Preparation and Properties of Polyhedral OligomericSilsesquioxane/Epoxy Hybrid Resins

Guojun Ding,1,2 Jifang Fu,1 Xing Dong,1 Liya Chen,1 Haisen Jia,1 Wenqi Yu,1,2 Liyi Shi11Nano-Science & Technology Research Center, Shanghai University, Shanghai 200444,People’s Republic of China

2College of Science, Shanghai University, Shanghai 200444, People’s Republic of China

Octaaminophenyl polyhedral oligomeric silsesquioxane(OAPS) was synthesized using three-step method andused to modify o-cresol-novolac epoxy resin (ECN) forprinted circuit board. The influence of OAPS on thereactivity and the final properties of the hybrid networkswere evaluated. The intercrosslinking reaction betweenECN and OAPS was confirmed by Fourier transforminfrared spectra. The ECN/OAPS hybrids have betterimpact strength, higher electrical resistivity and thermalstability, lower water absorption than the unmodifiedECN. The volume resistivity and surface resistivity ofthe hybrids increase by an order of magnitude or morecompared to the neat epoxy. The thermal stability ofthe hybrids improves by the incorporation of OAPS; theinitial decomposition temperature and char yield showan increasing tendency up to 4 wt% loading of OAPS.The hybrids exhibit higher storage modulus and glasstransition temperature (Tg) than the neat epoxy. The Tg

of the hybrids greatly improves up to 153.3�C at 3 wt%content, much higher than 119.4�C of the neat epoxy.POLYM. COMPOS., 34:1753–1760, 2013. VC 2013 Society ofPlastics Engineers

INTRODUCTION

Epoxy resin (EP) is one of the most important thermo-

setting materials due to their superior mechanical and

thermal properties and simplicity in processing, which has

been extensively used as adhesives, electronic encapsulat-

ing compounds, matrix of composites, coatings, and so

on. However, EP has many shortcomings such as brittle-

ness owing to high crosslinking densities, low stiffness

and strength, poor toughness, and so on. Therefore, it is

necessary to modify the EP to improve the comprehensive

properties of EP [1–4].

Meanwhile, organic–inorganic hybrid nanocomposite

materials have attracted increasing attentions because

they combine the advantages of inorganic materials

with those of organic polymers in recent years. Polyhe-

dral oligomeric silsesquioxanes (POSS) with empirical

formula RSiO1.5 [5] possesses a cage-like structure

ranging in size from 1 to 3 nm [6], which includes a

rigid inorganic core made up of silicon atoms linked by

oxygen atoms (SiO1.5) and organic groups (R) posi-

tioned at the vertices of the cages [7]. Compared with

traditional inorganic fillers, POSS has the advantages

of monodispersed size, low density, high thermal stabil-

ity, and good compatibility with polymer matrix. The

incorporation of POSS into EP can improve their ther-

mal resistance, mechanical strength, dielectric proper-

ties, flame retardancy [3,8]. Nowadays, many authors

have reported that EP modified by POSS through cur-

ing process promotes an improvement in use properties

[8–13]. The representative work was carried out by

Chen’s group [6], in which the nanocomposites involv-

ing diglycidyl ether of bisphenol A and octaamino-

phenyl polyhedral oligomeric silsesquioxane (OAPS)

were prepared.

Recently, many methods have been used to improve

the thermal stability, electrical properties, water absorp-

tion, mechanical properties, and dimensional stability of

EP for printed circuit board (PCB). In our work, OAPS

was synthesized based on the previous reports [13]

and was used directly to prepare a novel network with

o-cresol-novolac epoxy resin (ECN) for PCB. The aim

was to analyze the influence of OAPS on the reactivity

and the final properties of the network.

Correspondence to: Fu Jifang; e-mail: fjfshu@hotmail.com,

fjfshu@shu.edu.cn or Shi Liyi; e-mail: shiliyi@shu.edu.cn

Contract grant sponsor: Key Project of Chinese Ministry of Education;

contract grant number: 208182; contract grant sponsor: Shanghai Lead-

ing Academic Discipline Project; contract grant number: S30107; Con-

tract grant sponsor: Shanghai University Development Foundation;

contract grant number: A.10-0407-11-002; Contract grant sponsor: Pro-

gram for Professor of Special Appointment (Eastern Scholar) at Shang-

hai Institutions of Higher Learning; contract grant number: B.39-0411-

10-001; Contract grant sponsor: Education and Research for the Teacher

Professional Development Project; contract grant number: B.60-B407-

11-002; Contract grant sponsor: Key Subject of Shanghai Municipal

Education Commission; contract grant number: J50102.

