Synthesis and Characterization of PMMA/SiO2

Organic–Inorganic Hybrid Materials Via RAFT-MediatedMiniemulsion Polymerization

Jianying Ma,1,2 Mangeng Lu,2 Chunlei Cao,1 Huixuan Zhang1,3

1Engineering Research Center of synthetic resin and special fiber, Ministry of Education, Changchun Universityof Technology, Changchun 130012, People’s Republic of China

2Guangzhou Institute of Chemistry, Chinese Academy of Science, Guangzhou 510650,People’s Republic of China

3Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022,People’s Republic of China

In this article, we first carried out the surface modifica-tion of SiO2 using silane coupling agent KH570, andthen prepared PMMA/SiO2 organic–inorganic hybridmaterials by conventional free radical polymerizationand RAFT polymerization in miniemulsion, respectively.The kinetics comparisons of these two polymerizationswere studied. PMMA/SiO2 hybrid materials werecharacterized by gel permeation chromatography, dif-ferential scanning calorimetry and thermogravimetricanalysis. Experimental results indicated that the poly-merization behavior of MMA in miniemulsion showedcontrolled/living radical polymerization characteristicsunder the control of RAFT agent. Incorporation ofRAFT agent and SiO2 nanoparticles improved the ther-mal properties of polymers, the thermal stability ofpolymers increased with increasing content of SiO2

nanoparticles. The structures and morphologies ofSiO2, modified SiO2, and PMMA/SiO2 hybrid materialswere characterized by FT-IR and TEM. TEM resultsshowed that the addition of modified SiO2 nanopar-ticles to miniemulsion polymerization system obtaineddifferent morphology latex particles. Most of modifiedSiO2 nanoparticles were wrapped by polymer matrixafter polymerization. POLYM. COMPOS., 34:626–633, 2013.ª 2013 Society of Plastics Engineers

INTRODUCTION

Within past few decades, polymer/inorganic nanocom-

posites have attracted immense attention. In general, when

compared with conventional composites, the nanocompo-

sites exhibit significant improvements in physical proper-

ties such as thermal stability [1, 2], mechanical properties

[3], flame retardancy [4], and enhance modulus [5], due to

the much stronger interfacial interactions between nanopar-

ticles and polymer matrix [6–9]. Different types of nano-

particles are used depending on the purpose of the resulting

nanocomposites-common examples are silica, clay, carbon

nanotubes, and montmorillonite (MMT) [10]. The silica is

applied widely among these nanoparticles because of its

high strength and low density.

The mechanical properties of polymer/inorganic nano-

composites depend on the level of adhesion at the inter-

face between the dispersed and continuous phases. If the

surface of nanoparticles is incompatible with polymer

matrix, the polymer matrix and nanoparticles phases sepa-

rate, which will result in the agglomeration of the par-

ticles [11–13]. So the silica surface modification becomes

very important for its application in preparing polymer/

silica nanocomposites. Generally, the silica can be modi-

fied with silane coupling agents to improve the adhesion

between the particles and polymer matrix [14–17]. The

silane coupling agent can react with –OH groups of silica

surface, and an attached functionalized alkyl chain is

more compatible with the polymer matrix than the bare

surface of the silica. According to the functional groups

of coupling agent, either covalent bonds with the polymer

can be created or it may just provide an organic coating

on the silica which solvates the polymer.

In the last decade, the use of controlled/living radical

polymerization (CLRP) has attracted much attention in

the field of nanoscience and nanotechnology [18]. This is

due to many advantages that CLRP offers over other

polymerization techniques, such as precise control over

Correspondence to: Jianying Ma; e-mail: majianying60@163.com

DOI 10.1002/pc.22438

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

VVC 2013 Society of Plastics Engineers

POLYMER COMPOSITES—-2013

molecular architecture, the wide range of monomers that

can be used, and simple reaction conditions required. Up

to now, various controlled polymerization methods such

as nitroxide-mediated polymerization (NMP) [19, 20],

atom transfer radical polymerization (ATRP) [21, 22],

and reversible addition-fragmentation chain transfer

(RAFT) [23–27] are available and have been widely

applied to prepare polymer/inorganic hybrid materials. As

compared with the other CLRP techniques, RAFT poly-

merization has prominent advantages such as good

compatibility with a wide range of monomers and facile

experimental conditions which are similar to conventional

radical polymerization in adding chain transfer agents

(CTA) at the beginning of reaction [28, 29]. In RAFT

polymerization systems, pre-equilibrium and main equilib-

rium reactions lead to controlled and well-defined poly-

mers in a wide range of temperatures. Thus, it is a robust

method to prepare polymer-based nanocomposites having

a matrix with narrow polydispersity index (PDI).

