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A novel route to the synthesis of PP-g-PMMA copolymer via ATRP reaction initiated by Si–Cl bond
European Polymer Journal 43 (2007) 109–118
EUROPEAN POLYMER JOURNAL www.elsevier.com/locate/europolj
A novel route to the synthesis of PP-g-PMMA copolymer via ATRP reaction initiated by Si–Cl bond Huayi Li, Haichuan Zhao, Xiaofan Zhang, Yingying Lu, Youliang Hu
*
Joint Laboratory of Polymer Science and Materials, Key Laboratory of Engineering Plastics, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100080, PR China Received 11 August 2006; received in revised form 10 October 2006; accepted 16 October 2006 Available online 28 November 2006
Abstract The copolymerization of propylene with allyldimethylsilane (ADMS) was carried out with conventional Ziegler–Natta catalyst supported on MgCl2. The effects of the concentration of ADMS in the feed on the polymerization reaction and copolymer properties were investigated. The resulting copolymer PP-co-ADMS was chlorinated to PP–Si–Cl by refluxing the copolymer with SOCl2 in benzene. The chlorinated copolymer was used to initiate ATRP of MMA with CuCl/ PMDETA as catalyst to produce graft copolymer PP-g-PMMA, which was characterized with 1H NMR, 13C NMR, GPC and DSC. Polymer blend of iPP/PP-g-PMMA/PMMA was prepared and the results shown that PP-g-PMMA was an effective compatilizer. 2006 Elsevier Ltd. All rights reserved. Keywords: Polypropylene; Functionalization; Allyldimethylsilane; Copolymerization; Ziegler–Natta catalyst; Coordination polymerization; ATRP; Graft copolymer
1. Introduction Polyolefins are relatively inert materials with poor performance in adhesion, printability, paintability and compatibility. The functionalization of polyolefin has been a challenge in the academic and industrial fields. Direct copolymerization of aolefin with polar comonomers is one facile way to prepare functional polyolefin. However, the heteroatoms such as N, O and S with base nature in polar
* Corresponding author. Tel.: +86 10 6256 2815; fax: +86 10 6255 4061. E-mail address: [email protected] (Y. Hu).
comonomers usually poison the polymerization catalysts with Lewis acid nature. The functional reactions of polyolefin involving silane monomers have several advantages. Silane is almost neutral and has little negative effect on the coordination catalyst. The functional reactions of silane, which include hydrolysis, alcoholysis, free radial reaction, halogenation and Si–H addition with C@C bond, are diversified and the reaction conditions are mild [1]. Longi and Rossi [2] and Asanuma and Matsuyama [3] synthesized propylene/allylsilane and propylene/vinylsilane copolymers using the traditional Ziegler–Natta catalysts and studied the crosslinking reactions of the copolymers initiated by alkali/ alcohol and c-ray, respectively. In recent years,
0014-3057/$ - see front matter 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.eurpolymj.2006.10.010
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allyltrimethylsilane [4] and 7-octenyldimethylphenylsilane [5] were copolymerized with ethylene by metallocene catalysts to modify polyethylene. The reactive phenylsilane group was post treated to alcoxy- and halosilane groups [6]. Marks and Koo [7] synthesized silyl-capped and silyl-linked atactic polypropylene using single-site cationic metallocene catalysts and functionalized the prepared polymer via oxidative cleavage of C–Si bond to C–OH bond, obtaining OH-capped atactic polypropylene. However, the graft polyolefin copolymer has not been synthesized via the functional reactions mentioned above as a result of the absence of an appropriate initial system. Recently we found that chlorotrimethylsilane/CuCl/N,N,N 0 ,N00 ,N00 pentamethyldiethyltriamine could act as a new initiating system for the atom transfer radical polymerizations (ATRP) of methyl methacrylate (MMA) and styrene [8]. This ATRP reaction is expected to prepare graft and block polyolefin copolymers. In this paper, we designed a new silane comonomer, allyldimethylsilane (ADMS), to prepare polyolefin copolymer. The copolymer of propylene with allyldimethylsilane was synthesized in the presence of traditional MgCl2 supported Ziegler–Natta catalyst. The copolymer was chlorinated by SOCl2 to convert the Si–H bond to Si–Cl bond. Then the chlorinated copolymer was used to initiate the ATRP of MMA to prepare isotactic polypropylene (iPP) graft copolymer. 2. Experimental section 2.1. Materials All O2 and moisture-sensitive manipulations were carried out inside an argon-filled drybox. Toluene and ethyl ether were refluxed with sodium/benzophenone under argon for over 24 h and distilled before use. Allyl chloride was dried over anhydrous CaCl2 and distilled before use. Dichlorodimethylsilane and thionyl chloride (SOCl2) was distilled before use. Propylene (polymerization grade) was provided by YanShan Petrochemical Co. Ltd. and used as received. Conventional Ziegler–Natta catalyst (named CS-II catalyst, MgCl2/TiCl4/dibutyl phthalate, Ti: 3.38 wt.%) was provided by Yingkou Xiangyang chemical plant. N,N,N 0 ,N00 ,N00 -pentamethyldiethyltriamine (PMDETA, Aldrich, 99%) and triethylaluminum (TEA, Aldrich, diluted to 1.8 mol/L in toluene) were used as received. MMA and benzene were dried over CaH2 and distilled
under reduced pressure before use. CH2Cl2 was dried over P2O5 and distilled before use. CuCl was washed by glacial acetic acid, absolute ethanol and ethyl ether in turn and then dried under vacuum. The others reagents not mentioned were purchased from Beijing Chemical Reagents Company and used as received. Allylchlorodimethylsilane was synthesized by the reaction of allylmagnesium chloride and dichlorodimethylsilane [9]. PMMA (Mn = 2.26 · 105, Mw/Mn = 1.20) was synthesized according to the literature [8]. 2.2. Characterization The 1H NMR and 13C NMR spectra were recorded on a Bruker 300 MHz spectrometer with deuterated orthodichlorobenzene without internal standard (for polymer, at 100 C) or CDCl3 as solvents. Molecular weight (Mw and Mn) and molecular weight distribution (Mw/Mn) were determined by high temperature gel-permeation chromatography (GPC) at 140 C on a PL-GPC220 instrument using 1,2,4-trichlorobenzene as solvent and mobile phase. Polystyrene standard was used for calibration. The melting temperatures (Tm) and glass transition temperatures (Tg) of polymers were performed on differential scanning calorimetry (DSC) using Perkin–Elmer DSC-7 at the heat rate of 10 C/min and determined by the second scan. Field emission scanning electron microscopy (FESEM) was performed on JEOL JSM 6700 F at 3.0 kV. FESEM samples were prepared from cuboids cyrofractured in liquid N2 and coated with a thin layer of gold prior to FESEM observation. 2.3. Synthesis of Allyldimethylsilane (ADMS) To a slurry of 5.6 g (0.15 mol) of lithium aluminium hydride in 20 mL of anhydrous ethyl ether cooled in an ice-water bath was added dropwise 40.0 g (0.30 mol) of allylchlorodimethylsilane in 40 mL of ethyl ether during 1 h. The mixture was then stirred overnight and filtrated through celite. After most of the ether was distilled out at 50 C from the filtrate, the residue was distilled under reduced pressure at 50 C to give crude product, which was then subjected to a distillation through a short Vigreux. The fraction of 69–70 C was pure allyldimethylsilane. The yield was 25.6 g (86%). 1H NMR (300 MHz, CDCl3): d = 5.77–5.84 (m, 1H, CH2@CH), 4.86–4.91 (m, 2H, CH2@CH), 3.85–
H. Li et al. / European Polymer Journal 43 (2007) 109–118
111
3.89 (m, 1H, Si–H), 1.59–1.62 (dd, 2H, Si–CH2), 0.08–0.10 (d, 6H, Si–CH3).
