Solution Rheology of EthyleneâPropylene Copolymers in

Chapter 16

Solution Rheology of Ethylene—Propylene Copolymers in Hydrocarbon Solvents Isaac D. Rubin and Ashish Sen

1

Downloaded by UNIV OF AUCKLAND on December 26, 2017 | http://pubs.acs.org Publication Date: May 13, 1991 | doi: 10.1021/bk-1991-0462.ch016

Texaco Research Center, P.O. Box 509, Beacon, NY 12508

Dilute solution viscosities were determined for ethylene-propylene copolymers with 60-80 mole % ethylene in a series of hydrocarbon solvents at -10 to 50 C. Highest viscosities were obtained in methyl cyclohexane and lowest in toluene and tetrahydronaphthalene. In poor solvents, the slightly crystalline copolymers with 80 % ethylene had considerably lower intrinsic viscosities at low temperatures than the amorphous ones with 60-70 % ethylene. In better solvents, the two groups behaved identically. The behavior of the partially crystalline copolymers in poor solvents at low temperature is ascribed to ordering of the longer ethylene sequences into partially ordered domains.

Ethylene-propylene copolymers ( E P ) w i t h 60 o r m o r e m o l e % ethylene are widely utilized as viscosity index improvers. VI improvers f i l l a unique need i n our m o t o r i z e d s o c i e t y and are used by almost a l l of us. They are the materials which provide all-season p r o p e r t i e s to motor o i l s ; typically, most of today's o i l s contain 0.5-3.0 % polymer. Addition of polymer to an o i l increases its viscosity. Ideally, t h i s i n c r e a s e s h o u l d be very small a t low t e m p e r a t u r e where the o i l i t s e l f is sufficiently viscous, and become progressively larger as the temperature is raised, resulting in a reasonably

1

Current address: Dow Chemical Company, Midland, MI 48640

0097-6156/91/0462-0273$06.00/0 © 1991 American Chemical Society

Schulz and Glass; Polymers as Rheology Modifiers ACS Symposium Series; American Chemical Society: Washington, DC, 1991.


274

POLYMERS AS R H E O L O G Y MODIFIERS

constant v i s c o s i t y over the entire temperature range encountered in service. This flattening of the v i s c o s i t y - t e m p e r a t u r e c u r v e makes t h e lubricant useful over a wider temperature range and e l i m i n a t e s the need for seasonal o i l changes. Under ideal conditions, at low temperature, interactions between the o i l and VI i m p r o v e r a r e weak; p o l y m e r m o l e c u l e s a r e c o i l e d up and small in size, and i n t e r f e r e l i t t l e with the flow of oil. As the temperature i s r a i s e d , i n t e r a c t i o n improves and t h e polymer expands significantly, resulting in a p p r e c i a b l e o i l t h i c k e n i n g and improved l u b r i c a t i o n . Work i n o u r l a b o r a t o r y on EPs of widely d i f f e r i n g molecular weights and compositions dissolved in oils showed t h a t h i g h e t h y l e n e c o n t e n t and s m a l l amounts of crystallinity led to lower viscosity at low temperatures, e.g. -30 C, than in comparable solutions with t o t a l l y amorphous copolymers and g r e a t e r viscosity at 100 C (1). The purpose of t h i s work is to gain a better understanding of the effect of structure, c o m p o s i t i o n and morphology of EP copolymers used as VI improvers on their viscosity in oils over the temperature range encountered by motor o i l s i n service. With this in mind, we investigated the influence of model hydrocarbon s o l v e n t s , representative of different base o i l components, on the s o l u t i o n v i s c o s i t y o f five EP c o p o l y m e r s i n t h e t e m p e r a t u r e r a n g e o f - 1 0 * C t o 50*C. The model hydrocarbon s o l v e n t s were: hexane, isooctane (2,2,4-trimethylpentane), methyl cyclohexane, toluene and tetralin (tetrahydronaphthalene). The first two represented paraffinie base o i l components; methyl cyclohexane, a naphthenic component; and toluene and tetralin, simple and complex a r o m a t i c components. A l l were p u r c h a s e d m a t e r i a l s o f h i g h p u r i t y and were used as received. The copolymers were p r e p a r e d by conventional means w i t h a s o l u b l e Z i e g l e r - N a t t a c a t a l y s t composed o f an a l k y l a l u m i n u m h a l i d e and a v a n a d i u m s a l t . e

