Macromolecules 1988,21, 2175-2183 (14) Gervais, M.; Douy, R.; Gallot, B.; Erre, R. Polymer 1986, 27, 1513. (15) Kugo, K.; Hata, Y.; Hayashi, T.; Nakajima, A. Polym. J. 1982, 14, 401. (16) Gaines, G. L., Jr.; Bender, G. W. Macromolecules 1972,5,82. (17) Yamashita, Y. J. Macromol. Sci., Chem. 1979, A13, 401. (18) Owens, D. K. J. Appl. Polym. Sci. 1970, 14, 185. (19) Kendrick, T. C.; Kingston, B. M.; Lloyd, N. C.; Owen, M. J. J. Colloid Interface Sci. 1967, 24, 135. (20) Gaines, G. L., Jr. Macromolecules 1981, 14, 1366. (21) Fredrickson, G. H. Macromolecules 1987,20, 2535. (22) Gaines, G. L., Jr. J . Phys. Chem. 1969, 73, 3143. (23) Gaines, G. L., Jr. J . Polym. Sci. Part A-2 1969, 7, 1379. (24) Siow, K. S.; Patterson, D. J . Phys. Chem. 1973, 74, 356. (25) Ober. R.: Paz. L.: Tawin., C.:, Pincus.. P.:. Boileua. S. Macromolecules 1983, i6,5 6 (26) . , DiMeelio. J. M.; Ober, R.; Paz, L.: Taupin, C.; Pincus, P.; Boilek, S . J. Phys. (Les Ulis, Fr.) 1983,-44,1035. (27) Koberstein, J. T. In Encyclopedia of Polymer Science and Engineering; Wiley: New York, 1987; Vol. 8, p 237. (28) Busscher, H. J.; Hoogsteen, W.; Dijkema, L.; Sawatsky, G. A.; van Pelt. A. W. J.: de Jonc H. P.: Challa., G.:, Arends. J. Polvm. Commun. 1985,26, 252. (29) LeGrand. D. G.: Gaines. G. L.. Jr. J. Polvm. Sci.. Part C 1971, 34, 45. (30) Flory, P. J. Principles of Polymer Chemistry; Cornel1 University Press: Ithaca, NY, 1953. (31) Pan, D. H.; Prest, M. W., Jr. J . Appl. Phys. 1985, 58, 15. (32) McMaster, L. P. Macromolecules 1973, 6, 760. (33) Nishi, T.; Wang, T. T.; Kwei, T. K. Macromolecules 1975,8, 227. (34) Kwei, T. K.; Wang, T. T. In Polymer Blends; Paul, D. R., Newman, S., Eds.; Academic: New York, 1978; Vol. 1. (35) Hadziioannou, G.; Stein, R. Macromolecules 1984, 17, 567. (36) Shiomi, T.; Kohno, K.; Yoneda, K.; Tomita, T.; Miya, M.; Imai, K. Macrmolecules 1985, 18, 414. (37) Jelenic, T.; Kirste, R. G.; Oberthuer, R. C.; Schmitt-Streeker, S.; Schmitt, B. J. Makromol. Chem. 1984, 12, 185. (38) Bhatia, Q. S.; Chen, J. K.; Koberstein, J. T.; Sohn, J. E.; Emerson, J. A. J. Colloid Interface Sci. 1985, 106, 352. (39) Anastasiadis, S. H.; Chen, J. K.; Koberstein, J. T.; Sohn, J. E.; Emerson, J. A. Polym. Eng. Sci. 1986, 26, 1410. (40) Anastasiadis, S. H.; Chen, J. K.; Koberstein, J. T.; Sohn, J. E.;
(41) (42) . , (43) (44) (45) (46) (47) (48) (49)
~I
(50) (51) (52) (53) (54) (55) (56) (57) (58) (59) (60) (61) (62) (63) (64) (65) (66)
2175
Emerson, J. A.; Siegel, A. F. J . Colloid Interface Sci. 1987,119, 55. Bender, G. W.; Gaines, G. L., Jr. Macromolecules 1970,3, 128. Van Krevelen. D. W. ProDerties of. Polvmers: Elsevier: Am" sterdam, 1976. Kwei. T. K.: Nishi. T.: Roberts. R. F. Macromolecules 1974. 7, 667. Hartland, S.; Hartley, R. W. Axisymmetric Fluid-Liquid Interface; Elsevier: Amsterdam, 1976. Cahn, J. W. J. Chem. Phys. 1977,66, 3667. Poser, C. I.; Sanchez, I. C. Macromolecules 1981, 14, 361. de Gennes, P.