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Studies on the properties of concentrated solutions of high polymers—VI. The problem of the invariance of the rheograms
STUDIES ON THE P R O P E R T I E S OF CONCENTRATED SOLUTIONS OF H I G H P O L Y M E R S - - V I . THE P R O B L E M OF T H E INVARIANCE OF THE R H E O G R A M S * B. E. GELLER and V. K. PSHEDETSKAYA Tashkent Textile I n s t i t u t e
(Received 23 April 1962)
IT IS known that the anomalies in the viscosity properties of concentrated solutions of polymers demonstrated in their non-Newtonian flow on being forced through capillaries, is due to "the presence of relaxation properties in these liquids" [1]. Previous investigations have shown the dependence of the viscosity properties of concentrated solutions on the mobility of the macromolecules of the effective volume at low shearing forces. In addition, a study of the kinetics of the changes in the structure of concentrated solutions of polymers at high shearing stresses is of fundamental theoretical and, in particular, practical interest for the formation of chemical fibres. This paper gives the results of an investigation of the flow processes of concentrated solutions of chlorinated poly-(vinyl chloride) (CPVC) in acetone and dimethylformamide (DMF) and of polyacrylonitrile (PAN) in DMF over a wide range of concentrations and temperatures through capillaries of various dimensions at shearing stresses of up to 500,000 dyne/cm 2. EXPERIMENTAL The v i s c o s i t y p r o p e r t i e s o f s o l u t i o n s o f CPVC in a c e t o n e o v e r a r a n g e o f c o n c e n t r a t i o n s o f t h e p o l y m e r f r o m 15 t o 3 2 . 5 % b y w e i g h t a t 20-40 °, o f C P V C in D M F a t 25-75 ~, a n d o f a 15% s o l u t i o n o f P A N in D M F a t 25-75 ° w e r e i n v e s t i g a t e d . T h e m e a s u r e m e n t s were c a r r i e d o u t o n a s t a n d a r d A K V - 2 c a p i l l a r y v i s c o m e t e r a n d o n a specially c o n s t r u c t e d c o n s t a n t - p r e s s u r e v i s c o m e t e r w h i c h w e h a v e called S V K - 1 5 0 (see Fig. 1). The solution under investigation was forced from the cylinder 1 through capillary 2 b y t h e p r e s s u r e o f c o m p r e s s e d n i t r o g e n f r o m a r e s e r v o i r 3 fed w i t h gas a t t h e r e q u i r e d p r e s s u r e f r o m c y l i n d e r 4. T h e p r e s s u r e in t h e r e s e r v o i r a n d in t h e c y l i n d e r 1 w a s f o l l o w e d b y s t a n d a r d g a u g e s w i t h i n t h e ranges: u p t o 10 =I-0.05 a r m ; f r o m 10 t o 100 i 0 ' 2 a r m ; a n d f r o m 100 t o 150 ___0.5 a t m . A d j u s t m e n t o f t h e flow o f n i t r o g e n w a s c a r r i e d o u t b y m e a n s o f a s y s t e m o f n e e d l e v a l v e s 5 a r r a n g e d o n a special p a n e l 6. T h e a m o u n t o f s o l u t i o n forced through per unit time was determined gravimetrically. T h e c y l i n d e r a n d t h e c a p i l l a r y were carefully t h e r m o s t a t t e d a t t e m p e r a t u r e s of' up t~, 50 ° w i t h a n a c c u r a c y o f a b o u t 0.10 ° a n d a b o v e 50 "~'w i t h a n a c c u r a c y o f a b o u t 0.15% The tim~ o f flow w a s d e t e r m i n e d w i t h a n a c c u r a c y o f a b o u t 0.l see. The c a p i l l a r y was c a l i b r a t e d by * V y s o k o m o l . soyed. 5: No. 10, 1568-1573, 1963. 675
676
B.E.
GELLER and V. K. PSHEDETSKAYA
FIo. 1. General v i e w of the SVK-150 a p p a r a t u s .
a s t a n d a r d m e t h o d . The m a x i m u m s y s t e m a t i c error of t h e m e a s u r e m e n t s , neglecting small corrections for t h e r m a l expansion, was 2"1~o. T h e s c a t t e r of t h e values of t h e effective v i s c o s i t y in parallel d e t e r m i n a t i o n s did n o t exceed 15~/o. The m a x i m u m d e v i a t i o n s b e t w e e n parallel m e a s u r e m e n t s were f o u n d in t h e region of shearing stresses ~ greater t h a n 5 × 104 d y n e / c m ~. I n v i e w of t h e fact t h a t the values of the effective v i s c o s i t y d e t e r m i n e d on the A K V - 2 and SVK-150 i n s t r u m e n t s o v e r t h e g i v e n r a n g e of r p r o v e d to be practically identi-
300
240
.
