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Preparation and Characterization of POSS-SiO2/Cyanate Ester Composites With High Performance

Mengmeng Zhang, Hongxia Yan, Chao Liu, Junping ZhangDepartment of Applied Chemistry, School of Science, Northwestern Polytechnical University, XiAn, Shaanxi710129, Peoples Republic of China

In this article, a hybrid filler based on polyhedral oligo-meric silsesquioxane and silica, coded as POSS-SiO2,has been successfully synthesized. The structure ofPOSS-SiO2 was studied by Fourier-transform infraredspectra, X-ray diffraction, and scanning electronmicroscopy. Then the POSS-SiO2 was compoundedwith dicyclopentadiene bisphenol dicyanate ester(DCPDCE) resin to prepare composites. The effects ofPOSS-SiO2 on the curing reaction, mechanical, ther-mal, dielectric and tribological properties of DCPDCEresin were investigated systematically. Results of dif-ferential scanning calorimetry show that the additionof POSS-SiO2 can facilitate the curing reaction ofDCPDCE and decrease the curing temperature ofDCPDCE. Compared with pure DCPDCE resin, theimpact and flexural strengths of the composites mate-rials are improved markedly with up to 72 and 52%increasing magnitude, respectively. Meanwhile, thePOSS-SiO2/DCPDCE systems exhibit lower dielectricconstant and loss than pure DCPDCE resin over thetesting frequency from 10 to 60 MHz. In addition, thethermal stability and tribological properties of POSS-SiO2/DCPDCE composites are also superior to that ofpure DCPDCE resin. POLYM. COMPOS., 00:000000,2014. VC 2014 Society of Plastics Engineers

INTRODUCTION

Cyanate ester resins are important high-temperature

thermosetting resins. The cured cyanate ester resins

exhibit good mechanical properties, superior dielectric

properties, excellent adhesive properties and good mois-

ture resistance, etc. [1, 2]. These unique properties of cya-

nate resins make them excellent candidates for many

cutting-edge applications such as high-frequency numeric

printed circuit board, aerospace structures, adhesives and

functional materials [35]. It is well known that cyanate

ester monomers can be polymerized to form three-

dimensional networks of oxygen-linked triazine ring

through the cyclotrimerization reaction of three cyanate

ester groups. However, the cured cyanate ester resin con-

sists of stiff network of triazine groups with highly cross-

linking density, resulting in its brittleness that restricts its

further prosperity into the advanced industrial applica-

tions. Therefore, it has been a hot topic during the last

decade to modify and toughen cyanate ester resins. In

recent years, many researches have focused on improving

their performance by introducing different types of fillers,

such as nanoclays [6, 7], carbon nanotubes [8, 9], carbon

fibers [10, 11], and polyhedral oligomeric silsesquioxanes

[1214].

Polyhedral oligomeric silsesquioxanes (POSS) are a

family of nanoscale chemical structures that contain a

silicon-oxygen core based on (SiO1.5)n and have each

apex (silicon atom) connected to some organic groups

[15]. It is this combination of an inorganic core covered

with an organic shell at the molecular level that has led

POSS structures to being labeled as organicinorganic

hybrid materials. POSS are attracting increased attention

due to their unique cage-like molecular structures and

interesting physicochemical properties. In addition, POSS

possess not only good compatibility but also reactivity

with many thermosetting polymers. They have been used

to modify various thermosetting resins such as epoxy

[16], polyimide [17], phenolic resin [18], cyanate ester

resin [19], etc., and the results prove that they can be

used as effective fillers for the improvement in mechani-

cal, dielectric, thermal, and other physical properties.

As we all know, POSS are hard to process and very

expensive material. A composites that using only POSS

as a single filler is actually not relevant for certain indus-

trial purpose. This is where the idea of combination

POSS with other type of filler seems practical. Silica

(SiO2) is highly stable, chemically inert, shows high

mechanical strength and high susceptibility to modifica-

tions [20], and offers the possibility to improve properties

like mechanical [21, 22], thermal [23], and tribological

properties [24, 25]. In addition, it is much cheaper than

POSS, showing a great attraction for actual applications;

