ISSN 19950780, Nanotechnologies in Russia, 2014, Vol. 9, Nos. 3–4, pp. 175–183. © Pleiades Publishing, Ltd., 2014. Original Russian Text © S.V. Polshchikov, P.M. Nedorezova, O.M. Komkova, A.N. Klyamkina, A.N. Shchegolikhin, V.G. Krasheninnikov, A.M. Aladyshev, V.G. Shevchenko, V.E. Muradyan, 2014, published in Rossiiskie Nanotekhnologii, 2014, Vol. 9, Nos. 3–4.
Synthesis by Polymerization in Situ and Properties of Composite Materials Based on Syndiotactic Polypropylene and Carbon Nanofillers S. V. Polshchikova, P. M. Nedorezovaa, O. M. Komkovaa, A. N. Klyamkinaa, A. N. Shchegolikhinb, V. G. Krasheninnikova, A. M. Aladysheva, V. G. Shevchenkoc, and V. E. Muradyand a
Semenov Institute of Chemical Physics, Russian Academy of Sciences, ul. Kosygina 4, Moscow, 119991 Russia Emanuel Institute of Biochemical Physics, Russian Academy of Sciences, ul. Kosygina 4, Moscow, 119334 Russia c Enikolopov Institute of Synthetic Polymeric Materials, Russian Academy of Sciences, ul. Profsoyuznaya 70, Moscow, 117393 Russia d Institute of Problems of Chemical Physics, Russian Academy of Sciences, pr. Akademika Semenova 1, Chernogolovka, Moscow oblast, 142432 Russia email:
[email protected] b
Received July 3, 2013; in final form, December 12, 2013
Abstract—New composite materials based on a syndiotactic polypropylene (SPP) and nanosized carbon fill ers of various types (graphene nanoplates (GNP) and fullerene) are obtained by polymerization in situ. It is shown that the introduction of nanocarbon particles did not lead to a significant decrease in the activity and stereospecificity of a syndiospecific catalyst. Stressstrain and thermo and electrophysical properties of the composites are studied. Composites based on SPP are characterized by a higher plasticity than those based on isotactic polypropylene (IPP) at the same filling degrees. An enhancement of the thermal stability of SPP in the presence of carbon nanofillers is demonstrated. A noticeable effect of GNP and fullerene on melting and crystallization of SPP in the composites is found. In SPP/GNP composites, the dielectric permeability is practically independent of the filler concentration. In this case, nanofillers play the role of dielectric probes, making it possible to identify relaxation transitions in the polymer matrix. DOI: 10.1134/S1995078014020128
INTRODUCTION The modification of polyolefins by additives of nanosized carbon fillers, such as nanotubes, graphene nanoplates, fullerene, etc., is a prospective approach to the design of multifunctional polymer materials with an elevated thermal stability, electric conductiv ity, and improved barrier and frictional characteristics. Polymers are already significantly modified by low amounts of nanofillers [1, 2]. One known method for preparing polymer com posites with fillers of different types is the polymeriza tion filling method, or polymerization in situ. Using it allows composites with a homogeneous distribution of the filler over the bulk to be obtained in wide range of compositions. This method of introducing fillers into a polyolefin matrix was suggested in [3, 4] and was fur ther developed to obtain polypropylene (PP) composites with graphite [5, 6], multiwall nanotubes (MWNTs) [7], graphene nanoplates [8], and graphite oxide [9]. In most papers devoted to obtaining composites with PP, isotactic PP (IPP) is used as the polymer matrix. There are noticeably fewer papers on the preparation of nanocomposites with the use of a syndiotactic PP [10]. The complex of properties of composites is largely
determined by the polymer chain microstructure, its chemical composition, and molecular weight. In con trast to IPP, syndiotactic PP (SPP) is characterized by lower crystallinity, high transparency, higher impact toughness, and elasticity [11]. Papers are available on the preparation of SPPbased composites possessing enhanced antibacterial, barrier, and nucleating char acteristics [12–15]. Despite its attractive properties, SPP is much less industrially applied than IPP. One of the main drawbacks of SPP is its low crystallization rate, restricting the possibility of its processing. At the same time, additives of nucleating agents increase the rate of SPP crystallization, which is a favorable factor for its commercial use [16]. The present work is devoted to preparing nano composites based on SPP and carbon nanofillers of various types (graphene nanoplates or fullerenes C60/C70) by the method of polymerization in situ and a complex investigation of properties of the obtained materials. EXPERIMENTAL Graphene nanoplates (GNPs) were obtained according to the method based on a chemical oxida
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Ph C
Cl Zr
Ph Cl
Fig. 1. Scheme of Ph2C(CpFlu)ZrCl2.