catalyst residue and then dried under vacuum at 60 C for 12 h.
2.4. Synthesis of copolymer of propylene with ADMS (PP-co-ADMS)
2.7. Polymer blending
In a typical experiment, a round 250 mL flask equipped with a magnetic stirrer was dried in vacuo at 80 C for 1 h and then charged with propylene at atmospheric pressure. The flask was cooled down to the temperature needed and 60 mL of toluene, ADMS and 2 mL of TEA were injected into the reactor. After the solution was saturated with propylene, 50 mg of CS-II catalyst (Ti = 3.6 mmol, Al/Ti = 100) was added and the polymerization started. During the polymerization, propylene was feed continuously and the pressure kept constant at atmospheric pressure. The polymerization was carried out at 40 C for 30 min and terminated by the addition of 15 mL of ethanol. The produced polymer was washed with ethanol three times and dried under vacuum at 60 C for 12 h. 2.5. Chlorination of PP-co-ADMS A mixture of 2.6 g of PP-co-ADMS (run 6), 50 mL of benzene and 10 mL of SOCl2 was refluxed at 100 C under argon for 36 h and cooled to ambient temperature. The chlorinated PP-co-ADMS (PP–Si–Cl) was filtered and washed with CH2Cl2 under argon and dried under vacuum at 60 C for 12 h. 2.6. Synthesis of PP-g-PMMA graft copolymer via ATRP reaction initiated by PP–Si–Cl In a typical experiment, 0.30 g of PP–Si–Cl, 0.10 g of CuCl, 10 g of MMA and 20 mL of toluene were added to a 100 mL round flask equipped with a magnetic stirrer and a reflux condenser. The flask was degassed by three freeze-pump-thaw cycles and recharged with argon. PMDETA (0.20 g) was added and the mixture was stirred for 5 min at ambient temperature. The flask was placed in a thermostated oil bath at 100 C. The reaction was stopped by addition of a lager amount of ethanol and polymer powders precipitated. The graft copolymer was washed with ethanol to remove the Cu complex and subjected to a vigorous extraction process by refluxing acetone in a Soxhlet extractor under argon for 6 h to remove any PMMA homopolymer and
All the blends were performed in solution to obtain molecular level mixing. The mixture of polymers was dissolved in refluxing xylene under argon to prevent oxidation. After the polymer mixture formed a clear, homogeneous solution, the solution was precipitated quickly into cold alcohol. The blend was dried under vacuum and then moulded to prepare the FESEM sample. 3. Results and discussion 3.1. Synthesis of copolymer of propylene with ADMS (PP-co-ADMS) The conditions and results of the copolymerization of propylene with ADMS are listed in Table 1. The effect of the concentration of ADMS in the feed on the polymerization and copolymer properties was investigated. The content of ADMS in the copolymer increases linearly with the feed of ADMS (Fig. 1). The weight average molecular weight of the copolymer decreases when a little amount of comonomer ADMS is added, but keeps approximately constant with the further increase of the feed of ADMS. The activity of the Ziegler–Natta catalyst decreases with the addition of ADMS (Fig. 2). This can be explained by two reasons. Firstly, the enchainment of ADMS with large size pendent (CH3)2SiH group on the central metal hinders sterically the incorporation of the next propylene molecule. Secondly, the agostic interaction [10,11] between the hydrogen atom in Si–H bond and the Ti atom of Ziegler–Natta catalyst may hinder the incorporation of the propylene molecule because the electronegativity of H atom (2.1) is higher than Si atom (1.8). The electron cloud density around the H atom is stronger than that around the Si atom in Si–H bond, which is on the contrary to the case of C–H bond where the electronegativity of C atom is 2.5. The agostic interaction between the Ti atom and the H atom of Si–H bond can be established easily and strongly (Scheme 1). The molecular weight distributions of the copolymers are broad (9.3–10.5), which is the typical character of the conventional Ziegler–Natta catalyst with multiple active centers. The incorporation of ADMS units destroys the crystallinity of polypropylene
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Table 1 The conditions and results of the copolymerization of propylene with ADMSa Run
ADMS in the feed (mol/L)
Yield (g)
Activity (kg/mol Ti Æ h)
ADMS in copolymerb (mol.%)
Tm (C)
Mwc (103 g/mol)
Mw/Mnc
1 2 3 4 5 6 7
0 0.05 0.10 0.21 0.32 0.42 0.53
8.4 6.7 6.3 5.6 4.4 4.0 3.7
404 319 302 269 212 192 178
0 0.10 0.20 0.45 0.67 0.83 1.06
159.8 159.4 158.7 157.4 157.2 156.5 156.3
302.7 242.5 223.6 220.7 225.2 224.2 226.4
10.4 10.5 9.8 9.6 10.2 9.8 9.3
a
Activity of the Ziegler-Natta catalyst (kg/mol. Ti.h)
Content of ADMS in the copolymer (mol %)
Copolymerization conditions: toluene 60 mL; CS-II catalyst: 50 mg (Ti = 0.36 mmol); Al/Ti: 100; reaction time: 30 min; temperature: 40 C ; propylene: 1 atm. b Calculated from 1H NMR. c Determined by PC.