It is believed that by reducing the usage of POSS and

replaces it with SiO2, which is much cheaper as hybrid

fillers in composites will reduce the production cost

Correspondence to: H.X. Yan; e-mail: [email protected] 10.1002/pc.23091

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

VC 2014 Society of Plastics Engineers

POLYMER COMPOSITES2014

without compromising the mechanical properties of those

particular composites too much. However, SiO2 has a

strong tendency of particles to agglomerate because of its

high surface energy. The solgel process is one of the

techniques used to improve the dispersion of fillers in and

adhesion to a hydrophobic polymer matrix [26]. There-

fore, in order to develop POSS-based cyanate ester com-

posites with high performance and lower cost, the

combination of POSS and SiO2 through solgel process

can be a useful method for achieving homogeneous dis-

persion of fillers in cyanate ester matrix.

To our best knowledge, reports on the modification of

cyanate esters are mostly focused on bisphenol A dicya-

nate ester resins. However, comparing to bisphenol A

dicyanate ester, dicyclopendiene bisphenol dicyanate

esters (DCPDCE) have the advantages of higher glass

transformation temperature, better dielectric properties,

lower water absorption and more balanced mechanical

properties. Unfortunately, few works have been reported

on the studies of DCPDCE. Therefore, in this article, a

new hybrid filler based on POSS and SiO2, coded as

POSS-SiO2 was synthesized through sol mixing method

and used as a modifier to improve the properties of

DCPDCE resin. A series of POSS-SiO2/DCPDCE compo-

sites containing different contents of POSS-SiO2 were

developed by melt casting and then curing. The effects of

POSS-SiO2 on the mechanical, thermal, dielectric and tri-

bological properties of DCPDCE resin were investigated

to develop high performance materials.

EXPERIMENTAL

Materials

Dicyclopentadiene bisphenol diyanate ester (DCPDCE)

was purchased from Yangzhou Jiangdu Wuqiao Resin

Plant (Jiangsu, China), the structure of DCPDCE was

shown in Scheme 1. Chloropropyl POSS was synthesized

according to the literature [27]. Tetraethylorthosilicate

was purchased from Tianjin Fuchen Chemical Reagents

Factory (Tianjin, China). Ethanol was purchased from

Tianjin Tianli Chemical Reagents Co. Hydrochloric acid

was purchased from Beijing Chemical Works (Beijing,

China). Methanol was purchased from Tianjin Fuyu Fine

Chemical Co. (Tianjin, China). Dimethyl sulfoxide was

purchased from Guangdong Guanghua Sci-Tech Co.

(Guangdong, China). Sodium hydroxide was purchased

from Tianjin Jinbei Fine Chemical Co. (Tianjin, China).

Distilled water was produced from our laboratory. Other

reagents were all commercial products with analysis

grades.

Sample Preparation

Preparation of POSS-OH. In a 250-ml four-mouthflask holding a nitrogen inlet, mechanical stirrer, reflux-

condenser, constant-pressure funnel and thermometer,

optimum dimethyl sulfoxide (50 ml), and chloropropyl

POSS (2.0 g) were added. At 30C, sodium hydroxidesolution (0.1 mol/l, 50 ml) was slowly added into the

flask through the constant-pressure funnel. Then, the reac-

tion mass was slowly heated to 80C at which the reac-tion continued for 56 h. After that, the pH value of the

solution was adjusted to 7 using deionized water. Then

the water was removed from the product through a sepa-

ratory funnel. After separation, the obtained product was

dried at 60C in a vacuum oven for about 7 h to vaporizethe solvent. Finally, a white gel was obtained, which is

hydroxyl POSS, coded as POSS-OH.

Preparation of SiO2 sol. The SiO2 was prepared by asolgel technique using tetraethylorthosilicate as precur-

sor. In detail, tetraethylorthosilicate (25 ml) and ethanol

(25 ml) were charged into a glass beaker equipped with a

magnetic stirrer, then a mixture of distilled water (35 ml),

ethanol (25 ml), and hydrochloric acid (10 ml) was

slowly added into the breaker. And the reaction mass was

stirred at room temperature for 810 h. The obtained

SiO2 sol was kept still for further use.

