ISSN 15600904, Polymer Science, Ser. B, 2014, Vol. 56, No. 6, pp. 721–727. © Pleiades Publishing, Ltd., 2014. Original Russian Text © V.V. Istratov, E.V. Milushkova, I.A. Gritskova, V.A. Vasnev, 2014, published in Russian in Vysokomolekulyarnye Soedineniya, Ser. B, 2014, Vol. 56, No. 6, pp. 528–534.
POLYMERIZATION
Synthesis, Properties, and Application of SurfaceActive Block Copolymers Based on Poly(ethylene oxide) and Polyorganosiloxanes in the Heterogeneous Polymerization of Styrene V. V. Istratova*, E. V. Milushkovab, I. A. Gritskovab, and V. A. Vasneva a
Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, ul. Vavilova 28, Moscow, 119991 Russia b Lomonosov State University of Fine Chemical Technology, pr. Vernadskogo 86, Moscow, 119571 Russia *email:
[email protected] Received April 28, 2014; Revised Manuscript Received July 15, 2014
Abstract—A number of linear and combshaped organosilicon surfactants containing poly(ethylene oxide) blocks were synthesized and studied. The structures of the copolymers were varied systematically, and the obtained copolymers were characterized via elemental analysis, GPC, and 1H NMR. A comparative study of the surface activities of amphiphilic organosilicon block copolymers was performed. Their structures were shown to considerably affect the surface activities as well as the styrene polymerization rates and the sizes of microparticles obtained with the use of the studied copolymers as surfactants. DOI: 10.1134/S1560090414060104
INTRODUCTION
EXPERIMENTAL
The synthesis of polymeric monodisperse particles under heterophase polymerization conditions is still topical [1] because of the necessity of their application in different areas: from bioactive substance carriers in biology and medicine [2–4]; to photonic crystals [5, 6]; to nanostructured matrixes for magnetic, elec tronic, and optoelectronic devices [7, 8]; to calibra tion standards and model colloids.
Monomeric diethoxydimethylsilane (DDS, Acros, 97%), monomethyl ethers of poly(ethylene glycol) (MPEG) with Mw = 550 and 750 (MPEG550 and MPEG750, respectively, Aldrich), poly(ethylene gly col) with Mw = 1000 and 1500 (PEG1000 and PEG 1500, respectively, Aldrich), poly(ethylhydrosiloxane) with Mw = 1600 (macromonomer 1, Penta Junior), and styrene (≥99%, Aldrich) were used without addi tional purification. Phenol, potassium hydroxide, and potassium persulfate (reagent grade, Khimmed) and the solvents toluene, chloroform, ethanol, and trieth ylamine (reagent grade, Khimmed) were purified through standard procedures [18]. IR spectra were recorded on a Specord M80 IR spectrophotometer in the range 4000–400 cm–1. NMR spectra were obtained for 10% solutions of copolymers in CDCl3 on a Bruker spectrometer oper ating at 600.22 MHz for 1H and 150.84 MHz for 13C (with tetramethylsilane as an internal reference). Elemental gravimetric analysis was performed by the Group of Special Organic Analysis at the Nesmey anov Institute of Organoelement Compounds, Rus sian Academy of Sciences. Molecularmass characteristics of polymers were studied on a Waters 150 chromatograph equipped with a PLgel 5μ MIXED C column. The analysis was per formed in THF at a flow rate of 1 mL/min, molecular masses were calculated with the use of PS standards, and experiments were performed at the Petrov Plastics Institute.
A method for the preparation of monodisperse polymer suspensions in the presence of surfactants is known; the narrow particlesize distribution of these suspensions is due to their formation from monomer microdrops and probably to the formation of an interphase layer on the surfaces of polymer–mono mer particles at the initial stages of the process. The insolubility of the surfactant in water and its incom patibility with the resulting polymer are the requisite conditions [9]. Amphiphilic copolymers with polyorganosiloxane blocks are representatives of such surfactants. In spite of the wide application of such copolymers, little work has been dedicated to the studies of relationships between the structures of copolymers based on polyor ganosiloxanes and their surfaceactivity properties [10–17]. At present, there are no data on the effect of the structures of these surfactants on the polymeriza tion kinetics and characteristics of the obtained poly mer suspensions. Thus, it is very important to solve this task.
