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Large-scale polymer fractionation
EuropeanPolymerJournal, 1970,Vol. 6, pp. I-6. PergamonPress. Printedin England.
LARGE-SCALE POLYMER FRACT1ONATION* A. MULA and L. CHINELLATO Montecatini Edison S.p.A., Centro Ricerche, 20021 Bollate, Milano, Italy Abstract--Fractionations of polymethylmethacrylate were carried out by column elution at constant temperature with small (3 g) and large (150 g) amounts of substance. Acetone and n-hexane were used as solvent and non-solvent respectively. Column volumes of 600 cm ~ and 30 dm 3 were used; to avoid radical thermal gradient, the largest column was constructed with a circular corona section, with both internal and external thermostatic control. Good agreement in the fractionation data was observed notwithstanding the different amounts of polymer and column volumes. The mol. wts. were determined by means of osmotic pressure and light scattering for some fractions from the large fractionation; a comparison of the values obtained show that, despite the large amounts of material used, the fractions exhibit narrow rnol. wt. distribution.
INTRODUCTION COLUMN fractionations of polymers by elution are in general carried out for analytical purposes on small quantities of sample (1-5 g). However it is useful at times to o b t a i n large quantities of some fractions of polymer to carry out studies of practical interest. I n order to obtain good fractionation in the elution of a polymer, it is necessary to keep low the polymer c o n c e n t r a t i o n ; consequently for the fractionation of large q u a n tities of polymer, it is necessary to use large-volume columns. In order to achieve that, C a n t o w (t) adopted a set of c o l u m n s in parallel, whereas K e n y o n 12) increased the height of the c o l u m n to 6 m to avoid the use of large-section c o l u m n s which would adversely affect the thermostatic control of the system and the flow of the eluent because of channelling. F o r the fractionation of large quantities of polymer, in this work we used a largecapacity c o l u m n of design permitting good steadiness of temperature while the height was limited to 2 m. I n order to control the efficiency of fractionation, the data obtained from a largescale fractionation are c o m p a r e d with those o b t a i n e d from an analytical c o l u m n and, moreover, the molecular weights were controlled by means of refractionation, light scattering and osmotic measurements.
EXPERIMENTAL Columns. The analytical fractionation of a polymer sample (3 g) was made using a glass column 2.5
cm dia. and 130 cm high with thermostatic control provided from the outside only (Fig. 1). In order to scale-up the fractionation, we used a 30 1. column of 200 cm length, with a particular geometry, by maintaining comparable the principal operational parameters (such as polymer concentration, specific elution velocity, etc.). We therefore placed inside this column a coaxial tube through which the same thermostatic control fluid of the external jacket (Fig. 1) flowed. In this case the maximum distance between the two thermostatically controlled wails was 4" 5 cm. This permitted a much better control of temperature than that obtainable in the plain cylinder. Characteristic data of the two columns are illustrated in Table 1. * Paper presented at the Third Prague Microsymposium on Distribution Analysis and Fra~tionation of Polymers, 23-26 September 1968. I
2
A. M U L A and L. CHINELLATO
P •, o - - + .
f
t
d
P t
"-1
®
"
M
s , m o / ' ~ , / , m ,~ .. i ,
I
,¢' ,,,'c #% "- ,', - ( a
',,R
FiG. 1. Fractionation apparatus (Ct and C2, small and large-scale fractionation columns; S and M, solvent reservoir and mixer; P, micropump; T, thermostatic bath; F, fraction collector).
Polymer. For the fractionations, we used a sample of a commercial grade P M M A with [,7] t25, oluene = 31 (cm3/g). Elution. For the column loading, the polymer is dissolved in butanone (MEK) at 66 °, and cyclohexane is added until the cloud point is attained (~0 MEK volumefraction = 0"45). The solution is introduced in the column, thermostatically controlled at 70 °, which is packed with glass beads of 0.1 mm size (Superbrite type B---3M beads). The volume of the solution is such as to fill the spaces between the beads (about 1/3). The column is then slowly cooled at a scheduled speed of 10°/hr down to 15 °. The precipitant n-hexane is then allowed to flow through the column until the previous liquid is fully replaced. Fractionation is carried out by elution at 20 ° in an acetone-n-hexane mixture variable with exponential gradient from ~, in acetone 0" 52 to 0" 62. The fractionation conditions, as well as the course of the elution curve, are established by means of preliminary tests.