Preparation of POSS-SiO2. POSS-OH (50 ml) andSiO2 sol (50 ml) were combined in a 500-ml conical flask

equipped with a magnetic stirrer. Ethanol (50 ml) was

subsequently added into the conical flask to dilute the sol

mixture. Then the reaction mixture was stirred for 12 h at

room temperature. The synthesis route of POSS-SiO2 was

shown in Scheme 2. The obtained POSS-SiO2 sol was

kept still for another 24 h, and then the ethanol was

vaporized.

Preparation of POSS-SiO2/DCPDCE Composites.The DCPDCE was heated to 100C in a glass beaker andkept at this constant temperature until melting. The appro-

priate amount of POSS-SiO2 was then carefully mixed

with the melted DCPDCE using a mechanical high shear

dispersion process. The mixture, consisting of prepolymer

and POSS-SiO2, was heated to 140C in an oil bath and

kept at this temperature for 1520 min with stirring. Then

the mixture was put into a preheated mold with release

agent followed by degassing at 140C for 1 h in a vac-uum oven. After that the mixture was cured and post-

cured via the procedures of 160C/1 h1 180C/1h1 200C/2 h1 220C/2 h and 240C/2 h, respectively.Finally, the mold was cooled to room temperature and

demolded to get the samples of POSS-SiO2/DCPDCE

system.

SCH. 1. The structure of DCPDCE.

2 POLYMER COMPOSITES2014 DOI 10.1002/pc

The samples of pure DCPDCE resin were prepared in

the same manner as above. All samples were dried at

120C under vacuum for 6 h and kept in a dry environ-ment prior to testing.

Measurements

Fourier Transform Infrared (FTIR) spectrum was

recorded between 400 and 4,000 cm21 with a resolution

of 2 cm21 on a Nicolet FTIR 5700 spectrometer. The

POSS-OH or POSS-SiO2 powder was mixed with potas-

sium bromide (KBr) powder, to form the homogeneous

mixture using a grinder, and then the mixture was com-

pression molded at 10 bar pressure to make a thin disc

for the test.

X-ray diffraction (XRD) investigation was carried out

using a XPert Pro MPD diffractometer with Cu Ka radi-ation (k5 0.154178 nm). The tube voltage was 36 kV,and the current was 20 mA. Scans were taken over the 2hrange of 585 with the scanning rate of 0.02/s.

Gel time was determined with a standard hot-plate

with a temperature controller. The resin (3.0 g) was

spread on the surface of the hot-plate preheated to a cer-

tain temperature. And the resin was stirred by a glass rod.

The time required for the resin to stop legging is called

the gel time. For each condition, three samples were

tested, and the data were averaged. Differential scanning

calorimetry (DSC, MDSC2910, TA Instruments) experi-

ments were performed at a heating rate of 10C/min in anitrogen atmosphere.

Impact strength was determined according to GB/

T2571-1995. Samples were cut into strips of (506 0.02)3 (76 0.02) 3 (46 0.02) mm3 by a cutting machine.The impact strength tests were performed using a Charpy

impact machine tester (XCJ-L, China). Five samples were

tested for each composition, and the results are presented

as an average for tested samples.

Flexural strength was measured according to GB/

T2570-1995. Samples were cut into strips of (806 0.02)3 (106 0.02) 3 (46 0.02) mm3. The flexural tests wereperformed using an electronic universal testing machine

(RIGER-20, China) at a crosshead speed of 2 mm min21.

Five samples were tested for each composition, and the

results are presented as an average for tested samples.

Scanning electron micrographs (SEM) were performed

on a HITACHIS-570 instrument. For SEM samples prepa-

ration, the specimens was sputtered with a thin layer

(about 10 nm) of gold by vapor deposition on a stainless

steel stub using a vacuum sputter coater.

Thermal gravimetrical analysis (TGA) tests were per-

formed by using Perkin Elmer TGA-7 at a heating rate of

5C/min in a nitrogen atmosphere from 50 to 800C.The dielectric constant and loss factor were measured

by a high frequency QBG-3 Gauger and a S914 dielectric

loss test set (China) at the frequency between 10 and 50

MHz. The sample dimension was (256 0.02) 3(256 0.02) 3 (36 0.02) mm3. For each condition, fivesamples were tested the data were averaged.

