Macromolecules 1981,14, 128-130
128
Solution Properties and Chain Flexibility of Poly(thiolmethacry1ates). 2. Poly(cyclohexy1thiolmethacrylate) Nikos Hadjichristidis,'* Costas Touloupis,l* a n d L. J. Fetters*lb Department of Industrial Chemistry, The University of Athens, Athens 144, Greece, and Institute of Polymer Science, The University of Akron, Akron, Ohio 44325. Received July 3, 1980 ABSTRACT: The dilute-solution properties of eight poly(cyc_lohe_xylthiolmethacrylate) (PTCy) fractions covering the molecular weight (M,) range 4.8 X 105 to 5.9 X 105 (M,/M, E 1.4) were studied in tetrahydrofuran, toluene, and cyclohexane. The unperturbed dimensions were calculated by using light scattering and intrinsic viscosity data. The results indicate that PTCy is a less extended chain than poly(cyclohexy1 methacrylate).
The importance of the influence of the side groups on dilute-solution polymer behavior is well documented. In the case of polymethacrylates interest has centered on the changes induced by altering the identity of the side-group substituent^.^-^ The corresponding poly(thio1methacrylates) have received no attention except6i7for poly(phenyl thiolmethacrylate) (PTPh) and poly(o-methylphenyl thiomethacrylate). The dilute-solution properties of these poly(thiolmethacry1ates) indicated that their chains are more flexible than poly(pheny1methacrylate). In this paper, solution properties of poly(cyclohexy1 thiolmethacrylate) (PTCy), -CH2C(CH3)(COSCGH11)-, in tetrahydrofuran (THF), toluene, and cyclohexane are presented, and the results obtained are compared with those2 for poly(cyclohexy1 methacrylate) (PCy).
Light scattering measurements were carried out in a Sofica PGD instrument at 25 OC in cyclohexane with unpolarized light a t 436 nm [ R m w = 48.4 x lo4 cm-l].13 The refractive index increment, dnldc, measured under the same conditions was (140 f 2) X cm3 g-'. A Hewlett-Packard 503 osmometer (S and S-08 membranes) was used for osmotic pressure measurements in toluene at 37 "C. Intrinsic viscosities, in T H F at 35 "C and cyclohexane at 25 "C, were determined with Cannon-Ubbelohde viscometers having negligible kinetic energy corrections. The values for the weight- and number-average molecular weights, second virial coefficients, z-average root-mean-square end-to-end distance (r:)l/z, and intrinsic viscosities are given in Table I.
Experimental Section Cyclohexyl thiolmethacrylate was prepared by reaction of methacryloyl chloride with cyclohexyl mercaptan in aqueous sodium hydroxide solution. Purification of this monomer was achieved by repeated distillation under reduced pressure [102-103 "C (5 mmHg)] in the presence of iodine as an inhibitor. The monomer yield was ca. 50%. Composition analysis yielded the following. Calcd for Cl&160S (184.3): C, 65.17; H, 8.75; 0,8.68. Found: C, 64.9; H, 8.7; 0, 8.7. The purity of the monomer, by gas chromatography, was found to be virtually 100%. Two polymerizations of cyclohexyl thiolmethacrylate were carried out a t 50 "C in benzene solution (10% w/w) under vacuum (-lo+ mmHg) in the presence, respectively, of 0.01 and 0.05% (w/w) of 2,2'-azobis(isobutyronitri1e). The polymer microtacticity was determined from the 'H NMR spectrum of PTCy in o-dichlorobenzene (20% w/w) a t 120 "C with a Varian 300-MHz spectrometer. The percentage of isotactic (mm), atactic (mr), and syndiotactic (rr) triads was, respectively, 14, 38, and 48%. These values are virtually the same as those found* for PCy; thus the replacement of oxygen by sulfur does not alter the microtacticity of polymethacrylates obtained by radical polymerizations. The fractionation was carried out in toluene/methanol in the way previously d e ~ c r i b e d .The ~ polydispersity of the fractions