tion of graphite and its subsequent reduction [17]. Graphite oxide (GO) was obtained according to the modified Hummers’ method [18] via the oxidation of graphite by KMnO4 in concentrated H2SO4 [19]. GO in the form of its aqueous suspension was reduced with hydrazine hydrate upon ultrasound treatment at 70°C for 4 h, followed by boiling for 2 h. GNP powder washed with doubly distilled water and cryodried was heated in the flow of argon at 900°C for 1 h. The struc ture of the obtained powder was investigated by the Raman scattering (RS) method on a Senterra disper sion RSmicroscope (Bruker). The data obtained by us indicate that GNPs used in the paper contain an essential fraction of 35layered graphene [8]. A mixture of fullerenes C60/C70 was obtained by the electricarc evaporation of graphite electrodes using the method described in [20]. The content of C70 in the mixture was determined from the electron absorp tion spectra of toluene extracts in UV and visible ranges. The mixture of fullerenes used in the work contained ∼13% fullerene C70. The preparation of composite materials was per formed in the medium of liquid propylene in the pres ence of a highly efficient syndiospecific homoge neous catalytic system based on ansazirconocene Ph2C(CpFlu)ZrCl2 (Fig. 1) activated with polymethy lalumoxane (MAO) by the method described in [6]. Under the conditions of SPP synthesis used in the present work, this catalyst offers the acquisition of polymers with a high molecular weight (Mw = 320000 g/mol) and a content of syndiotactic pentads of 82% [21]. GNP and fullerene powders were preliminarily vacuumized at the temperature 200°C. For the syn thesis of composites, suspensions of fillers in toluene were prepared and treated with ultrasound (US) for 10 min. Afterwards, MAO was added and the ultra sound treatment was continued for another 10 min. The power of the US radiator was 50 W. After that, the suspension was introduced into a polymerization reac tor filled with propylene, and the catalyst solution was supplied. The composite composition was controlled
by the polymerization time and filler concentration in the reactor. The polymerization was carried out at a tempera ture of 60°C and pressure of about 2.5 MPa in a steel reactor with a volume of 0.2 L. The volume of liquid propylene was 0.1 L. After the process was complete, the material was unloaded from the reactor, washed from residues of the catalytic system components, and dried to a constant weight in vacuum at 60°C. Infrared (IR) spectra of SPP samples and SPP compositions with GNP and fullerene in the form of 100μmthick hotextruded films were recorded on a Vertex 70 FTIR spectrometer (Bruker). The stereo regularity of SPP was determined by the ratio of opti cal densities of absorption bands at 870 and 1155 cm–1 (D870/D1155). This ratio characterizes the presence of long syndiotactic sequences in the polymer chain [22]. Stress–strain characteristics of the obtained mate rials in the form of dumbbells (0.5 × 5 × 35 mm) were investigated on an Instron 1122 tensile machine at the strain rate 50 mm/min. Films for tests were prepared by extrusion at 190°C and the pressure 10 MPa with the melt cooling rate 16°C/min. Each test result was averaged over 5–6 measurements. The distribution of filler particles in the composite material was analyzed by scanning electron micros copy (SEM) with the use of a JSM5300LV micro scope (Jeol) on film samples subjected to brittle frac ture after their freezing in liquid nitrogen. The films were prepared by the hotextrusion method as was indicated above. Dynamical mechanical characteristics of materi als were studied on a DMA 242 C/1/F analyzer (Netzsch). The tests were conducted in the strain mode for samples in the form of 15 × 6 × 0.5 mm films in the temperature range from –60 to +160°C at the heating rate 2°/min, vibration frequency f = 1 Hz, and an amplitude of about 0.2%. The thermal physical characteristics (the tempera tures and enthalpies of melting and crystallization) of nanocomposites were determined with the use of scan ning differential calorimetry (DSC). DSC thermograms were recorded on a DSC7 device (PerkinElmer) at heating/cooling rates of 1–10°C/min. The thermogravimetric analysis (TGA) of the sam ples was performed on TG 209 F1 Iris thermal microbalances (Netzsch, Germany) under dynamic heating conditions in the atmosphere of argon of up to 600°C at a heating rate 10°C/min. Xray diffraction of polymers was analyzed by means of a DRON2 diffractometer (CuKαradiation; scanning rate 1°(2Θ)min). The degree of crystallin ity (K) of samples was calculated from the ratio of the integral intensity of the crystalline component and the total intensity. Dielectric properties of nanocomposites in the superhigh frequency (SHF) range were studied by the