-G. Macromolecules 1981, 14, 1637. Bhatia, Q. S. Ph.D. Thesis, Princeton University, 1987. Clark, D. T.; Dilks, A. J. Polym. Sci., Polym. Chem. Ed. 1976, 14, 533. Wagner, C. D.; Riggs, W. M.; Davis, L. E.; Moulder, J. F.; Muilenberg, J. E. Handbook of X-ray Photoelectron Spectroscopy, Perkin-Elmer Corp., 1979. Proctor, A,; Sherwood, P. M. A. Anal. Chem. 1982, 54, 13. Clark, D. T.; Thomas, H. R.; Dilks, A.; Shuttleworth, D. J. Electron Spectrosc. Relat. Phenom. 1971, 10, 435. LeGrand, D. G.; Gaines, G. L., Jr. J . Colloid Interface Sci. 1969, 31, 162. Wu, S. In Polymer Blends; Paul, D. R., Newman, S., Eds., Academic: New York, 1978. Goldblatt, R. D.; Scilla, G. J.; Park, J. M.; Johnson, J. N.; Huang, S. J. Appl. Polym. Sci., in press. Fadley, C. S.; Bergstrom, S. A. L. Phys. Lett. A 1971,35a, 375. Fadley, C. S. Prog. Surf. Sci. 1984, 16, 275. Clark, D. T.; Thomas, H. R. J. Polym. Sci., Polym. Chem. Ed. 1977, 15, 2843. Szajman, J.; Liesegang, J.; Jenkin, J. G.; Leckey, R. G. G. J . Electron Spectrosc. Relat. Phenom. 1978, 14, 247. Fadley, C. S.; Baird, R. J.; Sickhaus, W.; Novakov, T.; Bergstrom, S. A. L. J. Electron Spectrosc. 1974,4, 93. Edwards, S. F. Proc. Phys. SOC.,London 1966, 88, 265. Edwards, S. F.; Jeffers, E. F. J. Chem. Soc., Faraday Trans. 2 1979, 75, 1020. Daoud, M.; Jannink, G. J . Phys. (Les. Ulis, Fr.) 1975,37,973. Schaefer, D. W. Polymer 1984, 25, 387. Hashimoto et al., unpublished results quoted by Schichtel; Binder, Macromolecules 1987, 20, 1679. Schwan, D., et al. J. Chem. Phys., in press.
Entanglement in Blends of Monodisperse Star and Linear Polystyrenes. 1. Dilute Blends Hiroshi Watanabe,' Hirotsugu Yoshida, and Tadao Kotaka* Department of Macromolecular Science, Faculty of Science, Osaka University, Toyonaka, Osaka 560, J a p a n . Received October 1, 1987; Revised Manuscript Received J a n u a r y 19, 1988 ABSTRACT Viscoelasticproperties of binary blends composed of narrow molecular weight distribution (MWD) 4-arm star polystyrenes (2-chain) of molecular weight (MW) M2and narrow MWD linear polystyrenes (1-chain) of Ml were examined and compared with binary blends of narrow MWD linear polystyrenes of M2 and M1. In these blends, the volume fraction 4z of the 2-chain was kept small so that the 2-chains were entangling only with the matrix 1-chains but not with themselves. When the MW of the components of these dilute blends were such that M, < Ml > Ml > M, may relax as the surrounding 1-chains diffuse away so that the 1-2 entanglement has become ineffective. In the framework of the generalized tube model, this relaxation mechanism corresponds to the tube renewal mode. The limiting ratio of M2/Ml, for which these power laws are valid, is smaller for the star/linear chain blends than that for the linear chain blends. This is because the intrinsic relaxation time of the star 2-chain of M, is longer than that of the linear 2-chain of the same M2, observed in the bulk states. Thus, the star 2-chain exhibits the Rouse-Ham modes more easily than the corresponding linear 2-chain in the same matrix 1-chains.