e

COPOLYMER

PROPERTIES

This study was carried out with linear copolymers incorporating from 58 to 80 mole % ethylene. The i n c r e a s e i n e t h y l e n e c o n t e n t s was a c c o m p a n i e d b y a rise in the mean number of ethylene units i n the chain i n sequences o f 3 o r more, N, from 3.9 f o r EP-2 w i t h 58 % ethylene to 6.5 and 6.1 f o r E P - 4 a n d E P - 5 w i t h 80 % ethylene; the f r a c t i o n of ethylene sequences containing 3 or more ethylenes, En>3, r o s e from 0.3 0 t o 0.62 and 0.65. These data are shown in Table I. They were obtained from C-13 NMR r u n s i n o - d i c h l o r o b e n z e n e o n a V a r i a n VXR-300 s p e c t r o m e t e r u s i n g the method o f Randall (2) and Johnston et al (3). T a b l e I a l s o g i v e s IR r e s u l t s o b t a i n e d on f i l m s p r e s s e d from the copolymers (4). T h e y a r e c o n s i s t e n t w i t h t h e NMR r e s u l t s , showing an i n c r e a s e i n t h e CH2/CH3 r a t i o from 2.0 t o 7 . 5 - 7 . 8 as


16.

Solution Rheology of Ethylene-Propylene Copolymers

RUBIN & SEN

t h e e t h y l e n e c o n c e n t r a t i o n i n t h e EPs c h a n g e d f r o m 58 t o 80 m o l e %. W e i g h t a v e r a g e m o l e c u l a r w e i g h t s , Mw, and m o l e c u l a r weight distributions, Mw/Mn, f o r t h e copolymers are g i v e n below. EP

Copolymer

Mw X 10" Mw/Hn

3

EP-1

EP-2

EP-3

EP-4

EP-5

148 2.9

252 3.5

192 3.4

207 3.6

322 4.1

All results were obtained by gel permeation c h r o m a t o g r a p h y (GPC) i n 1 , 2 , 4 - t r i c h l o r o b e n z e n e a t 1 3 5 C utilizing a Waters 150 C GPC u n i t e q u i p p e d w i t h f i v e columns ( 1 x 1 0 , 1χ10 , 1x10* , 1χ10 ^ and 500 À) . E i g h t e e n p o l y s t y r e n e s a m p l e s r a n g i n g i n Mw f r o m 3,000 t o 3,300,000 were u s e d f o r c a l i b r a t i n g t h e e q u i p m e n t . Melting points, c r y s t a l l i n i t i e s and s e c o n d order transitions were obtained using d i f f e r e n t i a l scanning calorimetry (DSC). Samples EP-1 through EP-3 were c o m p l e t e l y amorphous w h i l e EP-4 and EP-5 c o n t a i n e d a b o u t 5-9 % c r y s t a l l i n e m a t e r i a l . The d a t a were o b t a i n e d on a Perkin E l m e r DSC-7 D i f f e r e n t i a l S c a n n i n g C a l o r i m e t e r a t a h e a t i n g r a t e of 10 C/min. calibrated as recommended by the manufacturer. C r y s t a l l i n i t y was a l s o d e t e r m i n e d f r o m w i d e - a n g l e x - r a y s c a t t e r i n g m e a s u r e m e n t s (WAXS) on a Scintag Pad V d i f f r a c t i o n system. As shown b e l o w , considering the difficulty of measuring such small amounts of crystallinity, agreement between t h e two methods was q u i t e g o o d .