was estimated by gel permeation chromatography with T H F as the solvent a t 35 "C. A Waters Ana-Prep instrument was used with a differential refractive index detector. A seven-column Styragel set (totallength of 28 ft) with a continuous porosity range of 2 X lo3to 5 X lo6 A was used for this analysis. The characteristics of this column arrangement are presented e l ~ e w h e r e . ~ ? ~ The polydispersity indices were determined by the method of Benoit e t al.'O with the following Mark-Houwink relations ([q] in dL g-'): [q] = 1.02 X l0-W 0.73 (polystyrene)" and [7] = 4.07 X 106A?w0.74 (PTCy) (this work! The calculations were done plith an IBM 370/158 computer. The polydispersity values (M,/ Mn)cpc,corrected for diffusion spreading,12 are given in Table I and agree well with those determined by light scattering and osmometry. The solvents used for dilute-solution measurements were reagent grade materials. Toluene and cyclohexane were fractionally distilled over calcium hydride, while THF was dried over calcium hydride and then fractionally distilled over sodium. 0024-9297/81/2214-0128$01.00/0
Results a n d Discussion Figure 1 shows conventional log-log plots of [ q ] against Mw for PTCy in T H F and cyclohexane. The following relationships were obtained by least-squares analyis for the two solvents used ( [ q ] in dL g-l): [T1THF350C = 4.07 X 10-5Mw0.74 25'C = 8.65 x 10-5Mw0.63 [~ICSHll It should be noted that if the Mark-Houwink exponent is greater than ca. 0.8, the relationship between intrinsic viscosity and molecular weight will yield14-16 incorrect values of Ke and, in turn, of the unperturbed dimensions. The foregoing intrinsic viscosity-molecular weight relations show that the Mark-Houwink exponents fall within the acceptable range. The relation between chain dimensions, in terms of the root-mean-square end-to-end distance and molecular weight for PTCy in cyclohexane a t 25 "C, is shown in Figure 2. The best-fit line is given as (( rz2))1/2= 0.395d?w0.56 The value of the exponent, 0.55, agrees well with the calculated value of 0.54. The latter value results from the use of the Mark-Houwink exponent a in the relation17 (a
+ 1)/3.
The dependence of the osmometric and light scattering second virial coefficients is shown in Figure 3. The relations found are as follows: Az = 7.3 X 10-3M;0.27 (osmometry, toluene, 37 "C)
A~ = 3.2 x 1 0 - 3 ~ ~ 4 3 . 2 6 (light scattering, cyclohexane, 25 "C) The foregoing exponents are comparable to values reportedlgZ4for a variety of flexible polymers in moderate to good solvents and are consistent with theory,25 which predicts a limiting value of -0.2 for very large molecular weights in very good solvents. The application26of the Burchard-Stockmayer-Fixman Figure 4, for the [q]-Mwdata in cyclohexane and T H F yields the parameter Ke,which in this case is equal
0 1981 American Chemical Society
Vol. 14, No. 1, January-February 1981
Poly(cyclohexy1thiolmethacrylate) 129
Table I Characterization Data for Poly(cyclohexyl thiolmethacrylate)a temp, "C
F1
F2
F3
F4
F5
F6
F7
THF
cyclohexane
35 25
cyclohexane
25
0.737 0.370 0.593 580 1.1 0.450 1.8 1.4 1.3
0.565 0.294 0.410 470 1.0 0.293 2.0 1.4 1.4
0.342 0.189 0.208 330 1.2 0.150 2.2 1.4 1.4
0.314 0.178 0.193 310 1.4 0.142 2.4 1.5 1.4
0.294 0.158 0.160 290 1.5 0.122 2.6 1.4 1.3
0.239 0.146 0.134 250 1.4 0.095 2.6
0.185 0.110 0.089 205 1.6 0.069 3.1 1.3 1.3
solvent [VI,
dL g-'
Mw x 10'6 ((rz*))l/*,A
4x
lo4,mL mol g-2
A1 X
LO4,mL mol g-z
M , x 10-6
toluene
37 35
THF
(_Mw/_Mn)GPC
Mw lMn
1.4
1.4
F1-F8 are the various PTCy frstiogs, [ q ] is the intrinsic viscosity, ((rzz))ll2 is the end-to-end distance, the polydispersity from GPC,and M w / M , is the polydispersity from light scattering and osmotic pressure.