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Table 1. The effect of polymerization conditions on the activity of the catalytic Ph2C(CpFlu)ZrCl2/MAO system. Tpol = 60°C Filler, g
Zr, 10–7 mol
Al/Zr
–
9.4
5130
0.010 0.034 0.030 0.048 0.100
11.9 11.8 10.2 11.2 10.8
5050 5110 5560 5390 5430
0.028 0.150
14.8 11.9
3980 4480
Experiment time, min
A*
Filler content in the composite, wt %
24
22
–
10 8.5 5.2 3.3 2.7
25 22 20 12 12
0.1 0.4 0.6 1.45 3.7
2.2 3.3
9 17
1.3 4.5
Yield, g
SPP 70 SPP/GNP 20 20 15 15 12 SPP/fullerene 10 10
* A is activity, kgPP/(mmol Zr h).
resonator method using voltage standingwave ratio (VSWR) indicators of the series P2 and rectangular resonators with the working mode H01n within the working frequency range 3.2–30 GHz. The resonator method is based on a determination of changes in the resonance frequency Δf and resonator Qfactor (1/Q– 1/Q0) when the material sample under analysis is placed into the resonator cavity. Samples for the mea surements were rectangular plates with dimensions 15 × 1 × 0.5 mm. The real and imaginary components of the dielectric permeability and losses of composite films in the frequency range 10–2–106 Hz were mea sured by means of a Novocontrol AlphaA impedance analyzer and a ZGS Alpha Active Sample Cell dielec tric cell with gild disc electrodes of diameters 20 and 30 mm. Aluminum foil electrodes with a diameter of 20 or 30 mm were glued onto films to provide a better electric contact. The temperature varied in the range from –120 to +110°C. RESULTS AND DISCUSSION Preparation of Composites To prepare a composite material of the required composition, the forming polymer amount was regu lated by varying the filler quantity, polymerization time, and catalyst concentration. Gray powders of SPP/GNP composites with the filler content from 0.1 to 10 wt % and light violet powder SPP/fullerene com posites with a content of fullerene of 1.3–4.5 wt % were obtained. Polymerization conditions, data on the catalytic Ph2C(CpFlu)ZrCl2/ÌÀÎ system, and the composition of the obtained composites are presented in Table 1. The introduction of carbon fillers into the reaction medium gives rise to a certain decrease in activity, its value being 9–25 kg/(mmol Zr · h). The activity values NANOTECHNOLOGIES IN RUSSIA
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are high enough to obtain composites of any required composition. Numerical values of the stereoregularity index determined from IR spectra of composites based on SPP with GNP and fullerene are presented in Table 2. It is seen that the introduction of carbon nanofillers causes practically no effect on the catalytic system ste reospecificity. The degree of regularity of SPP deter mined for homopolymer and samples with the content of GNP and fullerene 0.1 and 1.3 wt %, respectively, is 70–72%. The character of distribution of filler particles in the obtained composite materials may be evaluated from SEM micrographs of lowtemperature chips of the com posites. The SEM micrograph of SPP/fullerene sample is presented in Fig. 2. For comparison, the micrograph of IPP/fullerene sample is shown in the same figure. Comparing the micrographs, it is seen that fullerene particles are more inclined to the formation of agglomerates in the SPP matrix. The reason for that may be a lower melt viscosity for SPP compared to that for IPP that may promote a stronger interaction of fullerene particles with each other. Similar data were obtained by us earlier for SPP/MWNT composites [24]. The same results were expected for composites with GNP. However, as is seen from Fig. 3, where micrographs of SPP/GNP and IPP/GNP samples are Table 2. Parameters of stereoregularity of SPPbased com posites Sample
D870 /D1155
SPP SPP/0.1 wt % GNP SPP/1.3 wt % fullerene
0.72 0.70 0.71
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It is seen from Table 3 that the introduction of GNP and fullerene into SPP leads to a slight increase in the tensile modulus and a decline of deformational characteristics of composites. At the same time, the yieldpoint value is weakly dependent on the filling degree, evidencing the presence of a certain adhesion interaction of SPP with carbon fillers [26]. It is inter esting to note that the introduction of low amounts of GNP (0.4 wt %) causes a rise in the elongation at a break from 400 to 460%, which is probably due to a change in the character of crack growth in the com posite upon its deformation [27]. A further increase in the content of the filler in the composite leads to a decrease in the elongation at break.