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The surface properties of copolymers were deter mined on an IT Concept Tracker drop tensiometer (France). Gibbs adsorption values Γ were assessed from sur facetension isotherms via the following equation [20]: Г = dσ/(RT × dlnC), where R is the universal gas constant, Т is the absolute temperature, σ is the surface tension, and С is the molar concentration. The area occupied by one molecule on the inter phase boundary, S0, was calculated on the basis of obtained data as S0 = 1023/NАΓ The styrene polymerization rate was studied via dilatometry. An emulsion was formed via magnetic stir ring in the wide portion of a dilatometer at 600 rpm. Poly merization depth Р was calculated through the formula P = (Δh/Δhmax) × 100% Here, Δh is the current level change in the dilatom eter capillary (cm); Δhmax is the level change in CH3 n C2H5O Si OC2H5 + n – 1H2O CH3
CH2CH2O
n
where Vm is the monomer volume (cm3), ρm is the mono mer density (g/cm3), ρp is the polymer density (g/cm3), and S is the capillary crosssectional area (cm2) [21]. The particle sizes in the polymer suspensions were determined via scanning electron microscopy on a Hitachi S570 instrument. The weightaverage and numberaverage particle diameters, Dw and Dn, respectively, were found from the formulas Dn = ΣDiNi/ΣNi and 2
Dw = Σ D i Ni/ΣDiNi Synthesis of Macromonomers and Copolymers Oligomeric polydimethylsiloxane (macromono mer 2) was obtained through the reaction
CH3 C2H5O Si O C2H5 + 2(n – 1)C2H5OH CH3 n
The synthesis was conducted under an argon atmo sphere via the addition of a solution of KOH (0.375 g, 0.0067 mol) and water (10.08 g, 0.56 mol) in 25 mL absolute ethanol to a solution of DDC (100 g, 0.67 mol) in 25 mL absolute ethanol [19]. The reaction mixture was heated under reflux for 6 h, the solvent was distilled off under reduced pressure on a rotary evaporator, and the target oligomer was isolated via fractional distilla tion at 105°С and 1 mmHg [19]; the yield was 18%. Unreactive phenyl derivatives of macromonomers 1 and 2 were obtained for GPC analysis. For this pur pose, a solution of 1 g macromonomer, 5 g phenol, and 5 g triethylamine in 25 mL toluene was heated under reflux for 6 h, and the final product was isolated via column chromatography on silica gel. The 1H NMR spectrum of the phenyl derivative of macromonomer 1 shows multiplet signals at 0.96– CH3 C2H5O Si O C2H5 + 2 HO CH3 m
dilatometer capillary corresponding to 100% conver sion; and hmax = Vm(ρp – ρm)/(Sρp)
CH3
The copolymers were obtained under an argon atmosphere via the addition of a solution of MPEG 550 (2.18 g, 0.004 mol) or MPEG750 (2.97 g, 0.004 mol) in 2 mL absolute ethanol to a solution of 0.002 mol macromonomer 2 in 2 mL absolute etha
(1)
1.05 ppm (CH3 group), 0.62–0.70 ppm (CH2 group), and 7.93–8.31 ppm (aromatic protons). The integral intensity ratio of signals corresponding to the aliphatic and aromatic protons of macromonomer 1 makes it possible to determine the actual amount of its mono mer units (see below). The 1H NMR spectra of unmodified macromonomer 2 display distinct groups of multiplet signals at 0.13–0.31 ppm (СН3–Si group), 1.17–1.21 ppm (СН3–СН2 group), and 3.72– 3.79 ppm (СН2–О–Si group). The number of mono mer units of this macromonomer was found from the integralintensity ratio for signals corresponding to its ethoxy and methyl groups. Copolymers 1 and 2 were prepared according to the reaction
CH3
(CH2CH2O)n
CH3 Si O (CH2CH2O)n CH3 CH3 m
(2)
nol. The reaction mixture was heated under reflux for 6 h, and the copolymers were isolated from the reaction mixture and purified via column chroma tography on silica gel (2 : 1 (v/v) chloroform–meth anol as an eluent). The samples were dried in vac POLYMER SCIENCE
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Table 1. Characteristics of the macromonomers Macromono mer
