 and 149.0
3
2
(-N-Ar, 18C).
Synthesis of DPA-Boz monomer[35]: 1,3,5-Triphenylhexahydro-1,3,5-triazine
(0.02 mol), paraformaldehyde (0.083 mol), diphenolic acid (0.03 mol) and 150 mL of
toluene were placed into 500 mL three-necked round-bottom flask. The reaction
o
mixture was heated at 110 C for 6 h. The resulting light orange solution was filtered
and concentrated at reduced pressure to obtain yellow syrup. Finally, the yellow syrup
was subsequently dried in a vacuum oven giving a yellowish solid of DPA-Boz with a
yield of 94.8%. Characterization of DPA-boz was summarized as follows:
-1
IR (v/cm ): 3435, 1452 (-OH, v); 1705 (C=O, v); 1257 (C-O, v); 1234, 1165 (C-O-C,
v); 943 (C-H of oxazine ring, γ); 1496 (1,2,4-trisubstituted benzene, v)
1
H NMR (ppm, CDCl ): 7.30~6.70 (t, Ar-H, 16H); 5.34 (s, O-CH -N, 4H); 4.58 (s,
3
2
Ar-CH -N, 4H); 2.35 (t, -C-CH -CH -CO-, 2H); 2.13 (t, -C-CH -CH -CO-, 2H); 1.53
2
2
2
2
2
(
s, -CH , 3H).
3

ACCEPTED MANUSCRIPT
1
3
C NMR (ppm, CDCl ): 179.9 (-CO-, 1C); 152.5, 141.1, 126.9, 125.3, 120.4 and
3
116.7 (-C-Ar-O-, 12C); 148.5, 129.4, 121.4 and 118.1 (-N-Ar, 12C); 79.2 (-O-C-N-,
2
C); 50.7 (-Ar-C-N-Ar, 2C); 44.6 (CH -C-, 1C); 36.4 (-C-CH -CH -CO-O-, 1C); 30.2
3
2
2
(
-C-CH -CH -CO-O-, 1C); 27.8 (-CH , 1C).
2 2 3
2
.3. Synthesis of MDP-Boz monomer
The synthesis pathway of MDP-Boz was as follows (Scheme 2):
3
H C
OH
O
O
O
3
3
CH OH
HO
OH
HO
OH
3
H C
O
3
H C
O
O
O
3
6(CH
2
O)
n
2
N
3
O
N
O
N
2
6H O
N
N
HO
OH
Methyl diphenolic acid based benzoxazine (MDP-Boz)
Scheme 2 Schematic pathway of synthesis of MDP-Boz.
Synthesis of Methyl diphenolic acid (MDP) [35]: A 500 mL round-bottom
flask equipped with a condenser was charged with diphenolic acid (0.13 mol),
-2
p-toluenesulfonic acid monohydrate (2×10 mol), trimethyl orthoformate (0.19 mol)
and 100 mL of methanol. The mixture was refluxed for 16 h, then the methanol was
removed at reduced pressure. The resulting syrup was dissolved in ethyl ether and
washed three times with a NaHCO saturated solution and with water respectively.
3
Finally, the ethyl ether was removed with a rotary evaporator and the product was
dried at reduced pressure and room temperature. The resulting product of MDP was
milled and used without further purification in the next step. A yield of 88% was

ACCEPTED MANUSCRIPT
obtained. Characterization of MDP was summarized as follows:
-1
IR (v/cm ): 3385 ( -Ar-OH, s); 2956 ( -CH and -CH -, s); 1703 (C=O, v); 1608
3
2
(
-ArH, s); 1220 (C-O-C, v); 1450.5 (-CH -, v); 1386.2 (-CH , v);
2 3
1
H NMR (ppm, DMSO): 9.23(t, Ar-OH, 2H); 6.91(t, -Ar-H, 4H); 6.71(t, -Ar-H, 4H);
3
.61(t, -CO-O-CH , 3H,); 2.25 (t, -C-CH -CH -CO-, 2H,); 2.11(t, -C-CH -CH -CO-,
3
2
2
2
2
2
H,); 1.5 (s, -C-CH , 3H).
3
Synthesis of MDP-Boz monomer[35]: A 250 ml 3-necked round-bottom flask
equipped with a magnetic stirrer and a condenser was charged with
1
,3,5-triphenylhexahydro-1,3,5-triazine (0.02 mol), paraformaldehyde (0.08 mol),
o
MDP (0.03 mol) and 120 mL of toluene. The mixture was refluxed at 110 C for 20 h.
After cooling to room temperature, MDP-boz monomer was filtered, dissolved in
ethyl ether, and washed five times with a 3 mol/L sodium hydroxide solution and with
water respectively. After washing, the organic phase was dried over sodium sulfate
and the solvent was evaporated at reduced pressure and room temperature. A pale
yellowish solid of MPD-Boz was obtained with a yield of 92.2%. Characterization of
MDP-boz was summarized as follows:
-1
IR (v/cm ): 1734 (C=O, v); 1234, 1030 (C-O-C, v); 945 (C-H of oxazine ring, γ);
1
496 (1,2,4-trisubstituted benzene, v); 1368 (-CH , v) 1456.5 (-CH -, v).
3 2
1
H NMR (ppm, DMSO): 7.32~6.74 (t, Ar-H, 16H); 5.37 (s, O-CH -N, 4H); 4.62 (s,
2
Ar-CH -N, 4H); 3.63 (t, -CO-O-CH , 3H); 2.40 (t, -C-CH -CH -CO-, 2H); 2.14 (t,
2
3
2
2
-
C-CH -CH -CO-, 2H); 1.56 (s, -CH , 3H).
2 2 3
1
3
C NMR (ppm, DMSO): 174.4 (-CO-, 1C); 152.5, 141.2, 126.9, 125.3, 120.3 and