0.115 0.077 0.048 2.0 0.035 3.7 1.3 1.4
(aw/J?n)Gpc is
I
I
-8-
.
0
CYCLOHEXINE
AT
25OC
2 -9 -
I
1
I
I
//
/3
'2 -
In F i n CG In Mw
I
I
I
13
12
ll
In M
J
I
w
Figure 3. Second virial coefficient-molecular weight plots for poly(cyclohexy1 thiolmethacrylate).
Figure 1. Intrinsic viscosity-weight-average molecular weight plots for poly(cyclohexy1 thiolmethacrylate).
1
il
/P In
Mw
13
I
Figure 2. End-bend distance-weight-averagemolecular weight plot for poly(cyclohexy1 thiolmethacrylate) in cyclohexane.
1 ,~
3d0
CVC;EXX;AT I
25'C I
700
m w
Figure 4. Burchard-Stockmayer-Fixman plots for poly(cyc1ohexyl thiolmethacrylate in tetrahydofuran and cyclohexane.
to 2.90 X lo-* dL g-l. The value of Ke can then be used flexibility and (rof2)is the mean-square end-to-end disto determine the unperturbed dimension (ro2),according tance, assuming completely free rotation around the carto Flory's well-known equation bon-carbon bonds of the polymer chain. For this case, the Ke = @,((r02)/IM)3/2 is calculated5 value of where @ is the Flory c ~ n s t a n t . ~ ~ ~ ~ = O.23ml2 However, prior to the exploitation of the above equation, Hence, Q for PTCy is calculated to be 2.13. the Ke value must be corrected by a polydispersity factor of about 1.04, assuming a Schulz-Flory d i ~ t r i b u t i o n . ~ ~ For a comparison of the average dimensions of randomcoil chains, the characteristic ratio, C,, of Flory is used. Thus, the corrected value for Ke is 3.0 X dL g-'. The This is defined3' as value for CP is taken as 2.5 X lo2'. This value is the one determined from light scattering by McIntyre% and Berry35 C, = lim [(r,2>/(n12)] n-and very recently by Miyaki et al.36 Hence, the relation between (ro2)'l2,in A, and molecular weight is where n is the number of bonds in the polymer chain [n = 2(M/mo)] and 1 is the bond length (1.55 A). Table I1 ( r $ ) l J 2= 0.491W~ summarizes the pertinent data characterizing PTCy and The flexibility factor, Q, is defined as PCy.2 For purposes of comparison the Ke value for PCy has Q = ((ro2)/(rOf2))1/2 been corrected for polydispersity and the corresponding where CT represents the effect of local interactions on chain unperturbed dimensions have been calculated by using the
(rot)
Macromolecules
130 Hadjichristidis, Touloupis, and Fetters Table I1 Molecular Characteristics for Poly( cyclohexyl thiolmethacrylate) and Poly(cyclohexy1 methacrylate) PTCy ~~
microtacticity (rr in %) K e X LO4,dL g-’ ( ( r o z ) / M ) l /( zA ) (intrinsic viscosity)
((rofz)/iiT)ol/z (A)
48 3.0 0.49 0.23 0.26 0.57c 2.13 2.48 8.5 12.4
PCya ~
~~
51 4.5 0.56 0.24 0.35 0.65c 2.33d 3.04 10.2 14.8
11151-AC4,6)and the National Science Foundation (Grant GH-32583X), Polymers Program. The authors thank Mr. R. D. Vargo for his assistance with the GPC polydispersity calculations and the osmometry measurements. The authors also thank Professor W. H. Stockmayer for helpful suggestions. References and Notes