Large-scale Polymer Fractionation
3
TABLE I. COLUMN DATA Column Diameter Wall distance Height Section area Column volume Eluent volume Fractionation time
cm cm cm cm z cm 3 cm 3 hr cm ~
Elution velocity
h-)-"
cm 3
Specific elution velocity
cmL hr g
Polymer weight
1
2
2" 5 130 5 630 1,500 15
15.0 4, 5 200 150 30,000 70,000 58
100
1,200
20
8
3
150
0.65
L~ ~ /
0.60
I
//
0.55
0.50
~
ti
o-2sl__ 1 vet. |
[
o.so
o.7s
FIG. 2. Elution curve. To determine the exponential curve, we took into account the amount of polymer eluted as the composition of eluent varied (Fig. 2). For the large-scale fractionation, the exponential curve was obtained from cumulative linear gradients in order to use small containers. Each fraction is then concentrated under vacuum, diluted with M E K and precipitated in n-hexane. The fractions are dried at 60 ° under vacuum. Recovery: 97-98 per cent. Apparatus. The determination of intrinsic viscosity was made using Desreux-Bischoff viscometers.(3) The Mechrolab apparatus was used for the osmotic pressure measurements. Both measurements were carried out on toluene solutions. For the measurements of MLs, we used a SOFICA apparatus; M E K was used as solvent. The solutions were cleaned by means of centrifugation at 20,000 rev/min for 4 hr. The polymer concentration range varied in all measurements between 0" 1 and 1- 5 per cent.
RESULTS
AND
DISCUSSION
T h e f r a c t i o n s a r e e x a m i n e d b y d e t e r m i n i n g i n t r i n s i c v i s c o s i t y i n t o l u e n e a t 25 ° . T h e values of the large-scale fractionation are reported in Table 2 with the calculated molec u l a r w e i g h t s f r o m t h e r e l a t i o n [~7] t.tu,.c25° _-- 7- I x 10 . 3 MLs °'~3.(4~ T h e l a s t 2 o f t h e
A. M U L A and L. CHINELLATO TAm~ 2. FRACTIONATIONDATA Fraction No.
0 1 2 3 4 5 6 7 8* 9 I0 11 12 13 14 15 16 17 18 19 20 21" 22 23 24 25 26 27* 28 29 30 31 32 33* 34 35* 36 37* 38 39
Solution (cm 3)
10.000 1"490 1.500 1'485 1.545 1.455 2.231 1.384 1.509 1.498 1.445 1.427 1"526 1"227 1.473 1"520 1.470 1-455 1.470 1.450 1.505 1.460 1.520 1"425 1.460 1.433 1.485 1.575 1.715 1.575 1.525 1.700 1.702 2.214 2.230 2.175 2"650 4.360 12"065 5.200
Polymer (g)
In × 100
C × 102 (g.cm -3)
[7] Toluene 25°C
Mt.s × 10 -3
9"55 3.00 6.18 4-67 4.20 4.12 5.78 3.51 3.72 3"64 3-50 3.50 3"95 3-30 4"12 4-30 3.58 4-04 4.10 4.05 4"35 4.39 3.70 4.00 3.95 4.00 4.00 3.90 3.33 2-75 2.60 2.65 2.57 2.95 2.29 1.70 1.40 1.35 1.85 0-70
3.28 7-60 10.75 14.48 17.53 20-39 23"80 26'99 29.48 32.01 34-46 36.87 39.44 41.93 44"49 47.39 50-10 52-72 55.52 58-32 61.22 64.23 67.02 69.66 72-40 75.13 77.88 80.60 83.08 85.17 87.01 88.82 90"61 92.51 94.32 95.69 96.76 97.70 98"80 99.68
0-0955 0.201 0.413 0.314 0-272 0.282 0-259 0.254 0.247 0"243 0.242 0.245 0"259 0-269 0.279 0.283 0-243 0-278 0.279 0.279 0.289 0-301 0.243 0-281 0.270 0-279 0.269 0.247 0.194 0.1745 0.1705 0.1560 0.1510 0"133 0.1027 0.0781 0.0528 0-0310 0.0488 0.0134
8-0 10.0 13.0 15.0 16.0 17.5 19.0 20.0 21.0 21"5 22-0 23.0 23"5 24"5 25.0 26.5 27.5 28.5 29.0 30.5 32.0 33"0 34.5 35.5 37"0 38.5 40"5 42.5 44.0 46-0 47.5 50.0 51.5 55"0 58.0 62.5 65.5 73.5 44.0 58.0
15 21 30 36 40 45 50 54 57 59 61 65 67 71 73 79 83 87 90 96 102 106 112 117 125 130 140 150 157 167 175 188 200 215 230 255 272 320 157 230
31.0
98
Unfract.* polymer * MLs and MOSM measurements were carried out on these samples.