e

e

e

β

Β

e

EP

Copolymers #

T g , C , DSC Tm, *C, DSC Crystallinity, Crystallinity,

RELATIVE AND

%, DSC %, x - r a y

EP-1

EP-2

EP-3

EP-4

EP-5

-68

-59

-63

—

—

—

0 —

0 —

0 —

-50 43 9.3 8.4

-46 42 7.4 5.2

SPECIFIC VISCOSITIES

All viscosity measurements were made in Ubbelohde viscometers i n a bath c o n t r o l l e d t o w i t h i n ±0.01*C on solutions with concentration of 0.4 to 1.0 gm/dl, d e p e n d i n g on c o p o l y m e r m o l e c u l a r w e i g h t . Since solvent flow times were at least 100 sec. and intrinsic v i s c o s i t i e s o f most s a m p l e s were l e s s t h a n 3.00 dl/gm, no c o r r e c t i o n s were made f o r k i n e t i c e n e r g y o r r a t e o f shear (5,6). D e n s i t i e s of the solvents at the d i f f e r e n t temperatures were measured w i t h a M e t t l e r / P a a r DMA 45 D i g i t a l D e n s i t y M e t e r and c o p o l y m e r c o n c e n t r a t i o n s were corrected f o r the change of solvent density with temperature.


275


276


The r e l a t i v e v i s c o s i t y o f a polymer s o l u t i o n i s its kinematic viscosity d i v i d e d by t h a t of the s o l v e n t ; at any t e m p e r a t u r e , the r e l a t i v e v i s c o s i t i e s o f a polymer in a series o f s o l v e n t s t h u s p r o v i d e a r e a d y means o f r a n k i n g t h e i r s o l v a t i n g power. Figure 1 compares the relative viscosities of EP-5, one of the p a r t i a l l y c r y s t a l l i n e samples, in a l l f i v e s o l v e n t s at 20*C. As can be seen, methyl cyclohexane gave the highest v i s c o s i t y and t e t r a l i n , the lowest. Methyl cyclohexane was t h u s t h e r m o d y n a m i c a l l y t h e b e s t s o l v e n t , f o l l o w e d by hexane and isooctane, while toluene and tetralin were poorest. Results at other temperatures and f o r other copolymers were analogous. Specific viscosity i s o b t a i n e d by s u b t r a c t i n g the kinematic viscosity of the solvent from t h a t o f the solution and dividing the result by the kinematic viscosity of the solvent. It thus shows at any temperature the solution thickening a t t r i b u t a b l e to the solute. Specific viscosities of a l l copolymers as a function of polymer concentrations i n methyl cyclohexane and toluene at -10*C are given in F i g u r e s 2 and 3, respectively. In methyl cyclohexane, the samples were arranged in the expected o r d e r and t h e i r viscosities i n c r e a s e d w i t h m o l e c u l a r weight and concentration. In toluene, however, as d e p i c t e d i n F i g u r e 3, t h e situation was appreciably different. The viscosities of the partially crystalline EP-4 and EP-5 were lower than t h o s e o f t h e c o m p l e t e l y amorphous E P - 1 to EP-3. This occured in s p i t e of the fact that EP-5 had the highest m o l e c u l a r weight and the m o l e c u l a r weight of EP-4 was h i g h e r than those of EP-1 and E P - 3 . The b e h a v i o r i n the o t h e r t h r e e s o l v e n t s a t - 1 0 * C was s i m i l a r ; i n a l l cases the specific viscosities of EP-4 and E P - 5 were lower than expected on the basis of concentration and molecular weight. At 20* C and above, the specific v i s c o s i t i e s i n a l l f i v e s o l v e n t s were arranged in the same o r d e r a s i n F i g u r e 2. These data demonstrate that i n poor solvents, as temperature is lowered, parameters r e l a t e d to copolymer c o m p o s i t i o n and s t r u c t u r e such as e t h y l e n e c o n t e n t , size and number o f e t h y l e n e s e q u e n c e s , and c r y s t a l l i n i t y can have more i n f l u e n c e on s o l u t i o n v i s c o s i t y t h a n m o l e c u l a r weight.

INTRINSIC VISCOSITIES The concentration r e p r e s e n t e d by the η,ρ/

c

=

[η]

dependence of viscosity following equation (6):

+ K l [ n f c

3

z

+ K2[n] c +

can

be

(1)

where n is specific viscosity; n ^ c , reduced viscosity; [n], intrinsic viscosity; and c, polymer concentration. Without the t h i r d and h i g h e r terms, t h i s i s the familiar t f


16.


RUBIN & SEN

TABLE I .

