TEMPERATURE COEFFICIENT OF UNPERTURBED DIMENSIONS OF ATACTIC POLYSTYRENE
3057
On the Temperature Coefficient of Unperturbed Dimensions of
Atactic Polystyrene
by Umberto Bianchi, Eligio Patrone, and Enrico Pedemonte Istituto d i Chimica Industriale, Sez. V Centro Nazwnale d i Chimica delle Macromolecole, Universitct di Gemva, Gemva, Italy (Received February 16, 1966)
Conflicting results concerned with the temperature coefficient of unperturbed dimensions in atactic polystyrene are discussed, taking into account the method by which they have been derived. By measuring the specific solvent effect present in various @-solventseries, it is shown that positive values of the temperature coefficient (around room temperature) cannot be attributed to polystyrene on safe grounds, whereas evidence is increasing supporting the opposite tendency of the polystyrene chain to decrease its dimension on increasing the temperature.
Introduction The experimental study of the temperature variation of unperturbed mean-square end-to-end distance ( r 2 ) in atactic polystyrene started with the pioneering work of Flory and Fox. These authors found, from the values of K e = CP. [(rO2)/M]*" at two temperatures (34 and 70"), a value of d In (ro2)/dT = -1.8 X 10-3 deg-l, which has been subsequently confirmed. Very recently, Orofino and Ciferri3 reported a positive value of the temperature coefficient d In (ro2)/dT = 0.4 X deg-' derived both from solution and bulk studies, which has been used4 in discussing the conformational properties of vinyl polymers. I n an attempt to clarify the situation, we shall discuss the kind of evidence on which negative and positive values of d In (ro2)/dTare based.
Specific Solvent Effects in Solution As we have already pointed O U
~ , the ~ , ~ use of unrelated 8 solvents can easily arrive at misleading results, as in this case the experimental d In (ro2)/dT involves ) also not only the temperature variation of ( ~ 0 ~but the change in conformational properties due to shortrange solvent e f f e ~ t s . ~ - ' In ~ light of this observation, values of d In (ro2)/dT given in ref 1 and 13 are to be considered with caution. It is obvious that, to obtain a significant value of d In (ro2)/dT (attributable at least to the couple poly-
+
mer solvent), it is sufficient that solvent effects, if present, will not change sensibly in going from one 8 solvent to the other. This is the reason why Bianchi and Magnasco2 and Orofino and Ciferri3 have used a set of related 8 solvents: in the first case, three toluenemethanol mixtures with a methanol concentration slightly increasing from low (25") to high (45") e temperatures, and in the second case, three structurally similar e solvents, 1-chlorodecane (e = 6.6"), l-chloroundecane (0 = 32.S0), and 1-chlorododecane (e = 58.6") (referred to in the following as C110, C111, and C112). (1) T. G Fox and P. J. Flory, J. A m . Chem. SOC.,73, 1915 (1951). (2) U.Bianchi and V. Magnasco, J. Polymer Sci., 41, 177 (1959). (3) T.A. Orofino and A. Ciferri, J. Phys. Chem., 68, 3136 (1964). (4) J. E. Mark and P. J. Flory, J. A m . Chem. SOC.,87, 1423 (1965). (5) U. Bianchi, J. Polymer Sci., A2, 3083 (1964); A. Ciferri, ibid., A2, 3088 (1964). (6) U. Bianchi, E. Patrone, and M. DalPias, Makromol. Chem., 84, 230 (1965). (7) A. R. Schulta and P. J. Flory, J. Polymer Sci., 15, 231 (1955). (8) U. Bianchi, V. Magnasco, and C. Rossi, Chim. Ind. (Milan), 40, 263 (1958). (9) K. J. Ivin, H. A. Ende, and G. Meyerhoff, Polymer, 3, 129 (1962). (10) H . G . Elias and 0. Etter, Makromol. Chem., 6 5 , 56 (1963). (11) T. A. Orofino and J. W. Mickey, Jr., J. Chem. Phys., 38, 2512 (1963). (12) V. Crescenzi and P. J. Flory, J. A m . Chem. SOC.,86, 141 (1964). (13) G. V. Schulz and H. Baumann, Makromol. Chem., 60, 120 (1963).