I80
60
tO
I
I2
"~-~-,---~-3-~"--~1
24
38
3heopstpea~,dgne/cm = ~'480a
FIG. 2. R h e o g r a m s of t h e flow of 15 ~o solutions of P A N in D M F at v a r i o u s t e m p e r a tures: 1 - - 2 5 ° ; 2 - - 5 0 ° ; 3 - - 7 5 ° ; full e u r v e s - - O K V - 2 ; b r o k e n c u r v e s - - S V K - 1 5 0 ; r = 0 - 2 8 4 ram, / ~ 1 1 7 m m .
Studies on concentrated solutions of high p o l y m e r s - - V I
677
ca[ (see Fig. 2), the measurements in the range of shearing stresses up to 104 dyne/cm ~ was carried out on the AKV-2, a n d those for greater values of v on the SVK-150. Figure 3 gives the results of the influence of the temperature of the effective viscosity of 30% solutions of CPVC in DMF a n d in acetone and a 15°/o solution of PAN in DMF. An investigation of the influence of the dimensions of the capillary on the nature of th,, rheograms obtained was carried out with capillaries of the following radii (ram): 0.136, 0.207, 0.263, 0-284, 0.343, 0.481, 0.642, and 1-220, with lengths from 70 to 1250 mm. Since the most interesting problem was that of the invariance of the effective viscosity figures of the broken-down structures [2J--i.e. the viscosity ~/~ at sufficiently large values of, r, Fig. 4 shows the results of experiments carried out at 25 ° for solutions of the two polymers investigated. The dimensions of the capillary were characterized by the ratio r4/1 in the' well-known Huggins-Poiseuille equation. DISCUSSION The d e p e n d e n c e of the shape of the r h e o g r a m s on factors d e t e r m i n i n g the r e l a x a t i o n p r o c e s s e s d u r i n g t h e flow o f p o l y m e r s h a s b e e n s h o w n l o n g a g o [3]. However, the physical nature of this phenomenon has remained unclear. The a p p e a r a n c e o f l a b i l e s t r u c t u r e s i n c o n c e n t r a t e d s o l u t i o n s o f p o l y m e r s is d e t e r m i n e d both by the mobility of the macromolecules, which depends on the chemical nature of the polymer and the solvent, and by the concentration of the dissolved h i g h - m o l e c u l a r - w e i g h t c o m p o u n d (Fig. 5). I t c a n b e s e e n f r o m t h e d a t a g i v e n i n F i g . 3 t h a t t h e effective v i s c o s i t i e s o f e q u i - c o n e e n t r a t e d ( 3 0 % ) s o l u t i o n s o f C P V C in a c e t o n e a n d i n D M F a t c o n s t a n t T a r e d i f f e r e n t . W h e n t h e s h e a r i n g
lb
~ 200 $a
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o
3C
,
x
1Q
3c\ ",,-"'~&~...~~3a
5.10 3
I X104
....
--
5,10 4 I, IOs Shear sfre~ , "C= dyne/cm 2
-020
lb 5xlO 5
FIG. 3. Influence of the temperature on the viscosity at various shear stresses: a - - 30 °/o solution of CPVC in acetone at l -- 20°; 2-- 25 °; 3 -- 30 °; 4 -- 35 °; b-- 30 % solution of CPVC in DMF at 1--25°; 2--50°; 3--75°; c-- 15°/o solution of PAN in DMF at 1--25°; :2--50°; 3--75 °.
638
B . E . GELLER a n d V, K, PSHEDETSKAYA
stress ~ is increased to about 20,000 dyne/cm 2 under isothermal conditions, the effective viscosity of acetone solutions of CPVC remains lower t h a n t h a t of dimethylformamide solutions. However, under the conditions of flow of destructurized solutions at sufficiently large values of r, this difference practically disappears. Rheograms of 15% solutions of PAN in DMF have the same nature, in spite of the fact t h a t they have only half the concentration. I t is extremely difficult to prepare 30 % solutions of PAN in DMF at the given molecular weight (about 60,000) [4]. Even at 75 °, such a solution consists of a system resembling a gel in extea~al form. This fact is evidently explained by the considerably lower mobility of the PAN macromolecules as compared with those of CPVC and the more intense intermolecular reactions with the associated relatively complex structures in solution. At lower concentrations of the polymer, these structures are broken down as the temperature is raised, which explains the transition of the system to Newtonian flow at low values of r. In this connection, it must be mentioned t h a t the division of solvents into "good" and "poor" in the thermodynamic sense [5] is not clear-cut at sufficiently high concentrations of the polymer, since at high displacement stresses the difference in the viscosities of solutions of a given polymer in different solvents becomes small.