EP copolymer

Molecular c h a r a c t e r i s t i c s o f ethylene-propylene copolymers

En>3

Ν

Ethylene ( m o l e %)

(CH2) (CH3)

(NMR)


(FTIR)

EP-1

60

4.2

0.35

2.0

EP-2

58

3.9

0.30

2.1

EP-3

70

4.8

0.56

5.1

EP-4

80

6.5

0.62

7.8

EP-5

80

6.1

0.65

7.5

3.50-

3.00-

Tetralin

È 82.50-)

•Q Toluene

to

>

Isooctane

>

• Hexane

Ε 2.00-j

d

-X- Methyl Cyclohexane 1.50H

1.00—τ .050

1 .100

,

,

,

,

,

,

1

.150 .200 .250 .300 .350 .400 .450 CONCENTRATION OF EP-5 (gm/100 ml)

1

,

.500

.550

Figure 1. Relative viscosities of EP-5 in different solvents at 20 ° C.


277



278

Figure 2. Specific viscosities in methyl cyclohexane at -10 ° C.

1.20-,



16.

RUBIN & SEN


Huggins equation (7), and the d i m e n s i o n l e s s parameter K l is the Huggins constant. I n t r i n s i c v i s c o s i t i e s were o b t a i n e d from t h i s equation by e x t r a p o l a t i o n of p l o t s of η,ρ/c vs. c to i n f i n i t e d i l u t i o n while Huggins constants were c a l c u l a t e d from the s l o p e s o f the plots. Figure 4 shows the temperature dependence of intrinsic viscosities in methyl cyclohexane. For a l l cases, intrinsic viscosities decreased modestly as the temperature r o s e ; t h e b i g g e s t d e c r e a s e i n [ η ] , a b o u t 20 %, was obtained for EP-5. This indicates some deterioration in polymer-solvent interaction and solubility with increasing temperature. Analogous curves for toluene are plotted in Figure 5. The i n t r i n s i c v i s c o s i t i e s f o r the amorphous samples changed only modestly with temperature, f i r s t i n c r e a s i n g as the temperature rose from -10*C t o 20*C, and then remaining reasonably constant or d e c r e a s i n g s l i g h t l y as i t rose f u r t h e r t o 5 0 * C . T h i s was n o t t h e c a s e f o r t h e p a r t i a l l y crystalline samples EP-4 and E P - 5 . For these samples, [n] i n c r e a s e d b y o v e r 500 % b e t w e e n -10*C and 10*C, after which i t i n c r e a s e d much more m o d e r a t e l y when t h e s o l u t i o n s were warmed f u r t h e r t o 50* C . Such a rapid rise in [n] with t e m p e r a t u r e has been a s c r i b e d t o an endothermal heat of m i x i n g and i n c r e a s i n g s o l v e n t power with r i s i n g temperature (6,8,9). Plots of the r a t i o of i n t r i n s i c v i s c o s i t i e s for the copolymers i n methyl cyclohexane and toluene at the two extreme temperatures, -10*C and 50*C, a g a i n s t mole % e t h y l e n e a r e shown i n F i g u r e 6. T h i s r a t i o e x c e e d e d one for a l l copolymers i n methyl cyclohexane, indicating a d e c r e a s e i n [n] w i t h temperature but was essentially independent of molecular weight and composition. It was less than one in toluene, showing the improved polymer-solvent interaction as the temperature was r a i s e d and decreased enormously f o r the two copolymers with 80 mole % ethylene and small amounts of crystallinity. I n t r i n s i c v i s c o s i t i e s and Huggins c o n s t a n t s between -10* C and 50* C f o r EP-1, E P - 2 , and EP-5 i n hexane, i s o o c t a n e and tetralin are summarized i n T a b l e s I I - I V . In t e t r a l i n , i n t r i n s i c v i s c o s i t i e s f o r EP-1 and EP-2 d i d not change s i g n i f i c a n t l y w i t h temperature. However, the viscosity for E P - 5 i n c r e a s e d b y 200% b e t w e e n - 1 0 * C a n d 20*C and r e m a i n e d e s s e n t i a l l y c o n s t a n t between 20*C and 50*C. T e t r a l i n t h u s e x h i b i t e d t h e same g e n e r a l features as t o l u e n e , b e h a v i n g as a poor solvent for partially crystalline E P c o p o l y m e r s b e l o w 20" C a n d a satisfactory one for the amorphous samples. The viscositytemperature relationships for EP-1 and EP-2 i n hexane and isooctane were essentially similar to those d i s c u s s e d above f o r t o l u e n e and t e t r a l i n . For instance, f o r E P - 1 a n d E P - 2 , [n] v a l u e s i n h e x a n e decreased from 1.05 and 1.70 d l / g m a t -10 C t o 0.74 and 1.25 dl/gm at 50*C. T h e c o r r e s p o n d i n g [n] d e c r e a s e s i n i s o o c t a n e w e r e