DOI 10.1002/pc.22579

Published online in Wiley Online Library (wileyonlinelibrary.com).

VC 2013 Society of Plastics Engineers

POLYMER COMPOSITES—2013

EXPERIMENTAL

Materials

ECN was received from Shengyi Technology, China.

Phenyltrichlorosilane (PhSiCl3, �99%) was purchased

from Guangtuo Chemicals, Shanghai, China. Methyl hex-

ahydrophthalic anhydride (MeHHPA, �99%) was pur-

chased from Huicheng Electronic Material, Puyang,

Henan, China. Tetrahydrofuran (THF), acetone, ethyl ace-

tate, hydrazine, benzene were all analytically pure grade

and were supplied by Shanghai Reagent, China.

Synthesis of OAPS

According to the literature [13], OAPS was synthe-

sized following a three-step mechanism as described in

Scheme 1.

Synthesis of Octaphenyl Polyhedral OligomericSilsesquioxane (Ph8Si8O12)

PhSiCl3 (32 g, 0.154 mol) and benzene (120 mL) were

put into a three-necked flask (500 mL), equipped with a

magnetic stirrer, thermometer, and a dropping funnel. Then

the deionized water (225 mL) was added slowly into the

system at 10�C or lower. The hydrolysis was carried out at

room temperature for 2 days. Thereafter, the benzene layer

was isolated and washed for three times with deionized

water to remove the hydrochloric acid. The above benzene

solution and 10 mL of methanol solution of benzyltrime-

thylammonium hydroxide (50 wt%) were charged to a

flask equipped with a mechanical stirrer. The mixture was

refluxed for 48 h to ensure complete rearrangement reac-

tion. After that, the mixture was cooled to room tempera-

ture, and then white powder was obtained (14.17 g, 71.2

wt%). The product was extracted using benzene to remove

the soluble resin and further dried in vacuum.

Synthesis of Octanitrophenyl Polyhedral OligomericSilsesquioxane

The Ph8Si8O12 was nitrified using fuming nitric acid to

prepare octanitrophenyl polyhedral oligomeric silsesquioxane

(OnpPOSS). About 150 mL of fuming nitric acid was put

into a three-neck flask equipped with a magnetic stirrer, and

25 g of Ph8Si8O12 was added slowly within 30 min with stir-

ring at 0�C and followed by stirring at room temperature for

20 h. After that, the solution was poured into 250 g of ice.

A faintly yellow powder was collected by filtration. The pre-

cipitate was washed with saturated NaHCO3 aqueous solu-

tion and water, respectively, until the pH value is 7. The

obtained product was dried in a vacuum oven at 50�C for 24

h. Exhaustive extraction of solid with benzene afforded a

white microcrystalline powder (32.4 g, 89.7 wt%).

Synthesis of OAPS

OAPS was prepared by reducing OnpPOSS. 10 g of

OnpPOSS was dissolved in 80 mL of THF in a 250 mL

three-neck flask equipped with a water-cooled condenser

and a magnetic stirrer. Then, 1.22 g of Pd/C catalyst, 0.4

SCH. 1. The synthesis route of OAPS. [Color figure can be viewed in the online issue, which is available

at wileyonlinelibrary.com.]

1754 POLYMER COMPOSITES—2013 DOI 10.1002/pc

g of FeCl3�6H2O were put into the flask. The mixture

was heated to 54�C and hydrazine hydrate was slowly

dropped and then the mixture was reflexed for 5 h. After

that, the Pd/C catalyst was removed by filtration under

reduced pressure to obtain an orange solution and then

washed for several times using about 60 mL of ethyl ace-

tate. In the next step, the extracted organic solution was

washed using deionized water until it became almost col-

orless. Then the residual water in the colorless solution

was removed by reacting with magnesium sulfate

(MgSO4). Finally, the solution was precipitated with 1200

mL of petroleum ether. The pale powder was collected by

filtration under reduced pressure and further dried in vac-

uum at 50�C for 24 h. Yield: 6.2 g. Fourier transform

infrared (FTIR) spectra (cm21) with KBr powder: 3378

(NAH), 1120 (SiAOASi). 1H NMR (DMSO-d6): 7.7–8.8

(4H), 4.0–4.7 (2H).