1.2
1.0
0.8
0.6
0.4
0.2
0.0 0.0
0.1
0.2
0.3
0.4
0.5
0.6
350
300
250
200
150 0.0
Concentration of ADMS in the feed (mol/L)
0.1
0.2
0.3
0.4
0.5
0.6
Concentration of ADMS in the feed (mol/L)
Fig. 1. The dependence of the content of ADMS in copolymer on the concentration of ADMS in the feed.
chain and decreases the Tm of the copolymer. However, the extent of the decreasing is low, which results in less negative influence on the performance of the copolymer. The reactivity ratios of propylene and ADMS were estimated according to the Fineman–Ross extrapolation method [12]. The calculation is based on Eq. (1): a a=b ¼ rP ða2 =bÞ rC
400
ð1Þ
wherein a is the mole ratio of propylene (P) and comonomer (C) in the feed, b is the mole ratio of propylene and comonomer in the copolymer, rP is the reactivity ratio of propylene and rC is the reactivity ratio of comonomer. The propylene concentration in toluene was calculated according to the literature [13]. Fig. 3 shows the plot of a2/b versus a a/b and the least squares best-fit line. The
Fig. 2. The influence of the concentration of ADMS in the feed on the activity of catalyst.
P
LnTi+
δ−
H
δ+ Si
CH3
CH3
Scheme 1. The agostic interaction between the Ti atom and the H atom of the Si–H bond.
results are: rP = 78.73 ± 0.80, rC = 0.096 ± 0.006, rP · rC = 7.56 and the correlation coefficient R = 0.999. rP is much higher than rC, which indicates that it is hard to form the homopolymer of ADMS and the block copolymer of propylene and ADMS.
H. Li et al. / European Polymer Journal 43 (2007) 109–118
The typical 1H NMR and 13C NMR spectra of the copolymer (run 7) are shown in Fig. 4. The resonance signals centering at 0.91 ppm, 1.31 ppm and 1.62 ppm correspond to CH3, CH2 and CH in propylene units, respectively. The resonance signals at 0.11 ppm and 4.05–4.15 ppm correspond to Si–CH3 and Si–H, respectively. The chemical shift of Si–CH2 is immerged into the hydrogen chemical shifts of propylene unit and cannot be detected clearly. The content of ADMS in the copolymer is calculated by the ratio of two integrated intensities between Si–H and protons in propylene unit. Two resonance signals centered at 4.66 ppm and 4.72 ppm arise from the vinylidene end-group of copolymer [14], which indicates that b-H transfer chain-termination mechanism exists. The 13C NMR spectrum of PP-co-ADMS is similar to that
14
12
rP = 78.73 ± 0.80 rC = 0.096 ± 0.006 rP×rC = 7.56
10
a-a/b
8
6
4
2
0 0.00
0.02
0.04
0.06
0.08
0.10
0.12
0.14
0.16
0.18
2
a /b
Fig. 3. The reactivity ratios of propylene and ADMS estimated according to the Fineman–Ross extrapolation method.
Fig. 4. (a) 1H NMR and (b)
113
13
C NMR spectra of PP-co-ADMS.
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Fig. 5. 1H NMR spectrum of chlorinated PP-co-ADMS.
of typical isotactic polypropylene [14] except the chemical shift at 3.27 ppm corresponding to Si–CH3. 3.2. Chlorination of PP-co-ADMS SOCl2 is usually used as chlorination agent to change Si–H to Si–Cl [15]. This chlorination reaction is highly selective to the Si–H bond. The chlorination of PP-co-ADMS was carried out by refluxing PP-co-ADMS with SOCl2 in benzene. The polymer was swelled during the reaction. After the chlorination reaction, SOCl2 was separated easily by filtration. The 1H NMR spectrum of the chlorinated copolymer (PP–Si–Cl) is shown in Fig. 5. Compared with the 1H NMR spectrum of PP-co-ADMS, the intensities of doublet resonance signal at 0.11 ppm and signal between 4.05 and 4.15 ppm reduce and a new singlet signal at
0.43 ppm corresponding to Si(CH3)–Cl arises. The conversion of Si–H to Si–Cl can be calculated by the ratio of integrated intensities of these two signals. After reaction for 36 h, the conversion is up to 55%. The chlorination reaction was also carried out with CCl4 as solvent without the change of the other conditions. The 1H NMR spectrum shown that the conversion of Si–H to Si–Cl was about 15%. The lower conversion is possibly caused by the worse swelling of PP-co-ADMS by CCl4 than that by benzene. 3.3. Synthesis of PP-g-PMMA graft copolymer The graft polymerization of MMA initiated by PP–Si–Cl/CuCl/PMDETA was carried out in toluene at 100 C (Scheme 2). The effect of polymerization time on the conversion of MMA and Mn of
Ziegler-Natta catalyst +
CH2
CH n
CH2
CH m CH2
CH3 CH3
Si
CH3
CH3
H
SOCl2 benzene
Si
CH3
H
MMA CH2
CH x
CH2
CH y
CH2
CuCl/PMDETA CH2
CH3 CH3
Si
CH3
Cl
Scheme 2. The synthesis of PP-g-PMMA.