Miniemulsion polymerization is a convenient one-step

technique that can be used for the incorporation of

nanolayered filler materials such as clay [30] and carbon

nanotubes [31] in polymer matrix. This technique offers

several advantages over other dispersion polymerization

techniques: efficient use of surfactant, high conversions,

high rates of polymerization, and yields final latex par-

ticles with high solids content, small particle size, and

high molar mass. The obtained particles are a 1:1 copy of

the miniemulsion droplets [32, 33]. The latter can be

attributed to the fact that the miniemulsion droplets are

directly polymerized, thus, the resulting polymer particles

are often one-to-one copies of the monomer droplets [33].

So in this work, we carried out surface modification of

SiO2 nanoparticles using silane coupling agent KH570,

then the PMMA/SiO2 hybrid materials were prepared via

conventional free radical and RAFT polymerizations in

miniemulsion to study the effects of nanoparticles loading

content on the hybrid materials properties, respectively.

Polymerization kinetics was followed by recording the

variations of monomer conversions, molecular weights

(Mn) and PDI during polymerization. The structural

and morphological characteristics of modified SiO2 and

PMMA/SiO2 hybrid materials were studied by FT-IR and

transmission electron microscopy (TEM) analyses. Mean-

while, the effects of SiO2 nanoparticles and RAFT agent

on the thermal properties of PMMA/SiO2 hybrid materials

were also investigated by differential scanning calorimetry

(DSC) and thermogravimetric analysis (TGA).

EXPERIMENTAL

Materials

Nano-silica (SiO2) was purchased (with a mesh of 20

W, Guangdong Ona New Material, China) and handled at

1008C for 4 h in a vacuum oven to evaporate the water

which adsorbed on the surface. Silane coupling agent

c-methacryloxypropyl trimethoxy silane (KH570) was

purchased (Shanghai Jing Chun Industrial, China) and

used without further purification. Methyl methacrylate

(MMA) was washed with sodium hydroxide aqueous

solution (5 wt%) for three times to remove inhibitors, fol-

lowed by deionized water until neutralization, and then

distilled under reduced pressure prior to miniemulsion

polymerization. The RAFT agent 2-([(tert-butylsulfanyl)-

carbonothioyl] sulfanyl) propanoic acid (BCSPA) was

synthesized similar to the procedure described in detail by

Ferguson et al. [34]. Potassium persulfate (KPS, 99%),

dodecyl sulfate sodium salt (SDS) and cetyl alcohol (CA)

were used as received. All other chemical were used with-

out other purification.

Surface Modification of SiO2

Surface modification of SiO2 was carried out as fol-

lowed. First, 5.0 g SiO2 and 250 mL THF were mixed in

an erlenmeyer flask and subjected to sonication using ul-

trasonic processor at a power output of 600 W for 60 min

at room temperature. Second, 5.0 g silane coupling agent

KH570 was added into the above solution and stirred to

react for 4 h at 708C. The obtained reaction mixture was

centrifuged at the rate of 4,000 r/min, the products were

washed with deionized water for three times and dried

under vacuum for 24 h at 608C, and finally the surface

modified SiO2 was obtained.