Preparation of ECN/MHHPA/OAPS Nanocomposites

Various amounts of OAPS were previously dissolved

in THF and added into the desired quantity of ECN, and

then the mixture was kept stirring for 2 h at room temper-

ature. After that, a stoichiometric amount of MeHHPA

was added to the above mixture at room temperature, and

then the mixture of the three substances was stirred until

the mixture became homogenous. According to Table 1,

the contents of OAPS in the nanocomposites were con-

trolled to 1, 2, 3, 4, and 5 wt%, respectively.

The mixtures were degassed under vacuum at 80�C to

remove the solvent and gas. After that, the mixture was

poured into a preheated (80�C) aluminum mold (80 mm

310 mm 3 5 mm) and then cured and postcured following

the procedures of 90�C/1 h 1 100�C/1 h 1 110�C/1 h 1

120�C/12 h 1 160�C/6 h successively [14,15]. The result-

ing hybrids were transparent in each case. The reacting pro-

cess between ECN and OAPS is shown in Scheme 2:

CHARACTERIZATION

FTIR spectra were recorded between 400 and 4000

cm21 with a resolution of 4 cm21 on Avatar 370 spec-

trometer. The sample was pressed into a pellet with KBr.

Impact strength tests were performed using a JJ-20

impact tester according to China National Standard

GB1043-79. The three-dimension of specimen size was

80 mm 3 10 mm 3 4 mm. The flex strength was meas-

ured on an Instron Model 1185 test machine according to

ASTM D790-2010. The specimen size was also 80 mm

3 10 mm 3 4 mm. All of the mechanical properties

were obtained by averaging at least three measurements.

A JSM-6700F scanning electron microscope (SEM)

was used to study the morphology of the impact fracture

surface of EP containing POSS. The samples were coated

with a thin gold layer using a sputter coater prior to the

SEM observation to get a clear image of facture surface.

The resistivity was performed on an Angilent 4339B

megger at room temperature according to ASTM D257-

2007. The water absorption of the networks was tested

according to GB/T 1462-2005. Thermogravimetric analy-

ses (TGA) were also performed using TA Q500 HiRes

analyzer at a heating rate of 10�C/min in flowing nitrogen

from 25 to 700�C.

The dynamic mechanical tests were carried out on a

dynamic mechanical thermal analyzer (DMA, Q800, TA

Instrument Company) with the temperature range from 20

to 300�C. The frequency used is 1.0 Hz. The specimen

dimension was 35 mm 3 10 mm 3 2 mm.

RESULTS AND DISCUSSION

FTIR Spectral Analysis

Fig. 1 shows FTIR spectra of different contents of

OAPS-reinforced ECN/MeHHPA nanocomposites. The

disappearance of new peak at 1617 cm21 corresponding

to NAH bending included in OAPS demonstrated the

crosslinking reaction between the epoxy and OAPS. At

the same time, the SiAOASi peak at 1101 cm21 still

appeared after curing, which confirms that the cage struc-

ture made up of SiAOASi bond was very stable. In addi-

tion, OAH stretching of ECN was found at 3469 cm21

due to the reaction between ECN and OAPS [11].

Mechanical Properties

The effects of OAPS on impact strength of ECN/

MeHHPA are shown in Fig. 2. The incorporation of

OAPS (up to 5 wt%) into ECN/MeHHPA systems

enhanced impact strength, due to the presence of organic

groups such as phenyl, amino groups in the OAPS mole-

cule [16,17]. In the results, the impact strength reached

the highest when OAPS content was about 2 wt%, and

TABLE 1. Electrical properties of OAPS/ECN/MeHHPA hybrids.

