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poly(ethylene oxide) blends by dilute solution viscometry
Eur. Polwn. J. Vol. 32, No. 8. pp.927-933, 1996 Copyright (0 1996Published by ElsevierSilence Ltd Printed in Great Britam. All rights reserved OOW3057/96$15.00+ 0.00 PII: s0014-3057(%)ooo37-7
Pergamon
MISCIBILITY STUDIES ON POLYSTYRENE/POLY(ETHYLENE OXIDE) AND POLYBUTADIENE-graft-POLYSTYRENE/POLY(ETHYLENE OXIDE) BLENDS BY DILUTE SOLUTION VISCOMETRY ELVAN YILMAZ*,
OSMAN YILMAZ and HAMIT CANER
Department of Chemistry. Faculty of Arts and Sciences, Eastern Mediterranean University, G. Magusa, TRNC. Mersin IO. Turkey (Received 8 July 1995; accepted in final
form9
October
1995)
Abstract-Miscibility of polyethylene oxide (PEO) with polystyrene (PS) or polybutadiene-grqfi-polystyrene (PBS) was investigated by dilute solution viscometry. Miscibility parameters derived from the classical Huggins equation were used to estimate the miscibility of these polymer pairs. The results, which indicated immiscibility between PS and PEO, were compared with findings in bulk reported in the hterature. PBS was also found to be immiscible with PEO. The effect of temperature on miscibility was studied by the same method for a blend of PBS with 83% PEO. All miscibility parameters were observed to decrease with increasing temperature. Copyright (c 1996 Published by Elsevier Science Ltd
properties such as enthalpy of mixing or free energy of mixing. According to Flory-Huggins theory, high polymers are miscible if the interaction parameter x for the two polymeric species is negative. The polymer-solvent or polymer-polymer interaction parameter x can be estimated from the solubility parameters of the components through the FloryHuggins approach as follows:
INTRODUCTION
The miscibility of polymer mixtures is usually studied in bulk through various methods such as differential scanning calorimetry, dynamic mechanical analysis and electron microscopy. Decisions as to whether a mixture is miscible or not are not always clear-cut, and may show dependence on the method of examination, mixing history, solvent choice when films are cast from solution and on the intended use of the mixture [I]. Many investigators have studied polymer miscibility in solution in mutual solvents of blend components, because whether a bulk mixture is actually in an equilibrium state or not may sometimes be uncertain [l]. Thorough mixing in molecular dimensions is possible only in solution. Besides, solvation in a mutual solvent screens out extremely immiscible polymer mixtures. Miscible components form a single, transparent phase in the formed solution, while immiscible polymers exhibit phase separation if the solution is not extremely dilute [2,3]. Thermodynamic theories assume that a necessary requirement for solution is a negative Gibbs free energy change when the blend components are mixed: AG,=AH,-TAS,
(2) where e is the molar volume of component 1 and 6, and 6: are the solubility parameters of components 1 and 2, respectively. The major limitation of this approach is that it does not take into account specific interactions, like hydrogen bonds between the polymers. It allows only positive 1 values and positive heats of mixing. Generally, miscibility is predicted if the absolute value of the (6, - &) difference is zero or small. The main advantage of the solubility parameter theory is that it is a relatively simple and rapid way of predicting miscibility. Another approach to polymer miscibility proposed by Krigbaum and Wall [5], and later discussed in detail by Cragg and Bigelow [6], is the dilute solution viscosity method. Basically, miscibility parameters obtained by dilute solution viscometry are derived from the classical Huggins equation, which expresses the specific viscosity qrp of a single-solute solution as a function of concentration c:
(1)
where the subscript m stands for mixing. AG, is controlled by its enthalpic contribution because the entropic term is usually favorable but very small. Thus, negative values of AG, are generally assumed to be attained due to specific interactions between polymer segments. Solubility parameter theory [l] or Flory-Huggins theory [ 1,4], within their limitations, allow the estimation of miscibility of polymer mixtures through the evaluation of thermodynamic *To whom all correspondence
r/rp= [r/]c + bc’
(3)
where [q] is the intrinsic viscosity and b is related to the Huggins coefficient k by 6 = k[#.
(4)
The value of the Huggins coefficient is a measure
should be addressed. 927
E. Yllmaz rr 01
928
of the interpenetration of polymer coils, the extent of which depends upon the segment-segment and segment-solvent interactions. This, in turn, affects the intramolecular hydrodynamic interactton and the molecular dimensions [7l. Krigbaum and Wall [5] dertved an expresston for ideal mixture viscosity by redefining nrpin the classical Huggins equation [8] as: q5p.m = [tllmcm+ b,cH
(5)
where cm is the total polymer concentration. [n],,, is the intrinsic viscosity of the mixture and b., IS the Huggins slope coefficient which characterizes the interactions of all polymer species. The slope b, for a mixture of polymer A and polymer B is given by: b, = bAw; + bsw; + 2b,,eW,,u,B
(6)
where w’~and )zvB are weight fractions of the polymers. bae are the terms characterizing the interactions of the like (AA, BB) and unlike (AB) polymer molecules, respectively. The term bAB, which is a complex parameter including the thermodynamic and hydrodynamic interactions in the system. is given by:
k, given in equation (12); the formation of double molecules given by k,?; and intermolecular attraction or repulsion given by k,,. Thus, the overall k, turns out to be: k, = km, + k,: + k,?.