Preparation of PMMA/SiO2 Hybrid Materials

PMMA/SiO2 hybrid materials were prepared in minie-

mulsion mediated by RAFT mechanism as followed. The

miniemulsion polymerizations were performed in a 500-

mL four-necked flask which was placed in a water bath

thermostated at desired temperature. A number of minie-

mulsions were run with different contents of modified

SiO2 and RAFT agent. About 1.2 g surfactant SDS, 0.6 g

cosurfactant CA and different content of SiO2 were added

into 300 mL deionized water and stirred. RAFT agent

BCSPA and monomer MMA were added into the above

emulsion, and then the emulsion was subjected to sonica-

tion using ultrasonic processor at a power output of 600

W for 30 min at room temperature to obtain miniemul-

sion. The miniemulsion was moved into the 500-mL four-

necked flask with a mechanical stirrer, a thermometer, a

reflux cooler, and a N2 bubbler. About 5 mL deionized

water contained 0.12 g initiator KPS was injected to the

miniemulsion. The miniemulsion polymerization was ini-

tiated at 758C and lasted for 4 h under N2 protection. Dif-

ferent samples were taken to measure monomer conver-

sions at different reaction time during polymerization.

The polymer products were precipitated into methanol

and washed with distilled water for several times, then

dried under vacuum for 24 h at 508C, finally the PMMA/

SiO2 hybrid materials were obtained.

DOI 10.1002/pc POLYMER COMPOSITES—-2013 627

Solubility of PMMA/SiO2 Hybrid Materials

About 0.5 g pure PMMA and PMMA/SiO2 hybrid

materials with different content of modified SiO2 (0.5,

1.0, 2.0, and 5.0%) were added into 20 mL chloroform,

respectively. These mixtures were stirred 30 min to

observe the solubility.

Instrumentation

FT-IR. FT-IR spectra were carried out using RFX-65A

(Analects, America) Fourier transform-infrared spectrome-

ter at room temperature in the range from 4,000 to 500

cm–1, with a resolution of 2 cm–1 and 20 scans. Samples

were prepared by dispersing well the complexes in KBr

and compressing the mixtures to form disks.

Gel Permeation Chromatography. Gel permeation

chromatography (GPC) analysis were performed at a flow

rate of 0.80 mL min–1 and 258C in THF by using a

Waters 515 GPC (Waters, America) after calibrated with

standard polystyrene (PSt).

Differential Scanning Calorimetry. DSC measure-

ments were performed on Perkin-Elmer Pyris diamond

TA lab system (Perkin-Elmer, America) with a heating

rate of 108C min–1 under a nitrogen atmosphere.

Thermogravimetric Analysis. Thermal decomposition

behaviors were examined by means of TGA with a heat-

ing rate of 108C min–1 under a nitrogen atmosphere on a

Perkin-Elmer Pyris 1 thermogravimetric analysis (Perkin-

Elmer, America).

Transmission Electron Microscopy. The microstruc-

tures of samples were imaged using a JEM-100CX TEM

(JEOL, Japan). TEM samples were prepared by casting

one drop of a dilute miniemulsion onto a carbon-coated

copper grid.

RESULTS AND DISCUSSION

Structural Characterization

FT-IR spectra can characterize the molecular structures

of organic compounds, and different functional groups of

compounds can be distinguished based on different char-

acteristic peaks. In this article, we carried out the surface

modification of SiO2 using silane coupling agent KH570,

then the structures of SiO2 and modified SiO2 were con-

formed by FT-IR spectra.

According to the results shown in Fig. 1(a), some char-

acteristic peaks of SiO2 were observed. The characteristic

peaks at 1,000�1,150 cm–1 and 808 cm–1 corresponded to

the stretching vibration peaks of Si–O bond. The charac-

teristic peak at 1,640 cm–1 corresponded to the bending

vibration peaks of O-H bond. The characteristic peak at

3,412 cm–1 corresponded to the stretching vibration peaks

of Si–O–H and O–H, ascribed to the hydroxyl and

adsorbed water.

The general formula of silane coupling agent is repre-

sented by Y-R-SiX3. Here, X represents the alkoxy hydro-

lysis, and Y represents the reactive groups which can

react with polymers. During the surface modification of

SiO2, the X group firstly hydrolysis to silanol, then

reacted with the hydroxyl on the surface of SiO2 to form

chemical bonds. Meanwhile, the silanol of silane molecu-

lar also associated each other and formed network mem-

brane to cover on the surface of nanoparticles.

Figure 1(b) was the FT-IR spectra of modified SiO2.

When compared with Fig. 1(a), we found the appearance

of new characteristic peaks at 1,505 and 2,928 cm21. The

characteristic peak at 1505 cm21 was the vibration peak of

C–C, and at 2928 cm21 were the vibration peaks of –CH3

and –CH2. These results indicated the appearance of or-

ganic groups on the surface of modified SiO2, which would

improve the adhesion between the particles and polymer.