Introduction Blends of narrow molecular weight distribution ( M W D ) polymers are simple but important model s y s t e m s for On leave from the Department of Chemical Engineering and Materials Science, 151 Amundson Hall, University of MinnesotaTwin Cities, 421 Washington Ave. S.E., Minneapolis, MN 55455. 0024-9297/88/2221-2175$01.50/0
examining the effects of entanglement on the relaxation behavior of condensed polymer systems.l-" Recently, several groups including ourselves studied v i s c ~ e l a s t i c ~ - ~ ~ and d i f f u s i ~ n l properties ~-~~ of binary blends of n a r r o w MWD linear polymers of h i g h and low MW. In such a blend the -terminalrelaxation modes o f t h e high-MW chain (the test chain) a r e strongly affected b y the lifetime of the 0 1988 American Chemical Society
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Macromolecules, Vol. 21, No. 7, I988
e n t a n g l e m e n t n e t w o r k f o r m e d i n the blends. Table I Another important factor governing the relaxation Characteristics of 4-Arm S t a r Polystyrene Samples modes in condensed polymer s y s t e m s is the topological code" 10-3Mw Mw/M,, fb [?I' t y p e of the test c h a i n itself, s u c h as linear, branched, 4877 307 1.08 4.2 H shaped,21and ring.22*23Especially, bulk star48184 736 1.05 4.0 1.52 polymer s y s t e m s were examined extensively, and the 48310 1240 1.06 4.1 2.08 48410 1640 1.07 4.2 2.51 following features were revealed.lG20 The compliance is 48662 2650 1.06 3.9 3.92 proportional to the arm molecular weight Ma of the star molecules and described b y the Rouse-Ham t h e ~ r y , ~ ~ ? ~ ~ code number indicates the rounded number of the arm "The while the relaxation times and viscosity increase expomolecular weight Ma = M,/4 in units of 1000. * f = ( M w ) s ~ / (Mw)precursor. 'Intrinsic viscosity (in 100 cm3/g) in toluene 35 "C. nentially with Ma,18differring from linear-chain polymer systems for which the relaxation times and viscosity often Coupling of polystyryl anions with the hexafunctional bTSE o b e y power laws w i t h respect to the molecular weight.l yielded, a t most, 4-arm star P S samples. Thus, to avoid conTo e x a m i n e the effects of these two factors on the tertamination with components with less arms, we adjusted the mole minal relaxation modes of condensed polymer systems, we ratio of the chlorine atoms of bTSE to the polystyryl anions so extended our studies on binary3* and ternary' blends of that there was a large excess of the latter over the former, typically linear narrow MWD polystyrenes (PS)to those of star and from l/z to 1/5. We kept the mixture at 35 "C under gentle stirring linear polystyrenes. for 2 weeks to 2 months, depending on MW of the precursor PS. In this s t u d y , we have examined the behavior of binary Each crude reaction product prepared under such a condition blends consisting of high-MW 4-arm star PS chains diluted inevitably contained a large amount of precursor P S and other undesired components. Thus, the crude product was subjected i n low-MW linear PS matrices. The volume fraction of to fractionation by using benzene (BZ) and methanol (MeOH) the star chain, 42,was always k e p t s m a l l so that the star to separate the desired 4-arm star component in as pure form as chains entangled only with the matrix chains but not with possible. In a typical run, starting with approximately 5 g/L of themselves. We have two purposes i n mind: One was to BZ solution of the crude product, we added MeOH to make the examine the features of the relaxation mechanisms in such BZ:MeOH volume ratio approximately 4:1, equilibrated a t the blends due to d i s e n t a n g l e m e n t of the test chain from the ambient temperature, and recovered the gel phase. This procedure e n t a n g l e m e n t network formed by the matrix chains; the was repeated three times, during which nearly all the precursor o t h e r was to compare the features of the intrinsic relaxawas removed. Finally to remove possible high-MW contaminant, tion modes of the star versus linear c h a i n s in such d i l u t e we recovered the dilute solution phase from the phase-separated mixture. blends. Characterization of the Samples. The polymer samples were In terms of the generalized tube theory,26 the f o r m e r characterized by using a gel permeation chromatograph (GPC, process was often called constraint release by tube reTosoh Co., Model HLC-801A) equipped with a triple-detector newaLWB On the other hand, for the latter problem, Ham system consisting of a UV monitor (Tosoh Co., Model