(13)
In the absence of strong specific interactions that would encourage aggregation, and at sufficiently low concentrations, the second term k,,,?can be neglected. Reabbreviating k,3 as ct and rearranging the final equation then yields r = k, - km,,.
(14)
A positive LYvalue indicates miscibility. In contrast, Chee [lo] suggested that a simple measure of the intermolecular interactions in the ternary system is the arithmetic differential interaction parameter defined as
bA, bs and
bAB=
~J~IA[~IB.
(7)
In contrast, equation (6) yields
Combining equations (7) and (8) gives k,, wtth all experimental parameters:
where 6 = wAb* + wgbB
and b, 1s the observed interaction parameter for the polymer mixture. Values of b,, b, and bB can be obtained experimentally. A positive or zero AL?value indicates miscibility, whereas AB = 0 indicates phase separation. Chee suggested a more effective parameter, p, for blend solutions having sufficiently far apart [s]* and [v]~ values: bm- btt
(9) In the presence of only hydrodynamic interactions. theoretical values of bAB or kAB are calculated as geometric means of bn and bs or k, and k,:
(16)
P(=
be - bet
[rllm- h1A- his - [SIA
mIls - him)
. _,
!’ ‘J
Here. p > 0 indtcates miscibility and p < 0 indicates phase separation. In this study, evidence for miscibility or immiscibilb&B,= (b&)’ ’ 110) ity was searched for PS/PEO and PBS/PEO pairs by the use of the dilute solution viscometry method k m, = (k,ks)’ ‘. through the application of the various parameters (11) given above. Both PS and PEO are widely used Since experimental has or kkB values reflect both commodity polymers. Detailed studies on their hydrodynamic and thermodynamic interactions mtscibility may contribute to technological and between polymer segments, the difference between environmental applications. These polymers form an experimental and theoretical values, Ak48 = interesting pair to study since they exhibit contrasting kAB- kAB.trcould give information on the thermodynphysical properties. PS is a hydrophobic polymer, amic interactions of the polymers. A posttive whereas PEO is hydrophilic. PEO is a much softer difference is an indication of attractive interactions material than PS. It is known to be a biocompatible and miscibility, whereas a negative difference polymer and has found biomedical applications. indicates repulsion and immiscibility. PSiPEO blends have been reported as incompatible Sun et al. [9] suggested a new criterion, X. based on m the literature [ 11. 121.Blends of PS of fin = 3 x 10’ the classical Huggins equation and Huggins cowith PEO of n” = 1 x 10’ have been studied in bulk. efficient k, in the blends, starting from the following Their DSC thermograms indicate that there were no expression for the Huggins constant of a mixed significant attractive interactions between PS and polymer system: PEO (111. Blends of low molar mass PEO of 4.6 x lOI and PS of 1.8 x lo5 have been studied in bulk by inverse gas chromatography and scanning electron microscopy. Phase separation has been reported [12] (12) to occur at a composition higher than 30% PEO. According to Sun et al.‘s approach for a ternary, Various reports [ 13-161 are available in the literature polymer A-polymer B-solvent, system, three types of on the morphology and physical properties of blends interaction might contribute to the value k,. These or block copolymers of PEO and PS. No study has are long-range hydrodynamic interaction of pairs of been reported for PS/PEO solutions. This work single molecules, defined by k,,,, which is the same as attempts to search for the validity of the dilute
Miscibility of polystyrene-poly(ethylene oxide) blends solution viscometry method for this pair, reference to studies made in bulk.
with
EXPERIMENTAL Chemicals and their purification
All organic solvents were purified by simple distillation. Benzene (Merck) was of analysis quality and used without further purification. Polystyrene samples were products of PETKIM (Turkey). PS is a homopolymer of styrene of && = 2.84 x IO’ and is obtained by suspension polymerization. PBS is a graft copolymer of polystyrene with cis-1,4-polybutadiene, obtained by suspension polymerization and has tin = 3 x 10s. The copolymer contains 5.2% by mass cis-l&olybutadiene. Both polymers were purified by precipitation from toluene solution m ethanol. Dried samples were then redissolved in benzene and filtered through Teflon membrane filters with maximum pore size 0.45 pm. 15.2% of PBS was discarded during filtration as the insoluble fraction. PEO was a product of BDH and had a molar mass tin = 6 x 10s. It was used without further purification. -(a)
A 0 V 0 0 0
Apparatus
Ubbelohde type glass viscometem of different sizes were employed for dilute solution viscosity measurements at different temperatures. Viscosity measurements were carried out in constant temperature water baths. The temperature was kept constant within _+O.1°C sensitivity by an electronically controlled thermostat. Aldrich (type 31655) syringe-mountable filter holders with diameters of 25 mm were used. Aldrich S & S PTFE (Teflon) membrane filters with 25 mm diameter and 0.45 pm maximum pore size were used with this filter holder. Method Viscosity measurements. Viscosity measurements of both homopolymers and blends were obtained in filtered benzene solutions at 20,25,30 and 40°C. Each sample was studied at five concentrations around 0.6, 0.5. 0.4, 0.3 and 0.2 g/dl. All the solutions were prepared on the gravimetric basis. Thus, density corrections for benzene were carried out for each concentration.
