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Concerning the solubility of polyarylates based on phenolphthalein and dicarboxylic acids
Polymer Science U.S.S.R. Vol. 30, No. 7, laP. 1587-1594. 1988 Printed in Poland
0032-3950/88 $10.00+.00
@ 1989 Pergamon Press plc
CONCERNING THE SOLUBILITY OF POLYARYLATES BASED ON PHENOLPHTHALEIN AND DICARBOXYLIC ACIDS* S.-S. A. PAVLOVA, L. V. DUBROVlNA, 1. A.. RONOVA and N. Yu. KOBAK N. S. Negmeyanov Institute for Elemento-Organic Compounds, U.S.S.R. Academy of Sciences
(Received28 February 1987) Dissolution of polyarylates based on phenolphthalein and dicaxboxylic acids in dichloroethane and in THF is shown to occur exothermically, to be accompanied by the orientation of the solvent molecules around the polymer molecules and to depend on the structure of the polymer's monomeric link and the coordination properties (donor number) of the solvent. Theoretical values of the conformational parameters (obtained by computer simulation) and the experimental values of the Kuhn segment are compared. ToE process of dissolution is accompanied by the disruption of the structure of the polymer and solvent and by the formation of a solution with a new structure [1]. Considerable attention has been paid to this subject in recent years. Studies have been made of the structure of concentrated polymer solutions [2-4]. Two factors have been considered in the present work in an investigation of the properties of dilute solutions of polyarylates, namely, the macromolecular conformations in the solution and the orientational order of the solvent molecules solvating the macromolecules, the latter being assessed from the solution's thermodynamic parameters. The equilibrium rigidity of the polymeric chain has a great effect on the conformation of macromolecules in solution. In the present investigation an attempt has been made to follow how a change in the structure of the acidic component alone of a polyarylate macromolecule's elementary link affects the equilibrium rigidity of its chain and, consequently, how it affects the macromolecular conformation in the solution and the structure of the solution itself. Polyarylates with the following structures were investigated: Ii
R
K2X..o H "a I"',
I
0
-: -cgo * Vysokomol. soyed. 3.30: No. 7, 1505-1510, 1988. 1587
1588
S.-S. A. PAV'..OVAet eL
\/
zI
R
o
where s = l
II
"o
B
The polyarylates were synthesized by high,temperature condensation in a high boiling-point solvent (~-chloronaphthaiene) at 220°C with the duration of synthesis being 12 hr, using the method given in [5]. The polymers were fractionated into 12-15 fractions by distribution between two immiscible liquids, a mixture of tetrachiorethane (TCE) and phenol in the ratio 3 : 1 by weight being used as the solvent with n-heptane as the non-solvent. The molecular mass of the fractions and the second virial coefficient Az of the solutions were measured by light-scattering with a Fica photogoniodiffusometer. The solutions were purified by filtration through a system of filters 3 and 4. Before measurement of the intensity of the scattered light, the cells containing the solutions were held for 1 hi" in the thermostat at the temperature of measurement. The accuracy of the thel mostatic control was -i-0.I °C. The refractive increments of the solutions were determined with a Pulfrich?type refractometcr equipped with a differential cell. The solvents were purified by the usual methods [6], their purity being monitored by measurement of refractive index. We had previously found [7] that THF may be used as a 0-solvent for polymer I (0--22°C). Preliminary experiments on the temperature for the precipitation of the polymers from solution showed that THF may also be used as a 0 solvent for polymer If. It was found that, as the temperature was raised above 20°C, the solutions became cloudy and the 0 temperature was therefore sought in the temperature region below 20°C. Polymer Ill did not dissolve in THF. At room temperature, this polymer dissolved well in dichloroethane (DCE) and, as the temperature was raised above 45°C, the polymer precipitated, which was evidence of the existence of a lower critical miscibility temperature (LCMT). The 0 temperatures for all the polymers were found by extrapolating the temperature dependence of A~ to zero, using solutions of the unfractionated specimens and solutions of the fractions.
Solubility of polyaxylates based on phenolphthalein and dicarboxylic acids
1589
The temperature dependences of the polymer's specific partial volumes in the 0 solvents were determined by the method given in [8]. The intrinsic viscosities of solutions of the initial polymers and their fractions were determined by use of a suspended-level capillary viscometer in TCE at 25 +0,1°C and under the 0 conditions. Properties of the specimens investigated and the results of determining the 0 conditions are given in Table 1. TABLE 1. PROPERTIES OF THE POLYMERS INVESTIGATED 25"
21~'~,x I0 -a [r/]TC~, dl/g 37 0"800 27 0"735 30 0"510
Polymer I II III *
0°
[t/]o, dl/g
22 15 30
0.595 0"620 0.340*
a [ Kx 104 0-conditions 0"55 20"9 0"61 14"2 0"5 23"7
a [ Kx 10" A~'x 10-3 TCE, 25° 0"65 0"57 i0-90 0"75 2"75 9-50 0"67 5"23 6-70
Determined in DC.