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116.6 (-C-Ar-O-, 12C); 148.5, 129.3, 121.3 and 118.0 (-N-Ar, 12C); 79.2 (-O-C-N-,
2
C); 51.7 (-Ar-C-N-Ar, 2C); 50.7 (-CO-O-CH ); 44.6 (-C-CH , 1C); 36.6
3
3
(
-C-CH -CH -CO-O-, 1C); 30.1 (-C-CH -CH -CO-O-, 1C); 27.8 (-C-CH , 1C);
2 2 2 2 3
2
.4. Synthesis of DPA-PEPA-Boz monomer
The synthesis pathway of diphenolic acid pentaerythritol caged phosphate
benzoxazine (DPA-PEPA-Boz) was as follows (Scheme 3):
OH
OH
O
O
POCl
3
O
P
O
3HCl
OH
OH
OH
Pentaerythritol caged phosphate (PEPA)
O
P
O
O
O
OH
O
O
O
HO
OH
O
P
O
2
H O
O
O
OH
HO
OH
Diphenolic acid pentaerythritol phosphate (DPA-PEPA)
O
P
O
P
O
O
O
O
O
O
O
3
O
O
6(CH
2
O)
n
2
N
3
O
2
6H O
N
N
O
N
O
HO
OH
N
Diphenolic acid pentaerythritol caged phosphate benzoxazine (DPA-PEPA-Boz)
Scheme 3 Schematic pathway of synthesis of DPA-PEPA-Boz.
Synthesis of pentaerythritol caged phosphate (PEPA)[29]: Pentaerythritol
PEA) (0.25 mol) and 1,4-dioxane (80 ml) were placed into a 250 ml four-necked
(
round-bottom flask equipped with a magnetic stirring device, a condensation reflux
device, a thermometer and a constant pressure feeding hopper. 1 mol/L sodium

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hydroxide aqueous solution was used to absorb the exhaust gas. Under a flow of N2,
phosphorus oxychloride was put into the constant pressure feeding hopper, adjusting
the cock to make sure the phosphorus oxychloride gradually dripped into the flask
within 2 h. Then the mixture was refluxed for 5 h, cooled gradually to room
temperature and filtered out the white precipitate. The white precipitate was washed
once with 100 ml 1,4-dioxane followed by twice with 200 ml hexane, and then dried
o
in a vacuum oven at 80 C. Then white powder (PEPA) was obtained at a yield about
8
7.6 %. Characterization of the PEPA was summarized as follows:
-1
IR (v/cm ): 1299 (P=O, v); 1025 ( P-O-C, v); 1152 (C(CH ) -, v); 959 (-CH -OH, v);
2
4
2
8
76, 767, 669 and 632 (-P-O-C, v); 2963 (-CH -, v); 2910 (-CH -, γ).
2
2
1
H NMR (ppm, DMSO): 5.1 (s,
CH2-C, 6H).
C NMR (ppm, DMSO): 77.1 (-O-CH-C, 3C); 58.4 (C(CH ) -, 1C); 39.4 (-CH -OH,
-
OH, 1H); 3.31 (s,
-C-CH -OH, 2H); 4.52 (d,
2
-P-O-
1
3
2
4
2
1
C).
3
1
P NMR (ppm, DMSO): -7.02.
Synthesis of diphenolic acid pentaerythritol phosphate (DPA-PEPA):
Diphenolic acid (DPA) (0.05 mol), PEPA (0.1 mol), p-toluene sulfonic acid (2.86 g)
and 120 ml acetonitrile were placed into a 250 ml three-necked round-bottom flask
equipped with a magnetic stirring device, a condensation reflux device and a
o
thermometer. Under a flow of N , the mixture was heated at 70 C for 24 h and
2
evaporated through the rotary evaporation to obtain a pink powder. The pink powder
was dissolved in ethyl acetate, then washed three times with saturated sodium