1 μm
(а)
SPPbased composites filled with fullerene pre serve their capability of plastic deformation up to higher filling degrees than composites with GNP. At the same time, SPP/GNP composites possess higher deformation at break than the corresponding IPP/GNP composites [25]. It is shown by Xray structural analysis that no noticeable changes in the crystal structure of the poly mer matrix occur in the presence of carbon nanopar ticles. The degrees of crystallinity of samples of SPP and composites on its basis are estimated. The degree of crystallinity amounts to 36–40% (Table 3).
1 μm
(b)
1 μm
(c)
Fig. 2. SEM micrographs of chips of nanocomposite films in liquid nitrogen: (a) SPP/fullerene (1.5 wt %) ×10000; (b) IPP/fullerene (0.8 wt %) ×10000 [23].
presented, a more uniform distribution of filler parti cles is observed in the case of SPP compared to that for IPPbased composites. Thus, it may be assumed that the character of dis tribution of nanoparticles in a polymer depends not only on the structure and morphology of the polymer matrix but, first and foremost, on the degree of inter action between the filler and the polymer determined by the nature of the filler surface. Mechanical Properties Stress–strain properties of nanocomposites were studied at a quasistatic strain. From the stress–strain diagrams, the elastic modulus E, yield stress σy, yield strain εy, breaking strength σb, and elongation at break εb are determined (Table 3).
Mechanical properties of SPP/GNP and SPP/fullerene composites are investigated under dynamical strain conditions. It is shown that the dynamic elastic modulus of composites (E') increases with a rise in the content of fillers and remains higher than the E' value for the pristine polymer (Figs. 4a, 5a) in the investigated temperature range (up to the melt ing temperature). The maximum strengthening effect of GNP in the composites is about 20%. The strength ening effect of fullerene in the glassy state region is also 20%, increasing to 40% at temperatures above the glass transition temperature. In order to illustrate the growth of heat resistance of SPP upon its filling with carbon nanofillers, tem perature dependences of the dynamic modulus of materials in the hightemperature range were built (Figs. 4b, 5b). A conventional point was selected at which the modulus of the pristine polymer decreases approximately twofold as compared to its value at room temperature (25°C). It is seen from the pre sented dependences for all composites that their dynamic modulus values, corresponding to the indica tors of the pristine SPP, are shifted towards higher temperatures. Thus, e.g., upon the introduction of 3.7 wt % GNP or 4.5 wt % fullerene, this shift is about 10°C. Similar results were obtained earlier for com posites based on IPP and SPP filled with MWNT [24]. The preservation of elevated values of the dynamic modulus for the composites in the hightemperature range shows that the use of GNP and fullerene as fill ers, increasing the heat resistance of SPP, is promising.
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(а)
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1 μm
(b)
Fig. 3. SEM micrographs of chips of nanocomposite films in liquid nitrogen: (a) SPP/GNP (1.45 wt %) ×2000, (b) SPP/GNP (10 wt %) ×2000, and (c) IPP/GNP (1.8 wt %) ×2000 [25].
lization in the polymer matrix even at low filling degrees.
Thus, the introduction of relatively small amounts of carbon fillers into the SPP matrix results in a notice able widening of the temperature range of exploitation of the corresponding materials.
In Fig. 7, melting curves for SPP/GNP and SPP/fullerene samples with different contents of the fillers are presented.
The analysis of temperature dependences of the mechanical loss tangent showed that the introduction of a carbon nanofiller, both GNP and fullerene, prac tically does not affect the glass transition temperature of the polymer matrix (Tg) (Fig. 6).