Sample OAPS (wt%) Water absorption (%) Volume resistivity (X cm) Surface resistivity (X)

ECN/MHHPA 0 0.3491 6 0.0050 5.164 3 1016 2.459 3 1016

1 0.2194 6 0.0031 1.418 3 1017 6.899 3 1017

2 0.3380 6 0.0031 1.528 3 1017 1.886 3 1018

3 0.2328 6 0.0031 1.053 3 1017 1.839 3 1018

4 0.3195 6 0.0027 1.282 3 1017 7.094 3 1016

5 0.2587 6 0.0049 9.538 3 1016 2.569 3 1017

DOI 10.1002/pc POLYMER COMPOSITES—2013 1755

the impact strength of OAPS/ECN/MeHHPA was 15.31

kJ/m2, which was 1.3 times higher than that of ECN/

MeHHPA system. However, when OAPS content was

more than 3 wt%, the tendency of impact strength was

decreasing, but it was still higher than the unmodified

system.

Fig. 3 presents the flexural properties of neat ECN sys-

tems and OAPS/ECN/MHHPA systems. The introduction

of OAPS into ECN/MeHHPA network decreased the val-

ues of flexural strength compared to those of neat epoxy

systems due to the increased chain entanglement and

enhanced free volume imparted by OAPS [18,19].

As shown in Fig. 4, the samples were visually

observed in optical clarity of ECN/OAPS composites.

EP1, EP2, EP3 were transparent like EP0; with loading

content of OAPS increasing, PH4 and PH5 became dark.

In addition, the color of composites became deeper with

the increase of POSS content. One possible explanation

was that some OAPS did not react with ECN, which

could be oxidized by oxygen in the air to the color sub-

stances and the more OAPS content in composites led to

FIG. 1. FTIR spectra of different contents of OAPS-reinforced epoxy

nanocomposites. [Color figure can be viewed in the online issue, which

is available at wileyonlinelibrary.com.]

SCH. 2. The reacting process for the OAPS/ECN. [Color figure can be viewed in the online issue, which is

available at wileyonlinelibrary.com.]

1756 POLYMER COMPOSITES—2013 DOI 10.1002/pc

more color substances so that the color of composites

became deeper.

As shown in Fig. 5, the morphology of the cross-section

of samples after impact test was observed by SEM and was

used to analyze the influence of OAPS on the mechanical

properties of nanocomposites. Fig. 5a shows that the neat

epoxy has smooth surface [15]. Figure 5b–f present that the

ECN/OAPS hybrids had rougher surface with more river-

like lines than the pure ECN. The increased surface rough-

ness means that the matrix plastic deformation is the major

fracture surface phenomenon, which absorbs surface energy.

Therefore, ECN/OAPS hybrids had higher toughness than

the pure ECN, which was in agreement with the previous

results of impact strength. It is also observed that there

were no agglomerates of nanoparticles in the ECN/OAPS

hybrids, which suggests that the OAPS exhibits good dis-

persion in the ECN matrix.

Electrical Behavior

Water absorption of samples is presented in Table 1.

At first, the test was carried out by immersing specimens

of appropriate dimension in boiling water for 30 min 6

1min. It is very important for materials used for insulation

application to have low water absorption. Generally, the

absorbed water will affect the properties of the original

materials, such as thermal, mechanical, electrical proper-

ties, and so on, Through the experiment, compared with

that of ECN/MeHHPA curing systems, OAPS/ECN/

MeHHPA exhibited slightly lower values of water absorp-

tion, because the hydrophilic OH groups in EP react with

NH2 groups in OAPS. The presence of OAPS does not

influence the water absorption of the nanocomposites

very much due to the relatively small amount of OAPS.

Table 1 shows that the volume resistivity (qv) and the

surface resistivity (qs) of samples at various weight per-

cent of OAPS. The volume resistivity value of 5.164 3

1016 X cm and surface resistivity value of 2.549 3 1016

X cm2 were measured for the unmodified ECN. After

incorporation of OAPS, the volume resistivity and surface

resistivity increased by an order of magnitude or more,

which mean OAPS plays a key role in improving resistiv-

ity of resins. The nanocomposite at 2 wt% of OAPS dis-

played the highest resistivity, which substantially

increased the resistivity value to 1.528 3 1017 X cm and

FIG. 2. Impact strength curve of epoxy/OAPS composites.FIG. 3. Flexural properties]’ curve of ECN/MeHHPA/OAPS nanocom-

posites. [Color figure can be viewed in the online issue, which is avail-

able at wileyonlinelibrary.com.]