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hydrogen carbonate solution and saturated sodium chloride solution respectively. The
products dissolved in ethyl acetate were separated by the chromatographic column.
The selected expansion agent used was a mixture of ethyl acetate and petroleum ether
(volume 3:1). A white powder (DPA-PEPA) was obtained after drying in a vacuum
o
dryer at 40 C, and its yield was 80.2 %. Characterization of the DPA-PEPA was
summarized as follows:
-1
IR (v/cm ): 1735 (C=O, v); 1261 (C-O-C, as); 1157 (C(CH ) -, v); 2956 (-CH -,s);
2
4
2
3
376 (-OH, v); 863, 838, 672, 577 (-P-O-C-, v).
1
H NMR (ppm, DMSO): 9.22 (s, -Ar-OH, 2H); 6.96 and 6.67 (d, -Ar-H, 8H); 4.63
s,-P-O-CH -C-, 6H); 3.91 (d, -CO-O-CH -C-, 2H); 2.25 (t, -CH -CH -CO, 2H); 2.09
(
2
2
2
2
(
t, -C-CH -CH -, 2H); 1.46 (s, -CH , 3H).
2
2
3
1
3
C NMR (ppm, DMSO): 172.9 (-C-CO-O-, 1C); 155.2, 138.9, 127.6 and 115.5
(
HO-Ar-, 12C); 75.8 (-C-CH -O-P-, 3C); 59.5 (-CO-O-CH -C, 1C); 43.5 (CH -C-,
2
2
3
1
C); 36.9 (-CH -CH -CO-O-, 1C); 35.9 (-CO-O-CH -C-CH -, 1C); 29.5
2 2 2 2
(
-C-CH -CH -CO-, 1C); 27.1 (-C-CH , 1C).
2 2 3
Synthesis of diphenolic acid pentaerythritol caged phosphate Boz
(DPA-PEPA-Boz): A 250 ml three-necked round-bottom flask equipped with a
magnetic
stirrer
and
a
condenser
was
charged
with
1
,3,5-triphenylhexahydro-1,3,5-triazine (0.005 mol), paraformaldehyde (0.018 mol),
DPA-PEPA (0.0075 mol) and 120 ml toluene. Under a flow of N , the mixture was
2
refluxed for 20 h. After cooling to room temperature, the Boz monomer was filtered,
dissolved in ethyl ether and washed five times with 3 mol/L sodium hydroxide

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aqueous solution. Then the organic phase was dried over sodium sulfate and the
solvent was evaporated at reduced pressure and room temperature. A light yellow
powder (DPA-PEPA-boz) was obtained with a yield of 85.7 %. Characterization of the
DPA-PEPA-Boz was summarized as follows:
-1
IR (v/cm ): 1741 (C=O, v); 1234, 1041 (C-O-C, v); 1313 (P=O, v); 1155 (C-(CH ) -,
2
4
v); 858, 754, 696 (P-O-C-C-P, v); 947 (C-H of oxazine ring, γ); 1498
(1,2,4-trisubstituted benzene, v)
1
H NMR (ppm, DMSO): 7.25~6.64 (t, Ar-H, 16H); 5.42 (s, O-CH -N, 4H); 3.89 (s,
2
Ar-CH -N, 4H); 4.62 (t, -P-O-CH -C, 6H); 4.03 (t, -CO-O-CH -C, 2H); 2.26 (t,
2
2
2
-
C-CH -CH -CO-, 2H); 2.09 (t, -C-CH -CH -CO-, 2H); 1.48 (s, -CH , 3H).
2 2 2 2 3
1
3
C NMR (ppm, DMSO): 174.7 (-CO-, 1C); 151.8, 140.7, 129.1, 128.9, 126.4 and
20.3 (-C-Ar-O-, 12C); 147.8, 137.4, 125.1 and 117.4 (-N-Ar, 12C); 115.8 (-O-C-N-,
C); 78.4 (-C-CH -O-P-, 3C); 76.3 (-CO-O-CH -C-, 1C); 57.7 (-Ar-C-N-Ar, 2C);
1
2
4
1
2
2
2
9.2 (CH -C-, 1C); 44.1 (-C-CH -CH -CO-O-, 1C); 36.2 (C(CH ) -, 1C); 29.8 (-CH ,
3
2
2
2 4
3
C); 27.0 (-C-CH -CH -CO-O-, 1C).
2
2
.5. Preparation of benzoxazine resins
A certain amount of DPA-Boz, MDP-Boz and DPA-PEPA-Boz were taken
o
respectively into three beakers and heated in a vacuum oven at 110 C until a
transparent melt without bubbles was formed. Then the melt was transferred to the
3
PTFE mold (100 × 6 × 3 mm mold for limiting oxygen index (LOI) tests and 130 ×
3
o
1
3 × 3 mm mold for vertical burning tests) and placed in an oven at 110 C. The
o
o
o
o
curing procedures was designed as 120 C/1h, 140 C/1h, 160 C/1h, 180 C/1h, 200

ACCEPTED MANUSCRIPT
o
o
o
C/1h, 220 C/1h and 240 C/1h.
2
.6. Monomer and resin characterization
FTIR test of the synthesized monomers were carried out on a Nexus 470-Thermo
-1
FTIR spectrophotometer in the range of 400~4000 cm using solid KBr pellet.
1
13
31
H NMR, C NMR and P NMR of the synthesized compounds were conducted
on a BRUKER-Advance 2B (500 MHz) spectrometer at room temperature using
CDCl or DMSO as solvent.
3
Differential scanning calorimetry (DSC) measurements were performed with a
Netzsch 200 P C supported with a Netzsch TASC 414-5 computer for data acquisition.
DSC was calibrated with high purity indium, and the measurements were conducted
3
under a nitrogen flow of 20 cm /min. In DSC experiments, all the samples were
o
subjected to a dynamic DSC scanning from 50 to 300 C at a heating rate of 10
o
C/min.
Thermogravimetric (TG) analysis was carried out using a TGA 209 F1 Thermal
Analyzer (Netzsch, Germany) to study the thermal degradation behavior of the cured
o
resins. Samples were heated from room temperature to 950 C at a heating rate of 20
o
3
C/min under nitrogen with a flow rate of 40 cm /min or air with a flow rate of 50
3
cm /min.
X-Ray photoelectron spectroscopy (XPS) spectra of P-DPA-PEPA-bozs, along
o
with the char residues after keeping at 450 C in a muffle for 5 min, were obtained on
a Thermo ESCALAB 250 spectrometer.
Microscale combustibility experiments were conducted using an MCC-2

