Polymers as Lubricating-Oil Viscosity Modifiers - American Chemical

Chapter 15

Polymers as Lubricating-Oil Viscosity Modifiers

Downloaded by NORTH CAROLINA STATE UNIV on August 6, 2012 | http://pubs.acs.org Publication Date: May 13, 1991 | doi: 10.1021/bk-1991-0462.ch015

G. Ver Strate and M.

J . Struglinski

Polymers Group and Paramins Technology Division, Exxon Chemical Company, Linden, NJ 07036

The basic principles of "viscosity modification" of lubricating oils by high molecular weight polymers is discussed. The Newtonian viscosity-temperature characteristics of the oil are not strongly affected by the polymer. The use of polymers simply permits low viscosity basestocks with good temperature charac teristics to be employed. A variety of polymer types are used commercially, each having a different balance in cost-performance characteristics. A semiquantitative discussion of the polymer solution physics is presented which explains the general per formance of the different polymer types as a function of temperature and strain rate. Certain details of non-Newtonian behavior at low temperature are not completely understood. It i s economically and t e c h n i c a l l y u s e f u l t o employ p o l y m e r c o n t a i n i n g " m i n e r a l " o i l s as l u b r i c a t i n g f l u i d s f o r i n t e r n a l combustion engines. T h e r e a r e many i n t e r e s t i n g s c i e n t i f i c i s s u e s t o be u n d e r s t o o d i n t h e p e r f o r m a n c e o f s u c h f l u i d s as l u b r i c a n t s . The " o r i g i n a l " technology which employed simple o i l s o l u b l e polymers such a s p o l y i s o b u t y l e n e , to create f l u i d s with d e s i r a b l e v i s c o s i t y and viscosity-temperature c h a r a c t e r i s t i c s , has m a t u r e d t o see block, long chain branched, narrow molecular weight d i s t r i b u t i o n and i n t r a m o l e c u l a r l y t a p e r e d c o m p o s i t i o n m a t e r i a l s y i e l d s p e c i f i c tailored properties. The c o n t r i b u t i o n o f v i s c o e l a s t i c e f f e c t s t o t h e b a l a n c e o f f u e l economy and wear i s n o t y e t c o m p l e t e l y r e solved. Some p o l y m e r s a l s o c o n t a i n p o l a r f u n c t i o n a l g r o u p s so t h a t t h e y can a c t as d i s p e r s a n t s f o r s l u d g e e t c . as w e l l as " v i s c o s i t y modifiers."

0097-6156/91/O462-O256$06.00/0 © 1991 American Chemical Society

In Polymers as Rheology Modifiers; Schulz, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1991.

15.

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STRATE & S T R U G U N S K I