O%PEO 5040PEO 709bPEO 808PEO 908PEO 100% PEO
0.20
0.00
0.40
Concentration
3'50 r(b)
A O%PEO 0
22.9% PEO
V 33.78PEO 0 64.3% PEO 0 82.6% PEO
3.00
929
0.60
0.80
0.60
0.80
(gldl)
. 91.6%PEO A 95.8% PEO l 100% PEO
x 2.50 C i; s 2.00 'Z -0 4: 1.50 2
0.50 t 0.00
0.20
0.40
Concentration
(g/dl)
Fig. 1. Reduced viscosity, q,+ vs solution concentration for (a) PS/PEO, (b) PBS/PEO blends.
E.
930
I
Table Sample
T(
C) 20 2s 30 40 30 10 2s 30 40 30
PEO
PS PBS
PBS/PEO
PS,PEO
PBSlPEO
Yllmaz et ul.
VISCOSIIV and mwbdw [rll (dlig)
h
100 100 100 100 00 00 00 00 00 22 9 33 7
2 023 2 016 2000 I 908 0 750 0 807 0 804 0 802 0 778 I 132 I 203
54 3
14X8
82 6 91 5 95 8 50 0 70.0 80 0 90 0 82 6 82 h 82 6 82 6
833 86 959 443 651
I JII 1381 I 534 I 506 0 I46 0 204 0 200 0 227 0 N.7 0 284 0 3-n 0 679 I ‘bl I317 I 3Y? 0 609 0 970
-0686 - 0 71 0 518 -0 lb0 - 0 675 ~ IO60 - 0 462 ~0351
- 0 528 0 494 - 0 422 - 0 262
663
0972
889
842 I 833 I 833 I 784
RESULTS AND DISCUSSION
Theoretical
data for the samples studled
% PEO
tests qf miscibrlrt!,
Fiery-Huggim irtteructiotz parameter. It should be made clear when studying polymer blends in solution that polymer-polymer interactions exceed the blendsolvent interactions. This indicates that the solution measurements taken reflect mainly the behavior of the polymer blends. and the solvent effects are
AB
-0144 -0 129 - 0 069
- 0 247 -0 265 -0 142
-0006
0.082 -0240
0000
0 196 -
- I.011
- 0479
0 020 - O.OSS
- 0.281
-0009
~ 0.889
~ 0 304
- 0020
- 0.348
I311
~ 0 468
-0392
~ 0.011
- 0.067
I 185, I IYI
- 0 044 0 OS?
-0112
-0.008
I161
0 160
I IV5
~ 0 294
- 0031
-0064 0010
I38 0.196 0 082 0.049 0
0017
0 26-7
-0.006
- 0 670
~ 0
032
mmlmlzed. To achieve this, blend-solvent interaction I x) and polymer-polymer interaction parameters should be calculated. Values of xPSPEOand xptoP5 were calculated to be 0.28 and 0. I I. respectively, by the method explained in Ref. [17]. The former value is for the blend for which PS is considered as the first component. whereas the latter is that in which PEO is taken as the first component.
I 00 (a)
(b)
0 x0 060
0 60
IJ 40 i
40
-0 80 -1.00
Akrs
~ 0 396
IO0 080
0
x
P
I
0.00
0 20
I
I
040
060
I 0 80
I 00
040
0 20
0.00
IO0
-
0.60
-
0.40
-
020
-
0 80
IO0
0 60
0.80
1.00
W PEO
wPEO
0.80
0 60
I 00
(d)
0 80
('I
0
60
0 JO 2 ;5
020 0 00 -0 20 -040 -0 60
-0.80 -1.00
\ I
I 0.00
0 20
0.40
I
I
I
0.60
0 80
IO0
0
00
0.40
0.20
W PEO
WPEO Ftg.
Z
(a)
AS,
(b) /I. (c) r.
(d)
Ak*B wtth respect to compoution
for
PS/PEO
blends
Miscibility of polystyrene-poly(ethylene oxide) blends
931
1.00 0.80 -
tb)
0.60 0.40 0.20 0.00 -0.20 -
0.00
0.20
0.40
0.60
0.80
W'T
-0.40 -0.60 -0.80 -1.00 0.00
1.00
I
I
I
I
0.20
0.40
0.60
0.80
I 1.00
0.60
0.80
1.00
W PEO
0.00
0.20
0.40
WPEO
0.60
0.80
1.00
0.00
0.20
0.40
W PEO
WPEO
Fig. 3. (a) AB, (b) p, (c) a. (d) ALB with respect to composition for PBS/PEO blends.
Calculation for different blend compositions in benzene gave Xkmru_bktivalues below 0.11 at all compositions. This means that PSPEO interactions
are always more favorable
than PS-PEO-benzene interactions. Thus, studying PS/PEO miscibility in solution is acceptable within the limits of the
020 0 IO -
0
(b) 0
0.00 0.00
:
8
-0.10
-
-0.10 -020 -
-0.20 -0.30 -0.30
0
10
-0.40 20
30
40
50
0
I
I
I
I
10
20
30
40
T (“C)
O.‘O (c) -0.10
T (“‘2
o’30 r(d)
\
0.00
I SO
0.25 L
-
0.20
-0.20 -
0.15 2 a
s -0.30 -
0.10 0.05
-0.40 -0.50 -
\
-0.60 -0.70 0
I 10
20
30 TW)
40
I 50
0
10
20
30 TW)
Fig. 4. (a) AB, (b) p, (c) a, (d) Ak*s of PBSjPEO of 83% PEO with respect to temperature.