ACCEPTED MANUSCRIPT
microscale combustibility calorimeter (Govmark, USA). 5 mg sample was heated to
o
o
7
50 C at a heating rate of 1 C/s in a mixed stream of oxygen and nitrogen flowing at
3
2
0 and 80 cm /min respectively.
Limiting oxygen index (LOI) was measured by using an HC-2 Oxygen Index
Instrument (Jiangning Analytical Instrument Co. Ltd., Nanjing, China) on testing
specimens (100 × 6 × 3 mm) according to ASTM D2863-2008 procedure.
Vertical burning tests were performed with a CZF-3 Vertical Burning Tester
(Jiangning Analytical Instrument Co. Ltd., Nanjing, China) on testing specimens (130
3
×
13 × 3 mm ) according to ASTM D3801 standard.
3
. Results and discussion
3
.1. Determination of the structure of DPA-PEPA-Boz monomer
The bio-based Boz monomer (DPA-PEPA-boz) was synthesized using a
three-step process as shown in Scheme 3. First, pentaerythritol caged phosphate
PEPA) was obtained by treating pentaerythritol with phosphorus oxychloride. The
(
yield was 87.6 %. Second, the diphenolic acid (DPA) was reacted with PEPA in
o
acetonitrile at 70 C to obtain diphenolic acid pentaerythritol caged phosphate
(DPA-PEPA), and its yield was 80.2 %. Finally, DPA-PEPA-Boz was obtained by the
reaction
among
1,3,5-triphenylhexahydro-1,3,5-triazine,
DPA-PEPA
and
o
paraformaldehyde in toluene at 110 C for 20 h. The yield of DPA-PEPA-Boz was
8
5.7 %.

ACCEPTED MANUSCRIPT
100
-1
1377 cm
90
80
70
60
50
40
30
-1
6
96 cm
-1
7
54 cm
-1
8
58 cm
-
1
1741 cm
-1
-
1
947 cm
1
600 cm
-1
1
041 cm
-1
1
155 cm
-
1
1495cm
-1
1
234 cm
-
1
1
313 cm
4000
3500
3000
2500
2000
1500
1000
500
-1
Wavenumbers/cm
Fig. 2 The FTIR spectrum of DPA-PEPA-Boz.
Table 1 The characteristic absorption wavenumbers in FTIR spectrum of DPA-PEPA-Boz.
-
1
Chemical group
Absorption wavenumbers/cm
-
P-O-C-C-P ring
out-of-plane C-H
C-(CH ) -
858, 754, 696
947
1155
2
4
C-O-C
1234, 1041
1313
-
P=O
C-N-C
,2,4-trisubstituted benzene
alkene C=C stretching bands
C=O
1377
1
1498
1600
-
1741
The infrared spectrum of DPA-PEPA-Boz was shown in Fig. 2. The characteristic
absorption wavenumbers in FTIR spectrum were listed in Table 1. As shown in Fig. 2
and Table 1, the presence of cyclic ether in the benzoxazine structure was confirmed
-1
by the absorbance peaks at about 1234 and 1041cm due to the symmetric stretching
and asymmetric stretching modes of the C-O-C band of oxazine ring respectively.
There was an obvious characteristic peak of out-of-plane C-H of oxazine ring at 947
-1
-1
cm . The characteristic band at 1377 cm was assigned to the asymmetric stretching
vibrations of C-N-C bond of oxazine ring. There were characteristic bands at 858, 754

ACCEPTED MANUSCRIPT
-1
and 696 cm assigned to the symmetric stretching and asymmetric stretching modes
-1
-1
of -P-O-C- ring. The characteristic bands at 1313 cm and 1155 cm were assigned to
the symmetric stretching modes of -P=O and C-(CH ) - respectively. These results
2
4
could confirm the oxazine ring and PEPA in the structure of DPA-PEPA-Boz.
O
P
O
O
h
O
h
g
f
H O
2
O
e
O
d
j
k
p
c
b
i
l
O
N
O
p
a
n
m
o
N q
r
j
s
0
s
t
n
a
k
dmso
c
t
r
f
d
8
7
6
5
4
3
2
1
Chemical shift(ppm)
1
Fig. 3 H NMR spectrum of DPA-PEPA-Boz.
1
The H NMR spectrum of DPA-PEPA-Boz was shown in Fig. 3. The
DPA-PEPA-Boz exhibited not only the specific signals of the oxazine ring, but also
the chemical shifts that belong to PEPA. The two signals at 5.42 ppm (s, 4H) and 3.89
ppm (s, 4H) were corresponded to -O-CH -N and -Ar-CH -N- protons of oxazine ring
2
2
respectively. Methyl protons of the DPA appeared at 1.48 ppm (s, 3H). Methylene
protons of the DPA appeared at 2.26 ppm (t, -C-CH -CH -CO-, 2H) and 2.09 ppm (t,
2
2
-
C-CH -CH -CO-, 2H) respectively, while the two signals of methylene protons from
2 2
PEPA were at 4.62 ppm (t, -P-O-CH -C, 2H) and 4.03 ppm (t, -O-CH -C, 2H)
2
2
respectively. Moreover, integration analysis of the oxazine and aromatic proton peaks
pointed out that the closed-ring structured monomer was about 98%.