39 f r a c t i o n s s h o w a r e v e r s a l viscosity. T h e d a t a o f the fractions, a c c o r d i n g t o Schulz, ~5) are p l o t t e d a g a i n s t intrinsic v i s c o s i t y (Fig. 3). T h e i n t e g r a l c u r v e s t h u s o b t a i n e d f r o m t h e a n a l y t i c a l a n d large-scale f r a c t i o n a t i o n s h o w fairly g o o d a g r e e m e n t . I n o r d e r to a n a l y z e t h e p o l y d i s p e r s i o n w i t h i n a single f r a c t i o n , f r a c t i o n 32 w i t h [7] = 5 1 . 5 was f r a c t i o n a t e d . T h e p l o t in Fig. 3 s h o w s t h a t the d i s p e r s i o n o f this
Large-scale Polymer Fractionation
5
1.0'I
I I
el5
0
/'
0
II
/
J
I /
25
--LARGE SCAL(
2S'¢ [~] Ta4~n,
---SMALLSCALE
75
50 "~]
:m3g
-'-FRACTION 32
FIG. 3. Cumulative distribution curves.
fraction is limited. Moreover, we tested some fractions of the large-scale fractionation whose mol. wts. differed from one another by about 50,000; the tool. wt. of these fractions was determined by light scattering and osmotic pressure measurements. These measurements are represented in Table 3 together with those obtained on the whole polymer. The relation between the mol. wts. Mcs and MosM is indicated in the last column. An examination of the integral curves and of the relations of the mol. wts. shows that within each single fraction, the dispersion of the tool. wts. remains within fairly good TABLE 3. FRACTIONATION CHARACTERIZATION FR. Nr
MLX 10 -a
M ossd0 -3
MLs
[17] Toluene 25°C ~ OS~!
8 21 27 33 35 37 Un~act. Sample
21 33 42"5 55 62"5 73"5
46"5 91"9 135 202 237"8 315
42 86 125 170 199 235
1"13 1"07 1"08 1"18 1"19 1"40
31
100.4
44
2-28
limits. From Table 3 it can be seen that there is a deviation only at high mol. wts., whereas at medium and low mol. wts., the two values are close.
CONCLUSIONS The adopted column design for large-scale fractionation permits a good efficiency. It can be inferred that this column design gives good results in spite of the large amount of polymer involved; it is possible to obtain large quantities of fractions, useful to
6
A. MULA and L. CHINELLATO
carry out tests of a technical type (rheological, melt index, D T A , stress-strain, etc.) as a function of molecular weights.
Acknowledgements--Appreciation is expressed to Dr. C. Garbuglio for discussions and for interest in these investigations. Assistance of Mr. M. Solari, Dr. G. Giannotti and Mr. G. Fornari in mol. wt. measurement and characterization of fractions is gratefully acknowledged. REFERENCES (I) (2) (3) (4) (5)
M. J. R. Cantow, R. S. Porter and J. F. Johnson, Nature, Lond. 192, 752 (1961). A. S. Kenyon and I. O. Salyer, J. Polym. Sci. 43, 427 (1960). V. Desreux and I. Bischoff, Bull. So¢. Chim. Belg. 59, 93 (1950). S. N. Chinai, J. D. Matlack, A. L. Resnick and R. J. Samuels, J. Polym. Sci. 17, 391 (1955). G. V. Schulz and A. Dinglinger, Z. phys. Chem. B43, 47 (1939).