The tribological properties tests were measured accord-

ing to GB3960-83. The sample dimension was

(356 0.02) 3 (76 0.02) 3 (46 0.02) mm3. The tribolog-ical properties performed using a friction and wear testing

machine (MM-200). Before each test, the counterpart

steel ring and samples were abraded with No. 900 water-

abrasive paper. Then the steel ring and samples were

cleaned by acetone. All the friction and wear experiments

were conducted at room temperature. Friction coefficient

was measured under a load of 196 N and test duration of

120 min. The wear rate was measured using equation.

Wear rate5Dm/q. Where Dm is the weight loss of thesample and q is the density of samples in g/cm3.

SCH. 2. The synthesis route of POSS-SiO2.

DOI 10.1002/pc POLYMER COMPOSITES2014 3

RESULTS AND DISCUSSION

Characteristics of POSS-SiO2

The structure of POSS-SiO2 was characterized by various

spectroscopic measurements, including FTIR spectroscopy,

XRD, and SEM. Figure 1 shows FTIR spectra for the POSS-

OH and POSS-SiO2 hybrid. As expected, the FTIR spectrum

of POSS-OH shows the presence of hydroxyl groups

(3,409 cm21), CH (2,954 cm21), CSi (1,272 cm21), and

SiOSi (1,108 cm21). In the case of POSS-SiO2, as shown

in Fig. 1b, the peaks at around 3,410, 2,941, and 1,272 cm21,

which are assigned to OH, CH, and CSi, respectively,

continue to be observed. The broad band is found at around

1,090 cm21 corresponding to SiOSi and SiOC, and the

absorption peaks of SiOC are overlaid by the intense

absorption peaks of SiOSi. These observations suggest that

the SiO2 has been chemically grafted onto POSS-OH.

Further evidence on the successful grafting of the SiO2 onto

the POSS-OH can be demonstrated by XRD spectra, as shown

in Fig. 2. It can be seen that POSS-OH shows amorphous

bands over 2h 2022 in the XRD profile, and there stillexists some small sharp diffraction peaks, which indicates a

largely disordered structure with a low crystallinity. Although

SiO2 is crystalline, the XRD results of POSS-SiO2 show that

POSS-SiO2 is amorphous and displays a broad peak at 2h 22, which is a typical feature peak of amorphous silica [28,29]. This is because that SiO2 is chemically incorporated into

the POSS-OH and forms chemical bonds between POSS-OH

and SiO2, which destroyed the crystalline of SiO2.

SEM is used to investigate the morphology of POSS-

OH and POSS-SiO2 particles. Figure 3a represents the

micrograph of POSS-OH, it is found that the particles

size of POSS-OH is not uniform and there exists some

large aggregates. POSS-OH contains large amount of

reactive hydroxyl groups, so it is very easy for POSS-OH

molecules to copolymerize to form crosslinked network,

resulting in bigger molecular structures. In contrast, as

shown in Fig. 3b, the size of POSS-SiO2 particles is

much smaller. Because of the new chemical bonds form-

ing between POSS-OH and SiO2, the number of hydroxy

groups on the surface of POSS-OH is decreased and the

POSS-OH molecular aggregation is effectively prevented.

As a result, the particle size of POSS-SiO2 is decreased.

Curing behavior of POSS-SiO2/DCPDCE Composites

Gel time is generally used to evaluate the curing behav-

ior of a resin, a shorter gel time indicates a bigger curing

activity. Figure 4 depicts the gel time of DCPDCE resin

and POSS-SiO2/DCPDCE composites at different tempera-

tures, it can be observed that the addition of POSS-SiO2can effectively decrease the gel time of DCPDCE, indicting

that the addition of POSS-SiO2 can catalyze the gelation of

DCPDCE. This phenomenon is mainly contributed to the

intensive promotion of the curing reaction of DCPDCE by

OH groups in the molecule of POSS-SiO2 [12].

In order to further confirm the role of POSS-SiO2 on the

curing reaction of DCPDCE prepolymer, comparative DSC

analyses of DCPDCE resin and 1.0 wt% POSS-SiO2/

DCPDCE system at the heating rate of 10C/min were car-ried out, and the corresponding curves are depicted in Fig.

5. Comparing with DCPDCE, the maximum curing temper-

ature of POSS-SiO2/DCPDCE shifts to lower temperature

with a gap of about 10C, demonstrating that the curingprocess of DCPDCE can be accelerated by a small amount

of POSS-SiO2 loading. The decreased curing and post-

curing temperature is beneficial to manufacture cyanate

ester-based composites for industrial application.