We prepared PMMA/SiO2 hybrid materials using

modified SiO2 in miniemulsion mediated by RAFT mech-

anism. Figure 1(c) was the FT-IR spectra of PMMA/SiO2

FIG. 1. FT-IR spectra of SiO2, modified SiO2 and PMMA/SiO2 hybrid

materials.

628 POLYMER COMPOSITES—-2013 DOI 10.1002/pc

hybrid materials. We can see from this spectra that the

deformation vibration characteristic peak of –CH2–

appeared at 1,450 cm–1, but the characteristic peak of

hydroxyl at 3,400 cm–1 obviously weakened compared

with the SiO2, this result indicated the hydroxyl on the

surface of modified SiO2 reacted with silane coupling

agent. In addition, the appearance of stretching vibration

of Si–O at 1,450 cm–1 indicated that the double bond of

silane coupling agent successfully linked onto the surface

of SiO2. The characteristic absorption peak at 1,630 cm–1

of –CH¼CH– further proved this conclusion, and weaken

of this characteristic absorption peak indicated that the

double bond of silane coupling agent had reacted with

monomer MMA. Moreover, the characteristic peak at

1,760 cm–1 corresponded to the absorption peak of

carbonyl, which illustrated the existence of PMMA, and

the stretching vibration of Si–C at 790 cm–1 indicated the

existence of silane coupling agent.

Polymerization Kinetics

In our study, PMMA/SiO2 hybrid materials were pre-

pared via conventional free radical polymerization and

RAFT polymerization in miniemulsion, respectively. We

investigated the effects of modified SiO2 nanoparticles

addition on polymerization kinetics. The recipes of pre-

paring PMMA/SiO2 hybrid materials were listed in Table

1. Here, the content of modified SiO2 nanoparticles was

based on the content of monomer MMA. For these RAFT

polymerizations in miniemulsion, the initial molar ratio of

[initiator]0/[RAFT agent]0/[monomer]0 was set at 1/4/900,

and the content of surfactant SDS and cosurfactant CA

were also shown in Table 1.

The monomer conversions, Mn and PDI of PMMA/

SiO2 hybrid materials with different content of modified

SiO2 nanoparticles were shown in Table 2. For the case

of sample 1 and sample 2, that is, the samples of pure

PMMA and PMMA/SiO2 hybrid materials which were

prepared via conventional miniemulsion polymerization,

the obtained polymers had high monomer conversions and

high molecular weights, but wide PDI. However, once the

RAFT agent was added into the polymerization system,

that is, the polymerization was performed via RAFT

mechanism, the PDI became narrow. Meanwhile, we can

see from these four hybrid materials (PMMA/SiO2-

3�PMMA/SiO2-6) prepared by RAFT polymerization that

the monomer conversions and molecular weights

decreased with increasing content of modified SiO2 nano-

particles in hybrid materials.

According to these results shown in Table 2, we

depicted the curves of molecular weights and PDI of

PMMA/SiO2 hybrid materials. From these curves in Fig.

2, we can clearly observe the effects of modified SiO2

nanoparticles content on molecular weights and PDI of

PMMA/SiO2 hybrid materials. For the hybrid materials

prepared by RAFT polymerization, though the PDI slightly

increased with increasing content of modified SiO2 nano-

particles in hybrid materials, the PDI were controlled in a

relatively narrow range. For the molecular weights of

hybrid materials, we can see that the experimental values

of molecular weights (Mn,exp) were close to the theoretical

value (Mn, th). The theoretical values of molecular weights

were calculated according the following equation [35].

Mn;th ¼½monomer�03Conversion

½RAFT�03MWmonomer þMWRAFT

Here, MWmonomer and MWRAFT were the molecular

weights of monomer and RAFT agent, [monomer]0 and

[RAFT]0 were their initial molar concentrations, respec-

tively. Therefore, based on the discussion on the effects of

modified SiO2 nanoparticles content on molecular weights

TABLE 1. Recipes of preparing PMMA/SiO2 hybrid materials via

RAFT polymerization in miniemulsion.