Yield, %
1
2
Mw
Elemental composition, % Mw /Mn
GPC
NMR
calculated
–
1620
1600
1600
1.56
18
520
520
500
1.06
uum at 2 × 10–3 Pa and 25°С for 48 h; the yield was 83.7–88.1%. CH3 C2H5O Si O C2H5 + 2 HO CH3 m
C2H5 HO Si O H + HO H m CH2CH2O
N(C2H5)3
n
C2H5 Si O H
CH2CH2O
n
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n
CH3
H
+ mHO
С 32.07 Н 8.14 Si 37.41 С 21.33 Н 61.33 Si 8.00
С 32.32 Н 8.23 Si 37.01 С 21.04 Н 61.13 Si 7.7
CH2CH2O
CH2CH2O
CH2CH2O
k
n
CH3 Si O CH3
C2H5 Si O
n
H
(3) m
(4a) m
CH3 H
m
n
C2H5 Si O O (CH2CH2O)k CH3
The copolymers were obtained under an argon atmosphere via the addition of a solution of PEG 1000 (1.983 g, 0.002 mol) or PEG1500 (2.97 g, 0.002 mol) in 2 mL absolute ethanol to a solution of 0.002 mol corresponding macromonomer in 2 mL absolute ethanol. The reaction mixture was heated under reflux for 6 h, and then copolymers 3 and 4 were isolated from the reaction mixture, while copolymers 5 and 6 were obtained via the addition of a solution of 0.002 mol PEG550 and 0.004 mol triethylamine in 10 mL chloroform to the reaction mixture, and heat ing was continued for 2 h. The reaction course was monitored according to the disappearance of the band at 2175 cm–1, which is typical for Si–H bond vibra tions in the IR spectrum of the reaction mixture. After completion of the reaction, the solvents were removed under reduced pressure, and the copolymers were dis solved in chloroform and purified via column chroma tography on silica gel (2 : 1 (v/v) chloroform–metha nol as an eluent). Then, the samples were dried in vac uum; the yield was 78.8–83.7%. Styrene polymerization was conducted under con ditions [21] commonly used for the synthesis of poly POLYMER SCIENCE
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Copolymers 3–6 were obtained through reactions (3) and (4):
CH2CH2O
CH2CH2O
calculated
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(4b) m
mer suspensions for immunochemical studies: a 1 : 9 volumephase ratio of styrene to water, surfactant (copolymers 1–6) and initiator concentrations of 1 wt % per monomer, and T = 80 ± 0.5°C. RESULTS AND DISCUSSION In this study, a series of amphiphilic organosilicon block copolymers based on polysiloxane macromono mers 1 and 2 producing hydrophobic blocks of macro molecules were prepared. The macromonomers were characterized via NMR, GPC, and elemental analysis (Table 1). The table shows that the molecularmass values determined via NMR and GPC are close, while the polydispersity indexes are low for all compounds. The closeness of the theoretical and experimental val ues of the elemental composition confirms the purity of the macromonomers. All of the prepared copolymers may be divided into linear (copolymers 1–4, ABA and (AB)n type) and combshaped (copolymers 5 and 6, (A(BA))n type) as well as triblock (copolymers 1 and 2) and polyblock (copolymers 3–6). The shares of hydrophilic blocks in
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Table 2. Structures and characteristics of the obtained copolymers Copo lymer 1
2
3
4
5
Structure
CH3 Si CH3O CH2CH2O O CH2CH2O n CH3 m n = 12, m = 6
n
CH3 CH3O CH2CH2O Si O CH2CH2O n CH3 m n = 16, m = 6
n
CH3 Si CH2CH2O O n CH3 n = 23, m = 6 CH3 Si CH2CH2O O n CH3 n = 33, m = 6 CH2CH2O
n
Mw
Yield, %
CH3
CH3
Elemental composition, %
found
GPC
NMR
found
calculated
83.7
1530
1480
1480
С 47.7 H 8.8 Si 10.7
С 49.2 H 9.9 Si 9.4
88.1
1790
1690
1700
С 52.9 H 1.8 Si 9.1
С 54.3 H 2.4 Si 8.1
78.8
1430
1360
1380
С 47.9 H 8.8 Si 11.4
С 50.5 H 10.1 Si: 9.9
83.7
1900
1800
1800
С: 44.5 H: 8.6 Si 17.2
С: 46.5 H: 9.2 Si 16.7
79.3
14200
14100
14100
С 51.4 H 8.9 Si 4.2
С 54.0 H 9.9 Si 3.7
82.4
14700
14600
14600
С 51.4 H 8.9 Si 4.2
С 53.8 H 10.3 Si 3.8
m
m
C2H5 Si O
O CH2CH2O k CH3 m n =23, m = 21, k = 12 6
CH2CH2O
n
C2H5 Si O
O CH2CH2O k CH3 m n = 33, m = 21, k = 12 * Calculated from the monomer loaded.