Mechanical Properties of POSS-SiO2/DCPDCEComposites

Figure 6 shows the impact strengths of DCPDCE resin

and POSS-SiO2/DCPDCE systems. It is observed that all

FIG. 1. FTIR spectra of POSS-OH (a) and POSS-SiO2 (b). [Color fig-

ure can be viewed in the online issue, which is available at wileyonline-

library.com.]

FIG. 2. XRD spectra of POSS-OH (a) and POSS-SiO2 (b). [Color fig-

ure can be viewed in the online issue, which is available at

wileyonlinelibrary.com.]


the POSS-SiO2/DCPDCE composites exhibit higher

impact strengths than pure DCPDCE resin, and 1.0 wt%

POSS-SiO2/DCPDCE system has the maximum impact

strength (16.3 kJ/m2), which is increased by 72% com-

pared with that of pure DCPDCE, indicating that the

addition of POSS-SiO2 can significantly improve the

toughness of DCPDCE resin. Figure 7 shows the flexural

strengths of DCPDCE resin and POSS-SiO2/DCPDCE

systems, and a similar trend can be observed. The 1.0

wt% POSS-SiO2/DCPDCE system has the maximum flex-

ural strength (140.1 MPa), which is increased by 52%

compared with that of pure DCPDCE resin. Therefore, it

can be concluded that the addition of POSS-SiO2 can effi-

ciently improve the mechanical properties of DCPDCE

resin. The toughening and reinforcing effects of POSS-

SiO2 loading can be contributed to the two facts. First,

the POSS-SiO2 particles inherently posses excellent

mechanical properties, which can bring obviously tough-

ening and reinforcing effects on the molecular chains. On

one hand, they can efficiently distribute the stresses con-

centrated on the tip of the cracks. On the other hand, they

can exist in the way of cracks to prevent their develop-

ment [30]. Second, the OH groups in the molecule of

POSS-SiO2 can react with NCO in DCPDCE, leading to

improved interfacial bonding strength between fillers and

matrix. For the POSS-SiO2/DCPDCE system, the proba-

bility of forming a strong combination will be enhanced.

Therefore, the mechanical properties of POSS-SiO2/

DCPDCE system are increased as the contents of POSS-

SiO2 from 0.0 to 1.0 wt%. However, when the fillers con-

tent is high enough (>1.0 wt%), the mechanical proper-ties of the composites decrease with the increasing

concentration of fillers. When the content of fillers is too

large, the concentration of POSS-SiO2 is big enough to

form aggregates, and thus reducing the mechanical

FIG. 3. SEM photographs of POSS-OH and POSS-SiO2 particles (a: POSS-OH; b: POSS-SiO2).

FIG. 4. Dependence of gel time on temperature for DCPDCE and

POSS-SiO2/DCPDCE systems. [Color figure can be viewed in the online

issue, which is available at wileyonlinelibrary.com.]

FIG. 5. DSC curves of DCPDCE and 1.0 wt% POSS-SiO2/DCPDCE

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

able at wileyonlinelibrary.com.]


properties. But the 1.5 wt% POSS-SO2/DCPDCE system

still possesses better mechanical properties than neat

resin.

In order to further confirm the effect of POSS-SiO2 on

the toughness of DCPDCE resin, SEM images of the frac-

ture surfaces of samples after impact tests are taken and

shown in Fig. 8, it can be observed that pure DCPDCE

resin has smooth and river like surface, exhibiting a typi-

cal brittle feature (Fig. 8a). While with the incorporation

of POSS-SiO2 into DCPDCE resin, the fracture surface

becomes much rougher, and there exist large amount of

ductile sunken areas, exhibiting a typical rough feature

(Fig. 8b). It is also noted that there exists no obvious

aggregates on the fracture surface of POSS-SiO2/

DCPDCE system, which suggests that appropriate amount

of POSS-SiO2 particles can be dispersed in the DCPDCE

matrix homogeneously.

