Synthesis and characterization of thianthrene-based epoxy with high refractive index over 1.7

Article abstract of DOI:10.1080/10426507.2017.1370591

A novel glycidyl resin 2,7-bis(β-epoxypropylthio)thianthrene (4SEP) with high refractive index was synthesized and characterized by ¹H NMR, FT IR and FD-MS analyses. The kinetics of 4SEP cured with methylhexahydrophthalic anhydride (MeHHPA) was

Full text of DOI:10.1080/10426507.2017.1370591

Phosphorus, Sulfur, and Silicon and the Related Elements
ISSN: 1042-6507 (Print) 1563-5325 (Online) Journal homepage: http://www.tandfonline.com/loi/gpss20
Synthesis and characterization of thianthrene-
based epoxy with high refractive index over 1.7
Xiaojuan Zhao, Shengnan Li, Xinghua Liu, Xin Yang, Ying Zhang, Ran Yu,
Xiaobiao Zuo & Wei Huang
To cite this article: Xiaojuan Zhao, Shengnan Li, Xinghua Liu, Xin Yang, Ying Zhang, Ran Yu,
Xiaobiao Zuo & Wei Huang (2018) Synthesis and characterization of thianthrene-based epoxy with
high refractive index over 1.7, Phosphorus, Sulfur, and Silicon and the Related Elements, 193:1,
33-40, DOI: 10.1080/10426507.2017.1370591
To link to this article: https://doi.org/10.1080/10426507.2017.1370591
Accepted author version posted online: 24
Aug 2017.
Published online: 05 Sep 2017.
Submit your article to this journal
Article views: 48
View related articles
View Crossmark data
Full Terms & Conditions of access and use can be found at
http://www.tandfonline.com/action/journalInformation?journalCode=gpss20

PHOSPHORUS, SULFUR, AND SILICON
, VOL. , NO. , –
https://doi.org/./..
Synthesis and characterization of thianthrene-based epoxy with high refractive index
over .
Xiaojuan Zhaoa, Shengnan Lia, Xinghua Liua, Xin Yanga, Ying Zhanga, Ran Yua, Xiaobiao Zuob, and Wei Huanga
aInstitute of Chemistry, Chinese Academy of Sciences, Beijing, P. R. China; bAerosp Res Inst Mat & Proc Technol, Sci & Technol Adv Funct Composites
Lab, Beijing, P. R. China
ABSTRACT
ARTICLE HISTORY
Received  May 
Accepted  August 
A novel glycidyl resin 2,7-bis(β-epoxypropylthio)thianthrene (4SEP) with high refractive index was synthe-
sized and characterized by 1H NMR, FT IR and FD-MS analyses. The kinetics of 4SEP cured with methylhexahy-
drophthalic anhydride (MeHHPA) was investigated by nonisothermal differential scanning calorimetry. The
results revealed that the reactivity of 4SEP was higher compared with that of diglycidyl ether of bisphenol
A (DGEBA) due to the weakened electron-withdrawing effect of thioether on the epoxy group. The ther-
mal properties and refractive index of 4SEP/MeHHPA were investigated with differential scanning calorime-
try, thermogravimetric analyses, Abbe refractometer, prism coupler, and compared with those of the
DGEBA/MeHHPA. Experimental results showed that, due to the introduction of thianthrene and thioether
units, the glass transition temperature (Tg) was slightly enhanced, while the thermal stability was reduced.
The refractive index of 4SEP was over 1.7000, and the refractive index of 4SEP/MeHHPA was up to 1.6808.
KEYWORDS
Epoxy resins; refractive index;
thianthrene; thioether; sulfur
GRAPHICAL ABSTRACT
According to the Lorentz-Lorenz equation, the introduction
of substituents with high molar refractions, low molar volumes,
or high density can increase the refractive indices of conven-
tional polymers.6 Among the substituents, the sulfur-containing
groups might be one of the most promising candidates.