UV-8) and developed a t h e o r y for the intrinsic relaxation modes of a low-angle laser-light-scattering (LALLS) photometer (Tosoh an isolated star chain,26but the theory has not y e t been Co., Model LS-8000) with a built-in refractometer. The elution critically tested for star/linear chain blends. Thus in this solvent was chloroform, and commercially available standard P S article we will compare the relaxation behavior of the star samples (Tosoh Co., TSK PS) were used as the elution standards. versus h i g h - M W linear PS chains in the matrices of lowThe weight average molecular weight, M,, and the M , a t each MW linear PS chains. elution volume were determined by using the LALLS monitor. The results of the GPC characterization of the star P S samples Experimental Section are summarized in Table I. Intrinsic viscosities, [7], of the purified star PS fractions were Materials. Anionic polymerization was carried out in preparing determined in toluene at 35 "C. The results are also listed in Table narrow MWD 4-arm star PS ~ a m p l e s . ~Styrene ~ , ~ ~ monomer, I. The [ q ] versus M, data for the star PS samples are in good benzene, methanol, and other chemicals for the anionic polymagreement with those reported by Roovers and B y ~ a t e r . ~ ~ erization were purified by the methods recommended by Fetters3I To evaluate the heterogeneity of the samples, we also carried and by F u j i m o t ~as~ described ~ in our previous papers.33 1,2out sedimentation velocity experiments at 35.0 "C in cyclohexane Bis(trichlorosyly1)ethane (bTSE) was used as the coupling agent on a Beckman-Spinco Model E analytical ~ltracentrifuge.~~ The for polystyryl anions. The reagent was purified by repeating polymer concentration were 0.0629 to 0.144 X lo-* g ~ m - ~ . sublimation under high vacuum twice, dissolved in purified As an example, Figure 1 (left) shows gel permeation chromahexane, and stored in an ampule. The concentration of bTSE tograms of a crude reaction product and its star PS fraction was determined by titration with aqueous solution of sodium prepared from a precursor P S sample of M, = 389 x lo3. The hydroxide. circles in the figure indicate the M, of the fractions at each elution Star PS samples were prepared via the following procedures. count. Figure 1 (right) shows sedimentation velocity patterns of First, anionic polymerization of styrene was carried out in benzene the same samples. As seen in this figure, the crude product might by using sec-butyllithium as the initiator. After 48 h of reaction be contaminated with 3-arm star and/or dimer components beat ambient temperature, an aliquot was taken from the mixture sides the precursor. However, the chromatogram and sedimento recover the precursor PS sample for the convenience of later tation pattern of the purified star fraction suggest that the concharacterization. A prescribed amount of bTSE in hexane was taminants have been thoroughly removed during the fractionation then added and allowed to react with the rest of the polystyryl (Mw)precursor ratios, f , in Table I suggest procedure. The (Mw)8tu/ anions. that the 4-arm star samples are reasonably pure. Gervasi and GosnellZ9reported that in the coupling reaction Beside these star PS samples, we also used some narrow-MWD of polystyryl anions with bTSE, the maximum number of arms linear PS samples, some of which were prepared by ourselves,33 attained was only 4, in spite of the fact that the coupling agent and some of which were commercially available samples. The used was hexafunctional. This is because the reaction rate of molecular characteristics of these linear P S samples are sumespecially the last two chlorines with polystyryl anions became marized in Table 11. The MWD of all the samples used are extremely slow as the coupling reaction proceeded. On the other sufficiently narrow, as judged from the ratios of the weight average hand, in the coupling of polyisoprenyl anions with bTSE to obtain to number average molecular weight, M,/M,, shown in these star polyisoprene (PI) samples, 6-arm star samples were easily tables. Thus, in the followings, we designate all the 4-arm star obtained.30 This difference in the coupling behavior may be due (4s) and linear (L) narrow MWD P S samples as monodisperse to the difference in the steric hindrance of very long PS versus and will not distinguish M , and M,. The linear PS samples are PI chains. In our experiments, this fact was successfully utilized coded, for example, as L2810 with the number representing M,, for checking the purity of bTSE.