/0,.q ~1oo
1"500--~
~J'~-
l'000- ~ -~--~ ~ooo
3 ;~ x
I
4
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~ooo
~ooo
Logr 4/L
FIG. 4. ~nfluence of the dimensions of the capillary ONq~ at 25°: l--influence of the length of the capillary on t/oo of 30% acetone solutions of CPVC; 2--influence of the radius of the capillary on ~o of 30% acetone solutions of CPVC; 3--influence of the radius of the capillary on q ~of 30% DMF solutions of CPVC; 4-- influence of the radius of the capillary on ~/~ of 15°/o DMF solutions of PAN. In addition, it is well known t h a t viscosity anomalies in solutions rise markedly when the concentration of the polymer is increased. Figure 5 gives the results of measurements of the effective viscosity of acetone solutions of CPVC. While in 15°/o solutions structure break-down is found at values of r of the order of 104 dyne/em 2, in 32.5% solutions it is reached at displacement stresses ten orders of magnitude higher. I t has been repeatedly stated t h a t the effective viscosity of the limitingly broken-down structure q~ depends to some extent on
Studies on concentrated solutions of high p o l y m e r s - - V I
679
the properties of the polymer (molecular weight, etc.) [5, 6] and for a given polymer m a y be considered constant for equi-concentrated solutions. However, there are apparently insufficient for such a statement. 3"000
"! 2"000
o
c I0 ~
,
~ 10 4
~
o
n
Q ql
I0 s
Shear stress, r, dyne~cruZ
FI(~. 5. Influence of the concentration of acetone solutions of CPVC on the effective viscosity at various shear stresses at 25° (r= 0.263 ram, l= 120 ram): 1-15°,,~: 2--20.0%; 3--22.5% 4--25.0% ; 5--27.5°/o: 6-30.0%; 7--32.5°~,. Figure 5 gives data on the influence of the dimensions of the capillary on the apparent value of t/~. With an increase in the length of the capillary at constant radius, the viscosity of the limitingly broken-down structure rises. This m a y apparently be explained by an increase in the degree of orientiaton of the macromolecules during flow as a result of the intensification of intermolecular interaction. When the diameter of the orifice of the capillary increases, ~/+ again rises, but the rate of this rise gradually diminishes. In acetone solutions of CPVC. this rise is more considerable t h a n in dimethylformamide solutions. In addition, the change of ~/~ in 15~/~) solutions of PAN in DMF is comparatively small. In solutions of lower concentrations (for example, 10-15~o acetone solutions of CPVC), the results of the change in ~/~ obtained are practically identical at all diameters of the orifice of the capillary. In the flow through capillaries of different dimensions of 8 % solutions of PAN in DMF, the results are again found to be invariant [5]. Invariance using viseometers with capillaries of different diameters has also been found for 3 % solutions of cellulose nitrate in butyl acetate [3]. As can be seen from the experimental material discussed above, the invarianee of the rheograms of concentrated solutions must apparently be regarded as a relative conception. When the concentration of the polymer in the solution is increased, intermolecular interaction is enhanced and the mobility of the macromolecules is limited. At sufficiently high concentrations, the possibility of movement of the solvated macromolecules is limited.