Samples of SPP in their nascent state are charac terized by two melting peaks at 125 ± 2°C and 133 ± 2°C; the heat of melting is 45 J/g. The introduction of carbon fillers weakly affects both the heat and temper ature of melting of SPP in its composites with both GNP and fullerene. Meanwhile, the height and width of the melting peaks depend on the filler concentra tion and type. The position and intensity of a lowtem perature melting peak correspond, probably, to the formation of thin lamellae in the process of crystalliza tion [29]. With an increasing concentration of the filler, the lowtemperature melting peak shifts towards higher temperatures; i.e., larger lamellae, melting at elevated temperatures, are formed in the filler pres ence. At high filling degrees only one melting peak is observed (Fig. 7a, thermogram 5).
The values of Tg for compositions based on SPP fullerene and GNP are about 15°C. It may be noted that for compositions based on IPP with MWNT [28] and GNT, the value of Tg is also independent on the filler content, being about 6°C. Thermophysical Properties The investigation of thermophysical characteristics of the synthesized composite materials showed that the introduction of nanosized filler particles into SPP noticeably affects the processes of melting and crystal
Table 3. Results of mechanical tests for strain. V = 50 mm/min Filler content in the composite, wt %
E, MPa
σy, MPa
–
420
22.0
0.4 0.6 1.45 3.7
480 450 525 550
20.3 20.0 20.8 21.7
1.3 1.5 4.5
470 490 560
22.0 21.3 23.1
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σb, MPa
εb, %
K(XSA), %
24.3
400
40
26.1 24.7 21.2 18.5
460 405 335 18
36 37 39 –
24.0 18.5 16.8
370 270 160
40 – –
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E, MPa 3000
3
E, MPa 3600
4
3
2 1
(a)
3000
(a)
2
2400
2000
1800 1000
1200 600
0 –50
–10
30
70
110 0
800 700
0
20
40
60
80 100 120 140
800
(b)
700
600
(b)
600
500
500
400
400 43 2 1
300 46
200 40
–20
45
49
55.5
50
57
55 60 65 70 Temperature, °C
75
3 2
300 1
200
80
100 46
0 40
Fig. 4. Temperature dependences of the dynamic modulus of SPP and its composites with GNP: (1) SPP, (2) 0.4 wt % GNP, (3) 1.45 wt % GNP, and (4) 3.7 wt % GNP.
53
50
56
60 70 Temperature, °C
80
Fig. 5. Temperature dependences of the dynamic modulus of SPP and its composites with fullerene: (1) SPP, (2) 1.2 wt % fullerene, and (3) 4.5 wt % fullerene.
The introduction of GNP and fullerene leads to an increase in the temperature of crystallization of SPP. The position of the crystallization peak depends on the cooling rate and the filler type and content. In Table 4, the values of temperature and heat of crystallization at the cooling of SPP/GNP materials with rates of 2 and 10°C/min are presented. The growth of the crystallization temperature (Tcr) for SPP/GNP composites from 81.4 to 99.2°C at the cooling rate 10°C/min and from 98.2 to 111.4°C at the cooling rate 2°C/min indicates that the filler causes a nucleating effect upon polymer crystallization. For fullerenebased composites, the value of Tcr changes less considerably upon the filler introduction. It is seen that the additive of 1.3 wt % fullerene gives rise to an increase in Tcr by 3–5°C (Table 5).
An increase in Tcr upon the introduction of carbon nanofillers was observed by us earlier for composites based on IPP/MWNT [30], IPP/GNP [25], and IPP/fullerene [23]. However, the nucleating effect of small additives of the filler is especially important for SPP, since its practical application is limited due to low temperature and rate of crystallization [31]. Thermogravimetric Analysis The thermal stabilities of SPP and composites SPP/GNP and SPP/fullerene are studied by the TGA method. In Table 6 the data on the temperature of the maximum rate of the substance weight losses (Tmax)
Table 4. Temperatures and heats of crystallization for SPP and SPP/GNP composites SPP
0.4 wt % GNP
3.7 wt % GNP
10 wt % GNP
Cooling rate, °C/min
Tcr , °C
Hcr , J/g
Tcr , °C
Hcr , J/g
Tcr , °C
Hcr , J/g
Tcr , °C
Hcr , J/g
2 10
98.2 81.4
45.5 33.2
101.5 88.4
47 36.5
103.5 91
50 33.4
111.4 99.2
46.5 22.2
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SYNTHESIS BY POLYMERIZATION Mechanical loss tangent 0.14 2
(a) 5
0.12
4
(a)
3
0.10
3
1
0.08
181
0.06 Reduced heat flow, W/g
2
0.04 0.02 0 –50 –30 –10
10
30
50
70
90
110
0.15 2
(b)
1
(b) 3
3
0.10
2
1 0.05
1 0 –30
0
30 60 Temperature, °C
90
Fig. 6. The temperature dependence of the mechanical loss tangent for composites SPP/GNP (a): (1) SPP, (2) 0.4 wt % GNP, and (3) 3.7 wt % GNP; SPP/fullerene (b): (1) SPP, (2) 1.2 wt % fullerene, and (3) 4.5 wt % fullerene.