40
SO
932
E. Yilmaz ef al
solubility parameter and Flory-Huggms interaction parameter theories. Heat of mi.ring. The heat of mixing, AH,,,,,. IS an approximate measure of free energy of mixing and thus may indicate the degree of compatibility. AH,,,,, values for various compositions of PS!PEO blends were calculated according to an equation suggested by Schneier [18]. The values obtained an for AH,,, were all below 10 x IO-‘cal/mol. upper limit for thermodynamic miscibility for polymer blends in which the entropy factor is always positive, as suggested in Refs [ 17. 181. Dilute solution t+scometr.v studies Viscosity measurement. Reduced viscosity versus solution concentration graphs for polymers PBS. PS, PEO and for PSjPEO and PSB/PEO blends are shown in Figs l(a) and (b). respectively. Table I summarizes the intrinsic viscosity [q] and the Huggins slope values for all the samples studled For all the binary and ternary solutions studied. reduced viscosity was found to be a linear function of concentration. Composition and molar ~UJJ dependence of miscibility parameters. AB. p, x and AkkB values obtained for the blends studied are given m Table I. These values, with respect to the composition for blend PS/PEO, are shown in Fig. 1 No parameter exceeded the zero value criterion. indicating that PS and PEO are not miscible with each other at any composition at 30 C. However, a common trend is observed with all that there is a tendency towards parameters, in the composmon range 65570% miscibility PEO. Figure 3 illustrates the relation between the miscibility parameters and the composition of PBSjPEO blends. A similar trend IS exhibited b> these blends as observed for PS.‘PEO mixtures However. the maxlmum in miscibility curves has shifted towards higher PEO compositions. around 7585%. It can be realized from the graphs that miscibility parameters for PBSiPEO blends have shifted to less negative values than those for PSjPEO blends. Moreover. the maxImum AktB value for PBSjPEO pairs reaches a positive value. This may indicate that PBS/PEO blends are less immiscible than PSjPEO blends. Polymer-polymer miscibility is general11 known to be enhanced by specific interactions between the polymer pairs. The reason why misclbilit> shows a tendency to increase when PEO IS mixed with PBS copolymer rather than PS homopolymer might be attributed to this fact. In addition to favorable van der Waals type mteractions between the polymers, due to the presence of relatively polar C-O and polarizable C=C bonds, dipole-induced dipole-type forces can be expected to be present between PBS and PEO. increasing the miscibility between the polymers. Our results on the miscibility of the PSiPEO pair obtained by dilute solution vlscometry are consistent with the results reported in the literature, obtained in bulk [ll, 121. Unfortunately, no reports on the miscibility of the PBS/PEO pair could be
found m the literature for comparison. This polymer pair will be studied in bulk in the near future and a comparison of results of DSC with those of dilute solution viscometry will be reported. Temperature dependence of miscibilit! parameters. ‘4 blend of PBS with PEO (83%) was studied at different temperatures. Values of miscibility parameters are given in Table I All miscibility parameters increase linearly with decreasing temperature. as shown in Fig. 4. AB and p parameters Indicate that miscibility is approached at an average temperature of 20-21 C, the temperature at \vhlch miscibility parameter values approach zero. However, the I parameter approaches zero at about 27 C. Since Akhs values are all above zero for a system for which immiscibility is indicated by all other parameters, the temperature depenin dence of Akts values will not be helpful estimating the crltlcal temperature of phase separation for this sample. Further studies are planned to establish phase diagrams for the PBS/PEO system
CONCLUSION
Dilute solution vlscoslty analysis revealed immiscibility between PS and PEO. This result contributes data to the theory that the dilute solution viscometry method can be used to provide a clue to the miscibility of polymer pairs, generally studled by sophisticated techniques such as differential scanning calorimetry or electron microscopy. The PBS!PEO pair was also found to be immiscible by this method. All miscibihty parameters were observed to Increase with decreasing temperature for an lmmlscible blend of PBS/PEO with a PEO fraction of 83%
REFERENCES I
Rudm The Elemems of Polwner Scwnce and E~~gmeeringAcademic Press. New York (1982). .A
2 .4 K Kulshreshtha. B. P. Smgh and Y N. Sharma. b-u, PO/WI.J. 24. 19 (1988). 3 ‘4. K. Kulshreshtha. B. P. Smgh and Y N Sharma. Eltr PoIjm J 24, 33 (1988). 1 P J Flory Princrplesqf Polymer Chemistr?. Cornell Umversq Press, Ithaca (1953) 5 W R Krlgbaum and F. T Wall / PO/WI.Scl. 5, 505 (1950). ctted m M. Opahckl and H. J. Mencer. Eur. PoliY?r h
J
I 1955) 7 8 9
28, 5 (1992).
L H Cragg
M
and C C Blgelow. J. Po/Jm.