Macromolecules, Vol. 21, No. 7, 1988
Star/Linear Polystyrene Dilute Blends 2 177
I
A
35
6.0t
40
oooooo~oo~o
45
4s -Frac t ion
Figure 1. (Left) Gel permeation chromatograms and (right) sedimentation velocity patterns of the precursor L389 of the 4S410 star sample (top), the crude reaction product (center), and the purified 4S410 star fraction (bottom). The circles in the left half indicate MW of the fraction a t each elution count. Table I1 Characteristics of Linear-Chain Polystyrene Samples codea 10-3M, Mw/Mn codea 10-3Mw Mw/Mn 1.07 5.2 1.08 L8gb 88.5 L5b 1.06 10.5 1.08 LllOC 110 Lllb 1.07 L124b 124 1.05 L23 23.4 1.06 L172b 172 1.07 26.3 L26 1.07 L42 41.5 1.06 L315b 315 1.01 46.0 1.05 L775b 775 L46b 1.09 L72 72.4 1.06 L2810b 2810 "The code number indicates the rounded number of the weight average molecular weight M, in units of 1OOO. bFrom Tosoh Co. From Pressure Chemicals Co. and the 4-arm star samples as 4S410 with the arm molecular weight, Ma = Mw/4, both with the unit 1OOO. Thus, Ma does not necessarily agree with (Mw)precursor. Rheological Measurements. Dynamic measurements were carried out on a laboratory rheometer (Model IR-200: Iwamoto Seisakusho, Ltd., Kyoto) of a cone and plate type, similar to the one described p r e v i ~ u s l y . ~ ~ The systems examined were blends composed of the fractionated 4-arm star (4s) samples or high-MW linear PS (L) samples as the test (2-) chain and the low-MW linear PS (L)
samples as the matrix (1-) component. As the reference, the pure 4 s and L samples were also examined. First, we attempted to carry out the measurement on molten bulk systems. However, the high-MW 4 s samples did not relax in the temperature and frequency ranges accessible to the present experiment. In fact, the high-MW samples often degraded within 2' h a t the temperatures above 200 "C. Thus, we added to the systems dibutyl phthalate (DBP) as a plasticizer?*' For a few blends of much higher MW, we used dioctyl phthalate (DOP) as a less volatile plasticizer. The measurements were carried out in the temperature ranges between 15 and 90 "C for the DBP systems and between 35 and 150 "C for the DOP systems. The weight fraction of the plasticizer was always 40 wt % for the DBP systems and 38.5 wt 70 for the DOP systems, so that the volume fraction @p of the polymer component (1 + 2 chains) was always 60 ~ 0 1 % .Here, we neglected the volume change upon mixing the components. The characteristic molecular weight M, and the entanglement spacing Me for these plasticized blends were 51 X lo3 and 30 X lo3, respectively, for the DBP and DOP systems.* The timetemperature superposition principle' was applied to obtain master curves of the storage G'and loss G"modu1i. All the data were reduced to an isofriction state with the free-volume fraction f, = 0.0644. Although the results are not shown here, the shift factor was well represented by the previously reported
2178 Watanabe et al.
Macromolecules, Vol. 21, No. 7, 1988
6
f,
= 0.0644
-2
5
-
I
* il72lDOP
I
4 60
I
2
-3
-2 log
-1
-2
0,
-1
log +2
Figure 4. Dependences on dz of (a) the compliance JZbB and (b) the viscosity ?)2,bB of the star 2-chain in 4S410/L blends (with I # I ~ = 60 vol % but varying 4.J at the reference temperature TI. blends with 41 >> 42are nearly the same as those in the p-m systems. Thus, for these dilute blends we may use the previously proposed blending law5l6 HbB(T) = @lHl,m(T)+ @2HZ,bB(T)
(1)
m
2 8 85 124 17 2
31 5
,
’
L-_ -5
-‘
-3
C
*_
c l bqd
-2
0
- 3
log(wa,
-
_1
I
2
3
5 ’ )
Figure 3. Master curves of the storage moduli G’for 4S410/L blends with 4 = 60 vol % and & = 1 vol % at the reference temperature
f,.