279

280


4.003.50&3.00H

X EP--1

S ^2.50H "K

•O EP--2

12.00-1

•

- * EP--3


ο ο

ο "S

EP--4

+ EP--5

|I.5OH

x-

χ

χ

40

50

i.ocH 0.50—ι -20 -10

1

0

1 1 r10 20 30 Temperature (%)

ι 60

Figure 4. Intrinsic viscosities in methyl cyclohexane.

2.50-,

2.00E Χ ΕΡ--1 1.50H

•Ο ΕΡ--2

m

- * ΕΡ--3

δ

•

1.00-

ΕΡ--4

+ ΕΡ--5

c s c 0.50H

0.00—ι -20 -10

1

0

1

1

1

10 20 30 Temperature (°C)

1

40

1

50

1

60

Figure 5. Intrinsic viscosities in toluene.


16.


RUBIN & SEN

1.40-1

1.20-

σ

1.00-

8 ·*· Methyl Cyclohexane


~0.80-

• Toluene

g0.60JL §0.400.2050

V 1

1

1

1

1

1

1

1

55

60

65

70

75

80

85

90

Ethylene Content (mole X)

0.00-

Figure 6. Ratio of intrinsic viscosities at two extreme temperatures, -10 and 50 °C.

TABLE I I .

I n t r i n s i c v i s c o s i t i e s , [η], and Huggins constants, K l , o f E P - 1 , EP-2 and EP-5 i n hexane

(°C)

[n] (dl/gm)

EP-5

EP-2

EP-1 Kl

[n] (dl/gm)

Kl

[n] (dl/gm)

Kl

•10

1.05

0.52

1.70

1.54

1.20

5.12

0

1.05

0.53

1.65

1.52

2.20

4.85

10

0.90

0.56

1.55

1.54

2.30

4.53

20

0.93

0.63

1.50

1.55

2.20

4.32

30

0.75

0.69

1.35

1.60

2.10

4.26

40

0.73

0.65

1.30

1.67

2.05

4.30

50

0.74

0.62

1.25

1.66

2.00

4.28


281

282


TABLE I I I *

I n t r i n s i c v i s c o s i t i e s , [η], and Huggins constants, K l , o f EP-1, EP-2, and EP-5 i n isooctane

EP-1


Temperature (°C)

[n] (dl/gm)

EP-2 Kl

[n] (dl/gm)

EP-5 Kl

[n] (dl/gm)

Kl

-10

1.10

0.62

1.70

0.83

0.45

3.06

0

0.98

0.64

1.60

0.82

1.10

3.10

10

0.95

0.67

1.50

1.33

1.85

2.67

20

0.95

0.67

1.50

1.37

1.90

2.64

30

0.90

1.02

1.40

1.56

1.80

2.47

40

0.85

1.04

1.35

1.86

1.80

2.82

50

0.80

1.02

1.30

1.82

1.75

2.84

TABLE IV. I n t r i n s i c v i s c o s i t i e s , [η], and Huggins constants, K l , o f EP-1, EP-2, and EP-5 in tetralin

EP-1 Temperature (°C)

[n] (dl/gm)

EP-2 K l

[n] (dl/gm)

EP-5 K l

[n] (dl/gm)

K l

-10

0.90

0.35

1.10

1.33

0.70

2.55

0

0.95

0.32

1.10

1.17

1.15

2.67

10

1.00

0.38

1.15

1.25

1.90

1.50

20

0.95

0.38

1.15

1.33

2.10

1.58

30

1.00

0.42

1.15

1.38

2.10

1.60

40

1.00

0.50

1.15

1.35

2.05

1.63

50

0.95

0.46

1.10

1.34

2.05

1.62


16.