Bohdanecky
and
J. Kovar
Solutrons Elsevler. Amsterdam M L Huggins. J. Am Chem Z. Sun, W. Wang and Z Feng
Srr. 16, 177
C’rscosrf! qf Polymer (1982) Sot. 64, 2716 (1942). Eur. Polym. J. 28, 1259
(1992) IO K K. Chee. Eur. Polvnr. J 26, 423 (1990). II S. P Tmg. B J. Bulkin and E. M. Pearce. J. Polym. Ser.. Polym. Chem. 19, I451 (1981). T. lnm and Y. Takenam]. 12. T Suzuki. Y. Murakami,
Polj,merJ. 13, 1027 (1981).
13 C Prestidge
and TH. F Tadros
Sci. 124, 660 (1988).
J. Collard
Interphase
Miscibility of polystyrene-poly(ethylene 14. C. Tsitsilianis, G. Staikos and A. Dondos. Polwner 33, 3369 (1992). 15. M. Wagner and B. A. Wolf. Polymer 34, 1460 (1993).
oxide) blends
933
16. P. Sakellariou. Polymer 34, 3408 (1993). 17. Y. P. Singh and R. P. Singh. Eur. PO&~. J. 19, 535 (1983). 18. B. Schneier. J. Appl. Pofym. Sci. 17, 3175 (1973).
Pergamon
MISCIBILITY STUDIES ON POLYSTYRENE/POLY(ETHYLENE OXIDE) AND POLYBUTADIENE-graft-POLYSTYRENE/POLY(ETHYLENE OXIDE) BLENDS BY DILUTE SOLUTION VISCOMETRY ELVAN YILMAZ*,
OSMAN YILMAZ and HAMIT CANER
Department of Chemistry. Faculty of Arts and Sciences, Eastern Mediterranean University, G. Magusa, TRNC. Mersin IO. Turkey (Received 8 July 1995; accepted in final
form9
October
1995)
Abstract-Miscibility of polyethylene oxide (PEO) with polystyrene (PS) or polybutadiene-grqfi-polystyrene (PBS) was investigated by dilute solution viscometry. Miscibility parameters derived from the classical Huggins equation were used to estimate the miscibility of these polymer pairs. The results, which indicated immiscibility between PS and PEO, were compared with findings in bulk reported in the hterature. PBS was also found to be immiscible with PEO. The effect of temperature on miscibility was studied by the same method for a blend of PBS with 83% PEO. All miscibility parameters were observed to decrease with increasing temperature. Copyright (c 1996 Published by Elsevier Science Ltd
properties such as enthalpy of mixing or free energy of mixing. According to Flory-Huggins theory, high polymers are miscible if the interaction parameter x for the two polymeric species is negative. The polymer-solvent or polymer-polymer interaction parameter x can be estimated from the solubility parameters of the components through the FloryHuggins approach as follows:
INTRODUCTION
The miscibility of polymer mixtures is usually studied in bulk through various methods such as differential scanning calorimetry, dynamic mechanical analysis and electron microscopy. Decisions as to whether a mixture is miscible or not are not always clear-cut, and may show dependence on the method of examination, mixing history, solvent choice when films are cast from solution and on the intended use of the mixture [I]. Many investigators have studied polymer miscibility in solution in mutual solvents of blend components, because whether a bulk mixture is actually in an equilibrium state or not may sometimes be uncertain [l]. Thorough mixing in molecular dimensions is possible only in solution. Besides, solvation in a mutual solvent screens out extremely immiscible polymer mixtures. Miscible components form a single, transparent phase in the formed solution, while immiscible polymers exhibit phase separation if the solution is not extremely dilute [2,3]. Thermodynamic theories assume that a necessary requirement for solution is a negative Gibbs free energy change when the blend components are mixed: AG,=AH,-TAS,
(2) where e is the molar volume of component 1 and 6, and 6: are the solubility parameters of components 1 and 2, respectively. The major limitation of this approach is that it does not take into account specific interactions, like hydrogen bonds between the polymers. It allows only positive 1 values and positive heats of mixing. Generally, miscibility is predicted if the absolute value of the (6, - &) difference is zero or small. The main advantage of the solubility parameter theory is that it is a relatively simple and rapid way of predicting miscibility. Another approach to polymer miscibility proposed by Krigbaum and Wall [5], and later discussed in detail by Cragg and Bigelow [6], is the dilute solution viscosity method. Basically, miscibility parameters obtained by dilute solution viscometry are derived from the classical Huggins equation, which expresses the specific viscosity qrp of a single-solute solution as a function of concentration c:
(1)
where the subscript m stands for mixing. AG, is controlled by its enthalpic contribution because the entropic term is usually favorable but very small. Thus, negative values of AG, are generally assumed to be attained due to specific interactions between polymer segments. Solubility parameter theory [l] or Flory-Huggins theory [ 1,4], within their limitations, allow the estimation of miscibility of polymer mixtures through the evaluation of thermodynamic *To whom all correspondence
r/rp= [r/]c + bc’
(3)
where [q] is the intrinsic viscosity and b is related to the Huggins coefficient k by 6 = k[#.