Thermal Properties of POSS-SiO2/DCPDCE Composites

Figure 9 displays TGA and corresponding differential

thermogravimetric (DTG) thermograms for pure DCPDCE

and 1.0 wt% POSS-SiO2/DCPDCE system. Compared to

that of pure DCPDCE, the TGA curve of the POSS-SiO2/

DCPDCE system shifts toward higher temperature and

the onset temperature of thermal degradation for the

POSS-SiO2/DCPDCE system is increased from 390C for

pure DCPDCE to 408C. The peak decomposition tem-perature of the DTG curve represents the temperature at

which the maximum weight loss rate is reached. The

peak decomposition temperature of the POSS-SiO2/

DCPDCE system appears at about 433C and is increasedby about 10C compared to that of pure DCPDCE. Theseresults indicate that the addition of POSS-SiO2 improves

the thermal stability of DCPDCE resin, which can be

attributed to the following reasons. Firstly, POSS-SiO2introduces a large amount of SiO and SiC bonds, which

possess large bonding energies. This is favorable for

increasing the thermal stability of the composites. Sec-

ondly, the POSS-SiO2 particles dispersed in the resin act

as physical interlock points in the cured resin, which can

provide a sterically hindered environment and restrain the

mobility of polymer chains [31]. Thirdly, the good inter-

facial adhesion between POSS-SiO2 and DCPDCE resin

also provides contribution to the increase in thermal sta-

bility. Specifically, a strong interfacial adhesion is benefi-

cial in restricting the segmental motions and thus

increasing the energy consumption of polymer chains

degradation.

Dielectric Properties of POSS-SiO2/DCPDCE Composites

Figure 10 shows overlay plots of dependence of dielec-

tric constant on frequency for pure DCPDCE resin and

modified systems. It can be seen that the dielectric con-

stants of POSS-SiO2/DCPDCE systems are lower than

those of DCPDCE resin, and the higher the POSS-SiO2concentration is, the lower the dielectric constant. Mean-

while, the dielectric constant and loss of POSS-SiO2/

DCPDCE system remain stable over the testing frequency

band from 10 to 60 MHz. The decrease in dielectric con-

stant may be explained by the following reasons. First,

POSS-SiO2 possesses many unoccupied spaces. Incorpo-

ration of POSS-SiO2 into DCPDCE resin is like introduc-

ing air bubbles into the matrix, while the dielectric

constant of air is very low (about 1), so the addition of

POSS-SiO2 will inevitably reduce the dielectric constant

of DCPDCE matrix. Second, the addition of POSS-SiO2into DCPDCE resin promotes the self-polymerization of

NCO groups, which increases the productivity of symmet-

rical triazine rings (or decreases the polarization of the

resultant structure), and the modified DCPDCE system

tends to form networks with greater symmetry and larger

space hinder, which is beneficial for decreasing the

dielectric constant [32]. In addition, small amount of

FIG. 6. Impact strengths of DCPDCE resin and POSS-SiO2/DCPDCE

systems.

FIG. 7. Flexural strengths of DCPDCE resin and POSS-SiO2/DCPDCE

systems.


POSS-SiO2 can fill the space between polymeric chains

of DCPDCE. The regularity of the POSS-SiO2/DCPDCE

system will be enhanced, decreasing the number of polar-

ized groups in the resin [33]. This is also one reason that

POSS-SiO2/DCPDCE systems have lower dielectric con-

stants than DCPDCE resin.

Dielectric loss is mainly dependent on the polarity of

polymeric molecules and the density of polar groups. The

higher the polarity of molecules and the density of polar

groups, the higher the dielectric loss will be. Figure 11

displays the effect of POSS-SiO2 on the dielectric loss of

POSS-SiO2/DCPDCE systems. The change in dielectric

loss versus content of POSS-SiO2 is similar to that of

dielectric constant. As discussed earlier, the incorporation

of POSS-SiO2 can increase the symmetry and space

hinder of cured network, and the network will become

more insensitive to polarize relaxation. Moreover, with

POSS-SiO2 filling the molecular space between polymer

chains, the molecular space is smaller compared with the

original DCPDCE, and the mobility of chain segments

will be restricted, thus reducing the relaxation loss of con-

ductive dipole segment. As a result, the dielectric loss

factors of POSS-SiO2/DCPDCE systems are decreased

compared with pure DCPDCE resin.