CH x
CH2
CH y CH2
CH3 CH3
Si PMMA
CH3
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Table 2 The conditions and results of the graft copolymerization of MMA initiated by PP–Si–Cl/CuCl/PMDETAa Run
Time (h)
Yield (g)
Conversion (%)
PMMA in copolymer wt.%
MMA/P mol/mol
Tgb (C)
Mnc (g/mol)
Mw/Mnc
8 9 10 11 12
0 2 4 8 12
0.30 0.56 0.72 1.05 1.47
– 2.6 4.2 7.5 11.7
– 46.4 58.3 71.4 79.6
0 27/73 37/63 51/49 62/38
– n.d. n.d. n.d. 92.1
22,870 29,740 35,460 52,700 67,700
9.8 8.3 7.1 6.2 5.3
Polymerization conditions: PP–Si–Cl: 0.30 g (Si–Cl content: 3.26 · 105 mol); toluene: 20 mL; temperature: 100 C ; CuCl: 0.10 g; MMA: 10 g; PMDETA: 0.20 g. b Determined by DSC; n.d: not determined. c Determined by GPC. a
graft copolymer has been investigated (Table 2). The dependence of ln([M0]/[M]) of MMA on the polymerization time is linear (Fig. 6a), which is similar to the ATRP of MMA initiated by Me3SiCl/ CuCl/PMDETA [8]. The crude graft copolymer was extracted with acetone to remove the PMMA homopolymer. The result shows that the PMMA
0.14
0.12
ln([M0]/[M])
0.10
homopolymer is less than 5 wt.% of the crude copolymer. The Mn of the graft copolymer determined by GPC increases linearly with the conversion of MMA (Fig. 6b). The GPC curves of PP-co-ADMS (run 6) and PP-g-PMMA (run 11 and run 12) are shown in Fig. 7. The GPC traces of the grafted polypropylene shift toward high molecular weight region. According to the definition of molecular weight distribution, the molecular weight distribution of block and graft copolymer with two components (Mw co/Mn co) can be expressed as following equation: M wco aM w1 þ bM w2 ¼ M nco aM n1 þ bM n2
0.08
0.06
0.04
0.02
0.00 0
2
4
6
8
10
12
ð2Þ
where a and b are molecular fractions of two components respectively. Calculated according to Eq. (2), Mw co/Mn co is between Mw1/Mn1 and Mw2/ Mn2. Polypropylene (component 1) prepared by Ziegler–Natta catalyst is characterized with broad
Time (h)
PP-co-ADMS run 4 PP-g-PMMA run 11 PP-g-PMMA run 12
70000
Mn of PP-g-PMMA
60000
50000
40000
30000
20000 0
2
4
6
8
10
12
Conversion of MMA %
Fig. 6. (a): Dependence of ln ([M0]/[M]) on polymerization time of MMA, and (b) dependence of Mn of PP-g-PMMA on the conversion of MMA.
2
3
4
5
6
7
log M
Fig. 7. GPC curves of PP-co-ADMS (run 4) and PP-g-PMMA (run 11 and 12).
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H. Li et al. / European Polymer Journal 43 (2007) 109–118
molecular weight distribution, but PMMA (component 2) prepared by ATRP is characterized with narrow molecular weight distribution. For the graft copolymer of polypropylene and PMMA prepared in this study, a, b, Mw1 and Mn1 are constant but Mw2 and Mn2 increase with the content of PMMA. Therefore, Mw/Mn of PP-g-PMMA should decrease with the increase of the content of PMMA. As expected, Mw/Mn of PP-g-PMMA determined by GPC decreases from 9.8 (run 8) to 5.3 (run 12) with the increase of the PMMA content (Table 2). Tg of the PMMA side chain is detected by DSC, which is 92.1 C (run 12) (Fig. 8). The typical 1H NMR spectrum of PP-g-PMMA (run 12) is shown in Fig. 9. In addition to the major signals corre-
sponding to PP and PMMA, the signals corresponding to Si–H (0.11 ppm) and Si–CH3 (4.05– 4.15 ppm) are also observed. It was known that Si–H bond could react with carbon free radical to generate Si free radical and C–H bond [1]. However, the reaction between the Si–H bond in PP–Si–Cl and the free radical in the ATRP reaction of MMA can be ignored. Because the concentrations of the carbon radical of ATRP reaction [16] and the Si–H bond in PP–Si–Cl are both very low and the Si–H bond located in the swell polypropylene chain is less mobile. Therefore, the probability of the reaction between Si–H and carbon free radical in the ATRP reaction is very small. Moreover, 1H NMR spectrum (Fig. 9) proves that the Si–H bond is preserved after the ATRP reaction. It indicates that the Si–H bond do hardly participate in the ATRP reaction and the propagation carbon free radical is seldom disturbed by Si–H bond. 3.4. PP-g-PMMA used as compatilizer
Tg = 92.1 o C a
b 50
100
150
Temperature (ºC)
Fig. 8. DSC curves of (a) PP-co-ADMS (run 4) and (b) PP-gPMMA (run 12).
The graft copolymer was first proven by Molau test [17]. iPP (run 1), PP-g-PMMA (run 12) and PMMA were dispersed in acetone and milky colloidal suspension solution was produced, which indicated not only that the graft structure existed but also that the graft copolymer could be a potential good compatilizer in polymer blend. In order to investigate the compatibility of PP-g-PMMA copolymer in iPP and PMMA blends, two polymer blends have been performed. One is a simple mixture of 80/20 weight ratio of iPP and PMMA and
Fig. 9. 1H NMR spectrum of PP-g-PMMA (run 9).
H. Li et al. / European Polymer Journal 43 (2007) 109–118
117
Fig. 10. FESEM images of the cross-sections of two polymer blends: (a) two homopolymers with PP/PMMA = 80/20 (2000·); (b) (10000·); (c) two homopolymers and PP-g-PMMA with PP/PP-g-PMMA/PMMA = 75/10/15 (2000·) and (d) (10,000·).
the other is comprised of 75/15/10 weight ratio of iPP, PMMA and PP-g-PMMA (run 12). Fig. 10 shows the FESEM micrographs of the cross-sections of the two polymer blend samples cyrofractured in liquid N2. In the homopolymer blend (Fig. 10a and b), the polymer shows grossly phase-separated as can be seen by the PMMA phase which exhibits nonuniform and the size of PMMA phase is big. The PMMA domains are pulled out of the PP matrix. The polymer blend containing the graft copolymer shows a totally different morphology in Fig. 10c and d. The cross-section exhibits almost flat mesa-like regions similar to that of pure iPP and size of PMMA phase domains is smaller, which proves that PP-g-PMMA is an effective compatilizer in iPP/PMMA blends. 4. Conclusion The copolymerization of propylene with allyldimethylsilane (ADMS) was carried out in the pres-
ence of the conventional Ziegler–Natta catalyst. With the increase of the concentration of ADMS in the feed, the content of ADMS unit in the copolymer increased linearly, but the catalyst activity decreased. PP-co-ADMS was chlorinated to PP– Si–Cl by refluxing with SOCl2. PP–Si–Cl was used to initiate ATRP of MMA with CuCl/PMDETA as catalyst. The graft polymerization reaction occurred efficiently. This is a new route to prepare graft polyolefin copolymer via silane. The PP-gPMMA copolymer was proved to be an effective compatilizer in iPP/PMMA blends by FESEM.
Acknowledgement The authors express thanks for the supports of the National Science Foundation of China (No. 20334030, No. 50403024 and No. 50573081) and China Petroleum & Chemical Corporation (SINOPEC).