680
B.E. GELLERand V. K. PSHEDETSKAYA
When certain shearing stresses are applied, the flow of such a solution will be accompanied b y some positive straightening of the macromolecules which will limit their mobility still further. As a result, when the concentration of the polymer is increased the number of possible conformations of the polymer chains is limited and they tend to aggregate in bundles the density and dimensions of which are determined both b y the nature of the polymer and the solvent and b y the concentration. The primary associates formed--free-flowing bundles--, being characterized b y a definite regularity of the macromolecules, then aggregate into coarser sub-formations. The existence of such structures in solutions of P A N has recently been observed b y H e y n [8]. However, under certain conditions such transformations m a y lead to the formation of heterophase systems of independent interest which are not considered in the present case. ,~ 3.000 _A
B
c 2.000
At
iO
Bt
n
iO2 103 I0 4 i0 5 ,,Cheapsi~e~s , % dgne/cm 2
FIG. 6. Influence of the shear stress on the effective viscosity of 15% solutions of PAN and CPVC in DMF at 25°. The presence of different types of structural bonds in concentrated solutions of polymers (intra-bundle, inter-bundle) is responsible for the complex character of their break-down on flow under the action of different shear stresses. It is known t h a t it is extremely difficult to record rheograms over a wide range of values of r (from 0 to 105 and above dyne/cm ~) on a single apparatus. At the same time, it has been shown that to extend the range of values of T it is possible to use simultaneously sphere and capillary viscometers [9] and sphere and rotation viscometers [5]. Using the experimental results obtained in the present investigation together with some obtained earlier, we have plotted (Fig. 6) the rheograms of 15% solutions of P A N and CPVC [10, 11]. The section A B was plotted on the basis of falling sphere viscosimetric measurements, CD from the results obtained with a rotation viscometer, and D E from the results of measurements of the effective viscosity in AKV-2 and SVK-150 capillary viscometers. 15% solutions of CPVC exhibit comparatively little structure-formation. However, the complete rheogram of a 15°/o solution of P A N in DMF shows the complex nature of the structural break-down of the concentrated solution. Break-down of the structural elements of the solution to individual macromolecules during flow can apparently be achieved only at sufficiently high values
Emulsion polymerization of vinyl compounds
681
of ~, not, in a n y case, b e l o w 7 o r d e r s o f m a g n i t u d e . I t is p r o b a b l e t h a t i n v a r i a n c c of t h e m e a s u r e m e n t s o f r/~ is p o s s i b l e o n l y u n d e r t h e s e c o n d i t i o n s . CONCLUSIONS T h e r h e o l o g i c a l p r o p e r t i e s of s o l u t i o n s of p o l y a c r y l o n i t r i l e in d i m e t h y l f o r m a m i d e a n d o f c h l o r i n a t e d p o l y - ( v i n y l c h l o r i d e ) in a c e t o n e a n d d i m e t h y l f o r m a m i d e h a v e b e e n s t u d i e d b y t h e c a p i l l a r y v i s c o m e t e r m e t h o d o v e r a w i d e r a n g e of c o n c e n t r a t i o n s , t e m p e r a t u r e s , a n d s h e a r stresses. T h e d e p e n d e n c e of t h e effective v i s c o s i t y o f t h e b r o k e n - d o w n s t r u c t u r e s on t h e d i m e n s i o n s of t h e c a p i l l a r y h a s b e e n shown. Tra~slated by B. J. HAZZAR~) REFERENCES I. V. A. KARGIN, and G. L. SLONIMSKII Kratkiye ocherki po fiziko-khimii polimerov (Brief Outlines of the Physical Chemistry of Polymers.) p. 167, Izd. MGU, 1960 2. N. V. MIKHAILOV and P. A. REBINDER, Kolloidn. zh. 17: 107, ] 955 3. S. A. GLIKMAN, Zh. fiz. khim. 11: 825, 1938 4. A. B. PAKSHVER and B. E. GELLER, Khimiya i tekhnologiya volokna nitron. (Chemistry and Technology of Nitron Fibre.) Goskhimizdat, 1960 5. T. MACAO and P. MACAMOTO, Kobunsi kagaku 16: No. 165, 1958 tl. K. EDELMANN, Kautschuk und Gummi 8: 14, 1955 7. K. EDELMANN, Faserforsch. und Textiltechn. 3: 412, 1952 8. A. N. J. HEYN, J. Polymer Sci. 41: 23, 1959 9. S. A. GLIKMAN, N. Ya. VLADYKINA and T. M. PEREPELOVA, Dokl. Akad. Nauk SSSR 77: 483, 1949 10. E. A. PAKSHVER, B. E. GELLER and G. V. VINOGRADOV, Khim. volokna, No. 2, 21, 1959 1 i. V. K. PSHEDETSKAYA and B. E. GELLER, Khim. volokna. No. 2. 15, 1961
EMULSION POLYMERIZATION OF VINYL COMPOUNDS IN THE PRESENCE OF ORGANIC ACIDS AND AMINES* S. D. YEVSTRATOVA, M. F. M(ARGARITOVA a n d S. S. MEDVEDEV M. V. Lomonosov Moscow Instit.ute of Fine Chemical Technology (Received 8 ,lane 1962)
I~ECENTLY. s t a t e m e n t s h a v e a p p e a r e d in t h e l i t e r a t u r e on t h e p o s s i b i l i t y of p o l y m e r i z i n g v i n y l c o m p o u n d s w i t h i n i t i a t i n g s y s t e m s u s i n g o r g a n i c a c i d s (or d e r i v a t i v e s of t h e m ) a n d a m i n e s . *Vysokomol. soyed. 5: No. 10, 1574-1579. 1963.