Tribological Properties of POSS-SiO2/DCPDCEComposites

The curves of variation in friction coefficient with slid-

ing time for the composites with various POSS-SiO2 con-

tents are shown in Fig. 12. It can be seen that the friction

coefficient starts with a running-in period followed by a

steady state period. This is mainly due to the formation

of wear debris between the friction surfaces during the

running-in period. This wear debris is compacted and

back transfers onto the friction surface, lowering the fric-

tion coefficient in the steady state period [34]. In addi-

tion, it is found that the friction coefficient decreases

FIG. 8. SEM photographs of fracture surfaces for pure DCPDCE and POSS-SiO2/DCPDCE system (a: pure

DCPDCE; b: 1.0 wt% POSS-SiO2/DCPDCE system).

FIG. 9. Overlay TGA and DTG curves of DCPDCE resin and 1.0 wt%

POSS-SiO2/DCPDCE system. [Color figure can be viewed in the online

issue, which is available at wileyonlinelibrary.com.]

FIG. 10. Dielectric constants of DCPDCE resin and POSS-SiO2/

DCPDCE systems versus frequency. [Color figure can be viewed in the

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


from 0.38 to 0.32 with the small addition (0.5 wt%) of

POSS-SiO2 into DCPDCE resin, and which continually

decreases with the continuous increase in POSS-SiO2content in POSS-SiO2/DCPDCE systems. In case of 1.5

wt% POSS-SiO2/DCPDCE system, its friction coefficient

is 0.26, which is much lower than that of pure DCPDCE

resin.

Figure 13 shows the wear rates of the composites with

various POSS-SiO2 contents. It is observed that the addi-

tion of POSS-SiO2 also results in a decrease in the wear

rate, and the 1.0 wt% POSS-SiO2/DCPDCE system has

the minimum value of 1.7 3 106 mm3/Nm, which isdeceased by 65% compared with pure DCPDCE resin.

These results indicate that the incorporation of POSS-

SiO2 can improve the tribological properties of DCPDCE

resin. The improvement in tribological properties may be

attributed to the following facts. First, the rigid and hard

POSS-SiO2 particles in matrix can efficiently distribute

the stresses during constant sliding, and hence reduce fric-

tion and wear. Second, the interface adhesion between the

fillers and matrix is good, which is also favorable for

improving the tribological properties of DCPDCE resin.

Another assumption is a rolling effect of particles. In

some researches with various material pairs [35, 36], a

rolling effect of the nano- or microscale particles could

be expected under certain wear conditions, e.g., surface

roughness and hardness of the material pairs and particles

etc. This effect could reduce both the friction coefficient

and the wear rate.

CONCLUSIONS

A novel kind of high-performance composite has been

prepared by a melting mixing method with POSS-SiO2 as

filler and DCPDCE as matrix. The incorporation of

POSS-SiO2 can catalyze and accelerate the reaction of

DCPDCE resin. Meanwhile, the appropriate content of

POSS-SiO2 can significantly enhance the mechanical

properties including flexural and impact strengths of

DCPDCE resin. Moreover, the POSS-SiO2/DCPDCE sys-

tems exhibit better thermal stability, dielectric and tribo-

logical properties than pure DCPDCE resin. Especially,

when the concentration of POSS-SiO2 is 1.0 wt%, the

best overall performance of POSS-SiO2/DCPDCE compo-

sites can be achieved. The attractive features suggest that

POSS-SiO2/DCPDCE composites have great potential in

the fabrication of high-performance materials such as

adhesives, coating, electronic packaging, etc., for cutting-

edge industries.

REFERENCES

1. A. Gu, Compos. Sci. Technol., 66, 1749 (2006).

2. W. Ling, A. Gu, G. Liang, and L. Yuan, Polym. Composite.,31, 307 (2010).

FIG. 11. Dielectric loss factors of DCPDCE resin and POSS-SiO2/

DCPDCE systems versus frequency. [Color figure can be viewed in the

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

FIG. 12. Variation curves of friction coefficient with sliding time for

DCPDCE resin and POSS-SiO2/DCPDCE systems. [Color figure can be

viewed in the online issue, which is available at wileyonlinelibrary.

com.]

FIG. 13. Wear rates of DCPDCE resin and POSS-SiO2/DCPDCE

systems.


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