Analysis of the data for the change in Az with temperature (Fig. 1) gives evidence that, for all the polymers investigated, the solubility typically deteriorates with an increase in temperature, which confirms the existence of a lower critical miscibility temperature. L C M T are known to be observed in systems with strong intermolecular interactions which m a y be caused by various factors, in particular, by the formation of donoraccepter bonds in the solutions between polymer macromolecules and solvent molecules [1]. This type of Interaction between the positively charged carbon atom of the / ,=/O,%mz mote/9
#
x l 15'
'
-
r
-#
Fie. 1. Temperature dependence of A2 for polyarylates I-III.
carbonyl group and the unpaired p-electron pairs of the oxygen atom in T H F is possible when the polymers I and II dissolve in THF. Dissolution of the polyarylatc III in D C E may be caused by donor-accepter interactions between the g-electron of the polymer's benzene rings and free 3d orbitals of the solvent's chlorine atom. The polymers I and II also dissolve in D C E but their solubility improves with an increase in temperature, as shown by the results for the temperature dependence of ,42: for polymer I, ,42 changed from - 2 x 10 -4 to I x 10 -4 cma.mole/g 2 in the temperature range
S.-S. A. PAVLOVA
1590
et al .
.
.
.
20-35°C and for polymer II, it changed from - 1 0 × 10-4 to 2 x 10 -4 cma.mole/g2 in the temperature range 25-55°C. The results obtained thus indicated that the change in the structure of the polymer's elementary link affects the solution process and, consequently, it should also be reflected a
15
25
I
, .,~
,~ ,
I
35 -',¢
x
7 '~
i
>c-- ~ llI
-q
o,_..o._
o
-
II
-
•
T
.
o
b ,., I
,
I
I
TO Ill
o.
H
•
_o
I
°
0.I .
0
-04
Fie. 2. Temperature dependence of the following thermodynamic parameters: a-¥1; b - k 1 and c - ~ q - k l for polyarylates I-III. in the thermodynamic parameters of the solutions. The entropy and enthalpy contributions to the polymer-solvent interaction energy have been assessed by use of the temperature dependence of the second virial coefficient A2. According to Fiery [9], the following expression is valid at temperatures close to 0:
where ~, and kl correspond to the entropy and enthalpy contributions to the polymersolvent interaction energy, ~2 is the specific partial volume of the polymer in the solution and vl is the molar volume of the solvent. Figure 2 shows the temperature dependence of the parameters V1, k, and the differenc~ ~,~- k~. The data obtained showed that, for all three polymers, the solution process occurs exothermically (k, <0) and is accompanied by the orientation of the solvent molecules around the polymer molecules (~1 <0). It should be taken into account that donor-accepter bonds of the type mentioned above are not classified as weak bonds. Scatter in the experimental values of ~ and k~ is observed in the region close to the 0 temperature for both unfractionated specimens of polymers I and II
Solubility of polyarylates based on phenolphthaleinand dicarboxylicacids
1591
~z , r,t/g
t 0.68
,.,_
0"60~
t
. . . . .
15
•
,,_.
"
2.5
Z
v
~ 11I
"
I
35
Id
T
FIG. 3. Temperature dependence of ~= for polyarylatcs I-III in solutions with THF
(I, II) and DCE (III). (Fig. 2) and also for their fractions. A reduction in the difference (~/, - kt) is also typical of all three systems as the temperature increases, which reflects the deterioration in the solvent's thermodynamic quality on heating. Attention is drawn in Fig. 2a and b, to the following fact: for all the systems, the values of ~,~ and k~ remain practically constant in the temperature region below 0, this constancy being maintained over the entire temperature region investigated in the case of polymer III. TABLE 2. GEOMETRICALPARAMETERSOF TIlE STRUCTURALUNITSOF THE POLYMERSINVESTIGATED Polymer I-III
It, ,~ 1, = 5"67 12=5-67 13 ffi 1 - 3 4
I
II
/4 5.74 1,=1.34 !,= 10.04 =
Is = 1 . 3 4
III
/,ffi5.81 1s=5"81 /6=1.84
0~, deg
Rotation around virtual bonds*
01=64 Oa = 67 0~=66 0,=66 0 s = 67 o,=66 0 5 = 67 0,=64 0 s = 66 05=67
* f - Free; h - hindered. Note. The first three bolxls a t , the same in all the thrm polymers.