(a) The University of Athens. (b) The University of Akron. Hadjichristidis, N.; Devaleriola, M.; Desreux, V. Eur. Polym. J. 1972,8, 1193. Alexopoulos, J. B.; Hadjichristidis, N.; Vassiliadis, A. Polymer 1975, 16, 386. Niezette. J.: Hadiichristidis. N.: Desreux. V. Mukromol. Chem. 1976, 177, 2069.“ Hadjichristidis, N . Mukromol. Chem. 1977, 178, 1463. Kokkiaris. D.: Hadiichristidis. N. Polvmer 1977. 18. 639. a Reference 2. Based on fractions C,, C,, and C, of Kokkiaris; D.1 Touioupis, C.; Hadjichktidis, N.’Poiymer, in The correction for polydispersity was made acref 2. press. cording t o Kurata and Stockmayer.38 The value of u Ambler, M.; Fetters, L. J.; Kesten, Y. J . Appl. Polym. Sci. presented elsewhere was determined by using the approx1977,21, 2439. imate theoretical value of @ , 2.87 x loz1. McCrackin, F. L. J. Appl. Polym. Sci. 1977,21,639. Benoit, H.; Grubisic, Z.; Rempp, P.; Decker, P.; Zilliox, J. G. experimental value of ip of 2.5 X loz1. From Table I1 it J . Chim. Phys. 1966,63, 1507. Roovers, J. E. L.; Bywater, S. Macromolecules 1972, 5, 384. is clear that the extension of PTCy is less than that of PCy. Smith, M. V. J. J. Appl. Polym. Sci. 1974, 18, 925. An identical trend is seen in the comparison of the intrinsic Oth, A.; Oth, J.; Desreux, V. J. Polym. Sci. 1953, 10, 551. viscosity results6,’involving poly(pheny1 thiolmethacrylate) Florv. P. J. Mukromol. Chem. 1966. 98, 128. and poly(pheny1 methacrylate). Stoikmayer, W. H. Br. Polym. J. 1977,’9, 89. Yamakawa, H. “Modern Theory of Polymer Solutions”; HarAn indication of the relative amount of chain extension per and Row: New York, 1971; pp 364-72. exhibited by PTCy and PCy can be gained from the light Flory, P. J. “Principles of Polymer Chemistry”; Cornel1Uniscattering data available here and elsewhere2 from cycloversity Press: Ithaca, N.Y., 1953; p 629. hexane solutions. The results, obtained by Baumann’s Krigbaum, W. R.; Flory, P. J. J . Am. Chem. Soc. 1953, 75, 1775. method,39are compiled in Table 11. There it can be seen Cohn-Ginsberg,E.; Fox, T. G.; Mason, H. F. Polymer 1962,3, that u and C, for PTCy and PCy are larger than the 97. corresponding values obtained from the intrinsic viscosity Schulz, G. V.; Bauman, H.; Darskus, R. J. Phys. Chem. 1966, measurements. We have noted that the same trend is 70, 3647. observed from the light s ~ a t t e r i n g ~and ~ pintrinsic ~~~~ Kuwatara, N.; Higastida, S.; Nakata, M.; Kaneko, M. J. Polym. Sci., Part A-2 1969, 7, 285. viscosity r e ~ u l t sfor~ near-monodisperse ~ ~ , ~ ~ ~ ~ polystyrenes; Alexopoulos, J.; Hadjichristidis, N . Mukromol. Chem. 1979, i.e., the Baumann plot for data obtained in good solvents 180. 455. yields a larger value for (r:)/M than do the corresponding Dimarco, A.; Hadjichristidis, N.; Niezette, J.; Desreux, V. Bull. data obtained under 0 conditions and the intrinsic visSOC.R. Sci. Liege 1973,543, 253. Appelt, B.; Meyerhoff, G. Macromolecules 1980, 13, 657. cosity m e t h ~ of d Burchard, ~ ~ ~ ~ ~Stockmayer, and Fixman. Reference 16, pp 168-9. This observation is contrary to Baumann’s original asThe estimated error for K , is *lo%. This error could be ~ e s s m e n t . It ~ ~is of interest to note that the value of reduced by measurements under 0 conditions. However, the (ro2)/M for polystyrene obtained from the Burchardamount of polymer samples was insufficient to allow determination of a convenient 0 solvent. Stockmayer-Fixman treatment,27*28 using results for Burchard, W. Mukromol. Chem. 1960,50,20. benzene and toluene solutions, is virtually identical with Stockmayer, W. H.; Fixman, M. J. Polym. Sci., Part C 1963, that obtained from the combined series of light scatterNo. 