copolymers 1 and 3 and in copolymers 2 and 4 are practically identical. Table 2 shows that all compounds are obtained with good yields, while close values of theoretical and experimental molecular masses and elemental compositions indicate that the polymers have the presumed structures. The values of the critical micelle concentration (CMC) and surface tension at the CMC, σCMC, were determined, while the colloid–chemical properties of surfactants were calculated from surfacetension iso therms. The results are presented in Table 3. Depending on the polymer structures, the CMC values varied in the wide range (7.1 × 10–6)– (1.1 × 10 ⎯2) mol/L. For all pairs of copolymers of similar structures (copolymers 1 and 2, copolymers 3 and 4, and copolymers 5 and 6), the CMC values increased with PEO block size. No dependence between the structures of the studied copolymers and the values of surface tension was revealed. In addition, the Gibbs
adsorption values increased with the size of hydro philic blocks for the pairs of copolymers of similar structures. The increase in molecular mass of PEO blocks for the pairs with close structures led to lower S0 values. For ABA copolymers, the S0 values are slightly
Table 3. Surface activities of the prepared copolymers
Polymer
CMC × 104, mol/L
σCMC , mN/m2
Γ × 106, mol/m2
S0, Å2
1 2 3 4 5 6
1.4 6.8 1.2 5.3 1.6 20.0
26.5 26.3 28.6 29.5 22.2 25.8
2.28 2.80 2.10 2.51 2.50 3.30
73.0 59.7 77.7 66.2 65.9 50.4
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SYNTHESIS, PROPERTIES, AND APPLICATION OF SURFACEACTIVE BLOCK Conversion, % 100
6
5
1
3
2
725
4
75
50
25
0
100
200
300
400 Time, min
Fig. 1. Time dependences of conversion for the polymerization of styrene in the presence of the prepared amphiphilic surfactants. The curve numbers correspond to the polymer numbers in Table 2.
lower than those for (AB)n copolymers of similar structures, while for (A(BA))n copolymers, the S0 val ues are considerably lower. This outcome is likely due to the structural features of such macromolecules. The time dependences of conversion for styrene polymerization in the presence of polyorganosiloxane surfactants had the S shape typical for heterophase polymerization (Fig. 1). Each polymerization pro ceeded with a short induction period (10–15 min) and at a high constant rate until complete conversion of the monomer. The characters of the dependences obtained in the presence of the prepared surfactants are similar; they differ only in polymerization rate and complete conversion time. For example, styrene poly merization in the presence of ABA copolymers 1 and Table 4. Characteristics of polymer suspensions prepared with the use of the organosilicon copolymers as surfactants Polymer
Vp × 107, mol/L s
d, μm
Dw /Dn
Мη × 10–3
1 2 3 4 5 6
5.5 4.5 5.1 4.1 5.8 6.4
0.5 0.5 0.6 0.7 0.5 0.4
1.01 1.01 1.01 1.03 1.01 1.01
160 180 210 380 210 160
No coagulum. Suspensions are stable in 0.20 mol/L KCl. POLYMER SCIENCE
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2 proceeded at different rates: The polymerization rate in the presence of polymer 1, which has a lower degree of polyoxyethylation, is higher than that in the pres ence of copolymer 2. A similar scenario is observed for (AB)n copolymers 3 and 4. The comparison of copol ymers 1 and 3 and copolymer 2 and 4, with similar overall sizes of the polyoxyethyl and polysiloxane blocks but different structures, shows that higher poly merization rates are achieved when ABA copolymers are employed. The highest polymerization rate is observed in the presence of (A(BA))n copolymers; in this case, it is higher for the copolymer with a greater degree of oxyethylation. Similar features are observed for time of complete monomer conversion. Polystyrene suspensions obtained in the presence of PEOcontaining polyorganosiloxane surfactants show high stability during polymerization—a result that is evidenced by the lack of coagulum—and stabil ity in dilute electrolyte solutions. Polystyrene suspen sion particles have a spherical shape and a narrow size distribution (Fig. 2, Table 4). There is no considerable difference in the numbers of particles formed during initiation of polymerization in the presence of polyor ganosiloxane surfactants of different structures. At the same time, the diameters of particles of polystyrene suspensions differ. For example, the particles of the smallest diameter were obtained in the presence of copolymers 5 and 6, while particles of the largest diameter were prepared in the presence of copolymers 3 and 4. This outcome may be due to both the differ ence in macromolecule architecture (linear or comb
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ISTRATOV et al.