The small magnitude of the parameters ~1 and k, for polymer III are evidently connected with the fact that DCE forms weak complexes with the polymer, since its donor number, DNsbcls, is equal to 0.1 whereas, for THF, DNsbo,=20 [10]. This is confirmed by the data for the change in the polymers' specific partial volumes in the solutions with temperature (Fig. 3). The values of v2 for systems in THF are close together at temperatures below 0 and remain practically constant, whereas a marked changes in the values of ~2 occur around the 0 temperature. The values of ~2 are considerably higher in the case of polymer III in DCE and no appreciable changes are observed over the entire temperature range, as is also true for the entropy and enthalpy parameters. The results of measurement of the temperature dependence of ~2 have
1592
S.-S. A. PAVLOVAotal.
thus shown that the macromolecular coils have a more open packing in a solvent which forms weak donor-accepter bonds with the polymer. The next task of our investigation was to clarify the effect of a change in the structure of the polymer's elementary link on the conformation of the macromolecules in solution. Firstly, the macromolecular coil was modelled by a computer simulation using the Monte-Carlo method and a programme described in [11]. The structural units of the polyarylates were modelled on the basis of literature data for the structure of very I
TABLE 3. THEORETICAL AND EXPERIMENTAL CONFORMATIONAL PARAMETERS OF THE POLYMERS
Polymer I II III
I l [
Me
448 524 640
[ [ I
0 64 64 64
Lo, A 17.52 21 "77 22"51
At .... A
25.7 33-7 19.2
A,,p, A
30 ( +-2) 40 (__ 2) 23 (+_2)
a
1.09 1"09 1"09
simple molecules approximating in composition and structure to the monomeric links [12]. Table 2 shows the lengths of the virtual bonds ls and the angles between them, and the possibility of free rotation around the virtual bonds is also indicated; the angle 0 is complementary to the angle between the virtual bonds. Rotation around the C - O bond is impeded because it is considered to be a one-and-a-half bond, since its length is less than the sum of the covalent radii of the carbon and oxygen atoms. The conformational parameters obtained as a result of the computer simulation are shown in Table 3. Analysis of these results enables the following conclusions to be drawn regarding the effect of the link's chemical structure on the conformational parameters with free rotation: an increase in the angle between the virtual bonds as well as an increase in the length of the virtual bonds leads to an increase in the equilibrium chain rigidity whereas the replacement of one virtual bond, 14, by two bonds (in polymer III) reduces the rigidity. We have shown previously [7] that a Gaussian coil, formed by chains of finite length, and the experimentally found value of the Kuhn segment, equal to 30 A, may be used as a model to describe the behaviour of the macromolecules of polymer I in THF. In selecting a model to describe the behavi0ur of polymer II macromolecules in THF, we dealt with the same considerations as in [7], since, as in [7], the parameter a in the Mark-Kuhn-Houwink equation was not equal to 0.5 under 0 conditions (a-0.61) and the effect of the solvent on the hydrodynamic parameters (for example, on It/]) was appreciable. We also used a model consisting of a coil formed by chains of finite length. The dependence of M/[tl] on x/rM was plotted and calculations were made using the equation [13] M
bI ~
at
[r/---]=2.87 x 1021 +2"87 x 10 2 i ' where 2
A
1~
f ML~3/2
Solubility of polyarylates based on phenolphthalein and dicarbo×ylic acids
1593
A is the K u h n segment, M L is the ratio of the link's molecular mass to its contour length and d is the chain's effective hydrodynamic diameter. Since a=0.5 for polyarylate I I I under 0 conditions, in this case we used the model of a Gaussian impenetrable coil and the values of A were calculated from tbe equation [13]
)
M
cPo = 2" 87 x 1021. The results shown in Table 3 completely confirm the conclusions drawn from the computer simulation results. The introduction of an additional phenyl group into the acidic component of the macromolecule's elementary link was thus shown to lead to some increase in the length of the K u h n segment from 30 A for polymer I to 40 A for polymer II, which is evidence of an increase in the equilibrium chain rigidity. The introduction of an additional phthalide group (polymer III) was shown to reduce the chain rigidity and lower the length of the K u h n segment down to 23 A. Moreover, the steric hindrance parameters, a = dAE/AT for these polymers are approximately the same in value, being very small, that is, a large set of possible conformations is realized in solution. A change in the structure of the acidic component of the elementary link thus considerably affects the equilibrium rigidity of the macromolecular chain; the most marked effect of this factor is on the thermodynamic process of dissolution and, consequently, on the structure of the solution itself.