Thioethers and thioalcohols are usually used to prepare epoxy
resins with high refractive indexes.7–9 Cui et al.10 synthesized
a thioether glycidyl resin bis[3-(2,3-epoxypropylthio)phenyl]-
sulfone with high refractive index by condensation of bis(3-
mercaptophenyl)sulfone with epichlorohydrin. The epoxy was
cured with trimercaptothioethylamine to yield the cured resin
with a high refractive index of 1.67. Luo et al.11 synthesized a
novel curing agent containing phosphorus and sulfur, the cur-
ing agent was mixed with triethylenetetramine and an epoxy
prepolymer at a certain ratio to generate cured samples. The
cured product yielded a refractive index as high as 1.593.
Katsumasa et al.12 patented a diglycidyl ether of thiodiben-
zenethiol epoxy resin with the refactive index of 1.669, which
is the ever-reported highest refractive index of extant epoxy
resins.
Introduction
Epoxy resins, the most common and important thermosetting
polymers, have been widely used in industry, as coating, adhe-
sives, composite matrix, etc., due to their chemical resistance,
small shrinkage, good processability and excellent mechanical
properties. Light emitting diode (LED) encapsulation is one of
the important applications of epoxy resins.1 Gallium nitride chip
of LED possesses high refractive index of about 2.2, while the
refractive index of the ordinary epoxy-cured product is only
about 1.57, the refractive index difference of these two mediums
can cause total internal reflection when light travels from the
die into the encapsulant at certain incident angles and can result
in low light output (only 10% of the theoretical light extrac-
tion efficiency).2–4 Moreover, the trapped light is converted into
heat and brings problems to the LED. To effectively reduce the
trapped light and improve the light-extraction efficiency, the
refractive index of encapsulant materials should be as high as
possible. Theoretical calculations show that the light extraction
efficiency will be >30% when the refractive index of the encap-
sulant material is >1.7.5
CONTACT Xiaojuan Zhao
zhaoxj@iccas.ac.cn
, People’s Republic of China.
Laboratory of Advanced Polymer Materials, Institute of Chemistry, Chinese Academy of Sciences ICCAS, Beijing
Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/gpss.
©  Taylor & Francis Group, LLC

34
X. ZHAO ET AL.
The thianthrene group is a thermally stable heterocycle that
has been incorporated into the backbones of several different
types of polymers.13,14 The thianthrene moiety has two sulfur
atoms in the cyclic structure, which increases the sulfur content
of the repeating unit. Moreover, the bent structures of the
thianthrene ring may suppress packing between the polymer
chains, which is required for high transparency. Recently,
a series of thianthrene-containing polymers that exhibited
high refractive indices were synthesized and characterized for
optical applications, including polyimides,15 poly(phenylene
sulfide)s,16–18 and acrylates.19 Suzuki et al.20 prepared a series
of high refractive index poly(phenylene sulfide)s (PPSs) from
2,7-difluorothianthrene and dithiols. The PPSs showed excel-
lent thermal stabilities and very high refractive indices reaching
1.8020. You et al.19 prepared acrylate resins by photopolymer-
ization under UV irradiation. The acrylate resin derived from
2,7-bis[(2-acryloylethyl)sulfanyl]thianthrene exhibited a very
high-refractive index of 1.6645, which is one of the highest
refractive photocurable polymer resins developed so far. How-
ever, the thianthrene-containing epoxy resins have not been
reported to date.
To further increase the refractive index of epoxy resins, in this
study, we introduced both thianthrene and thioether groups into
the backbone of the epoxy resin. Firstly, the thianthrene group
has high sulfur content, its rigid structure facilitates the close
packing of the polymer chains, increasing the refractive index
and thermal properties of the resulting resins. Secondly, the
introduction of thioether groups can simultaneously increase
the refractive index and toughness of the resins. The synthesis
and characterization of the novel epoxy was reported. The ther-
mal properties and refractive indices of the cured resins were
investigated with those of DGEBA for comparison.
Figure . FT IR spectra of TDT and SEP.
and NaOH, then a ring-closure reaction gave rise to 4SEP with
a yield >68%. This procedure has been proven to be an efficient
pathway for the preparation of thioether glycidyl resin.10
Figure 1 shows the FTIR spectrum of 4SEP and TDT. It can
be seen that the –SH group appearing at 2530 cm−1 in TDT
disappeared in 4SEP, and the characteristic band of the oxirane
rings was detected at 920 cm−1 in 4SEP. Furthermore, the sym-
metric stretching vibration and asymmetric stretching vibration
absorptions of the saturated C-H bond of oxirane rings were
also observed at 2983 cm−1 and 2915 cm−1, respectively. The
absorption in the range of 3600–3300 cm−1 was assigned to the
hydroxyl groups which existed in the oligomers. The absorp-
tions of the thioether (C-S-C) was observed at 1102 cm−1 15
.