upon heating the composites obtained by the TGA method in an inert atmosphere are presented. As is seen from the obtained results, an increase in Tmax compared to analogous data for the pristine SPP is observed at small additives of the fillers. An increase in the thermal stability of PP upon additives of carbon nanofillers of various types has been reported in a number of papers [24, 26, 32]. This is commonly related to a retardation of the polymer decomposition due to a decrease in the termination rate of radicals on the filler surface. The increase in the thermal stability of SPP makes it possible to widen the temperature range of operation of products made of composite materials based on this polymer. Electric Properties In Fig. 8 the dependence of dielectric permeability on the concentration of GNP for composites based on IPP and SPP is presented. As was shown earlier [7], NANOTECHNOLOGIES IN RUSSIA
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120 130 140 Temperature, °C
150
Fig. 7. Thermograms of the 2nd melting of composites at a heating rate of 10°C/min for SPP/GNP (a): (1) SPP, (2) 0.4 wt % GNP, (3) 1.45 wt % GNP, (4) 3.7 wt % GNP, (5) 10 wt % GNP; SPP/fullerene (b): (1) SPP, (2) 1.5 wt % fullerene, and (3) 4.5 wt % fullerene.
these dependences allow the aggregation and shape of aggregates of electrically conducting nanoparticles in a polymer matrix to be estimated. It is seen from Fig. 8 that the value ε' for SPP/GNP composites is practically independent on the filler concentration. Within the framework of the model suggested in [7], this means that GNP nanoparticles are practically individually distributed in the compos ite or form aggregates of a small number of particles. Since the long axis of a particles is about 45 nm in Table 5. Temperatures and heats of crystallization for SPP and SPP/fullerene composite Cooling rate, °C/min
Tcr , °C
Hcr , J/g
Tcr , °C
Hcr , J/g
1 5 10
98 84.2 77.3
46 35.3 33
100.9 89.2 82.5
50.5 38.6 35.3
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Table 6. Temperature of the maximal rate of weight losses (Tmax) according to the data of TGA Filler type
Content in the composite, wt %
Tmax (argon), °C
0 1.3 4.5 0.6 1.45
473 480 485 483 482
– Fullerene GNP
length [8], at a measuring frequency of about 1010 Hz, only large aggregates, which are absent in the compos ite under investigation as follows from the presented dependence, may contribute to an increase in the dielectric permeability. The data evidence that filler particles are more uniformly distributed in the SPP polymer matrix when compared to the matrix of IPP. It is known that there is a correlation between dielectric properties (dielectric permeability and dielectric losses) and the structural organization of a polymer, making it possible to use these properties and their frequency or temperature dependences for eval uations of polymer structures and their changes.
grows with a rise in the filler concentration. In other words, in this case the nanofiller plays a role of a dielectric probe [33] and its dielectric relaxation fol lows relaxation processes in the polymer backbone that the probe interacts with. No such effect was found for composites with GNP and fullerene in which the matrix is formed by IPP. Since the main dielectric relaxation process occurs in an amorphous phase, the dipolar mobility being retarded in a crystal, it may be supposed that in the SPP matrix, where the amor phous phase fraction is higher, small particles of the filler keep pace with the segmental motion of the poly mer chain and the nanofiller behaves like a dielectric probe. Dielectric losses, ε'' 4
(a)
3 0.05
2
In Fig. 9, temperature dependences of dielectric losses for composites of SPP with GNP (a) and fullerene (b) at various concentrations of the fillers are presented. As can be seen from Fig. 9, the relaxation α transi tion, which is practically indistinguishable in the pure SPP, becomes clearly pronounced in the presence of both GNP and fullerene. It is worth a notion that the maximum position (glass transition temperature) does not change, while the intensity of the peak of losses
1 0
0.10 (b) 4
0.08 Dielectric permeability 8
3
0.06
1
6
0.04
4
0.02
2 1
0
2
2
–120 0
0.7
1.4
2.1 2.8 3.5 Filler content, vol %
Fig. 8. Dependence of the dielectric permeability on the concentration of GNP for composites (1) IPP/GNP and (2) SPP/GNP (the frequency 11 GHz).