(Received 23 April 1962)
IT IS known that the anomalies in the viscosity properties of concentrated solutions of polymers demonstrated in their non-Newtonian flow on being forced through capillaries, is due to "the presence of relaxation properties in these liquids" [1]. Previous investigations have shown the dependence of the viscosity properties of concentrated solutions on the mobility of the macromolecules of the effective volume at low shearing forces. In addition, a study of the kinetics of the changes in the structure of concentrated solutions of polymers at high shearing stresses is of fundamental theoretical and, in particular, practical interest for the formation of chemical fibres. This paper gives the results of an investigation of the flow processes of concentrated solutions of chlorinated poly-(vinyl chloride) (CPVC) in acetone and dimethylformamide (DMF) and of polyacrylonitrile (PAN) in DMF over a wide range of concentrations and temperatures through capillaries of various dimensions at shearing stresses of up to 500,000 dyne/cm 2. EXPERIMENTAL The v i s c o s i t y p r o p e r t i e s o f s o l u t i o n s o f CPVC in a c e t o n e o v e r a r a n g e o f c o n c e n t r a t i o n s o f t h e p o l y m e r f r o m 15 t o 3 2 . 5 % b y w e i g h t a t 20-40 °, o f C P V C in D M F a t 25-75 ~, a n d o f a 15% s o l u t i o n o f P A N in D M F a t 25-75 ° w e r e i n v e s t i g a t e d . T h e m e a s u r e m e n t s were c a r r i e d o u t o n a s t a n d a r d A K V - 2 c a p i l l a r y v i s c o m e t e r a n d o n a specially c o n s t r u c t e d c o n s t a n t - p r e s s u r e v i s c o m e t e r w h i c h w e h a v e called S V K - 1 5 0 (see Fig. 1). The solution under investigation was forced from the cylinder 1 through capillary 2 b y t h e p r e s s u r e o f c o m p r e s s e d n i t r o g e n f r o m a r e s e r v o i r 3 fed w i t h gas a t t h e r e q u i r e d p r e s s u r e f r o m c y l i n d e r 4. T h e p r e s s u r e in t h e r e s e r v o i r a n d in t h e c y l i n d e r 1 w a s f o l l o w e d b y s t a n d a r d g a u g e s w i t h i n t h e ranges: u p t o 10 =I-0.05 a r m ; f r o m 10 t o 100 i 0 ' 2 a r m ; a n d f r o m 100 t o 150 ___0.5 a t m . A d j u s t m e n t o f t h e flow o f n i t r o g e n w a s c a r r i e d o u t b y m e a n s o f a s y s t e m o f n e e d l e v a l v e s 5 a r r a n g e d o n a special p a n e l 6. T h e a m o u n t o f s o l u t i o n forced through per unit time was determined gravimetrically. T h e c y l i n d e r a n d t h e c a p i l l a r y were carefully t h e r m o s t a t t e d a t t e m p e r a t u r e s of' up t~, 50 ° w i t h a n a c c u r a c y o f a b o u t 0.10 ° a n d a b o v e 50 "~'w i t h a n a c c u r a c y o f a b o u t 0.15% The tim~ o f flow w a s d e t e r m i n e d w i t h a n a c c u r a c y o f a b o u t 0.l see. The c a p i l l a r y was c a l i b r a t e d by * V y s o k o m o l . soyed. 5: No. 10, 1568-1573, 1963. 675
676
B.E.
GELLER and V. K. PSHEDETSKAYA
FIo. 1. General v i e w of the SVK-150 a p p a r a t u s .
a s t a n d a r d m e t h o d . The m a x i m u m s y s t e m a t i c error of t h e m e a s u r e m e n t s , neglecting small corrections for t h e r m a l expansion, was 2"1~o. T h e s c a t t e r of t h e values of t h e effective v i s c o s i t y in parallel d e t e r m i n a t i o n s did n o t exceed 15~/o. The m a x i m u m d e v i a t i o n s b e t w e e n parallel m e a s u r e m e n t s were f o u n d in t h e region of shearing stresses ~ greater t h a n 5 × 104 d y n e / c m ~. I n v i e w of t h e fact t h a t the values of the effective v i s c o s i t y d e t e r m i n e d on the A K V - 2 and SVK-150 i n s t r u m e n t s o v e r t h e g i v e n r a n g e of r p r o v e d to be practically identi-
300
240
.