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EUROPEAN POLYMER JOURNAL www.elsevier.com/locate/europolj
A novel route to the synthesis of PP-g-PMMA copolymer via ATRP reaction initiated by Si–Cl bond Huayi Li, Haichuan Zhao, Xiaofan Zhang, Yingying Lu, Youliang Hu
*
Joint Laboratory of Polymer Science and Materials, Key Laboratory of Engineering Plastics, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100080, PR China Received 11 August 2006; received in revised form 10 October 2006; accepted 16 October 2006 Available online 28 November 2006
Abstract The copolymerization of propylene with allyldimethylsilane (ADMS) was carried out with conventional Ziegler–Natta catalyst supported on MgCl2. The effects of the concentration of ADMS in the feed on the polymerization reaction and copolymer properties were investigated. The resulting copolymer PP-co-ADMS was chlorinated to PP–Si–Cl by refluxing the copolymer with SOCl2 in benzene. The chlorinated copolymer was used to initiate ATRP of MMA with CuCl/ PMDETA as catalyst to produce graft copolymer PP-g-PMMA, which was characterized with 1H NMR, 13C NMR, GPC and DSC. Polymer blend of iPP/PP-g-PMMA/PMMA was prepared and the results shown that PP-g-PMMA was an effective compatilizer. 2006 Elsevier Ltd. All rights reserved. Keywords: Polypropylene; Functionalization; Allyldimethylsilane; Copolymerization; Ziegler–Natta catalyst; Coordination polymerization; ATRP; Graft copolymer
1. Introduction Polyolefins are relatively inert materials with poor performance in adhesion, printability, paintability and compatibility. The functionalization of polyolefin has been a challenge in the academic and industrial fields. Direct copolymerization of aolefin with polar comonomers is one facile way to prepare functional polyolefin. However, the heteroatoms such as N, O and S with base nature in polar
* Corresponding author. Tel.: +86 10 6256 2815; fax: +86 10 6255 4061. E-mail address: [email protected] (Y. Hu).
comonomers usually poison the polymerization catalysts with Lewis acid nature. The functional reactions of polyolefin involving silane monomers have several advantages. Silane is almost neutral and has little negative effect on the coordination catalyst. The functional reactions of silane, which include hydrolysis, alcoholysis, free radial reaction, halogenation and Si–H addition with C@C bond, are diversified and the reaction conditions are mild [1]. Longi and Rossi [2] and Asanuma and Matsuyama [3] synthesized propylene/allylsilane and propylene/vinylsilane copolymers using the traditional Ziegler–Natta catalysts and studied the crosslinking reactions of the copolymers initiated by alkali/ alcohol and c-ray, respectively. In recent years,
0014-3057/$ - see front matter 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.eurpolymj.2006.10.010
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allyltrimethylsilane [4] and 7-octenyldimethylphenylsilane [5] were copolymerized with ethylene by metallocene catalysts to modify polyethylene. The reactive phenylsilane group was post treated to alcoxy- and halosilane groups [6]. Marks and Koo [7] synthesized silyl-capped and silyl-linked atactic polypropylene using single-site cationic metallocene catalysts and functionalized the prepared polymer via oxidative cleavage of C–Si bond to C–OH bond, obtaining OH-capped atactic polypropylene. However, the graft polyolefin copolymer has not been synthesized via the functional reactions mentioned above as a result of the absence of an appropriate initial system. Recently we found that chlorotrimethylsilane/CuCl/N,N,N 0 ,N00 ,N00 pentamethyldiethyltriamine could act as a new initiating system for the atom transfer radical polymerizations (ATRP) of methyl methacrylate (MMA) and styrene [8]. This ATRP reaction is expected to prepare graft and block polyolefin copolymers. In this paper, we designed a new silane comonomer, allyldimethylsilane (ADMS), to prepare polyolefin copolymer. The copolymer of propylene with allyldimethylsilane was synthesized in the presence of traditional MgCl2 supported Ziegler–Natta catalyst. The copolymer was chlorinated by SOCl2 to convert the Si–H bond to Si–Cl bond. Then the chlorinated copolymer was used to initiate the ATRP of MMA to prepare isotactic polypropylene (iPP) graft copolymer. 2. Experimental section 2.1. Materials All O2 and moisture-sensitive manipulations were carried out inside an argon-filled drybox. Toluene and ethyl ether were refluxed with sodium/benzophenone under argon for over 24 h and distilled before use. Allyl chloride was dried over anhydrous CaCl2 and distilled before use. Dichlorodimethylsilane and thionyl chloride (SOCl2) was distilled before use. Propylene (polymerization grade) was provided by YanShan Petrochemical Co. Ltd. and used as received. Conventional Ziegler–Natta catalyst (named CS-II catalyst, MgCl2/TiCl4/dibutyl phthalate, Ti: 3.38 wt.%) was provided by Yingkou Xiangyang chemical plant. N,N,N 0 ,N00 ,N00 -pentamethyldiethyltriamine (PMDETA, Aldrich, 99%) and triethylaluminum (TEA, Aldrich, diluted to 1.8 mol/L in toluene) were used as received. MMA and benzene were dried over CaH2 and distilled
under reduced pressure before use. CH2Cl2 was dried over P2O5 and distilled before use. CuCl was washed by glacial acetic acid, absolute ethanol and ethyl ether in turn and then dried under vacuum. The others reagents not mentioned were purchased from Beijing Chemical Reagents Company and used as received. Allylchlorodimethylsilane was synthesized by the reaction of allylmagnesium chloride and dichlorodimethylsilane [9]. PMMA (Mn = 2.26 · 105, Mw/Mn = 1.20) was synthesized according to the literature [8]. 2.2. Characterization The 1H NMR and 13C NMR spectra were recorded on a Bruker 300 MHz spectrometer with deuterated orthodichlorobenzene without internal standard (for polymer, at 100 C) or CDCl3 as solvents. Molecular weight (Mw and Mn) and molecular weight distribution (Mw/Mn) were determined by high temperature gel-permeation chromatography (GPC) at 140 C on a PL-GPC220 instrument using 1,2,4-trichlorobenzene as solvent and mobile phase. Polystyrene standard was used for calibration. The melting temperatures (Tm) and glass transition temperatures (Tg) of polymers were performed on differential scanning calorimetry (DSC) using Perkin–Elmer DSC-7 at the heat rate of 10 C/min and determined by the second scan. Field emission scanning electron microscopy (FESEM) was performed on JEOL JSM 6700 F at 3.0 kV. FESEM samples were prepared from cuboids cyrofractured in liquid N2 and coated with a thin layer of gold prior to FESEM observation. 2.3. Synthesis of Allyldimethylsilane (ADMS) To a slurry of 5.6 g (0.15 mol) of lithium aluminium hydride in 20 mL of anhydrous ethyl ether cooled in an ice-water bath was added dropwise 40.0 g (0.30 mol) of allylchlorodimethylsilane in 40 mL of ethyl ether during 1 h. The mixture was then stirred overnight and filtrated through celite. After most of the ether was distilled out at 50 C from the filtrate, the residue was distilled under reduced pressure at 50 C to give crude product, which was then subjected to a distillation through a short Vigreux. The fraction of 69–70 C was pure allyldimethylsilane. The yield was 25.6 g (86%). 1H NMR (300 MHz, CDCl3): d = 5.77–5.84 (m, 1H, CH2@CH), 4.86–4.91 (m, 2H, CH2@CH), 3.85–
H. Li et al. / European Polymer Journal 43 (2007) 109–118
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3.89 (m, 1H, Si–H), 1.59–1.62 (dd, 2H, Si–CH2), 0.08–0.10 (d, 6H, Si–CH3).