(4)
The value of the Huggins coefficient is a measure
should be addressed. 927
E. Yllmaz rr 01
928
of the interpenetration of polymer coils, the extent of which depends upon the segment-segment and segment-solvent interactions. This, in turn, affects the intramolecular hydrodynamic interactton and the molecular dimensions [7l. Krigbaum and Wall [5] dertved an expresston for ideal mixture viscosity by redefining nrpin the classical Huggins equation [8] as: q5p.m = [tllmcm+ b,cH
(5)
where cm is the total polymer concentration. [n],,, is the intrinsic viscosity of the mixture and b., IS the Huggins slope coefficient which characterizes the interactions of all polymer species. The slope b, for a mixture of polymer A and polymer B is given by: b, = bAw; + bsw; + 2b,,eW,,u,B
(6)
where w’~and )zvB are weight fractions of the polymers. bae are the terms characterizing the interactions of the like (AA, BB) and unlike (AB) polymer molecules, respectively. The term bAB, which is a complex parameter including the thermodynamic and hydrodynamic interactions in the system. is given by:
k, given in equation (12); the formation of double molecules given by k,?; and intermolecular attraction or repulsion given by k,,. Thus, the overall k, turns out to be: k, = km, + k,: + k,?.
(13)
In the absence of strong specific interactions that would encourage aggregation, and at sufficiently low concentrations, the second term k,,,?can be neglected. Reabbreviating k,3 as ct and rearranging the final equation then yields r = k, - km,,.
(14)
A positive LYvalue indicates miscibility. In contrast, Chee [lo] suggested that a simple measure of the intermolecular interactions in the ternary system is the arithmetic differential interaction parameter defined as
bA, bs and
bAB=
~J~IA[~IB.
(7)
In contrast, equation (6) yields
Combining equations (7) and (8) gives k,, wtth all experimental parameters:
where 6 = wAb* + wgbB
and b, 1s the observed interaction parameter for the polymer mixture. Values of b,, b, and bB can be obtained experimentally. A positive or zero AL?value indicates miscibility, whereas AB = 0 indicates phase separation. Chee suggested a more effective parameter, p, for blend solutions having sufficiently far apart [s]* and [v]~ values: bm- btt
(9) In the presence of only hydrodynamic interactions. theoretical values of bAB or kAB are calculated as geometric means of bn and bs or k, and k,:
(16)
P(=
be - bet
[rllm- h1A- his - [SIA
mIls - him)
. _,
!’ ‘J
Here. p > 0 indtcates miscibility and p < 0 indicates phase separation. In this study, evidence for miscibility or immiscibilb&B,= (b&)’ ’ 110) ity was searched for PS/PEO and PBS/PEO pairs by the use of the dilute solution viscometry method k m, = (k,ks)’ ‘. through the application of the various parameters (11) given above. Both PS and PEO are widely used Since experimental has or kkB values reflect both commodity polymers. Detailed studies on their hydrodynamic and thermodynamic interactions mtscibility may contribute to technological and between polymer segments, the difference between environmental applications. These polymers form an experimental and theoretical values, Ak48 = interesting pair to study since they exhibit contrasting kAB- kAB.trcould give information on the thermodynphysical properties. PS is a hydrophobic polymer, amic interactions of the polymers. A posttive whereas PEO is hydrophilic. PEO is a much softer difference is an indication of attractive interactions material than PS. It is known to be a biocompatible and miscibility, whereas a negative difference polymer and has found biomedical applications. indicates repulsion and immiscibility. PSiPEO blends have been reported as incompatible Sun et al. [9] suggested a new criterion, X. based on m the literature [ 11. 121.Blends of PS of fin = 3 x 10’ the classical Huggins equation and Huggins cowith PEO of n” = 1 x 10’ have been studied in bulk. efficient k, in the blends, starting from the following Their DSC thermograms indicate that there were no expression for the Huggins constant of a mixed significant attractive interactions between PS and polymer system: PEO (111. Blends of low molar mass PEO of 4.6 x lOI and PS of 1.8 x lo5 have been studied in bulk by inverse gas chromatography and scanning electron microscopy. Phase separation has been reported [12] (12) to occur at a composition higher than 30% PEO. According to Sun et al.‘s approach for a ternary, Various reports [ 13-161 are available in the literature polymer A-polymer B-solvent, system, three types of on the morphology and physical properties of blends interaction might contribute to the value k,. These or block copolymers of PEO and PS. No study has are long-range hydrodynamic interaction of pairs of been reported for PS/PEO solutions. This work single molecules, defined by k,,,, which is the same as attempts to search for the validity of the dilute
Miscibility of polystyrene-poly(ethylene oxide) blends solution viscometry method for this pair, reference to studies made in bulk.