LARGE-SCALE POLYMER FRACT1ONATION* A. MULA and L. CHINELLATO Montecatini Edison S.p.A., Centro Ricerche, 20021 Bollate, Milano, Italy Abstract--Fractionations of polymethylmethacrylate were carried out by column elution at constant temperature with small (3 g) and large (150 g) amounts of substance. Acetone and n-hexane were used as solvent and non-solvent respectively. Column volumes of 600 cm ~ and 30 dm 3 were used; to avoid radical thermal gradient, the largest column was constructed with a circular corona section, with both internal and external thermostatic control. Good agreement in the fractionation data was observed notwithstanding the different amounts of polymer and column volumes. The mol. wts. were determined by means of osmotic pressure and light scattering for some fractions from the large fractionation; a comparison of the values obtained show that, despite the large amounts of material used, the fractions exhibit narrow rnol. wt. distribution.
INTRODUCTION COLUMN fractionations of polymers by elution are in general carried out for analytical purposes on small quantities of sample (1-5 g). However it is useful at times to o b t a i n large quantities of some fractions of polymer to carry out studies of practical interest. I n order to obtain good fractionation in the elution of a polymer, it is necessary to keep low the polymer c o n c e n t r a t i o n ; consequently for the fractionation of large q u a n tities of polymer, it is necessary to use large-volume columns. In order to achieve that, C a n t o w (t) adopted a set of c o l u m n s in parallel, whereas K e n y o n 12) increased the height of the c o l u m n to 6 m to avoid the use of large-section c o l u m n s which would adversely affect the thermostatic control of the system and the flow of the eluent because of channelling. F o r the fractionation of large quantities of polymer, in this work we used a largecapacity c o l u m n of design permitting good steadiness of temperature while the height was limited to 2 m. I n order to control the efficiency of fractionation, the data obtained from a largescale fractionation are c o m p a r e d with those o b t a i n e d from an analytical c o l u m n and, moreover, the molecular weights were controlled by means of refractionation, light scattering and osmotic measurements.
EXPERIMENTAL Columns. The analytical fractionation of a polymer sample (3 g) was made using a glass column 2.5
cm dia. and 130 cm high with thermostatic control provided from the outside only (Fig. 1). In order to scale-up the fractionation, we used a 30 1. column of 200 cm length, with a particular geometry, by maintaining comparable the principal operational parameters (such as polymer concentration, specific elution velocity, etc.). We therefore placed inside this column a coaxial tube through which the same thermostatic control fluid of the external jacket (Fig. 1) flowed. In this case the maximum distance between the two thermostatically controlled wails was 4" 5 cm. This permitted a much better control of temperature than that obtainable in the plain cylinder. Characteristic data of the two columns are illustrated in Table 1. * Paper presented at the Third Prague Microsymposium on Distribution Analysis and Fra~tionation of Polymers, 23-26 September 1968. I
2
A. M U L A and L. CHINELLATO
P •, o - - + .
f
t
d
P t
"-1
®
"
M
s , m o / ' ~ , / , m ,~ .. i ,
I
,¢' ,,,'c #% "- ,', - ( a
',,R
FiG. 1. Fractionation apparatus (Ct and C2, small and large-scale fractionation columns; S and M, solvent reservoir and mixer; P, micropump; T, thermostatic bath; F, fraction collector).
Polymer. For the fractionations, we used a sample of a commercial grade P M M A with [,7] t25, oluene = 31 (cm3/g). Elution. For the column loading, the polymer is dissolved in butanone (MEK) at 66 °, and cyclohexane is added until the cloud point is attained (~0 MEK volumefraction = 0"45). The solution is introduced in the column, thermostatically controlled at 70 °, which is packed with glass beads of 0.1 mm size (Superbrite type B---3M beads). The volume of the solution is such as to fill the spaces between the beads (about 1/3). The column is then slowly cooled at a scheduled speed of 10°/hr down to 15 °. The precipitant n-hexane is then allowed to flow through the column until the previous liquid is fully replaced. Fractionation is carried out by elution at 20 ° in an acetone-n-hexane mixture variable with exponential gradient from ~, in acetone 0" 52 to 0" 62. The fractionation conditions, as well as the course of the elution curve, are established by means of preliminary tests.