ACCEPTED MANUSCRIPT
O
P
dmso
O
O
O
h
g
f
O
e
O
d
j
k
c
b
i
l
O
N
O
p
a
n
m
o
N q
r
s
f
t
r
n
j
q
t k p
o
l
i
b
m
h
c
e
a
g
d
s
1
80
160
140
120
100
80
60
40
20
0
Chemical shift(ppm)
1
3
Fig. 4 C NMR spectrum of DPA-PEPA-Boz.
1
3
The C NMR spectrum of DPA-PEPA-Boz was shown in Fig. 4. The
1
3
corresponding C NMR spectrum also supported the structure of DPA-PEPA-Boz.
The two singles at 115.8 ppm and 57.7 ppm were the typical carbon resonances of
-
N-CH –O- and -N-CH –Ph- of the oxazine ring respectively. No detectable
2 2
resonances due to impurities were seen in the spectrum.
With the same methods the other synthesized monomers were characterized by
means of these spectra, and the results were given in the Experimental Section.
3
.2. Curing behavior of DPA-Boz, MDP-Boz and
DPA-PEPA-Boz
1
,3-benzoxazines exhibit exothermic ring-opening reaction in the condition of
heating and/or the existence of catalyst, which can be observed by DSC[36]. DSC was
carried out to study curing behavior of DPA-Boz, MDP-Boz and DPA-PEPA-Boz. Fig.
5
showed the typical nonisothermal DSC thermograms, and the results were
summarized in Table 2.

ACCEPTED MANUSCRIPT
DPA-Boz
MDP-Boz
DPA-PEPA-Boz
120
160
200
240
280
O
Temperature / C
Fig. 5 DSC curves of DPA-Boz, MDP-Boz and DPA-PEPA-Boz.
Table 2 Parameters relating to the curing behavior of DPA-Boz, MDP-Boz and DPA-PEPA-Boz.
Sample
DPA-Boz
Tonset/°C
151.7
Tmax1/°C
189.2
Tmax2/°C
T offset/°C
267.2
△H/J/g
323.7
353.9
115.4
-
-
MDP-Boz
166.5
230.6
280.5
DPA-PEPA-Boz
159.3
221.7
272.0
293.7
The DSC curve given in Fig. 5 showed a clear one-stage curing for MDP-Boz,
o
with a sharp exothermic peak in a temperature range of 166~280 C and the maximum
o
at 230.6 C (Tmax). The DSC curve of DPA-Boz also showed a broad one-stage curing
o
with a temperature range of 150~270 C, but shifted to a lower temperature with the
o
o
peak temperature (Tmax) changing from 230.6 C to 189.2 C due to the presence of
carboxyl group in DPA-Boz. Its △H value also decreased from 353.9 J/g to 323.7 J/g.
It is well known that proton acid is a common catalyst of Boz[37], and the carboxyl in
DPA-Boz played a catalytic role leading to the exothermic ring-opening reaction
shifting to a lower temperature. In contrast to MDP-Boz and DPA-Boz monomers, the
DSC curve of DPA-PEPA-Boz showed a two-stage curing with two maximums at
o
o
2
21.7 C and 272.0 C respectively. The first exothermic peak was the exothermic

ACCEPTED MANUSCRIPT
o
reactions of the oxazine-ring opening, with a temperature range of 159.3~257.3 C
o
and the maximum at 221.7 C (Tmax1). The second exothermic peak was the -P-O-C-
ring opening in PEPA, with a exothermic peak in a temperature range of 257.3~293.7
o
o
C and the maximum at 272.0 C[37]. The temperature range of the exothermic curing
o
peak of DPA-PEPA-Boz was close to that of MDP-Boz and about 30 C higher than
that of DPA-Boz. This was mainly because there was no proton acid in the structure of
DPA-PEPA-Boz due to the introduction of PEPA.
3
.3. Thermal properties of the cured benzoxazine resins
The thermal and thermal-oxidative decompositions of cured Bozs (denoted as P-)
were evaluated by using TG under nitrogen and air atmospheres. The TG curves of
cured Bozs and their derivatives (DTG) were shown in Figs. 6 and 7, and the results
were summarized in Tables 3 and 4. T , T and T50% were the temperatures for 5%,
5
%
10%
1
0% and 50% mass losses, respectively. T5% is defined as the onset temperature of the
degradation of the cured Bozs. Tmax is the temperature with the maximum mass loss
rate. Peak value is the maximum mass loss rate during the decomposition. Char is the
o
percentage of the char yielded at 800 C under nitrogen, and TChar=0 is the temperature
with no char residue under air atmosphere.