Sample

code SiO2 (g)

Monomer

(MMA, g)

RAFT

agent

(BCSPA, g)

Surfactant

Initiator

(KPS, g)SDS (g) CA (g)

PMMA/SiO2-1 0 40 0 1.2 0.6 0.12

PMMA/SiO2-2 0.2 40 0 1.2 0.6 0.12

PMMA/SiO2-3 0.2 40 0.423 1.2 0.6 0.12

PMMA/SiO2-4 0.4 40 0.423 1.2 0.6 0.12

PMMA/SiO2-5 0.8 40 0.423 1.2 0.6 0.12

PMMA/SiO2-6 2.0 40 0.423 1.2 0.6 0.12

TABLE 2. Results of preparing PMMA/SiO2 hybrid materials via

RAFT polymerization in miniemulsion.

Sample code Conversion (%) Mn (g/mol) PDI

PMMA/SiO2-1 98.4 38000 2.7

PMMA/SiO2-2 95.4 35000 2.2

PMMA/SiO2-3 92.6 21000 1.2

PMMA/SiO2-4 87.4 20000 1.2

PMMA/SiO2-5 83.2 19000 1.3

PMMA/SiO2-6 80.4 18000 1.4

FIG. 2. Effects of SiO2 content on the molecular weights and polydis-

persity index of PMMA/SiO2 hybrid materials.

DOI 10.1002/pc POLYMER COMPOSITES—-2013 629

and PDI of hybrid materials, we can conclude that the

RAFT polymerization in miniemulsion showed the charac-

teristics of controlled/living radical polymerization.

Solubility of PMMA/SiO2 Hybrid Materials

Generally, the solubility is an important influence

factor for applying polymer materials in some special

occasions, such as polymer coatings. The introduction of

inorganic nanoparticles to polymers can significantly

improve some properties, such as thermal stability, me-

chanical strength, flame retardance, and optical properties

[36–40]. Meanwhile, the inorganic nanoparticles also

affect the solubility of polymers. In our experiments, we

introduced modified SiO2 nanoparticles to PMMA and

investigated the solubility of hybrid materials in chloro-

form. The dissolving time of hybrid materials with differ-

ent content of modified SiO2 nanoparticles in chloroform

were different. Experimental results were shown in Table

3. From these results, we can see the pure PMMA could

quickly and completely dissolve in chloroform. However,

the solubility of polymers decreased with introduction of

modified SiO2 nanoparticles. PMMA/SiO2 hybrid materi-

als partly dissolved when the content of modified SiO2

nanoparticles was more than 2.0%. So we can speculate

that the PMMA/SiO2 hybrid materials can only partly dis-

solve or swelling with increasing content of modified

SiO2 nanoparticles. The pure PMMA and PMMA/SiO2

hybrid materials with lower content of modified SiO2

nanoparticles (0.5%, 1.0%) can completely dissolve in

chloroform. The SiO2 nanoparticles had higher surface

energy, and the PMMA molecular chains can be adsorbed

on the surface of SiO2 nanoparticles, then these molecular

chains entangled each other and formed physical cross-

linking. Meanwhile, the double bonds group of silane

coupling agent which were connected to the surface of

SiO2 nanoparticles reacted with the PMMA matrix and

formed chemical bonds, thus finally formed chemical

crosslinking. Therefore, the structures of hybrid materials

gradually became to insoluble crosslinked networks from

soluble linear molecular chains, which resulted in the sol-

ubility of PMMA/SiO2 hybrid materials decreased from

dissolving to swelling.

Thermal Properties of PMMA/SiO2 Hybrid Materials

Figure 3 illustrated the differential scanning calorime-

try traces for pure PMMA (1) and PMMA/SiO2 hybrid

materials (2�6). From the curves (2�6), we can see that

the Tg of these PMMA/SiO2 hybrid materials firstly

decreased after adding SiO2 nanoparticles to polymeriza-

tion system, then the Tg increased with increasing content

of modified SiO2 nanoparticles. The reason for decreasing

of Tg can be explained as followed. First, the silane cou-

pling agent with low Tg formed ductile interface layer

with polymers during polymerization, good compatibility

between polymer matrix and silane coupling agent made

the Tg of matrix decrease. Second, the small amount of

silane coupling agent can proliferate into matrix from the

surface of polymer particles and generate internal plastici-

zation with polymer matrix, resulting in decreasing of Tg.Third, the addition of SiO2 nanoparticles made the free

volume of its surrounding matrix slightly increase which

also resulted in decreasing of Tg. The SiO2 nanoparticles

which were modified by silane coupling agent played the

role of crosslinking points. On the one hand, these cross-

TABLE 3. Solubility of PMMA/SiO2 hybrid materials.