I80
60
tO
I
I2
"~-~-,---~-3-~"--~1
24
38
3heopstpea~,dgne/cm = ~'480a
FIG. 2. R h e o g r a m s of t h e flow of 15 ~o solutions of P A N in D M F at v a r i o u s t e m p e r a tures: 1 - - 2 5 ° ; 2 - - 5 0 ° ; 3 - - 7 5 ° ; full e u r v e s - - O K V - 2 ; b r o k e n c u r v e s - - S V K - 1 5 0 ; r = 0 - 2 8 4 ram, / ~ 1 1 7 m m .
Studies on concentrated solutions of high p o l y m e r s - - V I
677
ca[ (see Fig. 2), the measurements in the range of shearing stresses up to 104 dyne/cm ~ was carried out on the AKV-2, a n d those for greater values of v on the SVK-150. Figure 3 gives the results of the influence of the temperature of the effective viscosity of 30% solutions of CPVC in DMF a n d in acetone and a 15°/o solution of PAN in DMF. An investigation of the influence of the dimensions of the capillary on the nature of th,, rheograms obtained was carried out with capillaries of the following radii (ram): 0.136, 0.207, 0.263, 0-284, 0.343, 0.481, 0.642, and 1-220, with lengths from 70 to 1250 mm. Since the most interesting problem was that of the invariance of the effective viscosity figures of the broken-down structures [2J--i.e. the viscosity ~/~ at sufficiently large values of, r, Fig. 4 shows the results of experiments carried out at 25 ° for solutions of the two polymers investigated. The dimensions of the capillary were characterized by the ratio r4/1 in the' well-known Huggins-Poiseuille equation. DISCUSSION The d e p e n d e n c e of the shape of the r h e o g r a m s on factors d e t e r m i n i n g the r e l a x a t i o n p r o c e s s e s d u r i n g t h e flow o f p o l y m e r s h a s b e e n s h o w n l o n g a g o [3]. However, the physical nature of this phenomenon has remained unclear. The a p p e a r a n c e o f l a b i l e s t r u c t u r e s i n c o n c e n t r a t e d s o l u t i o n s o f p o l y m e r s is d e t e r m i n e d both by the mobility of the macromolecules, which depends on the chemical nature of the polymer and the solvent, and by the concentration of the dissolved h i g h - m o l e c u l a r - w e i g h t c o m p o u n d (Fig. 5). I t c a n b e s e e n f r o m t h e d a t a g i v e n i n F i g . 3 t h a t t h e effective v i s c o s i t i e s o f e q u i - c o n e e n t r a t e d ( 3 0 % ) s o l u t i o n s o f C P V C in a c e t o n e a n d i n D M F a t c o n s t a n t T a r e d i f f e r e n t . W h e n t h e s h e a r i n g
lb
~ 200 $a
~_
lc~llli
o
3C
,
x
1Q
3c\ ",,-"'~&~...~~3a
5.10 3
I X104
....
--
5,10 4 I, IOs Shear sfre~ , "C= dyne/cm 2
-020
lb 5xlO 5
FIG. 3. Influence of the temperature on the viscosity at various shear stresses: a - - 30 °/o solution of CPVC in acetone at l -- 20°; 2-- 25 °; 3 -- 30 °; 4 -- 35 °; b-- 30 % solution of CPVC in DMF at 1--25°; 2--50°; 3--75°; c-- 15°/o solution of PAN in DMF at 1--25°; :2--50°; 3--75 °.
638
B . E . GELLER a n d V, K, PSHEDETSKAYA
stress ~ is increased to about 20,000 dyne/cm 2 under isothermal conditions, the effective viscosity of acetone solutions of CPVC remains lower t h a n t h a t of dimethylformamide solutions. However, under the conditions of flow of destructurized solutions at sufficiently large values of r, this difference practically disappears. Rheograms of 15% solutions of PAN in DMF have the same nature, in spite of the fact t h a t they have only half the concentration. I t is extremely difficult to prepare 30 % solutions of PAN in DMF at the given molecular weight (about 60,000) [4]. Even at 75 °, such a solution consists of a system resembling a gel in extea~al form. This fact is evidently explained by the considerably lower mobility of the PAN macromolecules as compared with those of CPVC and the more intense intermolecular reactions with the associated relatively complex structures in solution. At lower concentrations of the polymer, these structures are broken down as the temperature is raised, which explains the transition of the system to Newtonian flow at low values of r. In this connection, it must be mentioned t h a t the division of solvents into "good" and "poor" in the thermodynamic sense [5] is not clear-cut at sufficiently high concentrations of the polymer, since at high displacement stresses the difference in the viscosities of solutions of a given polymer in different solvents becomes small.