WLF equation: log UT = -6.74(T- T1)/(133.6+ T - T1).5,6 The reference temperatures T , were 54 and 71 “C, respectively, for the DBP and DOP plasticized systems with MI > 23.4 X lo3 and bP = 60 vol %. Figure 2 compares the C’and G”master curves for L172/DBP and L172/DOP systems with dP = 60 vol % at their respective T,. We notice that the viscoelastic behavior at the TIare the same for the two systems. Thus, in the following, we do not distinguish the difference in the plasticizer when the data were reduced to the TI.
Results Complex Moduli of the Dilute Blends. Figure 3 shows the master curves of dynamic moduli, G’(uaT),in a double logarithmic scale for the blends of 4S410 and different L samples with 42 = 1 vol % and for the pure 4S410 sample, all with C$p = 60 vol %. The broken curves indicate those for the pure 1-chains (@p = @1 = 60 vol %) as the reference. Such systems will be referred to as the parent-monodisperse (p-m) systems for the blends. Comparing each blend with its p-m system, we see that the behaviors a t high frequencies coincide with each other, but slow relaxation modes due to the 2-chain prevail as a shoulder a t the low-frequency end of the G‘curve. Although not shown here, similar but less-enhanced trends were observed in the G”master curves of the blends and their p-m systems. The agreement found between the G‘ curves of the blends and p-m systems in the high-frequency region suggests that the relaxation modes of the 1-chain in the
Here, H b B is the relaxation spectrum of the blend, Hl,mthe spectrum of the 1-chain in the p-m system, and H2,bB the spectrum of the 2-chain in the blend. Note that and H 2 , b are ~ the spectra reduced to the unit volume of the 1and 2-chains7respectively. Thus, for example, the storage modulus, G’l,m, of the p-m system with the content of the 1-chain = @p can be given by W2T2
G’l,m(W) = 4plIHl,m(T)- 1 + w272 d In
T
(2)
By using eq 1, we can define the contribution of the 2-chain to the dynamic moduli, Gh,bB, and loss moduli, G”z,bB, as fOllOWS:
Here, G \B and G’\B are the observed moduli for the blend, and G‘l,m and G“l,m are those for the corresponding p-m system. Then, from eq 1-3, we can define the contributions of the 2-chain in the blend to the viscosity, ?)2,bB, the elastic coefficient, A2,bB,and the compliance, J 2 , b B , as follows:6 %.bB A2,bB
7 b B - (C$l?7l,m/@p)
(44
= AbB - (C$lAl,m/$p)
(4b)
=
J2bB
= A2,bB/(%2,bB)2
(4c)
Thus, the quantifies 7)2,b~, A2,b~,and J 2 , b ~Can be calculated directly from the corresponding quantities of the bB and p-m systems (which are evaluated from the observed G’ and G” curves in the low-frequency ends) without actually
Star/Linear Polystyrene Dilute Blends 2179
Macromolecules, Vol. 21, No. 7, 1988 I
I
I
-3 .....
-
h
LSLIOIL $p = 6 0 'lo
.
1 , -0.0644
F m
e
6
- 2
90
- 1
I
1
N
x
h
N'
h
I
-lI 5
6
7
l o g M2
Figure 6. M2 dependence of the weight average relaxation time the 2-chain in dilute 4S/L46 blends.
J z , b ~ ? l z , bof ~
-2
Me Mc
L
I
I
5
6
log
Figure 5. Ml dependence of the weight average relaxation time of the 2-chain in dilute 4S410/L blends (represented by circles). The horizontal dotted line indicates the relaxation time of the monodisperse 4S410 system with & = 60 vol %; the triangles indicate the shift factor X to superpose the low-frequency ends of the &-'G'Z,bB curves (see Figure 8 and the text). The broken line indicates the relaxation times of the Rouse-Ham modes estimated for the 4s410 chain by applying eq 9 to the data of the dilute L2810/L blends of M , < M I