1
Figure 2(A) is the H NMR spectra of 4SEP. The peaks at
2.92 ppm, 2.70 ppm and 2.47 ppm were assigned to the pro-
tons in the oxirane ring. The signal at 3.06 ppm was assigned
to the protons of methylene connected the thioether group and
the oxirane ring, the peaks at 7.42 ppm, 7.26 ppm and 7.19 ppm
Results and discussion
Synthesis and characterization
The epoxy resin 4SEP was synthesized through a five-step pro- were specified to the protons of benzene ring. Figure 2(B) is the
cedure, as shown in Scheme 1. In the experiments, thianthrene- 13C NMR spectra of 4SEP. Signals at 136.5, 135.7, 133.4, 129.6,
2,7-dithiol (TDT) reacted with epichlorohydrin (ECH) by 129.3 and 129.0 ppm were ascribed to the carbons in the aro-
ring-opening polyaddition reaction in the presence of ethanol matic rings, e.g. C9, C8, C7, C6, C5 and C4, respectively. The
Scheme . Synthesis of epoxy resin SEP.

PHOSPHORUS, SULFUR, AND SILICON
35

Figure . H-NMR (MHz, CDCl) (A) and C-NMR (MHz, CDCl) (B) spectra of SEP epoxy resin.
aliphatic carbons (C3, C2, and C1) were observed at 50.9, 47.5
and 36.6 ppm. The FD-MS spectra of 4SEP is shown in Figure 3.
The molecular ions peak was at m/z = 392.25, which was the
molecular weight of 4SEP. The purity of 4SEP, determined by
the relative abundance, was 88.8%. The product also contained
a small amount of oligomers, its molecular weight was 728.51,
which was in agreement with the results of FTIR.
Curing of epoxy resins
The curing kinetics of the epoxy resins was studied using non-
isothermal differential scanning (DSC) calorimeter at various
heating rates (β) 5, 10, 15 and 20 °C/min (Figure 4). The curing
of the two epoxy resin systems exhibited only one exothermic
peak during the non-isothermal DSC analysis. Table 1 lists the
exothermic peak temperature (Tp), which increase with increas-
ing heating rate. Based on the DSC data, activation energies
(Ea) were calculated using Ozawa’s equation21,22 and the reaction
orders were determined with Crane equation.23 The plots are
shown in Figure 5 and the results are summarized in Table 1. As
seen in Table 1, 4SEP/MeHHPA and DGEBA/MeHHPA show
the same reaction order of 1.1. The apparent activation energy
of 4SEP/MeHHPA was 61.38 kJ/mol, about 6 kJ/mol less than
that of DGEBA/MeHHPA, indicating the higher reactivity of
4SEP.
Figure . DSC thermograms of SEP/MeHHPA (A) and DGEBA/ MeHHPA (B) at , ,
,  °C/min heating rates in N atmosphere.
Table . DSC data for DGEBA/MeHHPA and SEP/MeHHPA.
Exothermic peak temperature (°C)
at different heating rate (°C/min)
Ozawa
Ea(kJ/mol)
Reaction
order
Samples




DGEBA/MeHHPA
SEP/MeHHPA
.
.
.
.
.
.
.
.
.
.
.
.
Figure . FD-MS spectrum of SEP.

36
X. ZHAO ET AL.
Figure . The plots of Ozawa of SEP/MeHHPA and DGEBA/ MeHHPA.
Figure . FTIR spectra of cured SEP/MeHHPA and DGEBA/ MeHHPA.