Solution Rheology of Ethylene—Propylene Copolymers

RUBIN & SEN

e

from 1.10 and 1.70 d l / g m a t - 1 0 C t o 0.80 and 1.30 dl/gm at 50 C. Intrinsic viscosity changes of EP-5 were likewise similar to those i n toluene and t e t r a l i n . In h e x a n e , t h e v a l u e i n c r e a s e d r a p i d l y between -10 and 10*C from 1.20 dl/gm to 2.30 dl/gm and then decreased s l o w l y t o 2.00 d l / g m as the temperature r o s e to 50*C. In isooctane, i t i n c r e a s e d from 0.45 d l / g m a t -10*C t o 1.90 d l / g m a t 20*C and t h e n g r a d u a l l y f e l l o f f to 1.75 dl/gm at 50 C. Hexane and i s o o c t a n e thus a l s o behaved as poor s o l v e n t s f o r EP-5 below 10-20*C. e


e

HUGGINS

CONSTANTS

Huggins constants, K l , for a l l copolymers i n methyl cyclohexane and toluene are p l o t t e d as a f u n c t i o n o f t e m p e r a t u r e i n F i g u r e s 7 and 8. In methyl cyclohexane, a l l K l values increased with temperature. In toluene, a much p o o r e r s o l v e n t , they passed through a minimum and then rose. A s e x p e c t e d f r o m t h e [n] v a l u e s , results for E P - 5 showed t h e g r e a t e s t c h a n g e ; K l d e c r e a s e d from 2.94 at - 1 0 * C t o 2.35 a t 20*C and then i n c r e a s e d t o 2.58 at 50*C. The K l v a l u e s i n the other solvents, shown in Tables II-IV, exhibited similar trends with respect to their intrinsic viscosities. In general, the trend for the K l values was i n t h e o p p o s i t e d i r e c t i o n f r o m t h a t observed for i n t r i n s i c v i s c o s i t i e s , as has been r e p o r t e d in the l i t e r a t u r e (9,10).

INTERPRETATION OF RESULTS In considering the results discussed above, it is necessary to take into account both the solvents and copolymers. I t i s c l e a r t h a t m e t h y l c y c l o h e x a n e was the best solvent as it gave the highest relative and intrinsic viscosities for a l l copolymers. Intrinsic viscosities i n methyl cyclohexane decreased with rising temperature, indicating that heats of mixing were negative over the entire temperature range. Since [n] decreased, copolymer-solvent i n t e r a c t i o n d i m i n i s h e d as temperature rose and, therefore, the EPs contributed less to solution viscosity at elevated temperatures, just the opposite of what is required for good VI improvers. Intrinsic viscosity-temperature data i n the other s o l v e n t s showed t h a t t h e y were good solvents for the amorphous copolymers, EP-1, EP-2 and E P - 3 , though not q u i t e as good as methyl c y c l o h e x a n e . F i g u r e 5, w h i c h is typical for these solvents, showed that [n] either increased slightly or did not change much with temperature. However, below 10-20*C t h e s e s o l v e n t s had v a s t l y r e d u c e d s o l v a t i n g power f o r the two copolymers


283

284


•X EP--1 -O EP--2 Downloaded by UNIV OF AUCKLAND on December 26, 2017 | http://pubs.acs.org Publication Date: May 13, 1991 | doi: 10.1021/bk-1991-0462.ch016

- * EP--3 •

•O-

-•

-20

χ

X

-*

*

*

X

X·

"

X· "

"

1

1

1

1

-10

1

0


*

"*

χ

x

1

40

1

50

EP--4

-+-EP--5

1

60

Figure 7. Huggins constants in methyl cyclohexane.

•XEP--1 •O EP--2 - * EP--3 •

EP--4

+ EP--5

-20

1

-10

1

0

1

1

1


1

40

1

50

1

60

Figure 8. Huggins constants in toluene.



16.