/0,.q ~1oo
1"500--~
~J'~-
l'000- ~ -~--~ ~ooo
3 ;~ x
I
4
×
~ooo
~ooo
Logr 4/L
FIG. 4. ~nfluence of the dimensions of the capillary ONq~ at 25°: l--influence of the length of the capillary on t/oo of 30% acetone solutions of CPVC; 2--influence of the radius of the capillary on ~o of 30% acetone solutions of CPVC; 3--influence of the radius of the capillary on q ~of 30% DMF solutions of CPVC; 4-- influence of the radius of the capillary on ~/~ of 15°/o DMF solutions of PAN. In addition, it is well known t h a t viscosity anomalies in solutions rise markedly when the concentration of the polymer is increased. Figure 5 gives the results of measurements of the effective viscosity of acetone solutions of CPVC. While in 15°/o solutions structure break-down is found at values of r of the order of 104 dyne/em 2, in 32.5% solutions it is reached at displacement stresses ten orders of magnitude higher. I t has been repeatedly stated t h a t the effective viscosity of the limitingly broken-down structure q~ depends to some extent on
Studies on concentrated solutions of high p o l y m e r s - - V I
679
the properties of the polymer (molecular weight, etc.) [5, 6] and for a given polymer m a y be considered constant for equi-concentrated solutions. However, there are apparently insufficient for such a statement. 3"000
"! 2"000
o
c I0 ~
,
~ 10 4
~
o
n
Q ql
I0 s
Shear stress, r, dyne~cruZ
FI(~. 5. Influence of the concentration of acetone solutions of CPVC on the effective viscosity at various shear stresses at 25° (r= 0.263 ram, l= 120 ram): 1-15°,,~: 2--20.0%; 3--22.5% 4--25.0% ; 5--27.5°/o: 6-30.0%; 7--32.5°~,. Figure 5 gives data on the influence of the dimensions of the capillary on the apparent value of t/~. With an increase in the length of the capillary at constant radius, the viscosity of the limitingly broken-down structure rises. This m a y apparently be explained by an increase in the degree of orientiaton of the macromolecules during flow as a result of the intensification of intermolecular interaction. When the diameter of the orifice of the capillary increases, ~/+ again rises, but the rate of this rise gradually diminishes. In acetone solutions of CPVC. this rise is more considerable t h a n in dimethylformamide solutions. In addition, the change of ~/~ in 15~/~) solutions of PAN in DMF is comparatively small. In solutions of lower concentrations (for example, 10-15~o acetone solutions of CPVC), the results of the change in ~/~ obtained are practically identical at all diameters of the orifice of the capillary. In the flow through capillaries of different dimensions of 8 % solutions of PAN in DMF, the results are again found to be invariant [5]. Invariance using viseometers with capillaries of different diameters has also been found for 3 % solutions of cellulose nitrate in butyl acetate [3]. As can be seen from the experimental material discussed above, the invarianee of the rheograms of concentrated solutions must apparently be regarded as a relative conception. When the concentration of the polymer in the solution is increased, intermolecular interaction is enhanced and the mobility of the macromolecules is limited. At sufficiently high concentrations, the possibility of movement of the solvated macromolecules is limited.