The reaction mechanism for epoxy anhydride curing with
Figure 7 shows the FT IR spectra of the cured epoxy resins.
phosphonium salts by Smith dates back to 1973.24 The cur- The absorptions at 3400∼3600 cm−1 were attributed to the sec-
ing mechanism of 4SEP and MeHHPA with BPP is shown in ondary hydroxyl groups generated by the ring-opening reac-
Figure 6. The acidic protons of the methylene group attatched to tion of epoxy groups. The characteristic epoxy absorptions at
the phosphine phosphorus atom would be available for bonding 920 cm−1 in 4SEP and 915 cm−1 in DGEBA disappeared, indi-
with nucleophiles such as an epoxy oxygen. Thus, the epoxy- cating the complete cure of the epoxy resins.
phosphonium salt adduct is formed, which is vulnerable to
The X-ray diffractograms of the cured epoxy resins (Figure 8)
attack by another epoxy molecule resulting in the formation indicated that all the resins were amorphous polymers, in which
of an oxonium ion. Also, reaction of this epoxy-phosphonium no absorption attributed to the crystal structure was detected.25
salt adduct with MeHHPA is likely to form active hydroxyl The intermolecular distance of epoxy resins can be calculated
compounds.
from the peaks of the halo using Bragg’s equation and the results
As the electronegativity of sulfur is less than that of oxy- are listed in Table 2. It can be seen that the intermolecular dis-
gen, the electron-withdrawing effect of thioether on the epoxy tance of 4SEP/MeHHPA was 4.79 A°, 0.3 A° less than that of
group of 4SEP is weakened compared with that of DGEBA, so DGEBA/MeHHPA. This is inconsistent with the reduced level
the epoxy-phosphonium salt adduct is more easily formed in the of crystallinity of thianthrene-containing polymers reported in
case of 4SEP, thus the activation energy of 4SEP/MeHHPA is less the literature.26,27 The possible reason might be that the bent
than that of DGEBA/MeHHPA.
structures of thianthrene ring suppressed packing between the
Figure . Proposed mechanism of the curing of SEP with MeHHPA with phosphonium salt (BPP).

PHOSPHORUS, SULFUR, AND SILICON
37
Figure . X-ray diffraction patterns of cured SEP/MeHHPA and DGEBA/MeHHPA.
Table . XRD diffraction patterns and thermal properties of the cured epoxy resins.
Halo
a
Samples
θ
d(A°) Tg (°C) T (°C) T a (°C) Wb (%)
SEP/MeHHPA
DGEBA/MeHHPA . .
. .
.
.
.
.
.
.
.
.
aTemperatures at %, % weight loss. b Residue at  °C.
polymer chains, while the flexible thioether groups increased
the flexibility of the polymer chains, as a competition result, the
molecular chains of 4SEP/MeHHPA packed more tightly than
those of the DGEBA/MeHHPA.
Figure . TG (A) and DTG (B) curves of the cured SEP/MeHHPA and DGEBA/
MeHHPA.
Thermal properties of the cured epoxy resin
This is attributable to the rigid thianthrene unit which prohibits
the free motions of the molecular chains.
The thermal properties of the polymers were evaluated by DSC
and TGA measurements under a nitrogen atmosphere. The
results are summarized in Table 2. The glass transition temper-
ature (Tg) of the polymers, which is one of the most important
key parameters for optical device fabrication, was determined by
DSC (Figure 9). It can be seen that the Tg of 4SEP/MeHHPA was
150.9 °C, about 14°C higher than that of DGEBA/MeHHPA.
The TG and DTG curves are shown in Figure 10. The cured
epoxy resins exhibit good thermal stability up to 323°C. How-
ever, the degradation temperatures of 4SEP/MeHHPA are lower
than those of the DGEBA/MeHHPA. The low thermal stabil-
ity of 4SEP/MeHHPA was attributed to the introduction of
thioether into the backbone of 4SEP/MeHHPA, as the bond-
ing energy of C-S (272 kJ/mol) is much lower than that of C-O
(326 kJ/mol). The residual weight at 700°C of 4SEP/MeHHPA
was much higher than that of DGEBA/MeHHPA, indicating its
potential as fire retardant.28,29
Optical properties of the cured epoxy resin
The refractive indexes of the epoxy prepolymers and the cured
epoxy resins were summarized in Table 3. The refractive index
Table . Refractive indexes of prepolymer, uncured and cured resins of SEP and
DGEBA.