Content of

SiO2 (wt%) Solubility

0 Quickly and completely dissolved (3 min)

0.5 Completely dissolved after stirring a moment (5 min)

1.0 Completely dissolved after stirring a period of time (10 min)

2.0 Partly dissolved after stirring a period of time (10 min)

5.0 Partly dissolved after stirring a long time (30 min)

FIG. 3. DSC curves of PMMA/SiO2 hybrid materials with different

content of modified SiO2.

FIG. 4. TGA curves of PMMA/SiO2 hybrid materials with different

content of modified SiO2.

630 POLYMER COMPOSITES—-2013 DOI 10.1002/pc

linking points were beneficial to chain entanglement of

PMMA molecular segments, forming physical crosslink-

ing. On the other hand, the silane coupling agent reacted

with polymer matrix and formed the interface layer

between the nanoparticles and polymer matrix, forming

chemical crosslinking. The crosslinking density increased

with increasing content of modified SiO2, finally resulted

in increasing of Tg.Figure 4 showed the typical TGA thermograms of

weight loss as a function of temperature for pure PMMA

and PMMA/SiO2 hybrid materials. The figure showed no-

ticeable improvements in the thermal stability of PMMA/

SiO2 hybrid materials compared to pure PMMA,

expressed by a shift in the decomposition temperature to

higher temperatures. So the addition of modified SiO2

nanoparticles to polymers increased the thermal stability

of PMMA, and the thermal stability increased with

increasing content of modified SiO2 nanoparticles.

Generally, the addition of inorganic nanoparticles to

polymers can affect the thermal decomposition tempera-

tures Td of polymers. The Td was affected by these fac-

tors. First, the modified SiO2 nanoparticles played the role

of crosslinking points and resulted in increasing of ther-

mal decomposition temperatures. Second, the thermal

decomposition temperatures may decrease if the silane

coupling agent can not completely react with polymer

matrix during polymerization. In addition, the unreacted -

OH on the surface of SiO2 nanoparticles may continue to

TABLE 4. Initial decomposition temperature of PMMA/SiO2 hybrid materials with different content of modified SiO2.

PMMA/SiO2-1 PMMA/SiO2-2 PMMA/SiO2-3 PMMA/SiO2-4 PMMA/SiO2-5 PMMA/SiO2-6

T5%/8C 209 250 263 277 291 306

FIG. 5. TEM images of PMMA/SiO2 hybrid materials with different content of modified SiO2. (a) PMMA/SiO2-1, (b) PMMA/SiO2-2, (c) PMMA/

SiO2-3, (d) PMMA/SiO2-4, (e) PMMA/SiO2-5, and (f) PMMA/SiO2-6.

DOI 10.1002/pc POLYMER COMPOSITES—-2013 631

react and generate water. The existence of these small

molecules can decrease the thermal decomposition tem-

peratures.

From Fig. 4, we can see that the addition of modified

SiO2 nanoparticles increased the thermal decomposition

temperatures, and the thermal stability increased with

increasing content of modified SiO2 nanoparticles. The

phenomenon of decreasing of the thermal decomposition

temperatures did not appear. This result indicated that the

crosslinking points played the main role for the thermal

stability of polymers. The existence of modified SiO2

nanoparticles caused the appearance of a large number of

crosslinking networks, and the crosslinking networks den-

sity increased with increasing content of modified SiO2

nanoparticles. The length of motive molecular chains seg-

ments decreased when the crosslinking networks density

increased to a certain extant, and prevented the thermal

decomposition of materials, finally improved thermal sta-

bility of polymers.