FIG. 4. The photos of epoxy/OAPS composites. [Color figure can be viewed in the online issue, which is

available at wileyonlinelibrary.com.]

DOI 10.1002/pc POLYMER COMPOSITES—2013 1757

1.886 3 1018 X cm2, respectively. This is because OAPS

has hollow structure, and the incorporation of OAPS

restricts the motion of the chain of polymer [3,16].

Thermal Properties

The TGA curves were carried out to evaluate the ther-

mal stability of ECN/MeHHPA and their POSS nanocom-

posites as shown in Fig. 6. The initial decomposition

temperature at 10 wt% loss weight (T10) of the hybrids

containing 1, 3, 4, and 5 wt% is 219.43, 284.78, 240.62,

and 112.26�C, respectively. T10 of the neat epoxy is

216.03�C. T10 of the hybrids showed an increasing tend-

ency up to 4 wt% loading of OAPS, but further addition

of OAPS decreased the decomposition temperature. 1

wt% of OAPS showed a little influence on EP. In

FIG. 5. SEM images of different contents of OAPS-reinforced epoxy nanocomposites: 0 (a), 1 wt% (b), 2

wt% (c), 3 wt% (d), 4 wt% (e), and 5 wt% (f).

FIG. 6. TGA of epoxy/OAPS composites. [Color figure can be viewed

in the online issue, which is available at wileyonlinelibrary.com.]

1758 POLYMER COMPOSITES—2013 DOI 10.1002/pc

addition, the char yield had the same tendency as the

decomposition temperature. The char yield of 3 wt% of

OAPS incorporated ECN/MeHHPA system was the high-

est. There have been many mechanisms proposed to

explain how OAPS improved thermal stability of EP. The

better explanation is that the incorporation of OAPS

restricts polymer chain motions and when OAPS

degraded, it can form an inert silica layer, which can pre-

vent further decomposition of the material [2,10,20].

However, the excessive OAPS at higher content may not

react with polymer completely and lead a decrease in the

crosslinking density [20–23].

DMA Analysis

As show in Fig. 7a, the tand (a) peak at 119.4�C is

attributed to the glass transition temperature (Tg) of the

neat epoxy. Hybrids containing 1, 3 wt% POSS give the

Tg of 119.8, 153.3�C, respectively. 1 wt% POSS exert lit-

tle influence on Tg and heat resistance. However, the

addition of 3 wt% POSS greatly improve the Tg of

hybrids. The increase in Tg can be explained that the

amine group of POSS can react with epoxy and increase

the effective crosslinking density at certain content. The

hybrids exhibit wider glass state and high modulus than

the neat epoxy, demonstrating the additional stiffness

imparted by POSS. These are due to the entangled net-

works and strong interaction between the ECN and rigid

POSS. The POSS with rigid cores and organic groups

play a great role in enhancing thermomechanical proper-

ties of the hybrids, which improve the filler–polymer

compatibilities and interaction [21,24,25].

CONCLUSION

In this article, various weight percentages of OAPS

were used to reinforce ECN. The hybrid networks con-

taining OAPS up to 5 wt% were obtained via in situ poly-

merization of ECN and curing agent MHHPA in the

presence of OAPS. FTIR analysis confirmed the chemical

interactions between ECN and OAPS. The impact

strength of nanocomposites increased with loading of

POSS, the good compatibility and uniform dispersion of

OAPS molecules in the polymer matrix and the toughness

mechanism were observed by SEM. However, the results

of flexural strength were not ideal, which will improve by

addition of sphere silica particles in our future work. The

addition of OAPS led to an increase in volume resistivity

and surface resistivity by an order of magnitude or more

compared to the unmodified ECN. The water absorption

of hybrids decreases slightly. The thermal stability of the

hybrids improves by the incorporation of OAPS, the T10

and char yield increases up 4 wt% POSS content and

decreased with further addition of OAPS. The DMA anal-

ysis indicates that the Tg and storage modulus of the

hybrids increase greatly compared to the neat epoxy,

demonstrating the additional stiffness and heat resistance

imparted by POSS.

ACKNOWLEDGMENTS

The authors would like to thank Mr. Y.L. Chu and Mr.

W.J Yu from Instrumental Analysis & Research Center of

Shanghai University for help with the SEM and TEM

measurement.

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