Samples
Prepolymers
Uncured resins
Cured resins
SEP
DGEBA
SEP/MeHHPA
DGEBA/MeHHPA
>.
.
—
—
—
.
.
—
—
.
.
—
Figure . DSC curves of cured SEP/MeHHPA and DGEBA/ MeHHPA.

38
X. ZHAO ET AL.
Synthesis of 2,7-dibenzylthiothianthrene (DBTT)16
of 4SEP was over 1.70, beyond the range of Abbe refractome-
ter, which is higher than the ever-reported highest refractive
index of extant epoxy resins.12 The refractive indices of uncured
and cured 4SEP/MeHHPA were 1.6338 and 1.6808, which were
0.0886 and 0.1169 higher than the corresponding values of
DGEBA/MeHHPA resin. The introduction of nonplanar thi-
anthrene moieties was expected to increase molecular free vol-
ume of the obtained resins27 and thus cause a possible decrease
in the refractive indexes according to the Lorentz-Lorenz equa-
tion. In contrast, the refractive indexes of 4SEP increased. As
shown by the XRD results, the thioether of 4SEP increased the
dense molecular packing of 4SEP/MeHHPA. Moreover, the sul-
fur atoms having a high atomic refraction also increased the
refractive index of 4SEP/MeHHPA, as 4SEP has a much higher
sulfur content (32.67 wt%) than DGEBA (0 wt%). Both the
dense molecular packing and high sulfur content contributed to
the high refractive index of 4SEP/MeHHPA.
Potassium tert-butoxide (9.70 g, 86.0 mmol), 2,7-DFT (7.96 g,
31.6 mmol) and N,N-dimethylformamide (DMF) (30 mL) were
added into a 100 mL round flask under a nitrogen atmosphere.
Benzylmercaptan (10.2 mL, 84 mmol) was slowly added into
the mixture cooled with an ice bath. The solution was stirred
at 60 °C for 30 h and was poured into water (150 mL). The pre-
cipitate was filtered and dried at 80 °C in vacuum. The crude
product was recrystallized from 2-methoxyethanol to give 5.56 g
of 2,7-dibenzylthiothianthrene as a yellow crystal (70% yield).
FT IR (KBr), (νmax, cm−1): 3064, 3035 (C-Harom), 2954, 2925
1
=
(C-Haliph), 1603, 1563, 1450 (C C), 1103 (C-S-C). H-NMR
(400 MHz, CDCl3): δ = 7.37 (d, 2H, Ar-H), 7.30 (s, 1H, Ar-
H), 7.27 (m, 5H, Ar-H), 7.23–7.24 (m, 6H, Ar-H), 7.13 (d, 1H,
Ar-H), 7.06 (d, 1H, Ar-H), 4.07 (s, 4H, CH2). Anal. Calcd. for
C26H20S4 (460): C, 67.78; H, 4.38. Found: C, 67.56; H, 4.58%.
Synthesis of thianthrene-2,7-dithiol (TDT)16
Conclusions
DBTT (2.76 g, 6.0 mmol), Cp2TiCl2 (0.156 g, 0.62 mmol)
and diglyme (20 mL) were added into a freshly dried 100 mL
three necked round flask under a nitrogen atmosphere at 0 °C.
Dibutylmagnesium (40 mL, 2.5 M) was slowly added to the mix-
ture and the solution was stirred for 5 h. The aqueous solution of
Na2CO3 (40 mL) was slowly added to the reaction mixture at 0
°C. 50 mL dichloromethane was added to the reaction mixture
and mixed thoroughly, after laid still for 1 h, the mixture sep-
arated into two layers. The upper aqueous layer was separated,
then 30 mL × 3 water was added to the mixture. With a sim-
ilar procedure, the aqueous layer was separated. The separated
aqueous layers were combined, hydrochloric acid was added and
the solution was stirred for 1 h. The precipitate was filtered and
dried in vacuum to give an ivory-colored powder TDT (0.814 g,
48% yield).