Large-scale Polymer Fractionation
3
TABLE I. COLUMN DATA Column Diameter Wall distance Height Section area Column volume Eluent volume Fractionation time
cm cm cm cm z cm 3 cm 3 hr cm ~
Elution velocity
h-)-"
cm 3
Specific elution velocity
cmL hr g
Polymer weight
1
2
2" 5 130 5 630 1,500 15
15.0 4, 5 200 150 30,000 70,000 58
100
1,200
20
8
3
150
0.65
L~ ~ /
0.60
I
//
0.55
0.50
~
ti
o-2sl__ 1 vet. |
[
o.so
o.7s
FIG. 2. Elution curve. To determine the exponential curve, we took into account the amount of polymer eluted as the composition of eluent varied (Fig. 2). For the large-scale fractionation, the exponential curve was obtained from cumulative linear gradients in order to use small containers. Each fraction is then concentrated under vacuum, diluted with M E K and precipitated in n-hexane. The fractions are dried at 60 ° under vacuum. Recovery: 97-98 per cent. Apparatus. The determination of intrinsic viscosity was made using Desreux-Bischoff viscometers.(3) The Mechrolab apparatus was used for the osmotic pressure measurements. Both measurements were carried out on toluene solutions. For the measurements of MLs, we used a SOFICA apparatus; M E K was used as solvent. The solutions were cleaned by means of centrifugation at 20,000 rev/min for 4 hr. The polymer concentration range varied in all measurements between 0" 1 and 1- 5 per cent.
RESULTS
AND
DISCUSSION
T h e f r a c t i o n s a r e e x a m i n e d b y d e t e r m i n i n g i n t r i n s i c v i s c o s i t y i n t o l u e n e a t 25 ° . T h e values of the large-scale fractionation are reported in Table 2 with the calculated molec u l a r w e i g h t s f r o m t h e r e l a t i o n [~7] t.tu,.c25° _-- 7- I x 10 . 3 MLs °'~3.(4~ T h e l a s t 2 o f t h e
A. M U L A and L. CHINELLATO TAm~ 2. FRACTIONATIONDATA Fraction No.
0 1 2 3 4 5 6 7 8* 9 I0 11 12 13 14 15 16 17 18 19 20 21" 22 23 24 25 26 27* 28 29 30 31 32 33* 34 35* 36 37* 38 39
Solution (cm 3)
10.000 1"490 1.500 1'485 1.545 1.455 2.231 1.384 1.509 1.498 1.445 1.427 1"526 1"227 1.473 1"520 1.470 1-455 1.470 1.450 1.505 1.460 1.520 1"425 1.460 1.433 1.485 1.575 1.715 1.575 1.525 1.700 1.702 2.214 2.230 2.175 2"650 4.360 12"065 5.200
Polymer (g)
In × 100
C × 102 (g.cm -3)
[7] Toluene 25°C
Mt.s × 10 -3
9"55 3.00 6.18 4-67 4.20 4.12 5.78 3.51 3.72 3"64 3-50 3.50 3"95 3-30 4"12 4-30 3.58 4-04 4.10 4.05 4"35 4.39 3.70 4.00 3.95 4.00 4.00 3.90 3.33 2-75 2.60 2.65 2.57 2.95 2.29 1.70 1.40 1.35 1.85 0-70
3.28 7-60 10.75 14.48 17.53 20-39 23"80 26'99 29.48 32.01 34-46 36.87 39.44 41.93 44"49 47.39 50-10 52-72 55.52 58-32 61.22 64.23 67.02 69.66 72-40 75.13 77.88 80.60 83.08 85.17 87.01 88.82 90"61 92.51 94.32 95.69 96.76 97.70 98"80 99.68
0-0955 0.201 0.413 0.314 0-272 0.282 0-259 0.254 0.247 0"243 0.242 0.245 0"259 0-269 0.279 0.283 0-243 0-278 0.279 0.279 0.289 0-301 0.243 0-281 0.270 0-279 0.269 0.247 0.194 0.1745 0.1705 0.1560 0.1510 0"133 0.1027 0.0781 0.0528 0-0310 0.0488 0.0134
8-0 10.0 13.0 15.0 16.0 17.5 19.0 20.0 21.0 21"5 22-0 23.0 23"5 24"5 25.0 26.5 27.5 28.5 29.0 30.5 32.0 33"0 34.5 35.5 37"0 38.5 40"5 42.5 44.0 46-0 47.5 50.0 51.5 55"0 58.0 62.5 65.5 73.5 44.0 58.0
15 21 30 36 40 45 50 54 57 59 61 65 67 71 73 79 83 87 90 96 102 106 112 117 125 130 140 150 157 167 175 188 200 215 230 255 272 320 157 230
31.0
98
Unfract.* polymer * MLs and MOSM measurements were carried out on these samples.