1, 137. ing34)4@43 and intrinsic v i s ~ o s i t measurements y ~ ~ ~ ~ ~ ~ ~ ~ ~ ~Flory, ~ P. J. “Statistical Mechanics of Chain Molecules”; Interscience: New York; pp 36-8. under 0 conditions. Flory, P. J. J. Chem. Phys. 1949, 17, 303. Hence, the light scattering derived values for u and C, T. G.; Flory, P. J. J. Phys. Chern. 1949, 53, 197. Fox, for PTCy and PCy are, we believe, overestimate^.^^ Reference 17, pp 546-54, 600-2. However, from a relative standpoint, these values seemBareiss, R. E. “Polymer Handbook, 2nd ed.; Bandrup, J., Immergut, E., Eds.; Wiley: New York, 1975; p IV-115. ingly indicate that PTCy is a more flexible, i.e., less exMcIntyre, D.; Wims, A,; Williams, L. C.; Mandelkern, L. J. tended, chain than PCy. As a consequence, the replacePhvs. Chem. 1962.66. 1932. ment of the ester oxygen by sulfur in the side group of Behy, G. C. J . C&m.’Phys. 1967, 46, 1338. polymethacrylates apparently leads to an increase in the Mivaki, Y.: Einaga, Y.: Fuiita, H.: Fukada, M. Maromolecules main-chain flexibility. This would appear to be due, in 1980,13, 588. These authors have recorded a value for of 1.76 X loz1 as that reported in ref 34. In reality, the value the main, to a change in the local intramolecular interacgiven for by the authors of ref 34 is 2.5 X loz1. tions and to the greater flexibilitp of the sulfur-containing Reference 29, p 11. side group. Kurata, M.; Stockmayer, W. H. Adu. Polym. Sci. 1963,3,196. In conclusion, a comment is perhaps in order regarding Baumann, H. Polym. Lett. 1965, 3, 1069. Yamamoto, A.; Fujii, M.; Tanaka, G.; Yamakawa, H. Polym. comparison of poly(cyclohexy1 thiolmethacrylate) and J. 1971, 2, 799. poly(pheny1 thiolmethacrylate). The former is apparently Fukada, M.; Fukutomi, M.; Kato, Y.; Hashimoto, T. J . Polym. a more flexible chain than the indicating that Sci., Polym. Phys. Ed. 1974, 12, 871. specific interactions between aromatic side groups decrease Miyake, Y.; Einaga, Y.; Fujita, H. Macromolecules 1978, 11, ( ( r z 2)/M,),3/2 ( A 3 ) (light scattering) ( A ) (light scattering) u (intrinsic viscosity) u (light scattering) C, (intrinsic viscosity) C, (light scattering)
((ro2)/n)1/z
the flexibility of the main chain. This is the anticipated effect.
Acknowledgment. The portion of this work carried out at the Institute of Polymer Science was supported by grants from the Petroleum Research Fund (Grants
I
,
1180.
Beiry, G. C. J. Chem. Phys. 1966,45, 4550. Altares, T., Jr.: Wvman, . D. P.: Allen. V. R. J. Polym. Sci., Part A 1964; 2,’4533. We have noted that curvature in the Baumann plot for polystyrene appears at molecular weights >4 X lo6. Ake, A. Macromolecules 1980, 13, 541, 546.