ACCEPTED MANUSCRIPT
100
P-DPA-Boz
P-MDP-Boz
(a)
P-DPA-PEPA-Boz
8
6
4
2
0
0
0
0
0
200
300
400
500
600
700
800
900
o
Temperature/ C
0
2
4
6
8
(b)
P-DPA-Boz
P-MDP-Boz
P-DPA-PEPA-Boz
-
-
-
-
-
10
200
300
400
500
600
700
800
900
o
Temperature/ C
Fig. 6 TG curves of the cured benzoxazine resins from DPA-Boz, MDP-Boz and DPA-PEPA-Boz
under nitrogen atmosphere, (a) TG curves and (b) DTG curves.
Table 3 TG results of the cured benzoxazine resins from DPA-Boz, MDP-Boz and
DPA-PEPA-Boz under nitrogen atmosphere.
o
Temperature( C)
Peak value
ꢀwt%/minꢁ
-8.64
Sample
Char (%)
T5%
T10%
376.6
361.3
385.4
Tmax
T50%
501.2
479.3
ꢂ950
P-DPA-Boz
343.6
335.3
341.5
442.2
448.4
452.0
37.9
32.5
55.4
P-MDP-Boz
-8.79
P-DPA-PEPA-Boz
-4.50
T ,, T and T50% are the temperatures for 5%, 10% and 50% mass losses, respectively.
5%
10%
As shown in Fig. 6 and Table 3, T , T and Tmax of P-DPA-Boz were 343.6,
10%
5
%

ACCEPTED MANUSCRIPT
o
o
3
76.6 and 442.2 C respectively, and the residual char at 800 C was 37.9 %.
P-DPA-Boz showed good thermal stability. In its DTG curve, P-DPA-Boz showed a
one-stage weight loss process with its peak value at 8.64 wt%/min. Compared to
P-DPA-Boz, thermal stability of P-MDP-Boz was slightly weakened with the lower
values of T , T10%, T50% and the residual char. This was mainly because the methyl
5
%
group introduced in the structure of P-MDP-Boz was more readily to be decomposed.
As for P-DPA-PEPA-Boz, its T5% was 341.5 °C, slight lower than that of P-DPA-Boz.
o
This was because PEPA first decomposed at about 300 C during the decomposition
process. PEPA is a highly effective flame retardant, and can form an insulating layer
to cover the resin surface after decomposition, which isolates air and hinders further
combustion of resins[38]. As the results, the residual char of P-DPA-PEPA-Boz
(55.4 %) was much higher than that of P-DPA-Boz (37.4 %) and P-MDP-Boz (32.5 %)
o
at 800 C. From the DTG results, the mass loss rate of P-DPA-PEPA-Boz was the
lowest under the same temperature due to the existence of PEPA in the molecular
structure, whereas that of P-MDP-Boz was the highest because methyl group
promoted decomposition of the carbon sources. Peak value of P-DPA-PEPA-Boz was
4
.50 wt%/min, which was only 52.09% of P-DPA-Boz (8.64 wt%/min) and 51.20 %
of P-MDP-Boz (8.79 wt%/min). T50% is another parameter to effectively evaluate
o
thermal stability of polymer. T50% of P-DPA-PEPA-Boz was higher than 950 C while
o
o
that of P-DPA-Boz and P-MDP-Boz were only 498.4 C and 482.8 C respectively.
The results revealed that the introduction of PEPA in the structure of bio-based boz
could enhance effectively the control of thermal transmission and at the same time

ACCEPTED MANUSCRIPT
form the protective intumescent char layer on the surface during thermal degradation.
100
P-DPA-Boz
P-MDP-Boz
(a)
P-DPA-PEPA-Boz
8
6
4
2
0
0
0
0
0
200
300
400
500
600
700
800
900
o
Temperature/ C
0
(b)
-
2
4
6
8
-
-
-
P-DPA-Boz
P-MDP-Boz
P-DPA-PEPA-Boz
200
300
400
500
600
700
800
900
o
Temperature/ C
Fig. 7 TG curves of cured benzoxazines from DPA-Boz, MDP-Boz and DPA-PEPA-Boz under air
atmosphere, (a) TG curves and (b) DTG curves.
Table 4 TG results of cured benzoxazines from DPA-Boz, MDP-Boz and DPA-PEPA-Boz under
air atmosphere.
o
Temperature( C)
Peak value1
Peak value2
T
Char=0
o
Sample
T5%
T10% Tmax1 Tmax2 T50% ꢀwt%/minꢁ ꢀwt%/minꢁ ( C)
P-DPA-Boz
360.3 400.3 437.1 656.0 589.3
355.7 392.7 433.1 648.2 581.7
-5.46
-6.16
-
-7.78
-7.37
-
747.4
746.2
ꢂ950
P-MDP-Boz
*
P-DPA-PEPA-Boz 355.5 399.5
-
-
615.5
*
The DTG curve of P-DPA-PEPA-Boz showed a four-stage weight loss process. Their Tmaxs were