with
EXPERIMENTAL Chemicals and their purification
All organic solvents were purified by simple distillation. Benzene (Merck) was of analysis quality and used without further purification. Polystyrene samples were products of PETKIM (Turkey). PS is a homopolymer of styrene of && = 2.84 x IO’ and is obtained by suspension polymerization. PBS is a graft copolymer of polystyrene with cis-1,4-polybutadiene, obtained by suspension polymerization and has tin = 3 x 10s. The copolymer contains 5.2% by mass cis-l&olybutadiene. Both polymers were purified by precipitation from toluene solution m ethanol. Dried samples were then redissolved in benzene and filtered through Teflon membrane filters with maximum pore size 0.45 pm. 15.2% of PBS was discarded during filtration as the insoluble fraction. PEO was a product of BDH and had a molar mass tin = 6 x 10s. It was used without further purification. -(a)
A 0 V 0 0 0
Apparatus
Ubbelohde type glass viscometem of different sizes were employed for dilute solution viscosity measurements at different temperatures. Viscosity measurements were carried out in constant temperature water baths. The temperature was kept constant within _+O.1°C sensitivity by an electronically controlled thermostat. Aldrich (type 31655) syringe-mountable filter holders with diameters of 25 mm were used. Aldrich S & S PTFE (Teflon) membrane filters with 25 mm diameter and 0.45 pm maximum pore size were used with this filter holder. Method Viscosity measurements. Viscosity measurements of both homopolymers and blends were obtained in filtered benzene solutions at 20,25,30 and 40°C. Each sample was studied at five concentrations around 0.6, 0.5. 0.4, 0.3 and 0.2 g/dl. All the solutions were prepared on the gravimetric basis. Thus, density corrections for benzene were carried out for each concentration.
O%PEO 5040PEO 709bPEO 808PEO 908PEO 100% PEO
0.20
0.00
0.40
Concentration
3'50 r(b)
A O%PEO 0
22.9% PEO
V 33.78PEO 0 64.3% PEO 0 82.6% PEO
3.00
929
0.60
0.80
0.60
0.80
(gldl)
. 91.6%PEO A 95.8% PEO l 100% PEO
x 2.50 C i; s 2.00 'Z -0 4: 1.50 2
0.50 t 0.00
0.20
0.40
Concentration
(g/dl)
Fig. 1. Reduced viscosity, q,+ vs solution concentration for (a) PS/PEO, (b) PBS/PEO blends.
E.
930
I
Table Sample
T(
C) 20 2s 30 40 30 10 2s 30 40 30
PEO
PS PBS
PBS/PEO
PS,PEO
PBSlPEO
Yllmaz et ul.
VISCOSIIV and mwbdw [rll (dlig)
h
100 100 100 100 00 00 00 00 00 22 9 33 7
2 023 2 016 2000 I 908 0 750 0 807 0 804 0 802 0 778 I 132 I 203
54 3
14X8
82 6 91 5 95 8 50 0 70.0 80 0 90 0 82 6 82 h 82 6 82 6
833 86 959 443 651
I JII 1381 I 534 I 506 0 I46 0 204 0 200 0 227 0 N.7 0 284 0 3-n 0 679 I ‘bl I317 I 3Y? 0 609 0 970
-0686 - 0 71 0 518 -0 lb0 - 0 675 ~ IO60 - 0 462 ~0351
- 0 528 0 494 - 0 422 - 0 262
663
0972
889
842 I 833 I 833 I 784
RESULTS AND DISCUSSION
Theoretical
data for the samples studled
% PEO
tests qf miscibrlrt!,
Fiery-Huggim irtteructiotz parameter. It should be made clear when studying polymer blends in solution that polymer-polymer interactions exceed the blendsolvent interactions. This indicates that the solution measurements taken reflect mainly the behavior of the polymer blends. and the solvent effects are
AB
-0144 -0 129 - 0 069
- 0 247 -0 265 -0 142
-0006
0.082 -0240
0000
0 196 -
- I.011
- 0479
0 020 - O.OSS
- 0.281
-0009
~ 0.889
~ 0 304
- 0020
- 0.348
I311
~ 0 468
-0392
~ 0.011
- 0.067
I 185, I IYI
- 0 044 0 OS?
-0112
-0.008
I161
0 160
I IV5
~ 0 294
- 0031
-0064 0010
I38 0.196 0 082 0.049 0
0017
0 26-7
-0.006
- 0 670
~ 0
032
mmlmlzed. To achieve this, blend-solvent interaction I x) and polymer-polymer interaction parameters should be calculated. Values of xPSPEOand xptoP5 were calculated to be 0.28 and 0. I I. respectively, by the method explained in Ref. [17]. The former value is for the blend for which PS is considered as the first component. whereas the latter is that in which PEO is taken as the first component.
I 00 (a)
(b)
0 x0 060
0 60
IJ 40 i
40
-0 80 -1.00
Akrs
~ 0 396
IO0 080
0
x
P
I
0.00
0 20
I
I
040
060
I 0 80
I 00
040
0 20
0.00
IO0
-
0.60
-
0.40
-
020
-
0 80
IO0
0 60
0.80
1.00
W PEO
wPEO
0.80
0 60
I 00
(d)
0 80
('I
0
60
0 JO 2 ;5
020 0 00 -0 20 -040 -0 60
-0.80 -1.00
\ I
I 0.00
0 20
0.40
I
I
I
0.60
0 80
IO0
0
00
0.40
0.20
W PEO
WPEO Ftg.
Z
(a)
AS,
(b) /I. (c) r.
(d)
Ak*B wtth respect to compoution
for
PS/PEO
blends
Miscibility of polystyrene-poly(ethylene oxide) blends
931
1.00 0.80 -
tb)
0.60 0.40 0.20 0.00 -0.20 -
0.00
0.20
0.40
0.60
0.80
W'T
-0.40 -0.60 -0.80 -1.00 0.00
1.00
I
I
I
I
0.20
0.40
0.60
0.80
I 1.00
0.60
0.80
1.00
W PEO
0.00
0.20
0.40
WPEO
0.60
0.80
1.00
0.00
0.20
0.40
W PEO
WPEO
Fig. 3. (a) AB, (b) p, (c) a. (d) ALB with respect to composition for PBS/PEO blends.