Some thermal properties of PMMA/SiO2 hybrid mate-

rials were summarized in Table 4. According to these

results, we can see that the addition of modified SiO2

nanoparticles had a considerable effect on the thermal sta-

bility of polymers. The pure PMMA (1) began to decom-

pose at a low initial decomposition temperature 2098C,but the PMMA/SiO2 hybrid materials prepared by con-

ventional miniemulsion (2) had a higher initial decompo-

sition temperature 2508C compared with pure PMMA.

Meanwhile, the effect of RAFT agent on the thermal sta-

bility of polymers was similar to the effect of RAFT

agent on the Tg of polymers. The existence of RAFT

agent made the molecules chains regularly arrange in

polymers and finally increased the decomposition temper-

ature of polymers. We can clearly see from Table 4 that

the decomposition temperature of PMMA/SiO2 hybrid

materials prepared by RAFT polymerization in miniemul-

sion (3�6) were higher than 2608C. In addition, for these

several hybrid materials (3�6), the decomposition temper-

ature increased with increasing content of modified SiO2

nanoparticles in hybrid materials. These results indicated

that the addition of modified SiO2 nanoparticles can effec-

tively improve the thermal stability of polymers.

Morphological Characteristics of Hybrid Materials

The TEM images of pure PMMA and PMMA/SiO2

hybrid materials with different content of modified SiO2

nanoparticles were shown in Fig. 5. From these TEM

micrographs, we can see that the pure PMMA latex par-

ticles prepared by conventional miniemulsion polymeriza-

tion had smooth surface, and uniform sphericity, but

uneven particle sizes distribution. The addition of modi-

fied SiO2 nanoparticles to the polymerization system

obtained different morphology latex particles. Most of

modified SiO2 nanoparticles were wrapped by polymer

matrix after polymerization. So from these TEM micro-

graphs of PMMA/SiO2 hybrid materials, we can see the

brighter spherical particles of PMMA latex particles, and

there were no the existence of SiO2 nanoparticles.

CONCLUSIONS

A series of experiments were carried out to synthesize

PMMA and PMMA/SiO2 hybrid materials via conven-

tional free radical and RAFT polymerization in miniemul-

sion. The effects of modified SiO2 nanoparticles content

and incorporation of RAFT agent on the kinetics of poly-

merization and properties of corresponding hybrid materi-

als were investigated, respectively. Polymerization

kinetics studies showed that the monomer conversions

and molecular weights decreased with increasing content

of modified SiO2 nanoparticles in hybrid materials, but

the PDI increased with increasing content of modified

SiO2 nanoparticles. The PMMA/SiO2 hybrid materials

prepared by RAFT mechanism had narrower PDI. The

structures of modified SiO2 and PMMA/SiO2 hybrid

materials were analyzed by FT-IR. Experiments results

showed that organic groups were successfully introduced

to the SiO2 nanoparticles and reacted with polymer ma-

trix. The thermal properties of hybrid materials were char-

acterized by DSC and TGA. DSC characterization indi-

cated that the Tg of polymers first decreased with increas-

ing content of modified SiO2 nanoparticles then increased

again. TGA results showed that the introduction of modi-

fied SiO2 nanoparticles effectively improved the thermal

stability of polymers mainly because of the role of cross-

linking points of modified SiO2 nanoparticles, and the

thermal stability of polymers increased with increasing

content of modified SiO2 nanoparticles.

ABBREVIATIONS

SiO2 Nano-silica

KH570 c-methacryloxypropyl trimethoxy silane

MMT Montmorillonite

MMA Methyl methacrylate

BCSPA 2-([(tert-butylsulfanyl)-carbonothioyl] sulfanyl) pro-

panoic acid

KPS Potassium persulfate

SDS Dodecyl sulfate sodium salt

CA Cetyl alcohol

CLRP Controlled/living radical polymerization

NMP Nitroxide mediated polymerization

ATRP Atom transfer radical polymerization

RAFT Reversible addition fragmentation chain transfer

CTA Chain transfer agents

Mn Molecular weights

PDI Polydispersity index

FTIR Fourier transform-infrared

GPC Gel permeation chromatography

DSC Differential scanning calorimetry

TGA Thermogravimetric analysis

TEM Transmission electron microscopy

632 POLYMER COMPOSITES—-2013 DOI 10.1002/pc

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DOI 10.1002/pc POLYMER COMPOSITES—-2013 633