A novel epoxy resin, containing thianthrene and thioether units,
was synthesized and characterized by 1H NMR, FT IR and FD-
MS analyses. The curing kinetics of 4SEP/MeHHPA was stud-
ied using nonisothermal differential scanning calorimetry. The
reactivity of 4SEP was improved compared to that of DGEBA,
due to weakened electron-withdrawing effect of thioether on the
epoxy group.
Cured 4SEP exhibited higher Tg compared with the cured
DGEBA, while the thermal stability of the cured 4SEP was lower
than that of the cured DGEBA. Due to the high sulfur content,
the novel epoxy resin 4SEP showed a very high refractive index
(nd > 1.70), which is one of the highest refractive index epoxy
resins developed so far.
FT IR (KBr), (νmax, cm−1): 3062, 3042 (C-Harom), 2533 (-SH),
Experimental
1
=
1568, 1447 (C C), 1103 (C-S-C). H-NMR (400 MHz, CDCl3):
δ = 7.39 (d, 2H, Ar-H), 7.32 (s, 1H, Ar-H), 7.29 (s, 1H, Ar-
H), 7.15 (d, 1H, Ar-H), 7.12 (d, 1H, Ar-1H), 3.45 (s, 2H, Ar-
H). 13C-NMR (400 MHz, CDCl3): δ = 136.80 (C1), 132.27 (C2),
131.02 (C3), 129.12 (C4), 129.04 (C5), 128.63 (C6). Anal. Calcd.
for C12H8S4 (279): C, 51.39; H, 2.88. Found: C, 51.18; H, 3.02%.
Materials
4-Fluorothiophenol, potassium tert-butoxide, benzylmercap-
tan, Bis(cyclopenta -dienyl) titanium(IV)dichloride (Cp2TiCl2)
and dibutylmagnesium were purchased from Sigma-Aldrich,
and used as received. DGEBA epoxy resin with an epoxide
equivalent weight of 185 g/equiv was purchased from Wuxi resin
factory of Blue Star New Chemical Materials Co., Ltd and used
Synthesis of 2,7-bis(β-epoxypropylthio)thianthrene (4SEP)
as received. MeHHPA and the curing accelerator benzyltriph- TDT (4.21 g, 0.015 mol), ethanol (8 mL) and epichlorohy-
enylphosphonium chloride (BPP) were purchased from new drin (11.8 mL) were added into a 50 mL three-necked round-
Japan Chemical Co., Ltd. and Aldrich, respectively. Epichlorohy- bottomed flask, which was equipped with a thermometer, stirrer,
drin (ECH), sodium hydroxide, methyl isobutyl ketone (MIBK) reflux condenser and nitrogen inlet. When the reaction solution
and ethanol were supplied by Beijing Chemical Reagents Com- was heated to 50 °C, 1 mL of 20% solution of sodium hydrox-
pany (China) and used as received. Other commercially avail- ide was added and stirred for 30 min. Then 12 mL MIBK was
able reagents and solvents were used as received.
added at a time and 13 mL 20% solution of sodium hydrox-
ide was added drop-wise for 30 min. After stirring at 50 °C for
another 2 h, 15 mL MIBK was added. The organic phase was
separated and washed with distilled water until neutral. Finally,
Synthesis of 2,7-difluorothianthrene (2,7-DFT)
The compound was synthesized according to the reported pro- the solvent and excess epichlorohydrin were distilled out under
cedure.30 FT IR (KBr), (νmax, cm−1):3082 (C-Harom), 1596 and reduced pressure to yield the thiother glycidyl resin 4SEP as a
1
=
1458 (C C), 1251 and 1213 (C-F), 1101 (C-S-C). H-NMR light yellow transparent viscous liquid (4.0 g, 68% yield). FT
(400 MHz, DMSO-d6, ppm): 7.61 (m, 2H, Ar-H), 7.54(m, 2H, IR (KBr) (νmax, cm−1): 3487 (OH), 3058 (C-Harom), 2999, 2918
=
Ar-H), 7.24(m, 2H, Ar-H).
(C-Haliph), 1568, 1532, 1443 (C C), 1102 (C-S-C), 920 (epoxy

PHOSPHORUS, SULFUR, AND SILICON
39
Eq. (2)
d(ln β)
d(1/T p)
Ea
nR
=
(2)
where n is the reaction order, other parameters are the same as
Eq. (1).