Translated by G. F. MOIgL~N !REFERENCES
I. A. A. TAGER, Vysokomol. soyed. 26: 659, 1984 2. K. D. GOELL and G. C. BERRY, J. Polymer Sci. Phys. Ed. 15: 555, 1977 3. A. A. TAGER, V. Ye. DREVAL', M. KURBANALIYEV, M. S. LUTSKII, N. B. BERKOVETS, I. M. GRANOVSKAYA and T. A. CHARIKOVA, Vysokomol. soyed. A10: 2044, 1968 (Translated in Polymer Sci. U.S.S.R. 10: 9, 2379, 1968) 4. M. KURBANALIYEV, A. A. TAGER and V. Ye. DREVAL', Mekhanika polimerov, 2, 358, 1968 5. V. Vo KORSHAK, S. V. VINOGRADOVA and S. N. SALAZKIN, Vysokomol. soyed. 4: 339, 1962 (Not translated in Polymer Sci. U.S.S.R.) 6. A. WEISSBERGER, E. S. PROSKAUER, 3. A. RIDDICK and E. E. TOOPS, Organicheskiye rastvoriteli (Organic Solvents). Moscow, 1958 (Russian translation) 7. V. V. KORSHAK, S.-S. A. PAVLOVA, L. V. DUBROVINA, N. Yu. KOBAK and Ye. A. GLADKOVA, Vysokomol. soyed. A12: 1458, 1980 (Translated in Polymer Sci. U.S.S.R. 12: 7, 1653, 1980) 8. I. N. SERDYUK and V. Ye. ESKIN, Vestnik LGU 2: 10, 57, 1970 9. P. FLORY, Principles of Polymer Chemistry, p. '532, N.Y., 1953 10. V. GUTMANN, Khimiya koordinatsionnykh soyedinenii v nevodnykh sredakh (Chemistry of Coordination Compounds in Non-Aqueous Media). p. 165, Moscow, 1971 (Russian translation) 11. S.-S. A. PAVLOVA, G. I. TIMOFEEVA and L. PANCRATOVA, J. Polymer Sci. Polymer Phys. Ed. 18: 1, 1980
1594
N. M. LxvAsOVA and G. Ys. ZAJKov
12. P. FLORY, Statisticheskaya mekhanika tsepnykh molekul (Statistical Mechanics of Chain Molecules). Moscow, 1971 (Russian translation) 13. S. R. RAFIKOV, V. P. BUDTOV and Yu. B. MONAKOV, Vvedeniye v fizikokhimiya rastvorov polimerov (Introduction to the physical chemistry of polymer solutions). Moscow, 1978
Polymer Science U.S.S.R. Vol. 30, No. 7, pp. 1594-1601, 1988 Printed in Poland
0032-3950/88 $10.00+.00 0 1989 Pergamon Press pie
MODEL FOR THE RUPTURE OF ORIENTED POLYPROPYLENE FILMS DURING OXIDATION UNDER LOAD* N. M . LIVANOVA and G. YIz. Z A m o v Institutefor Chemical Physics,U.S.S.R. Academy of Sciences
(Received28 February 1987) The life to failure of oriented isotactic PP films of various width has been investigated under conditions of intensive oxidation at low stresses. A size effect is observed as the specimen width is reduced; this appears as a considerable increase in the scatter of the experimental data, which is caused by a reduction in the probability of finding sufficient defects in positions favourable for linking up. In the case of narrow specimens, the life to failure is found to have discrete values or values that are integral multiples of the discrete values. It is concluded that the differences in the lives to failure are determined not so much by the nature of the polymers' defect areas so much as by the number of defects capable of linking up, which depends on their statistical distribution in the matrix. A L~O~ number of papers have been devoted to the investigation of the fracture mechanism in polymers but much remains unclear in this process. This is partly explained by differences in the experimental materials investigated. Apart from the chemical and physical nature of the solids, the specimen dimensions (the size factor) and the specimen shape affect the experimentally determined strength of materials. Differences in test methods and in the materials investigated have given rise to different theoretical approaches to the study of the fracture process in solid bodies [1]. The greatest successes have been achieved with the development of the kinetic theory of strength [2] but it does not take account of the effect of a random distribution of different types of defects, existing in real solids, on their strength. In addition to more or less regularly repeated defects in a structure (for example, the ends of microfibrils in oriented polymers [3]), there are statistically distributed random defects such as inclusions of solid particles, pores, microcracks etc. The effects of defects existing in a material on its strength may be taken into account by using statistical methods; the combination of these methods with a morphological analysis can be very fruitful but there are very few examples of such work [4]. One of the most important questions is to establishthe connection between the lifeto failure and the nature of the distribution of defects in the specimen and to determine their nature. Without * Vysokomol. soyed. A30: No. 7, 1511-1517, 1988.
