Reports of the Academy of Sciences of the USSR
1965. Volume 160, No. 1

CHEMISTRY

Corresponding Member of the Academy of Sciences of the USSR V. V. Korshak, S. A. Pavlova, G. I. Timofeeva, S. V. Vinogradova, V. A. Pankratov

ON THE INFLUENCE OF THE STERIC FACTOR ON THE VISCOMETRIC PROPERTIES AND POLYDISPERSITY OF POLYARYLATES

The influence of the steric factor on the viscometric properties and polydispersity of high-molecular-weight compounds has still been very little studied. We investigated these relationships using as an example polyarylates based on isophthalic acid and such dihydric phenols as 4,4′-dioxydiphenylpropane (equilibrium polyarylate D-1), phenolphthalein (equilibrium polyarylate F-1) (^1) and 9,9-bis-(4-hydroxyphenyl)-fluorene (equilibrium polyarylate D-10), which differ from one another in the size of the side substituent.

Fig. 1. Dependences \(\lg[\eta] = f(\lg M)\) for polyarylates in tetrachloroethane: 1 — D-1 interfacial, 2 — D-1 equilibrium, 3 — D-10 equilibrium.

Fig. 2. Dependence of the exponent \(a\) on the weight of the side substituent. \(a\) — data corresponding to the polyarylates studied; \(b\) — data of the authors (^5). 1 — straight line corresponding to equation (I) for equilibrium polymers; 2 — corresponding to equation (II) for interfacial polymers.

The polyarylates studied were synthesized by the method of equilibrium polycondensation (^2), and, for comparison of properties, the polyarylate based on isophthalic acid and 4,4′-dioxydiphenylpropane was also synthesized by the method of interfacial polycondensation (^3) (interfacial polyarylate D-1). Fractionation, measurement of the molecular weights of the fractions by the light-scattering method, measurement of viscosities, and determination of the characteristic viscosity of the fractions were carried out according to the methods indicated by us earlier (^1). Equilibrium polyarylate D-1 (2 samples) was refractionated into 26 and 18 fractions; equilibrium F-1 (2 samples) into 28 and 17 fractions; equilibrium D-10 into 19 fractions; and interfacial D-1 into 28 fractions. Processing of the fractionation results was carried out by the usual method of constructing integral and differential distribution curves (^4). The number-average \(\overline{M}n\) and weight-average \(\overline{M}w\) molecular weights of the unfractionated samples studied were measured by independent methods and also calculated from the molecular-weight distribution curves.

On the basis of the data obtained, relationships were derived between the molecular weight and the intrinsic viscosity of the fractions in tetrachloroethane (TCE) (Table 1 and Fig. 1).

From the data in Table 1 it is evident that, with an increase in the side substituent, the value of the exponent \(a\) decreases. Figure 2 shows the dependence of the exponent \(a\) on the weight of the side substituent \((\Delta M)\). As can be seen from the figure, for polyaryltes synthesized by the methods of equilibrium and interfacial polycondensation, the dependences between the exponent \(a\) and the weight of the side substituent do not coincide and are expressed by approximately parallel straight lines.

Table 1

Values of the constants \(K\) and \(a\) of the Mark—Houwink equation \([\eta]=K\cdot M^a\)

Although it is premature to extend this result to other polymers, it may nevertheless be thought that the analytical dependences we have found,

\[ a=0.64-\Delta M\cdot 10^{-3} \tag{I} \]

for polyaryltes obtained by the method of equilibrium polycondensation, and

\[ a=0.77-\Delta M\cdot 10^{-3} \tag{II} \]

for polyaryltes obtained by the method of interfacial polycondensation, may have a more general character; this is confirmed by the data of other authors, given by us in the same figure, for benzene solutions of carbocyclic polymers with various substituents (5), and also by good agreement with the theoretical premises of Zimm and Stockmayer (10).

Fig. 3. Dependence of \(K\) on \(a\) for aliphatic polyesters, corresponding to equation (III)

Apparently, an increase in the volume of the substituent increases the density of the macromolecular coil in such a way that, with a large substituent, such as, for example, the biphenylene group in polyarylate D-10 or the octadecyloxy group in polyvinyl octadecyl ether (5), the value of the exponent \(a\) becomes less than 0.5, i.e., the polymer in solution behaves as, according to Flory’s theory, a branched polymer should behave. The same effect of increased interaction between side radicals with an increase in their size was observed by Tsvetkov and Bychkova in studying the anisotropy of double refraction in a solution of polymethacrylates with different substituents (6).

To verify the derived relations, we made an attempt, using relation (II) for interfacial polyarylates, as well as the analogous equation published earlier \((^7)\) for the dependence between the parameters \(K\) and \(a\) for aliphatic polymers (Fig. 3),

\[ K = 0{,}289(6{,}8\cdot 10^{-5})^{a}, \tag{III} \]

to calculate the parameters \(K\) and \(a\) of the Mark—Houwink equation for polyarylate D-10, synthesized by the method of interfacial polycondensation, for which no dependence between viscosity and molecular weight had previously been derived, and then from them to calculate the molecular weights of several fractions. The values of \(K\) and \(a\) calculated by the indicated method are: \(K = 6{,}22\cdot 10^{-4}\), \(a = 0{,}64\).

As is seen from the data of Table 2, the agreement with the molecular weights of these same fractions measured by the light-scattering method proved, within experimental error, to be quite satisfactory.

Table 2

Comparison of measured and calculated molecular weights of fractions of polyarylate based on isophthalic acid and 9,9-bis-(4-oxyphenyl)-fluorene, synthesized by the method of interfacial polycondensation (polyarylate D-10 interfac.)

In addition, we established that, with an increase in the side substituent, the polydispersity coefficient of polyarylates synthesized by the method of equilibrium polycondensation increases (Table 3). The increase in polydispersity may be explained by the fact that, in the presence of large side substituents, chain-exchange reactions,

Table 3

Value of the polydispersity coefficient of some polyarylates

* Measured by the light-scattering method \((^1)\).
** Measured by the isopiestic method \((^8)\).

leading to equalization of the length of polymer chains, are more hindered in the course of synthesis because of a purely steric factor. This conclusion is also confirmed by the data of our studies on destruc-

… of polyarylates synthesized by the equilibrium polycondensation method under the action of sebacic acid (Table 4).

As is evident from the data in Table 4, degradation of polyarylates with a small substituent proceeds more deeply than in polyarylates with large side substituents, which also indicates that, in the case of degradation as well, an increase in the volume of the side substituents creates steric hindrances to the occurrence of exchange and destructive processes.

Table 4

Dependence of the intrinsic viscosity on the concentration of the degrading agent for the polyarylates studied

Note. Degradation was carried out for 12 h at 200° in a Savol medium.

Apparently, precisely this explains the fact that, with increasing substituent size, the polydispersity coefficient approaches the value found for the products of interfacial polycondensation (see Table 3). In the process of interfacial polycondensation, as is known, interchain exchange reactions are practically absent.

Institute of Organoelement Compounds
Academy of Sciences of the USSR

Received
25 VII 1964

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