–80
–40 0 40 Temperature, °C
80
Fig. 9. The temperature dependence of dielectric losses for SPP and composites SPP/GNP (a): (1) SPP, (2) 0.4 wt % GNP, (3) 1.4 wt % GNP, and (4) 3.7 wt % GNP; SPP/fullerene (b): (1) SPP, (2) 1.27 wt % fullerene, (3) 1.5 wt % fullerene, and (4) 4.5 wt % fullerene. The fre quency is 10 kHz.
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The effective activation energy values for αtransi tion were calculated which are practically indepen dent on the filler concentration and type. This evi dences that relaxation processes in the unfilled poly mer and those in the nanofiller presence are similar. Thus, the study of temperature dependences of dielec tric losses of composites allows relaxation transitions to be identified even in a nonpolar polymer as SPP, since the introduction of carbon nanoparticles into the polymer matrix makes these transitions well resolved. CONCLUSIONS As a result of our work, new polymer materials based on SPP and carbon nanofillers, possessing enhanced thermal stability, heat resistance, and crys tallization temperature are obtained. An analysis of dielectric characteristics showed that carbon nanopar ticles behave as dielectric probes, making it possible to identify relaxation transitions in the polymer matrix. ACKNOWLEDGMENTS This work was done with the use of the equipment from the Common Use Center of Moscow Institute of Physics and Technology (MIPT) and the Nanotech nologies Research and Education Center (RES) at MIPT and supported by the Russian Foundation for Basic Research (projects nos. 120331059mol_a, 11 0300771a) and a grant for the support of young sci entists (no. 41/2013) from OPTEK. The authors are grateful to S.N. Chvalun for the opportunity to carry out dielectric measurements. REFERENCES 1. H. Kim, A. A. Abdala, and C. Macosco, Macromole cules 43, 6515 (2010). 2. E. R. Badamshina and M. P. Gafurova, Vysokomolek. Soed. A 50 (8), 1572 (2008). 3. N. S. Enikolopov, L. A. Novokshonova, F. S. Dyach kovskii, et al., US Inventor’s Certificate No. 763370, Byull. Izobret. No. 34, 129 (1980); US Patent No. 4241112 (1980). 4. F. S. D’yachkovskii and L. A. Novokshonova, Usp. Khim. 2, 200 (1984). 5. N. M. Galashina, P. M. Nedorezova, V. I. Tsvetkova, F. S. D’yachkovskii, and N. S. Enikolopov, Dokl. Akad. Nauk SSSR 3 (278), 620–624 (1984). 6. P. M. Nedorezova, V. G. Shevchenko, A. N. Shche golikhin, V. I. Tsvetkova, and Yu. M. Korolev, Polym. Sci. Ser. A 46 (3), 242 (2004). 7. A. A. Koval’chuk, V. G. Shevchenko, A. N. She golikhin, P. M. Nedorezova, A. N. Klyamkina, and A. M. Aladyshev, Macromolecules 41, 7536–7542 (2008). 8. S. V. Polschikov, P. M. Nedorezova, A. N. Klyamkina, A. A. Kovalchuk, A. M. Aladyshev, A. N. Shche golikhin, V. G. Shevchenko, and V. E. Muradyan, J. Appl. Polym. Sci. 127 (2), 904–911 (2013). 9. Y. Huang, Y. Qin, Y. Zhou, H. Niu, Z. Z. Yu, and J. Y. Dong, Chem. Mater. 22, 4096–4102 (2010). 10. Z. Mlynarcikova, D. Kaempfer, R. Thomann, R. Mul haupt, and E. Borsig, Polym. Adv. Technol. 16, 362 (2005). NANOTECHNOLOGIES IN RUSSIA
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Translated by A. Yakimansky 2014
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