0032-3950/88 $10.00+.00
@ 1989 Pergamon Press plc
CONCERNING THE SOLUBILITY OF POLYARYLATES BASED ON PHENOLPHTHALEIN AND DICARBOXYLIC ACIDS* S.-S. A. PAVLOVA, L. V. DUBROVlNA, 1. A.. RONOVA and N. Yu. KOBAK N. S. Negmeyanov Institute for Elemento-Organic Compounds, U.S.S.R. Academy of Sciences
(Received28 February 1987) Dissolution of polyarylates based on phenolphthalein and dicaxboxylic acids in dichloroethane and in THF is shown to occur exothermically, to be accompanied by the orientation of the solvent molecules around the polymer molecules and to depend on the structure of the polymer's monomeric link and the coordination properties (donor number) of the solvent. Theoretical values of the conformational parameters (obtained by computer simulation) and the experimental values of the Kuhn segment are compared. ToE process of dissolution is accompanied by the disruption of the structure of the polymer and solvent and by the formation of a solution with a new structure [1]. Considerable attention has been paid to this subject in recent years. Studies have been made of the structure of concentrated polymer solutions [2-4]. Two factors have been considered in the present work in an investigation of the properties of dilute solutions of polyarylates, namely, the macromolecular conformations in the solution and the orientational order of the solvent molecules solvating the macromolecules, the latter being assessed from the solution's thermodynamic parameters. The equilibrium rigidity of the polymeric chain has a great effect on the conformation of macromolecules in solution. In the present investigation an attempt has been made to follow how a change in the structure of the acidic component alone of a polyarylate macromolecule's elementary link affects the equilibrium rigidity of its chain and, consequently, how it affects the macromolecular conformation in the solution and the structure of the solution itself. Polyarylates with the following structures were investigated: Ii
R
K2X..o H "a I"',
I
0
-: -cgo * Vysokomol. soyed. 3.30: No. 7, 1505-1510, 1988. 1587
1588
S.-S. A. PAV'..OVAet eL
\/
zI
R
o
where s = l
II
"o
B
The polyarylates were synthesized by high,temperature condensation in a high boiling-point solvent (~-chloronaphthaiene) at 220°C with the duration of synthesis being 12 hr, using the method given in [5]. The polymers were fractionated into 12-15 fractions by distribution between two immiscible liquids, a mixture of tetrachiorethane (TCE) and phenol in the ratio 3 : 1 by weight being used as the solvent with n-heptane as the non-solvent. The molecular mass of the fractions and the second virial coefficient Az of the solutions were measured by light-scattering with a Fica photogoniodiffusometer. The solutions were purified by filtration through a system of filters 3 and 4. Before measurement of the intensity of the scattered light, the cells containing the solutions were held for 1 hi" in the thermostat at the temperature of measurement. The accuracy of the thel mostatic control was -i-0.I °C. The refractive increments of the solutions were determined with a Pulfrich?type refractometcr equipped with a differential cell. The solvents were purified by the usual methods [6], their purity being monitored by measurement of refractive index. We had previously found [7] that THF may be used as a 0-solvent for polymer I (0--22°C). Preliminary experiments on the temperature for the precipitation of the polymers from solution showed that THF may also be used as a 0 solvent for polymer If. It was found that, as the temperature was raised above 20°C, the solutions became cloudy and the 0 temperature was therefore sought in the temperature region below 20°C. Polymer Ill did not dissolve in THF. At room temperature, this polymer dissolved well in dichloroethane (DCE) and, as the temperature was raised above 45°C, the polymer precipitated, which was evidence of the existence of a lower critical miscibility temperature (LCMT). The 0 temperatures for all the polymers were found by extrapolating the temperature dependence of A~ to zero, using solutions of the unfractionated specimens and solutions of the fractions.
Solubility of polyaxylates based on phenolphthalein and dicarboxylic acids
1589
The temperature dependences of the polymer's specific partial volumes in the 0 solvents were determined by the method given in [8]. The intrinsic viscosities of solutions of the initial polymers and their fractions were determined by use of a suspended-level capillary viscometer in TCE at 25 +0,1°C and under the 0 conditions. Properties of the specimens investigated and the results of determining the 0 conditions are given in Table 1. TABLE 1. PROPERTIES OF THE POLYMERS INVESTIGATED 25"
21~'~,x I0 -a [r/]TC~, dl/g 37 0"800 27 0"735 30 0"510
Polymer I II III *
0°
[t/]o, dl/g
22 15 30
0.595 0"620 0.340*
a [ Kx 104 0-conditions 0"55 20"9 0"61 14"2 0"5 23"7
a [ Kx 10" A~'x 10-3 TCE, 25° 0"65 0"57 i0-90 0"75 2"75 9-50 0"67 5"23 6-70
Determined in DC.