Calculation for different blend compositions in benzene gave Xkmru_bktivalues below 0.11 at all compositions. This means that PSPEO interactions
are always more favorable
than PS-PEO-benzene interactions. Thus, studying PS/PEO miscibility in solution is acceptable within the limits of the
020 0 IO -
0
(b) 0
0.00 0.00
:
8
-0.10
-
-0.10 -020 -
-0.20 -0.30 -0.30
0
10
-0.40 20
30
40
50
0
I
I
I
I
10
20
30
40
T (“C)
O.‘O (c) -0.10
T (“‘2
o’30 r(d)
\
0.00
I SO
0.25 L
-
0.20
-0.20 -
0.15 2 a
s -0.30 -
0.10 0.05
-0.40 -0.50 -
\
-0.60 -0.70 0
I 10
20
30 TW)
40
I 50
0
10
20
30 TW)
Fig. 4. (a) AB, (b) p, (c) a, (d) Ak*s of PBSjPEO of 83% PEO with respect to temperature.
40
SO
932
E. Yilmaz ef al
solubility parameter and Flory-Huggms interaction parameter theories. Heat of mi.ring. The heat of mixing, AH,,,,,. IS an approximate measure of free energy of mixing and thus may indicate the degree of compatibility. AH,,,,, values for various compositions of PS!PEO blends were calculated according to an equation suggested by Schneier [18]. The values obtained an for AH,,, were all below 10 x IO-‘cal/mol. upper limit for thermodynamic miscibility for polymer blends in which the entropy factor is always positive, as suggested in Refs [ 17. 181. Dilute solution t+scometr.v studies Viscosity measurement. Reduced viscosity versus solution concentration graphs for polymers PBS. PS, PEO and for PSjPEO and PSB/PEO blends are shown in Figs l(a) and (b). respectively. Table I summarizes the intrinsic viscosity [q] and the Huggins slope values for all the samples studled For all the binary and ternary solutions studied. reduced viscosity was found to be a linear function of concentration. Composition and molar ~UJJ dependence of miscibility parameters. AB. p, x and AkkB values obtained for the blends studied are given m Table I. These values, with respect to the composition for blend PS/PEO, are shown in Fig. 1 No parameter exceeded the zero value criterion. indicating that PS and PEO are not miscible with each other at any composition at 30 C. However, a common trend is observed with all that there is a tendency towards parameters, in the composmon range 65570% miscibility PEO. Figure 3 illustrates the relation between the miscibility parameters and the composition of PBSjPEO blends. A similar trend IS exhibited b> these blends as observed for PS.‘PEO mixtures However. the maxlmum in miscibility curves has shifted towards higher PEO compositions. around 7585%. It can be realized from the graphs that miscibility parameters for PBSiPEO blends have shifted to less negative values than those for PSjPEO blends. Moreover. the maxImum AktB value for PBSjPEO pairs reaches a positive value. This may indicate that PBS/PEO blends are less immiscible than PSjPEO blends. Polymer-polymer miscibility is general11 known to be enhanced by specific interactions between the polymer pairs. The reason why misclbilit> shows a tendency to increase when PEO IS mixed with PBS copolymer rather than PS homopolymer might be attributed to this fact. In addition to favorable van der Waals type mteractions between the polymers, due to the presence of relatively polar C-O and polarizable C=C bonds, dipole-induced dipole-type forces can be expected to be present between PBS and PEO. increasing the miscibility between the polymers. Our results on the miscibility of the PSiPEO pair obtained by dilute solution vlscometry are consistent with the results reported in the literature, obtained in bulk [ll, 121. Unfortunately, no reports on the miscibility of the PBS/PEO pair could be
found m the literature for comparison. This polymer pair will be studied in bulk in the near future and a comparison of results of DSC with those of dilute solution viscometry will be reported. Temperature dependence of miscibilit! parameters. ‘4 blend of PBS with PEO (83%) was studied at different temperatures. Values of miscibility parameters are given in Table I All miscibility parameters increase linearly with decreasing temperature. as shown in Fig. 4. AB and p parameters Indicate that miscibility is approached at an average temperature of 20-21 C, the temperature at \vhlch miscibility parameter values approach zero. However, the I parameter approaches zero at about 27 C. Since Akhs values are all above zero for a system for which immiscibility is indicated by all other parameters, the temperature depenin dence of Akts values will not be helpful estimating the crltlcal temperature of phase separation for this sample. Further studies are planned to establish phase diagrams for the PBS/PEO system
CONCLUSION
Dilute solution vlscoslty analysis revealed immiscibility between PS and PEO. This result contributes data to the theory that the dilute solution viscometry method can be used to provide a clue to the miscibility of polymer pairs, generally studled by sophisticated techniques such as differential scanning calorimetry or electron microscopy. The PBS!PEO pair was also found to be immiscible by this method. All miscibihty parameters were observed to Increase with decreasing temperature for an lmmlscible blend of PBS/PEO with a PEO fraction of 83%
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