RUBIN & SEN


with high ethylene content and small amount of crystallinity. Our data showed that the naphthenic structure favored solubility and solvent-polymer i n t e r a c t i o n i n comparison with p a r a f f i n i e solvents and that the copolymers were least soluble in aromatics. T h e d i s t i n c t i o n b e t w e e n g o o d a n d p o o r s o l v e n t s was most pronounced for the p a r t i a l l y c r y s t a l l i n e copolymers EP-4 and E P - 5 a t low t e m p e r a t u r e . The e f f e c t o f the EP s t r u c t u r e on s o l u b i l i t y can be seen most c l e a r l y by comparing the behavior of the copolymers with 58-70 mole % ethylene to those w i t h 80%, particularly a t low temperatures. In the poorer solvents, the i n t r i n s i c viscosities of the two partially crystalline copolymers decreased rapidly as the temperature was lowered below about 10* C . No s u c h decrease was o b s e r v e d for the three amorphous copolymers. T h e s m a l l [n] v a l u e s f o r E P - 4 a n d EP-5 at low temperatures in a l l solvents except methyl cyclohexane can be understood by examining the differences in structure between the two sets of copolymers. A s shown i n T a b l e I , E P - 4 a n d EP-5 had a larger fraction of longer ethylene sequences than the t h r e e t o t a l l y amorphous c o p o l y m e r s , and i t i s presumably these longer ethylene sequences which formed the crystallites i n the bulk copolymer. We b e l i e v e t h a t at low temperature in reasonably poor solvents these ethylene sequences can organize into partially ordered domains o r aggregates which are h e l d i n s o l u t i o n by the more soluble mixed ethylene-propylene sequences and shorter ethylene and propylene segments i n c a p a b l e of crystallizing. T h i s p i c t u r e i s s i m i l a r t o one proposed some time ago by F i l i a t r a u l t and Delmas (11). These p a r t i a l l y o r d e r e d domains would l e a d to contraction of the copolymer in solution and some reduction in viscosity. In a d d i t i o n , they could also give solutions with fewer c h a i n entanglements and i n c r e a s e d copolymer mobility, leading to further viscosity decrease (12). It is thus c l e a r from t h i s study t h a t the presence of a high amount of ethylene ( 8 0 m o l e %) and l o n g e r ethylene sequences i n EP copolymers can significantly lower the solution viscosity of EP copolymers in relatively poor solvents at temperatures below 20"C. Dilute solution viscosities o f amorphous EP copolymers show relatively l i t t l e variation with temperature under s i m i l a r conditions.

REFERENCES 1. 2. 3.

Kapuscinski, M. M.; Sen, Α.; Rubin, I. D. SAE Pub. No. 892152, 1989. Randall, J . C. Polymer Sequence Determination. C-13 NMR Method, Academic Press, New York, 1977. Johnston, J . E . ; Bloch, R.; Ver Strate, G. W.; Song, W. R. US Patent 4,507,515, 1985.


285

286



4.

Ham, G. E. High Polymers, Interscience, New York, 1964. 5. Fox, T. G., J r . ; Fox, J. C . ; Flory, P. J. J. Amer. Chem. Society. 73, 1901, 1951. 6. Bohdanecky, M.; Kovar, J. Viscosity of Polymer Solutions, Elsevier Publishing, New York, 1982. 7. Huggins, M. L. J. Am. Chem. Soc. 64, 2716, 1942. 8. Maderek, E . ; Wolf, B. A. Angew. Makromol. Chemie, 161, 157, 1988. 9. Schott, N.; Will, B.; Wolf, B. A. Makromol. Chem., 189, 2067, 1988. 10. Schmidt, J. R.; Wolf, B. A. Macromolecules, 15, 1192, 1982. 11. Filiatrault, D.; Delmas, G. Macromolecules, 12, 65, 69, 1979. 12. Rubin, I. D.; Stipanovic , A. J.; Sen, Α., presented at 1990 meeting of Society of Tribologists and Lubrication Engineers (STLE), Denver, May 1990. Received July 18, 1990


Solution Rheology of EthyleneâPropylene Copolymers in

Recommend Documents

Solution Rheology of EthyleneâPropylene Copolymers in