39 f r a c t i o n s s h o w a r e v e r s a l viscosity. T h e d a t a o f the fractions, a c c o r d i n g t o Schulz, ~5) are p l o t t e d a g a i n s t intrinsic v i s c o s i t y (Fig. 3). T h e i n t e g r a l c u r v e s t h u s o b t a i n e d f r o m t h e a n a l y t i c a l a n d large-scale f r a c t i o n a t i o n s h o w fairly g o o d a g r e e m e n t . I n o r d e r to a n a l y z e t h e p o l y d i s p e r s i o n w i t h i n a single f r a c t i o n , f r a c t i o n 32 w i t h [7] = 5 1 . 5 was f r a c t i o n a t e d . T h e p l o t in Fig. 3 s h o w s t h a t the d i s p e r s i o n o f this
Large-scale Polymer Fractionation
5
1.0'I
I I
el5
0
/'
0
II
/
J
I /
25
--LARGE SCAL(
2S'¢ [~] Ta4~n,
---SMALLSCALE
75
50 "~]
:m3g
-'-FRACTION 32
FIG. 3. Cumulative distribution curves.
fraction is limited. Moreover, we tested some fractions of the large-scale fractionation whose mol. wts. differed from one another by about 50,000; the tool. wt. of these fractions was determined by light scattering and osmotic pressure measurements. These measurements are represented in Table 3 together with those obtained on the whole polymer. The relation between the mol. wts. Mcs and MosM is indicated in the last column. An examination of the integral curves and of the relations of the mol. wts. shows that within each single fraction, the dispersion of the tool. wts. remains within fairly good TABLE 3. FRACTIONATION CHARACTERIZATION FR. Nr
MLX 10 -a
M ossd0 -3
MLs
[17] Toluene 25°C ~ OS~!
8 21 27 33 35 37 Un~act. Sample
21 33 42"5 55 62"5 73"5
46"5 91"9 135 202 237"8 315
42 86 125 170 199 235
1"13 1"07 1"08 1"18 1"19 1"40
31
100.4
44
2-28
limits. From Table 3 it can be seen that there is a deviation only at high mol. wts., whereas at medium and low mol. wts., the two values are close.
CONCLUSIONS The adopted column design for large-scale fractionation permits a good efficiency. It can be inferred that this column design gives good results in spite of the large amount of polymer involved; it is possible to obtain large quantities of fractions, useful to
6
A. MULA and L. CHINELLATO
carry out tests of a technical type (rheological, melt index, D T A , stress-strain, etc.) as a function of molecular weights.
Acknowledgements--Appreciation is expressed to Dr. C. Garbuglio for discussions and for interest in these investigations. Assistance of Mr. M. Solari, Dr. G. Giannotti and Mr. G. Fornari in mol. wt. measurement and characterization of fractions is gratefully acknowledged. REFERENCES (I) (2) (3) (4) (5)
M. J. R. Cantow, R. S. Porter and J. F. Johnson, Nature, Lond. 192, 752 (1961). A. S. Kenyon and I. O. Salyer, J. Polym. Sci. 43, 427 (1960). V. Desreux and I. Bischoff, Bull. So¢. Chim. Belg. 59, 93 (1950). S. N. Chinai, J. D. Matlack, A. L. Resnick and R. J. Samuels, J. Polym. Sci. 17, 391 (1955). G. V. Schulz and A. Dinglinger, Z. phys. Chem. B43, 47 (1939).