ACCEPTED MANUSCRIPT
o
4
67.0, 569.0, 650.0 and 744.0 C respectively, and their Peak values were -3.73, -4.20, -4.54 and
-3.20 wt%/min respectively.
The TG curves of the cured Bozs under air atmosphere were shown in Fig. 7. The
results also showed that P-DPA-PEPA-Boz had much better thermal-oxidative
stability than other two resins. P-DPA-Boz and P-MDP-Boz had a similar
decomposition behavior with a distinct two-step decomposition process. As shown in
o
Table 4, T , T10%, Tmax1, Tmax2 of P-DPA-Boz were 360.3, 400.3, 437.1 and 656.0 C
5
%
o
respectively, and the no residual char temperature was about 750 C. In its DTG curve,
the peak value and peak value were 5.46 and 7.78 wt%/min respectively. The results
1
2
for P-MDP-Boz were similar and slightly lower because of the methyl group.
However, the P-DPA-PEPA-Boz decomposition occurred very differently in a distinct
o
four-step process and there was still 10.5 % of the residual char at 900 C. Its Tmax
s
o
were 467.0, 569.0, 650.0 and 744.0 C respectively and peak values were 3.73, 4.20,
4
4
.54 and 3.20 wt%/min respectively. Its residual char at temperatures ranging from
o
00 to 950 C was significantly higher than those of P-DPA-Boz and P-MDP-Boz.
These results indicated the lower mass loss rate and much more efficient char
formation during thermal-oxidation decomposition of P-DPA-PEPA-Boz. The
literature suggested that the second decomposition step was mostly ascribed to the
oxidation degradation of the char layer and the following release of CO and CO [22].
2
Therefore, the higher thermal oxidation stability in the second stage was most likely
due to the formation of thick and dense stable intumescent chars in the first stage,
which could efficiently hinder the oxygen permeability and the simultaneous thermal
transmission. Thus, PEPA acted as intrinsic flame retardant and produced remarkable

ACCEPTED MANUSCRIPT
effects on the thermal-oxidative decomposition of the cured Boz under air
environment.
1
1
1
1
1
80000
60000
40000
20000
00000
1000
900
800
700
P-DPA-PEPA-Boz
Char residue of P-DPA-PEPA-Boz
a
P2p scan
b
C1s
O1s
600
500
400
300
200
100
0
80000
60000
40000
20000
0
N1s
P2p
P-DPA-PEPA-Boz
Char residue of P-DPA-PEPA-Boz
6
00
500
400
300
200
100
136
134
132
130
128
126
Binding Energy / eV
Binding Energy / eV
4
3
3
2
2
1
1
0000
5000
0000
5000
0000
5000
0000
C1s scan of P-DPA-PEPA-Boz
c
40000
C1s scan of char residue of P-DPA-PEPA-Boz
d
C-C
C-C
3
5000
0000
Name
C-C
C-O-C
C=C
Content
80.8%
15.7%
3.5%
Name
C-C
C-O-C
C=C
Content
81.7%
10.1%
8.2%
3
25000
20000
1
5000
0000
5000
0
1
C-O-C
C-O-C
C=C
5
000
C=C
0
-
5000
294
292
290
288
286
284
282
280
294
292
290
288
286
284
282
280
Binding Energy / eV
Binding Energy / eV
Fig. 8 XPS survey scan (A), P2p (B), C1s ((C) and (D)) scan of P-DPA-PEPA-Boz and its char
residue.
Table 5 Element content of P-DPA-PEPA-Boz and its char residue determined by XPS
Elements (At. %)
P-DPA-PEPA-Boz
C
N
O
P
63.94
83.80
2.40
3.66
31.54
10.12
2.12
2.42
Residue of P-DPA-PEPA-Boz
The XPS spectra of P-DPA-PEPA-Boz and its char residue were shown in Fig. 8,
and their element contents were summarized in Table 5. The surface content of
phosphorus was also increased slightly from 2.12 wt% to 2.42 wt%, while the surface
content of oxygen was decreased from 31.54 wt% to 10.12 wt%. Obviously, the
surface content of carbon was increased from 63.94 wt% to 83.80 wt% and the surface
content of C-C and C=C of char residue was higher than those of P-DPA-PEPA-Boz,
revealing that PEPA endowed P-DPA-PEPA-Boz good char-forming ability and then

ACCEPTED MANUSCRIPT
P-DPA-PEPA-Boz had excellent thermal stability.
3
.4. Combustion properties and flame retardancy of the cured
benzoxazine resins
In order to further analyze the correlation between the crosslinked structure and
flammability for cured Bozs, their aerobic pyrolysis and the subsequent reactions
between the volatile pyrolysis products and a mixture of nitrogen/oxygen (80/20) gas
under high temperatures were simulated by microscale combustibility calorimeter
experiments. The key combustion parameters, including heat release capacity (HRC),
total heat release (THR), peak heat release rate (PHRR) and the temperature for the
PHRR (TPHRR), were obtained. The representative heat release rate curves of the cured
Bozs were presented in Fig. 9, and the detailed data were summarized in Table 6.
160
140
120
100
P-DPA-Boz
P-MDP-Boz
P-DPA-PEPA-Boz
80
60
40
20
0
100
200
300
400
500
600
O
Temperature / C
Fig. 9 MCC curves of the cured benzoxazine resins from DPA-Boz, MDP-Boz and
DPA-PEPA-Boz.
Table 6 MCC results of the cured benzoxazine resins from DPA-Boz, MDP-Boz and
DPA-PEPA-Boz.
*
HRC
HRC
PHRR
w/g
THR
kJ/g
T
PHRR
Sample
o
J/g K
J/g K
C
·
·