TGA was carried out on a SII EXSTAR6000-TGA6300 in
nitrogen at 10 °C/min. Wide-angle X-ray diffraction measure-
ments were performed at room temperature on a PANalytical
EMPYREAN X-ray diffractometer at 40 KV and 40 mA with
CuKα radiation (λ = 0.1541 nm). Refractive indexes of the
epoxy monomers and epoxy systems before curing were
determined using WZS-1 Abbe refractometer (Shanghai optical
instrument factory). Refractive indexes of the 2 mm cured epoxy
films formed on 7.62 cm silicon wafers were measured at the
wavelength of 632.8 nm with a Metricon Model 2010/M prism
coupler.
Scheme . Chemical structures of epoxy resins and curing agent.
1
group). H-NMR (400 MHz, CDCl3): δ = 7.42 (s, 2H, Ar-H),
7.26 (d, 2H, Ar-H), 7.19 (d, 2H, Ar-H), 3.00–3.06 (m, 4H, CH2),
2.89–2.93 (m, 2H, CH epoxy), 2.70 (t, 2H, CH2 epoxy), 2.47(dd,
J = 6.0 Hz, 2H, CH2 epoxy). 13C-NMR (400 MHz, CDCl3): 136.5
(C9), 135.8 (C8), 133.4 (C7), 129.6 (C6), 129.2 (C5), 129.0 (C4),
50.9 (C3), 47.3 (C2), 36.6 (C1). FD-MS (m/z): 392.25 (M+).
Preparation of cured epoxy resins
Acknowledgments
MeHHPA were used as curing agent to thermally cure the 4SEP
and DGEBA epoxy resins. The chemical structures of the epoxy
resins and curing agent are shown in Scheme 2. The reaction
compositions were mixed homogeneously in a 1:1 molar ratio
according to the EEW values. The mass ratio of the accelera-
tor BPP to resin was 0.5:100. The mixtures were degassed in a
vacuum and poured into a preheated stainless steel mold, and
was cured according to the following curing regime: 120 °C-2 h,
150 °C-1 h.
This study is financially supported by the National Natural Science Foun-
dation of China (No. 51203163).
References
1. Tao, P.; Li, Y.; Siegel, R. W.; Schadler, L. S. J. Appl. Polym. Sci. 2013, 130,
3785-3793.
2. Huang, J. C.; Chu, Y. P.; Wei, M. Adv. Polym. Technol. 2004, 23, 298-306.
3. Zhou, Y.; Tran, N.; Lin, Y. C.; He, Y. Z.; Shi, F. IEEE Trans. Adv. Packag.
2008, 31, 484-489.
4. Yang, S.; Kim, J.; Jin, J.; Kwak, S.; Bae, B. J. Appl. Polym. Sci. 2010, 117,
2140-2145.
5. Ma, M.; Mont, F. W.; Yan, X.; Cho, J.; Schubert, E. F.; Kim, G. B.; Sone,
C. Opt. Soc. Am. 2011, 49, 1135-1140.
6. Matsuda, T.; Funae, Y.; Yoshida, M.; Tsuguo, T. J. Macromol. Sci., Pure
Appl. Chem. 1999, A36, 1271-1288.
7. Harumichi, A.; Yoshinobu, K. JP10130250, Japan, 1998.
8. Luo, C. Y.; Zhao, J. Q.; Yuan, Y. C.; Zuo, J. D.; Lin, X. C.; Zhao, Y. Polym.
Bull. 2012, 69, 337-345.
9. Luo, C. Y.; Zuo, J. D.; Zhao, J. Q. High Perform. Polym. 2013, 25, 986-
991.
10. Cui, Z. C.; LÜ, C. L.; Yang, B.; Shen, J. C.; Su, X. P.; Yang, H. Polymer
2001, 42, 10095-10100.
11. Luo, C. Y.; Zuo, J. D.; Wang, F. Q.; Yuan, Y. C.; Lin, F.; Huang, H. H.;
Zhao, J. Q.. Polym. Degrad. Stabil. 2016, 129, 7-11.
12. Katsumasa, Y.; Michio, S.; Koji, S.; Katsuya, I. JP9316421A, Japan,
1997.