catalyst residue and then dried under vacuum at 60 C for 12 h.
2.4. Synthesis of copolymer of propylene with ADMS (PP-co-ADMS)
2.7. Polymer blending
In a typical experiment, a round 250 mL flask equipped with a magnetic stirrer was dried in vacuo at 80 C for 1 h and then charged with propylene at atmospheric pressure. The flask was cooled down to the temperature needed and 60 mL of toluene, ADMS and 2 mL of TEA were injected into the reactor. After the solution was saturated with propylene, 50 mg of CS-II catalyst (Ti = 3.6 mmol, Al/Ti = 100) was added and the polymerization started. During the polymerization, propylene was feed continuously and the pressure kept constant at atmospheric pressure. The polymerization was carried out at 40 C for 30 min and terminated by the addition of 15 mL of ethanol. The produced polymer was washed with ethanol three times and dried under vacuum at 60 C for 12 h. 2.5. Chlorination of PP-co-ADMS A mixture of 2.6 g of PP-co-ADMS (run 6), 50 mL of benzene and 10 mL of SOCl2 was refluxed at 100 C under argon for 36 h and cooled to ambient temperature. The chlorinated PP-co-ADMS (PP–Si–Cl) was filtered and washed with CH2Cl2 under argon and dried under vacuum at 60 C for 12 h. 2.6. Synthesis of PP-g-PMMA graft copolymer via ATRP reaction initiated by PP–Si–Cl In a typical experiment, 0.30 g of PP–Si–Cl, 0.10 g of CuCl, 10 g of MMA and 20 mL of toluene were added to a 100 mL round flask equipped with a magnetic stirrer and a reflux condenser. The flask was degassed by three freeze-pump-thaw cycles and recharged with argon. PMDETA (0.20 g) was added and the mixture was stirred for 5 min at ambient temperature. The flask was placed in a thermostated oil bath at 100 C. The reaction was stopped by addition of a lager amount of ethanol and polymer powders precipitated. The graft copolymer was washed with ethanol to remove the Cu complex and subjected to a vigorous extraction process by refluxing acetone in a Soxhlet extractor under argon for 6 h to remove any PMMA homopolymer and
All the blends were performed in solution to obtain molecular level mixing. The mixture of polymers was dissolved in refluxing xylene under argon to prevent oxidation. After the polymer mixture formed a clear, homogeneous solution, the solution was precipitated quickly into cold alcohol. The blend was dried under vacuum and then moulded to prepare the FESEM sample. 3. Results and discussion 3.1. Synthesis of copolymer of propylene with ADMS (PP-co-ADMS) The conditions and results of the copolymerization of propylene with ADMS are listed in Table 1. The effect of the concentration of ADMS in the feed on the polymerization and copolymer properties was investigated. The content of ADMS in the copolymer increases linearly with the feed of ADMS (Fig. 1). The weight average molecular weight of the copolymer decreases when a little amount of comonomer ADMS is added, but keeps approximately constant with the further increase of the feed of ADMS. The activity of the Ziegler–Natta catalyst decreases with the addition of ADMS (Fig. 2). This can be explained by two reasons. Firstly, the enchainment of ADMS with large size pendent (CH3)2SiH group on the central metal hinders sterically the incorporation of the next propylene molecule. Secondly, the agostic interaction [10,11] between the hydrogen atom in Si–H bond and the Ti atom of Ziegler–Natta catalyst may hinder the incorporation of the propylene molecule because the electronegativity of H atom (2.1) is higher than Si atom (1.8). The electron cloud density around the H atom is stronger than that around the Si atom in Si–H bond, which is on the contrary to the case of C–H bond where the electronegativity of C atom is 2.5. The agostic interaction between the Ti atom and the H atom of Si–H bond can be established easily and strongly (Scheme 1). The molecular weight distributions of the copolymers are broad (9.3–10.5), which is the typical character of the conventional Ziegler–Natta catalyst with multiple active centers. The incorporation of ADMS units destroys the crystallinity of polypropylene
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Table 1 The conditions and results of the copolymerization of propylene with ADMSa Run
ADMS in the feed (mol/L)
Yield (g)
Activity (kg/mol Ti Æ h)
ADMS in copolymerb (mol.%)
Tm (C)
Mwc (103 g/mol)
Mw/Mnc
1 2 3 4 5 6 7
0 0.05 0.10 0.21 0.32 0.42 0.53
8.4 6.7 6.3 5.6 4.4 4.0 3.7
404 319 302 269 212 192 178
0 0.10 0.20 0.45 0.67 0.83 1.06
159.8 159.4 158.7 157.4 157.2 156.5 156.3
302.7 242.5 223.6 220.7 225.2 224.2 226.4
10.4 10.5 9.8 9.6 10.2 9.8 9.3
a
Activity of the Ziegler-Natta catalyst (kg/mol. Ti.h)
Content of ADMS in the copolymer (mol %)
Copolymerization conditions: toluene 60 mL; CS-II catalyst: 50 mg (Ti = 0.36 mmol); Al/Ti: 100; reaction time: 30 min; temperature: 40 C ; propylene: 1 atm. b Calculated from 1H NMR. c Determined by PC.