Volume 70, Number 10 October 1966
U. BIANCHI,E. PATRONE, AND E. PEDEMONTE
3058
Even so, our result (d In (roz)/dT = -1.8 (j=0.4) X is in striking disagreement with that of Orofino This is a surprising result, and Ciferri (0.4 X as it is by no means clear why one set of 0 solvents should be considered more structurally related than the other. A possible explanation of the disagreement between the two values of d In (ro2)/dT, both obtained in at least apparently related 0 solvents, is the existence of a varying specific effect within one or both the 0-solvent series. We have already shown14*15how it is possible to discover the existence of solvent effects by measuring the constant K Oin the equation [q] =
KoM"'
(1)
which has been found to be valid in sufficiently low molecular weight ranges for many polymer~~*-~0 in normal (non-8) solvents. It has been shown that K O is very near K O provided specific solvent effects are absent or very small. Previous work^'^^^^ have shown that the range in which eq 1 is applicable goes from M = 5 X loz to about lo4 for atactic polystyrene in good solvents (benzene, toluene, etc.) and extends to higher molecular weights in poorer solventsz0(methyl ethyl ketone). By measuring, at the same temperature, [ q ] ( = K O . &I1") for some polystyrene fractions (with molecular weight comprised in this range) in the various 0 solvents, it should then be possible to discover the existence of a varying solvent effect. Experimental Section Polystyrene fractions, with iVa ranging from 2.7 X 103 to 9.5 X lo3,calculated from the equation log [ q ] = -3.05
+ 0.5 log M
(2)
have been obtained from previously described fractionations. l4 The range of temperature covered by the two setjs of 8 solvents being 25-45' in our casez and 6-58' in ref 3 , we have chosen 35' as the temperature a t which to measure [ q ] ( = KoM"'), Polydispersity, if present, would not matter, as we are comparing [ q ] in different solvents but all measured on the same fractions. Figures 1 and 2 show some of the qspl0us. c plots and Table I collects the experimental values of [VI.
Discussion Viscosity measurements in Table I show that, for all of the polystyrene fractions examined, [ q ] values a t 35' in C112 are consistently higher than values in CllO or C111. Even supposing the expansion coefThe Journal of Physical Chemistry
f
,
3
3
4
5
6
?
8
9
w
c,94a9u
Figure 1. Plot of qapious. c for some polystyrene (PS) fractions in l-chlorodecane (open circles) and l-ohlorododecane (squares) a t 35".
fl
2
3
4
5
6
7
8
C,~p/+&cc
-
Figure 2. Plot of q.p/o us. c for some polystyrene fractions in 6, (squares), 82 (open circles), and ea (triangles). el, eZ,and ea have the same meaning as in Table I.
ficient a not to be strictly equal to 1 for such low molecular weights, one would expect [ q ]in (3112 to be less than in CllO or (2111, as polystyrene in (3112 a t 35' is below 0 conditions (C112 is 0 a t 58.6') and above 0 conditions in CllO (0 = 6.6") and C l l l (0 = 32.8'). The opposit'e result thus strongly points toward the presence of a specific solvent effect, which alters the polystyrene conformational properties to a different (14) C. Rossi, U. Bianchi, and E. Bianchi, Makromol. Chem., 41, 31 (1960). (15) U. Bianchi, M. Dal Piaz, and E. Patrone, ibid., 80, 112 (1964). (16) E. Patrone and U. Bianchi, ibid., 94, 52 (1966). (17) C. Rossi and C. Cuniberti, J. Polymer Sci., B2, 681 (1964). (18) T. G Fox, J. B. Kinsinger, H. F. Mason, and E. M. Schuele, Polymer, 3 , 71 (1962). (19) T. Altares, D. P. Wyman, and V. R. Allen, J. Polymer Sci., A2, 4533 (1964). (20) R. Okada, T. Toyoshima, and H. Fujita, Makromol. Chem., 59, 137 (1963).
TEMPERATURE COEFFICIENT OF UNPERTURBED DIMENSIONS OF ATACTICPOLYSTYRENE
Table I : Intrinsic Viscosities (dl/g) of Various Polystyrene (PS) Fractions in C110, C111, and C112 in el, and 0 3 a t 35"" Fraction
PSioFl PSIOF2 6PSF6
PSsaF8 PS6sF9 PSiiF4 PSasF12
anx
7
lo-:
CllO
9.5 5.6 5.5 5.2 4.4 3.6 2.7
0.079
.. .
0.0605
0.067 0.0635
...
...
0.0565 0.0515 0.044
...
... ...
0.0815 0.067 0.0655 0.0645 0.0585 0.053 0.046
... 0.0675
... 0.0645 0.059 0.054
...
el, e2,and e3are toluene-methanol mixtures with 23.1,24.8, and 27.2% methanol (in volume), respectively. Only [ q ] in el is given, [v]e2and [?]e,being identical. extent in going from CllO to C112. Moreov