Analysis of the data for the change in Az with temperature (Fig. 1) gives evidence that, for all the polymers investigated, the solubility typically deteriorates with an increase in temperature, which confirms the existence of a lower critical miscibility temperature. L C M T are known to be observed in systems with strong intermolecular interactions which m a y be caused by various factors, in particular, by the formation of donoraccepter bonds in the solutions between polymer macromolecules and solvent molecules [1]. This type of Interaction between the positively charged carbon atom of the / ,=/O,%mz mote/9
#
x l 15'
'
-
r
-#
Fie. 1. Temperature dependence of A2 for polyarylates I-III.
carbonyl group and the unpaired p-electron pairs of the oxygen atom in T H F is possible when the polymers I and II dissolve in THF. Dissolution of the polyarylatc III in D C E may be caused by donor-accepter interactions between the g-electron of the polymer's benzene rings and free 3d orbitals of the solvent's chlorine atom. The polymers I and II also dissolve in D C E but their solubility improves with an increase in temperature, as shown by the results for the temperature dependence of ,42: for polymer I, ,42 changed from - 2 x 10 -4 to I x 10 -4 cma.mole/g 2 in the temperature range
S.-S. A. PAVLOVA
1590
et al .
.
.
.
20-35°C and for polymer II, it changed from - 1 0 × 10-4 to 2 x 10 -4 cma.mole/g2 in the temperature range 25-55°C. The results obtained thus indicated that the change in the structure of the polymer's elementary link affects the solution process and, consequently, it should also be reflected a
15
25
I
, .,~
,~ ,
I
35 -',¢
x
7 '~
i
>c-- ~ llI
-q
o,_..o._
o
-
II
-
•
T
.
o
b ,., I
,
I
I
TO Ill
o.
H
•
_o
I
°
0.I .
0
-04
Fie. 2. Temperature dependence of the following thermodynamic parameters: a-¥1; b - k 1 and c - ~ q - k l for polyarylates I-III. in the thermodynamic parameters of the solutions. The entropy and enthalpy contributions to the polymer-solvent interaction energy have been assessed by use of the temperature dependence of the second virial coefficient A2. According to Fiery [9], the following expression is valid at temperatures close to 0:
where ~, and kl correspond to the entropy and enthalpy contributions to the polymersolvent interaction energy, ~2 is the specific partial volume of the polymer in the solution and vl is the molar volume of the solvent. Figure 2 shows the temperature dependence of the parameters V1, k, and the differenc~ ~,~- k~. The data obtained showed that, for all three polymers, the solution process occurs exothermically (k, <0) and is accompanied by the orientation of the solvent molecules around the polymer molecules (~1 <0). It should be taken into account that donor-accepter bonds of the type mentioned above are not classified as weak bonds. Scatter in the experimental values of ~ and k~ is observed in the region close to the 0 temperature for both unfractionated specimens of polymers I and II
Solubility of polyarylates based on phenolphthaleinand dicarboxylicacids
1591
~z , r,t/g
t 0.68
,.,_
0"60~
t
. . . . .
15
•
,,_.
"
2.5
Z
v
~ 11I
"
I
35
Id
T
FIG. 3. Temperature dependence of ~= for polyarylatcs I-III in solutions with THF
(I, II) and DCE (III). (Fig. 2) and also for their fractions. A reduction in the difference (~/, - kt) is also typical of all three systems as the temperature increases, which reflects the deterioration in the solvent's thermodynamic quality on heating. Attention is drawn in Fig. 2a and b, to the following fact: for all the systems, the values of ~,~ and k~ remain practically constant in the temperature region below 0, this constancy being maintained over the entire temperature region investigated in the case of polymer III. TABLE 2. GEOMETRICALPARAMETERSOF TIlE STRUCTURALUNITSOF THE POLYMERSINVESTIGATED Polymer I-III
It, ,~ 1, = 5"67 12=5-67 13 ffi 1 - 3 4
I
II
/4 5.74 1,=1.34 !,= 10.04 =
Is = 1 . 3 4
III
/,ffi5.81 1s=5"81 /6=1.84
0~, deg
Rotation around virtual bonds*
01=64 Oa = 67 0~=66 0,=66 0 s = 67 o,=66 0 5 = 67 0,=64 0 s = 66 05=67
* f - Free; h - hindered. Note. The first three bolxls a t , the same in all the thrm polymers.