1.2
1.0
0.8
0.6
0.4
0.2
0.0 0.0
0.1
0.2
0.3
0.4
0.5
0.6
350
300
250
200
150 0.0
Concentration of ADMS in the feed (mol/L)
0.1
0.2
0.3
0.4
0.5
0.6
Concentration of ADMS in the feed (mol/L)
Fig. 1. The dependence of the content of ADMS in copolymer on the concentration of ADMS in the feed.
chain and decreases the Tm of the copolymer. However, the extent of the decreasing is low, which results in less negative influence on the performance of the copolymer. The reactivity ratios of propylene and ADMS were estimated according to the Fineman–Ross extrapolation method [12]. The calculation is based on Eq. (1): a a=b ¼ rP ða2 =bÞ rC
400
ð1Þ
wherein a is the mole ratio of propylene (P) and comonomer (C) in the feed, b is the mole ratio of propylene and comonomer in the copolymer, rP is the reactivity ratio of propylene and rC is the reactivity ratio of comonomer. The propylene concentration in toluene was calculated according to the literature [13]. Fig. 3 shows the plot of a2/b versus a a/b and the least squares best-fit line. The
Fig. 2. The influence of the concentration of ADMS in the feed on the activity of catalyst.
P
LnTi+
δ−
H
δ+ Si
CH3
CH3
Scheme 1. The agostic interaction between the Ti atom and the H atom of the Si–H bond.
results are: rP = 78.73 ± 0.80, rC = 0.096 ± 0.006, rP · rC = 7.56 and the correlation coefficient R = 0.999. rP is much higher than rC, which indicates that it is hard to form the homopolymer of ADMS and the block copolymer of propylene and ADMS.
H. Li et al. / European Polymer Journal 43 (2007) 109–118
The typical 1H NMR and 13C NMR spectra of the copolymer (run 7) are shown in Fig. 4. The resonance signals centering at 0.91 ppm, 1.31 ppm and 1.62 ppm correspond to CH3, CH2 and CH in propylene units, respectively. The resonance signals at 0.11 ppm and 4.05–4.15 ppm correspond to Si–CH3 and Si–H, respectively. The chemical shift of Si–CH2 is immerged into the hydrogen chemical shifts of propylene unit and cannot be detected clearly. The content of ADMS in the copolymer is calculated by the ratio of two integrated intensities between Si–H and protons in propylene unit. Two resonance signals centered at 4.66 ppm and 4.72 ppm arise from the vinylidene end-group of copolymer [14], which indicates that b-H transfer chain-termination mechanism exists. The 13C NMR spectrum of PP-co-ADMS is similar to that
14
12
rP = 78.73 ± 0.80 rC = 0.096 ± 0.006 rP×rC = 7.56
10
a-a/b
8
6
4
2
0 0.00
0.02
0.04
0.06
0.08
0.10
0.12
0.14
0.16
0.18
2
a /b
Fig. 3. The reactivity ratios of propylene and ADMS estimated according to the Fineman–Ross extrapolation method.
Fig. 4. (a) 1H NMR and (b)
113
13
C NMR spectra of PP-co-ADMS.
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Fig. 5. 1H NMR spectrum of chlorinated PP-co-ADMS.
of typical isotactic polypropylene [14] except the chemical shift at 3.27 ppm corresponding to Si–CH3. 3.2. Chlorination of PP-co-ADMS SOCl2 is usually used as chlorination agent to change Si–H to Si–Cl [15]. This chlorination reaction is highly selective to the Si–H bond. The chlorination of PP-co-ADMS was carried out by refluxing PP-co-ADMS with SOCl2 in benzene. The polymer was swelled during the reaction. After the chlorination reaction, SOCl2 was separated easily by filtration. The 1H NMR spectrum of the chlorinated copolymer (PP–Si–Cl) is shown in Fig. 5. Compared with the 1H NMR spectrum of PP-co-ADMS, the intensities of doublet resonance signal at 0.11 ppm and signal between 4.05 and 4.15 ppm reduce and a new singlet signal at
0.43 ppm corresponding to Si(CH3)–Cl arises. The conversion of Si–H to Si–Cl can be calculated by the ratio of integrated intensities of these two signals. After reaction for 36 h, the conversion is up to 55%. The chlorination reaction was also carried out with CCl4 as solvent without the change of the other conditions. The 1H NMR spectrum shown that the conversion of Si–H to Si–Cl was about 15%. The lower conversion is possibly caused by the worse swelling of PP-co-ADMS by CCl4 than that by benzene. 3.3. Synthesis of PP-g-PMMA graft copolymer The graft polymerization of MMA initiated by PP–Si–Cl/CuCl/PMDETA was carried out in toluene at 100 C (Scheme 2). The effect of polymerization time on the conversion of MMA and Mn of
Ziegler-Natta catalyst +
CH2
CH n
CH2
CH m CH2
CH3 CH3
Si
CH3
CH3
H
SOCl2 benzene
Si
CH3
H
MMA CH2
CH x
CH2
CH y
CH2
CuCl/PMDETA CH2
CH3 CH3
Si
CH3
Cl
Scheme 2. The synthesis of PP-g-PMMA.