ACCEPTED MANUSCRIPT
P-DPA-Boz
P-MDP-Boz
139±2
146±1
68±1
227
249
188
127.3±1.8
114.2±1.6
55.4±1.1
18.3±0.2
19.4±0.1
8.6±0.1
424.4±0.3
408.8±0.9
417.2±0.2
P-DPA-PEPA-Boz
*
HRC was calculated for bio-based Bozs from their chemical structures by Ref. 39.
As shown in Fig. 9 and Table 6, all three Bozs had one wide overlapping
o
exothermic peak from 50 to 600 C in the MCC curve. The THR, HRC and PHRR of
P-DPA-Boz and P-MDP-Boz were similar at about were 19 kJ/g, 140 J/g K and 120
·
w/g respectively. However, the results of P-DPA-PEPA-Boz were much lower, only
half of that of P-DPA-Boz and P-MDP-Boz, at 8.6 kJ/g, 55.4 w/g and 68 J/g K
·
respectively. As shown in Table 6, the changes of HRC values for these bio-based
bozs were consistent with those﹥calculated for bio-based bozs according to their
chemical structures[39]. The introduction of PEPA flame retardant moiety, which was
o
decomposed to produce a layer of char layer at 300 C, significantly improved the
flame retardancy of the materials. The results indicated that PEPA was an excellent
intrinsic flame retardant for the cured Bozs and could effectively retard their
combustion, reduce their combustion speed, burning degree and combustion heat
release.
Table 7 Flame retardant properties of the cured benzoxazine resins from DPA-Boz, MDP-Boz and
DPA-PEPA-Boz.
Vertical burning tests
Sample
LOIꢀ%ꢁ
t1 (s)
fail
t2(s)
fail
UL-94 rate
No rating
No rating
V-0
P-DPA-Boz
26.1
25.7
33.5
P-MDP-Boz
fail
fail
P-DPA-PEPA-Boz
1.68
0.12
The flame retardant property of the cured Bozs was also assessed by the LOI and
the vertical flame tests, as shown in Table 7. The LOI values of the P-DPA-Boz and
P-MDP-Boz were only 26.1 % and 25.7 % respectively. P-DPA-Boz and P-MDP-Boz
showed no rating in UL94 test. For the P-DPA-PEPA-Boz, LOI value was even higher,

ACCEPTED MANUSCRIPT
at 33.5 %. Its t and t were 1.68 and 0.12 s respectively, which were significantly
1
2
lower than the maximum permissible values of 10 s, indicated in flame retardancy
standards. P-DPA-PEPA-Boz achieved V0 rating in UL94 test. LOI values of the
bio-based Bozs from eugenol[40, 41] and phosphorus flame retardant P-DPA-Bozs[27]
were shown in Table 8. As shown in Table 8, LOI value of P-DPA-PEPA-Boz was
higher than those of the bio-based bozs from eugenol except F-BZ and almost same as
those of DOPO flame retardant P-DPA-Boz. Therefore, P-DPA-PEPA-Boz behaved as
a very good intrinsic flame retardant bio-based Boz.
Table 8 LOI values of the bio-based Bozs from eugenol ) and phosphorus flame retardant
P-DPA-Bozs [27, 40, 41]
Phosphorus
Boz
S-Bz F-Bz Bz-OXY Bz-PHE Bz-DDS
Bz-SUL
flame retardant
P-DPA-Bozs
31.6~35.4
LOI(%)
27.1 39.0 29.4 32.1 30.3
26.9
4
. Conclusions
In this study, an intrinsically flame retardant bio-based boz (DPA-PEPA-Boz) had
been synthesized and characterized. The DSC curve of DPA-PEPA-Boz monomer
o
o
showed a two-stage curing with two maximums at 221.7 C and 272.0 C, assigned to
the exothermic opening reactions of oxazine rings and -P-O-C ring in PEPA, and its
o
exothermic curing peak was close to that of MDP-Boz monomer and about 30 C
higher than that of DPA-Boz monomer. Compared with P-DPA-Boz and P-MPA-Boz,
o
T5% of P-DPA-PEPA-Boz was slightly lower. However, its residual char after 400 C
was higher, especially under nitrogen atmosphere. The THR, PHRR and HRC of
P-DPA-PEPA-Boz were less than half of those of P-DPA-Boz and P-MDP-Boz.
P-DPA-PEPA-Boz achieved a significantly high LOI value at 33.5% and V0 rating in

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the UL94 test. Therefore, P-DPA-PEPA-Boz behaved as a very good intrinsic thermal
stable and flame retardant bio-based Boz.
Acknowledgements
We gratefully acknowledge the financial supports from the National Natural
Science Foundation of China (No. 51103129), Zhejiang Provincial Natural Science
Foundation of China (No. LY14E030006), Ningbo Science and Technology
Innovation Team (No. 2015B11005), and Ningbo Natural Science Foundation
(No.2015A610028).
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