The small magnitude of the parameters ~1 and k, for polymer III are evidently connected with the fact that DCE forms weak complexes with the polymer, since its donor number, DNsbcls, is equal to 0.1 whereas, for THF, DNsbo,=20 [10]. This is confirmed by the data for the change in the polymers' specific partial volumes in the solutions with temperature (Fig. 3). The values of v2 for systems in THF are close together at temperatures below 0 and remain practically constant, whereas a marked changes in the values of ~2 occur around the 0 temperature. The values of ~2 are considerably higher in the case of polymer III in DCE and no appreciable changes are observed over the entire temperature range, as is also true for the entropy and enthalpy parameters. The results of measurement of the temperature dependence of ~2 have
1592
S.-S. A. PAVLOVAotal.
thus shown that the macromolecular coils have a more open packing in a solvent which forms weak donor-accepter bonds with the polymer. The next task of our investigation was to clarify the effect of a change in the structure of the polymer's elementary link on the conformation of the macromolecules in solution. Firstly, the macromolecular coil was modelled by a computer simulation using the Monte-Carlo method and a programme described in [11]. The structural units of the polyarylates were modelled on the basis of literature data for the structure of very I
TABLE 3. THEORETICAL AND EXPERIMENTAL CONFORMATIONAL PARAMETERS OF THE POLYMERS
Polymer I II III
I l [
Me
448 524 640
[ [ I
0 64 64 64
Lo, A 17.52 21 "77 22"51
At .... A
25.7 33-7 19.2
A,,p, A
30 ( +-2) 40 (__ 2) 23 (+_2)
a
1.09 1"09 1"09
simple molecules approximating in composition and structure to the monomeric links [12]. Table 2 shows the lengths of the virtual bonds ls and the angles between them, and the possibility of free rotation around the virtual bonds is also indicated; the angle 0 is complementary to the angle between the virtual bonds. Rotation around the C - O bond is impeded because it is considered to be a one-and-a-half bond, since its length is less than the sum of the covalent radii of the carbon and oxygen atoms. The conformational parameters obtained as a result of the computer simulation are shown in Table 3. Analysis of these results enables the following conclusions to be drawn regarding the effect of the link's chemical structure on the conformational parameters with free rotation: an increase in the angle between the virtual bonds as well as an increase in the length of the virtual bonds leads to an increase in the equilibrium chain rigidity whereas the replacement of one virtual bond, 14, by two bonds (in polymer III) reduces the rigidity. We have shown previously [7] that a Gaussian coil, formed by chains of finite length, and the experimentally found value of the Kuhn segment, equal to 30 A, may be used as a model to describe the behaviour of the macromolecules of polymer I in THF. In selecting a model to describe the behavi0ur of polymer II macromolecules in THF, we dealt with the same considerations as in [7], since, as in [7], the parameter a in the Mark-Kuhn-Houwink equation was not equal to 0.5 under 0 conditions (a-0.61) and the effect of the solvent on the hydrodynamic parameters (for example, on It/]) was appreciable. We also used a model consisting of a coil formed by chains of finite length. The dependence of M/[tl] on x/rM was plotted and calculations were made using the equation [13] M
bI ~
at
[r/---]=2.87 x 1021 +2"87 x 10 2 i ' where 2
A
1~
f ML~3/2
Solubility of polyarylates based on phenolphthalein and dicarbo×ylic acids
1593
A is the K u h n segment, M L is the ratio of the link's molecular mass to its contour length and d is the chain's effective hydrodynamic diameter. Since a=0.5 for polyarylate I I I under 0 conditions, in this case we used the model of a Gaussian impenetrable coil and the values of A were calculated from tbe equation [13]
)
M
cPo = 2" 87 x 1021. The results shown in Table 3 completely confirm the conclusions drawn from the computer simulation results. The introduction of an additional phenyl group into the acidic component of the macromolecule's elementary link was thus shown to lead to some increase in the length of the K u h n segment from 30 A for polymer I to 40 A for polymer II, which is evidence of an increase in the equilibrium chain rigidity. The introduction of an additional phthalide group (polymer III) was shown to reduce the chain rigidity and lower the length of the K u h n segment down to 23 A. Moreover, the steric hindrance parameters, a = dAE/AT for these polymers are approximately the same in value, being very small, that is, a large set of possible conformations is realized in solution. A change in the structure of the acidic component of the elementary link thus considerably affects the equilibrium rigidity of the macromolecular chain; the most marked effect of this factor is on the thermodynamic process of dissolution and, consequently, on the structure of the solution itself.