CH x
CH2
CH y CH2
CH3 CH3
Si PMMA
CH3
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Table 2 The conditions and results of the graft copolymerization of MMA initiated by PP–Si–Cl/CuCl/PMDETAa Run
Time (h)
Yield (g)
Conversion (%)
PMMA in copolymer wt.%
MMA/P mol/mol
Tgb (C)
Mnc (g/mol)
Mw/Mnc
8 9 10 11 12
0 2 4 8 12
0.30 0.56 0.72 1.05 1.47
– 2.6 4.2 7.5 11.7
– 46.4 58.3 71.4 79.6
0 27/73 37/63 51/49 62/38
– n.d. n.d. n.d. 92.1
22,870 29,740 35,460 52,700 67,700
9.8 8.3 7.1 6.2 5.3
Polymerization conditions: PP–Si–Cl: 0.30 g (Si–Cl content: 3.26 · 105 mol); toluene: 20 mL; temperature: 100 C ; CuCl: 0.10 g; MMA: 10 g; PMDETA: 0.20 g. b Determined by DSC; n.d: not determined. c Determined by GPC. a
graft copolymer has been investigated (Table 2). The dependence of ln([M0]/[M]) of MMA on the polymerization time is linear (Fig. 6a), which is similar to the ATRP of MMA initiated by Me3SiCl/ CuCl/PMDETA [8]. The crude graft copolymer was extracted with acetone to remove the PMMA homopolymer. The result shows that the PMMA
0.14
0.12
ln([M0]/[M])
0.10
homopolymer is less than 5 wt.% of the crude copolymer. The Mn of the graft copolymer determined by GPC increases linearly with the conversion of MMA (Fig. 6b). The GPC curves of PP-co-ADMS (run 6) and PP-g-PMMA (run 11 and run 12) are shown in Fig. 7. The GPC traces of the grafted polypropylene shift toward high molecular weight region. According to the definition of molecular weight distribution, the molecular weight distribution of block and graft copolymer with two components (Mw co/Mn co) can be expressed as following equation: M wco aM w1 þ bM w2 ¼ M nco aM n1 þ bM n2
0.08
0.06
0.04
0.02
0.00 0
2
4
6
8
10
12
ð2Þ
where a and b are molecular fractions of two components respectively. Calculated according to Eq. (2), Mw co/Mn co is between Mw1/Mn1 and Mw2/ Mn2. Polypropylene (component 1) prepared by Ziegler–Natta catalyst is characterized with broad
Time (h)
PP-co-ADMS run 4 PP-g-PMMA run 11 PP-g-PMMA run 12
70000
Mn of PP-g-PMMA
60000
50000
40000
30000
20000 0
2
4
6
8
10
12
Conversion of MMA %
Fig. 6. (a): Dependence of ln ([M0]/[M]) on polymerization time of MMA, and (b) dependence of Mn of PP-g-PMMA on the conversion of MMA.
2
3
4
5
6
7
log M
Fig. 7. GPC curves of PP-co-ADMS (run 4) and PP-g-PMMA (run 11 and 12).
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H. Li et al. / European Polymer Journal 43 (2007) 109–118
molecular weight distribution, but PMMA (component 2) prepared by ATRP is characterized with narrow molecular weight distribution. For the graft copolymer of polypropylene and PMMA prepared in this study, a, b, Mw1 and Mn1 are constant but Mw2 and Mn2 increase with the content of PMMA. Therefore, Mw/Mn of PP-g-PMMA should decrease with the increase of the content of PMMA. As expected, Mw/Mn of PP-g-PMMA determined by GPC decreases from 9.8 (run 8) to 5.3 (run 12) with the increase of the PMMA content (Table 2). Tg of the PMMA side chain is detected by DSC, which is 92.1 C (run 12) (Fig. 8). The typical 1H NMR spectrum of PP-g-PMMA (run 12) is shown in Fig. 9. In addition to the major signals corre-
sponding to PP and PMMA, the signals corresponding to Si–H (0.11 ppm) and Si–CH3 (4.05– 4.15 ppm) are also observed. It was known that Si–H bond could react with carbon free radical to generate Si free radical and C–H bond [1]. However, the reaction between the Si–H bond in PP–Si–Cl and the free radical in the ATRP reaction of MMA can be ignored. Because the concentrations of the carbon radical of ATRP reaction [16] and the Si–H bond in PP–Si–Cl are both very low and the Si–H bond located in the swell polypropylene chain is less mobile. Therefore, the probability of the reaction between Si–H and carbon free radical in the ATRP reaction is very small. Moreover, 1H NMR spectrum (Fig. 9) proves that the Si–H bond is preserved after the ATRP reaction. It indicates that the Si–H bond do hardly participate in the ATRP reaction and the propagation carbon free radical is seldom disturbed by Si–H bond. 3.4. PP-g-PMMA used as compatilizer
Tg = 92.1 o C a
b 50
100
150
Temperature (ºC)
Fig. 8. DSC curves of (a) PP-co-ADMS (run 4) and (b) PP-gPMMA (run 12).
The graft copolymer was first proven by Molau test [17]. iPP (run 1), PP-g-PMMA (run 12) and PMMA were dispersed in acetone and milky colloidal suspension solution was produced, which indicated not only that the graft structure existed but also that the graft copolymer could be a potential good compatilizer in polymer blend. In order to investigate the compatibility of PP-g-PMMA copolymer in iPP and PMMA blends, two polymer blends have been performed. One is a simple mixture of 80/20 weight ratio of iPP and PMMA and
Fig. 9. 1H NMR spectrum of PP-g-PMMA (run 9).
H. Li et al. / European Polymer Journal 43 (2007) 109–118
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Fig. 10. FESEM images of the cross-sections of two polymer blends: (a) two homopolymers with PP/PMMA = 80/20 (2000·); (b) (10000·); (c) two homopolymers and PP-g-PMMA with PP/PP-g-PMMA/PMMA = 75/10/15 (2000·) and (d) (10,000·).
the other is comprised of 75/15/10 weight ratio of iPP, PMMA and PP-g-PMMA (run 12). Fig. 10 shows the FESEM micrographs of the cross-sections of the two polymer blend samples cyrofractured in liquid N2. In the homopolymer blend (Fig. 10a and b), the polymer shows grossly phase-separated as can be seen by the PMMA phase which exhibits nonuniform and the size of PMMA phase is big. The PMMA domains are pulled out of the PP matrix. The polymer blend containing the graft copolymer shows a totally different morphology in Fig. 10c and d. The cross-section exhibits almost flat mesa-like regions similar to that of pure iPP and size of PMMA phase domains is smaller, which proves that PP-g-PMMA is an effective compatilizer in iPP/PMMA blends. 4. Conclusion The copolymerization of propylene with allyldimethylsilane (ADMS) was carried out in the pres-
ence of the conventional Ziegler–Natta catalyst. With the increase of the concentration of ADMS in the feed, the content of ADMS unit in the copolymer increased linearly, but the catalyst activity decreased. PP-co-ADMS was chlorinated to PP– Si–Cl by refluxing with SOCl2. PP–Si–Cl was used to initiate ATRP of MMA with CuCl/PMDETA as catalyst. The graft polymerization reaction occurred efficiently. This is a new route to prepare graft polyolefin copolymer via silane. The PP-gPMMA copolymer was proved to be an effective compatilizer in iPP/PMMA blends by FESEM.
Acknowledgement The authors express thanks for the supports of the National Science Foundation of China (No. 20334030, No. 50403024 and No. 50573081) and China Petroleum & Chemical Corporation (SINOPEC).
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