100
4.3 µm
80 60 40 20 0
7.5 µm 0.4
0.5
80 60 40 20 0 0.4
4.3 µm 0.5
0.8 0.9 D, µm
0.7
80 60 40
0
60 40 20 4.3 µm 0.6
0.6 D, µm
100
6
0.5
0.5
0.4
80
0
20
0.6 0.7 D, µm
Ni/ΣNi × 100%
Ni/ΣNi × 100% 6.0 µm
40
20
100
3
60
100
5
Ni/ΣNi × 100%
Ni/ΣNi × 100% 6.0 µm
80
0 0.6
0.6 D, µm
100
2
100
4
Ni/ΣNi × 100%
Ni/ΣNi × 100%
1
0.7 D, µm
80 60 40 20 0 0.3
0.4
0.5 0.6 D, µm
Fig. 2. Micrographs of polystyrene suspension particles obtained via the polymerization of styrene in the presence of the prepared amphiphilic block copolymers and histograms of their size distributions. The curve numbers correspond to the polymer numbers in Table 2.
shaped) and the diverse structures of organosilicon blocks. The results indicate that the formation of poly mer particles proceeds at various intensities and depends on surfactant structure. CONCLUSIONS The surface activities of the studied polyorganosi loxane surfactants are considerably dependent on their structures. In the presence of the studied PEOcon taining polyorganosiloxane surfactants, polystyrene can be polymerized until complete conversion over
4.0–6.5 h to yield stable polystyrene suspensions with particle diameters of 0.4–0.7 µm and a narrow size distribution. The styrene polymerization rate and polystyrene particle diameter are affected by both the ratio of poly(ethylene oxide) and polysiloxane blocks in the copolymer and their sequences and chain struc tures. REFERENCES 1. T. Hubbard, Encyclopedia of Surface and Colloid Science (Marcel Dekker, New York, 2002). POLYMER SCIENCE
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SYNTHESIS, PROPERTIES, AND APPLICATION OF SURFACEACTIVE BLOCK 2. H. Kawaguchi, Prog. Polym. Sci. 25 (8), 1171 (2000). 3. N. I. Prokopov, I. A. Gritskova, V. R. Cherkasov, and A. E. Chalykh, Russ. Chem. Rev. 65 (2), 167 (1996). 4. I. A. Gritskova, I. G. Krasheninnikova, D. I. Al’Kha varin, P. V. Nuss, E. A. Dorokhova, and I. Gzhiva Niksin’ska, Colloid J. 57 (2), 182 (1995). 5. H. Nakamura, M. Ishii, A. Tsukigase, M. Harada, and H. Nakano, Langmuir 21, 8918 (2005). 6. Y. Jin, Y. Zhu, X. Yang, H. Jiang, C. Li, J Colloid. Inter face Sci. 301 (1), 130 (2006). 7. H. Du, P. Chen, F. Liu, F. Meng, T. Li, and X. Tang, Mater. Chem. Phys. 51 (3), 277 (1997). 8. P. Tartaj and C. J. Serna, J. Am. Chem. Soc. 125 (51), 15754 (2003). 9. O. V. Chirikova, Candidate’s Dissertation in Chemistry (MITKhT, Moscow, 1994). 10. T. Stoebe, Z. Lin, R. M. Hill, M. D. Ward, and H. T. Davis, Langmuir 12 (2), 337 (1996). 11. F. Han, Y. Deng, Y. Zhou, and B. Xu, J. Surfactants Deterg. 15 (2), 123 (2012). 12. M. Srividhya, K. Chandrasekar, G. Baskar, and B. S. R. Reddy, Polymer 48 (5), 1261 (2007).
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13. P. L. Kuo, S. S. Hou, C. K. Teng, and W. J. Liang, Col loid Polym. Sci. 279 (3), 286 (2001). 14. P. Somasundaran, S. C. Mehta, and P. Purohit, Adv. Colloid Interface Sci. 128–130, 103 (2006). 15. S. C. Mehta, P. Somasundaran, and R. Kulkarni, J. Colloid Interface Sci. 333 (2), 635 (2009). 16. Zh.L. Peng, Q. Wu, Y.L. Wang, and S.T. Yang, J. Surfactants Deterg. 7 (3), 277 (2004). 17. D.W. Chung and J. C. Lim, Colloids Surf. A 336 (1– 3), 35 (2009). 18. W. L. E. Armarego and D. D. Perrin, Purification of Laboratory Chemicals (ButtleworthHeinemann, 1998). 19. K. A. Andrianov, Organosilicon Compounds (GKhI, Moscow, 1955) [in Russian]. 20. A. G. Pasynskii, Colloid Chemistry (Vysshaya shkola, Moscow, 1959) [in Russian]. 21. I. A. Gritskova, V. S. Papkov, I. G. Krasheninnikova, and A. M. Evtushenko, Polym. Sci., Ser. A 49 (3), 235 (2007).
Translated by I. Kudryavtsev