Translated by G. F. MOIgL~N !REFERENCES
I. A. A. TAGER, Vysokomol. soyed. 26: 659, 1984 2. K. D. GOELL and G. C. BERRY, J. Polymer Sci. Phys. Ed. 15: 555, 1977 3. A. A. TAGER, V. Ye. DREVAL', M. KURBANALIYEV, M. S. LUTSKII, N. B. BERKOVETS, I. M. GRANOVSKAYA and T. A. CHARIKOVA, Vysokomol. soyed. A10: 2044, 1968 (Translated in Polymer Sci. U.S.S.R. 10: 9, 2379, 1968) 4. M. KURBANALIYEV, A. A. TAGER and V. Ye. DREVAL', Mekhanika polimerov, 2, 358, 1968 5. V. Vo KORSHAK, S. V. VINOGRADOVA and S. N. SALAZKIN, Vysokomol. soyed. 4: 339, 1962 (Not translated in Polymer Sci. U.S.S.R.) 6. A. WEISSBERGER, E. S. PROSKAUER, 3. A. RIDDICK and E. E. TOOPS, Organicheskiye rastvoriteli (Organic Solvents). Moscow, 1958 (Russian translation) 7. V. V. KORSHAK, S.-S. A. PAVLOVA, L. V. DUBROVINA, N. Yu. KOBAK and Ye. A. GLADKOVA, Vysokomol. soyed. A12: 1458, 1980 (Translated in Polymer Sci. U.S.S.R. 12: 7, 1653, 1980) 8. I. N. SERDYUK and V. Ye. ESKIN, Vestnik LGU 2: 10, 57, 1970 9. P. FLORY, Principles of Polymer Chemistry, p. '532, N.Y., 1953 10. V. GUTMANN, Khimiya koordinatsionnykh soyedinenii v nevodnykh sredakh (Chemistry of Coordination Compounds in Non-Aqueous Media). p. 165, Moscow, 1971 (Russian translation) 11. S.-S. A. PAVLOVA, G. I. TIMOFEEVA and L. PANCRATOVA, J. Polymer Sci. Polymer Phys. Ed. 18: 1, 1980
1594
N. M. LxvAsOVA and G. Ys. ZAJKov
12. P. FLORY, Statisticheskaya mekhanika tsepnykh molekul (Statistical Mechanics of Chain Molecules). Moscow, 1971 (Russian translation) 13. S. R. RAFIKOV, V. P. BUDTOV and Yu. B. MONAKOV, Vvedeniye v fizikokhimiya rastvorov polimerov (Introduction to the physical chemistry of polymer solutions). Moscow, 1978
Polymer Science U.S.S.R. Vol. 30, No. 7, pp. 1594-1601, 1988 Printed in Poland
0032-3950/88 $10.00+.00 0 1989 Pergamon Press pie
MODEL FOR THE RUPTURE OF ORIENTED POLYPROPYLENE FILMS DURING OXIDATION UNDER LOAD* N. M . LIVANOVA and G. YIz. Z A m o v Institutefor Chemical Physics,U.S.S.R. Academy of Sciences
(Received28 February 1987) The life to failure of oriented isotactic PP films of various width has been investigated under conditions of intensive oxidation at low stresses. A size effect is observed as the specimen width is reduced; this appears as a considerable increase in the scatter of the experimental data, which is caused by a reduction in the probability of finding sufficient defects in positions favourable for linking up. In the case of narrow specimens, the life to failure is found to have discrete values or values that are integral multiples of the discrete values. It is concluded that the differences in the lives to failure are determined not so much by the nature of the polymers' defect areas so much as by the number of defects capable of linking up, which depends on their statistical distribution in the matrix. A L~O~ number of papers have been devoted to the investigation of the fracture mechanism in polymers but much remains unclear in this process. This is partly explained by differences in the experimental materials investigated. Apart from the chemical and physical nature of the solids, the specimen dimensions (the size factor) and the specimen shape affect the experimentally determined strength of materials. Differences in test methods and in the materials investigated have given rise to different theoretical approaches to the study of the fracture process in solid bodies [1]. The greatest successes have been achieved with the development of the kinetic theory of strength [2] but it does not take account of the effect of a random distribution of different types of defects, existing in real solids, on their strength. In addition to more or less regularly repeated defects in a structure (for example, the ends of microfibrils in oriented polymers [3]), there are statistically distributed random defects such as inclusions of solid particles, pores, microcracks etc. The effects of defects existing in a material on its strength may be taken into account by using statistical methods; the combination of these methods with a morphological analysis can be very fruitful but there are very few examples of such work [4]. One of the most important questions is to establishthe connection between the lifeto failure and the nature of the distribution of defects in the specimen and to determine their nature. Without * Vysokomol. soyed. A30: No. 7, 1511-1517, 1988.