13. Friedrich, R.; Janietz, S.; Wedel, A. Macromol. Chem. Phys. 1999, 200,
731-738.
Characterization
The 1H-NMR was recorded on a BRUKER AVANCE 400 MHz
NMR spectrometer, using deuterated chloroform as solvent and
tetramethylsilane as internal reference.
The FT IR AQ2 measurement was performed on a BRUKER
TENSOR-27 FT IR spectrometer at room temperature in the
range of 4000–400 cm−1. Field Desorption mass spectrometry
(FD-MS) was carried out on Thermo Fisher Scientific DFS High
resolution dual focusing magnetic mass spectrometer with aver-
age molecular weight ranging from 80 to 1200 g.mol−1, using
chloroform as solvent.
DSC was used to investigate the curing behavior of epoxy
blends by scanning with a SII EXSTAR6000-DSC6220 from 50
to 300 °C at a heating rate of 5, 10, 15, 20 °C/min in nitrogen.
The instrument was calibrated with a high-purity indium stan-
dard, and α-Al2O3 was used as the reference material. The aver-
age activation energy (Ea) for each epoxy system was determined
using the Ozawa’s methods, as shown Eqs. (1).
14. Knauss, D. M.; Edson, J. B. Polymer 2006, 47, 3996-4003.
15. Liu, J. G.; Nakamura, Y.; Shibasaki, Y.; Ando, S.; Ueda, M. Macro-
molecules 2007, 40, 4614-4620.
16. Nakagawa, Y.; Suzuki, Y.; Higashihara, T.; Ando, S.; Ueda, M. Macro-
molecules 2011, 44, 9180-9186.
17. Nakagawa, Y.; Suzuki, Y.; Higashihara, T.; Ando. S.; Ueda, M. Polym.
Chem. 2012, 3, 2531-2536.
18. Robb, M. J.; Knauss, D. M. J. Polym. Sci. Part A: Polym. Chem. 2009,
47, 2453-2461.
d(ln β)
d(1/T p)
1.052Ea
=
(1)
R
where β is heating rate, A is preexponential factor, R is universal
gas constant, Ea is activation energy of the reaction, and Tp is
peak temperature at which the reaction rate is maximum. The
plots of lnβ vs 1/Tp give straight lines. Ea values were calculated
from the respective slopes of the straight line of the plots. The
reaction order was determined using Crane equation shown in
19. You, H. H.; Higashihara, T.; Ando, S.; Ueda, M. J. Polym. Sci. Part A:
Polym. Chem. 2010, 48, 2604-2609.
20. Suzuki Y.; Murakami, K.; Ando, S.; Higashihara, T.; Ueda, M. J. Mater.
Chem. 2011, 21, 15727-15731.
21. Ozawa, T. J. Therm. Anal. 1970, 2, 369-373.
22. Ozawa, T. Bull. Chem. Soc. Jpn. 1965, 38, 1881-1886.
23. Crane, L. W. J. Polym. Sci., Polym. Lett. Ed. 1973, 11, 533-540.

40
X. ZHAO ET AL.
24. Smith, J. D. B. J. Appl. Polym. Sci. 1979, 23, 1385-1396.
25. Wan, Y. J.; Tang, L. C.; Gong, L. X.; Yan, D.; Li, Y. B.; Wu, L. B.; Jiang, J.
X.; Lai, G. Q. Carbon. 2014, 69, 467-480.
26. Johnson, R. A.; Mathias, L. J. Macromolecules. 1995, 28, 79-85.
27. Niume, K.; Toda, F.; Uno, K.; Hasegawa, M.; Iwakura, Y. Macromol.
Chem. 1981, 182, 2399-2407.
28. Lan, X. K.; Huang, W.; Yu, Y. Z. Eur. Polym. J. 2010, 46, 1545–
1556.
29. Vogel, W.; Dingemans, T. J.; Varley, R. J.; Tian, W.; Dao, B.;
Tucker, S. J.; Christensen, S. High Perform. Polym. 2014, 26,
420-423.
30. Terui, T.; Ando, S. J. Photopolym. Sci. Technol. 2005, 18, 337-340.