680
B.E. GELLERand V. K. PSHEDETSKAYA
When certain shearing stresses are applied, the flow of such a solution will be accompanied b y some positive straightening of the macromolecules which will limit their mobility still further. As a result, when the concentration of the polymer is increased the number of possible conformations of the polymer chains is limited and they tend to aggregate in bundles the density and dimensions of which are determined both b y the nature of the polymer and the solvent and b y the concentration. The primary associates formed--free-flowing bundles--, being characterized b y a definite regularity of the macromolecules, then aggregate into coarser sub-formations. The existence of such structures in solutions of P A N has recently been observed b y H e y n [8]. However, under certain conditions such transformations m a y lead to the formation of heterophase systems of independent interest which are not considered in the present case. ,~ 3.000 _A
B
c 2.000
At
iO
Bt
n
iO2 103 I0 4 i0 5 ,,Cheapsi~e~s , % dgne/cm 2
FIG. 6. Influence of the shear stress on the effective viscosity of 15% solutions of PAN and CPVC in DMF at 25°. The presence of different types of structural bonds in concentrated solutions of polymers (intra-bundle, inter-bundle) is responsible for the complex character of their break-down on flow under the action of different shear stresses. It is known t h a t it is extremely difficult to record rheograms over a wide range of values of r (from 0 to 105 and above dyne/cm ~) on a single apparatus. At the same time, it has been shown that to extend the range of values of T it is possible to use simultaneously sphere and capillary viscometers [9] and sphere and rotation viscometers [5]. Using the experimental results obtained in the present investigation together with some obtained earlier, we have plotted (Fig. 6) the rheograms of 15% solutions of P A N and CPVC [10, 11]. The section A B was plotted on the basis of falling sphere viscosimetric measurements, CD from the results obtained with a rotation viscometer, and D E from the results of measurements of the effective viscosity in AKV-2 and SVK-150 capillary viscometers. 15% solutions of CPVC exhibit comparatively little structure-formation. However, the complete rheogram of a 15°/o solution of P A N in DMF shows the complex nature of the structural break-down of the concentrated solution. Break-down of the structural elements of the solution to individual macromolecules during flow can apparently be achieved only at sufficiently high values
Emulsion polymerization of vinyl compounds
681
of ~, not, in a n y case, b e l o w 7 o r d e r s o f m a g n i t u d e . I t is p r o b a b l e t h a t i n v a r i a n c c of t h e m e a s u r e m e n t s o f r/~ is p o s s i b l e o n l y u n d e r t h e s e c o n d i t i o n s . CONCLUSIONS T h e r h e o l o g i c a l p r o p e r t i e s of s o l u t i o n s of p o l y a c r y l o n i t r i l e in d i m e t h y l f o r m a m i d e a n d o f c h l o r i n a t e d p o l y - ( v i n y l c h l o r i d e ) in a c e t o n e a n d d i m e t h y l f o r m a m i d e h a v e b e e n s t u d i e d b y t h e c a p i l l a r y v i s c o m e t e r m e t h o d o v e r a w i d e r a n g e of c o n c e n t r a t i o n s , t e m p e r a t u r e s , a n d s h e a r stresses. T h e d e p e n d e n c e of t h e effective v i s c o s i t y o f t h e b r o k e n - d o w n s t r u c t u r e s on t h e d i m e n s i o n s of t h e c a p i l l a r y h a s b e e n shown. Tra~slated by B. J. HAZZAR~) REFERENCES I. V. A. KARGIN, and G. L. SLONIMSKII Kratkiye ocherki po fiziko-khimii polimerov (Brief Outlines of the Physical Chemistry of Polymers.) p. 167, Izd. MGU, 1960 2. N. V. MIKHAILOV and P. A. REBINDER, Kolloidn. zh. 17: 107, ] 955 3. S. A. GLIKMAN, Zh. fiz. khim. 11: 825, 1938 4. A. B. PAKSHVER and B. E. GELLER, Khimiya i tekhnologiya volokna nitron. (Chemistry and Technology of Nitron Fibre.) Goskhimizdat, 1960 5. T. MACAO and P. MACAMOTO, Kobunsi kagaku 16: No. 165, 1958 tl. K. EDELMANN, Kautschuk und Gummi 8: 14, 1955 7. K. EDELMANN, Faserforsch. und Textiltechn. 3: 412, 1952 8. A. N. J. HEYN, J. Polymer Sci. 41: 23, 1959 9. S. A. GLIKMAN, N. Ya. VLADYKINA and T. M. PEREPELOVA, Dokl. Akad. Nauk SSSR 77: 483, 1949 10. E. A. PAKSHVER, B. E. GELLER and G. V. VINOGRADOV, Khim. volokna, No. 2, 21, 1959 1 i. V. K. PSHEDETSKAYA and B. E. GELLER, Khim. volokna. No. 2. 15, 1961
EMULSION POLYMERIZATION OF VINYL COMPOUNDS IN THE PRESENCE OF ORGANIC ACIDS AND AMINES* S. D. YEVSTRATOVA, M. F. M(ARGARITOVA a n d S. S. MEDVEDEV M. V. Lomonosov Moscow Instit.ute of Fine Chemical Technology (Received 8 ,lane 1962)
I~ECENTLY. s t a t e m e n t s h a v e a p p e a r e d in t h e l i t e r a t u r e on t h e p o s s i b i l i t y of p o l y m e r i z i n g v i n y l c o m p o u n d s w i t h i n i t i a t i n g s y s t e m s u s i n g o r g a n i c a c i d s (or d e r i v a t i v e s of t h e m ) a n d a m i n e s . *Vysokomol. soyed. 5: No. 10, 1574-1579. 1963.