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The b a s i s f o r t h i s t e c h n o l o g y has been r e v i e w e d t o v a r y i n g d e g r e e s i n a number o f a r t i c l e s ( 1 - 1 3 ) . T h e s e r e f e r e n c e s p r o v i d e a s a m p l i n g o f t h e t e c h n o l o g y as i t e x i s t s t o d a y . In c e r t a i n i n s t a n c e s t h e r e a p p e a r s t o be some m i s c o n c e p t i o n as t o what i s g o i n g on. We p r e s e n t a b r i e f r e v i e w o f what we p e r c e i v e t o be t h e facts. Multigrade O i l Formulation. Petroleum r e f i n e r i e s produce a range o f h y d r o c a r b o n " c u t s " f o r use as l u b e o i l b a s e s t o c k s , w h i c h c o n t a i n m o l e c u l e s r a n g i n g i n m o l e c u l a r w e i g h t f r o m a few h u n d r e d t o a few thousand. T h e s e h y d r o c a r b o n f l u i d s a c t as u s e f u l l u b r i c a n t s v i a a hydrodynamic mechanism, a l t h o u g h i n t y p i c a l g a s o l i n e o r d i e s e l f i r e d e n g i n e s some b o u n d a r y l u b r i c a t i o n a l s o o c c u r s . I t s h o u l d be n o t e d t h a t m i n e r a l and s y n t h e t i c b a s e s t o c k s a r e N e w t o n i a n l i q u i d s above t h e i r c l o u d p o i n t , v i s c o s i t y i s i n d e p e n d e n t o f s h e a r s t r e s s . The g l a s s t r a n s i t i o n t e m p e r a t u r e o f t h e s e o i l s i s i n t h e -70°C + 30°C r a n g e and t h e y e x h i b i t a v e r y s i g n i f i c a n t v i s c o s i t y c h a n g e i n t h e t e m p e r a t u r e r a n g e f r o m -40°C t o 170°C where t y p i c a l g a s o l i n e engines operate. A m i n e r a l o i l w h i c h has h i g h enough m o l e c u l a r w e i g h t t o have a d e q u a t e v i s c o s i t y a t h i g h t e m p e r a t u r e , e . g . 2.5-5.0 cP a t 150°C, w i l l have t o o h i g h a v i s c o s i t y , >30,000 cP, a t -25°C. T h i s i s an o r d e r o f m a g n i t u d e t o o h i g h t o p e r m i t e n g i n e c r a n k i n g w i t h b a t t e r i e s and s t a r t e r m o t o r s t y p i c a l l y f o u n d i n t o d a y ' s engines. Some m i n e r a l o i l b a s e s t o c k s have b e t t e r v i s c o s i t y t e m p e r a t u r e c h a r a c t e r i s t i c s t h a n o t h e r s , and s y n t h e t i c b a s e s t o c k s ( u s u a l l y m i x t u r e s o f p o l y a l p h a o l e f i n s and d i - o r t r i e s t e r s o f a d i c a r b o x y l i c a c i d and a p o l y a l k y l e n e g l y c o l ) a r e p a r t i c u l a r l y g o o d , b u t e x p e n s i v e t o make. A l l n a t u r a l p a r a f f i n i c b a s e s t o c k s u s e d as c r a n k c a s e l u b r i c a n t s have m e t h y l e n e s e q u e n c e - b a s e d waxes i n them ( l i n e a r and 2-methyl a l k a n e s h a v i n g c a r b o n numbers between 18 and 3 0 ) , w h i c h can a l s o i n c r e a s e low s t r e s s v i s c o s i t y a t low t e m p e r a t u r e s i f a n i s o t r o p i c wax c r y s t a l s f o r m . The l o w e r m o l e c u l a r w e i g h t b a s e s t o c k s ( e . g . SAE 5W v s . SAE 30) g e n e r a l l y have a l e s s s t e e p t e m p e r a t u r e d e p e n d e n c e o f v i s c o s i t y . T h i s i s b a s i c a l l y a f r e e volume e f f e c t , w i t h T d e c r e a s i n g as m o l e c u l a r w e i g h t d e c r e a s e s , s i n c e t h e y have s i m i l a r c o m p o s i t i o n s apart from m o l e c u l a r weight. As c a n be s e e n i n F i g u r e 1, t h e d i f f e r e n c e between an SAE 5W and an SAE 30 o i l a t 100°C i s a b o u t a f a c t o r o f 2.5 i n v i s c o s i t y , w h e r e a s a t 10°C i t i s a b o u t a f a c t o r o f 10. I f t h e SAE 5W b a s e s t o c k i s t h i c k e n e d w i t h enough p o l y m e r ( i n t h i s c a s e , a random e t h e n e - p r o p e n e c o p o l y m e r ) t o g i v e i t t h e same 100°C v i s c o s i t y as t h e SAE 30 o i l , i t g e n e r a l l y m a i n t a i n s t h e v i s c o s i t y - t e m p e r a t u r e s l o p e o f t h e SAE 5W o i l ( F i g u r e 1 ) . T h i s i s r e f e r r e d t o as a " m u l t i g r a d e " o i l , and g i v e n t h e d e s i g n a t i o n SAE 5W-30, f o r r e a s o n s t o be d i s c u s s e d b e l o w . P o l y m e r i s added t o a c o n c e n t r a t i o n , c, s u c h t h a t ο[η] i s a b o u t 1, c o r r e s p o n d i n g t o t h e r e g i o n where t h e p o l y m e r c o i l s b e g i n t o o v e r l a p as t h e s o l u t i o n moves w i t h i n c r e a s i n g c o n c e n t r a t i o n f r o m t h e d i l u t e t o t h e s e m i d i l u t e regime. The i n t r i n s i c v i s c o s i t y [η] i s 0.5 t o 2 d l / g m f o r p o l y m e r s u s e d as VM's so t h e p o l y m e r i s p r e s e n t a t a b o u t 0.5 t o 2 w e i g h t %. T h i s p o l y m e r c o n c e n t r a t i o n has o n l y a s m a l l e f f e c t on t h e o v e r a l l ry-T r e l a t i o n , u n l e s s some s t r o n g a s s o c i a t i o n o r phase change behavior o c c u r s . The Newtonian v i s c o s i t y o f t h e SAE 5W-30 o i l i s f o u r t i m e s l o w e r t h a n t h a t o f t h e SAE 30 a t 10°C, and t h e g



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POLYMERS AS R H E O L O G Y MODIFIERS

m a r g i n grows f u r t h e r a s t h e t e m p e r a t u r e i s l o w e r e d . T h i s i s why any o i l s o l u b l e p o l y m e r t h a t u n d e r g o e s n o u n u s u a l " p h a s e " c h a n g e b e h a v i o r c a n be a s o - c a l l e d " v i s c o s i t y m o d i f i e r . " We d o n o t show d a t a h e r e below a b o u t 10°C, b e c a u s e o f c o m p l i c a t i o n s due t o wax c r y s t a l l i z a t i o n at lower temperatures. T h i s a l s o does n o t t a k e i n t o account the non-Newtonian shear t h i n n i n g t h a t occurs a t high shear s t r e s s e s f o r the polymerc o n t a i n i n g o i l , r e s u l t i n g i n s t i l l lower v i s c o s i t i e s . I t t u r n s out t h a t a t h i g h s h e a r s t r e s s , t h e SAE 5W-30 o i l d e s c r i b e d above has t h e same v i s c o s i t y a t -25°C as a N e w t o n i a n SAE 5W o i l . T h u s , m u l t i g r a d e o i l s c a n be p r o d u c e d u s i n g v i s c o s i t y m o d i f i e r s , due t o a more f a v o r a b l e v i s c o s i t y - t e m p e r a t u r e r e l a t i o n s h i p from t h e u s e o f a l o w e r m o l e c u l a r w e i g h t m i n e r a l o i l , and s h e a r t h i n n i n g o f t h e p o l y mer a t h i g h s h e a r r a t e s . There a r e important p e r t u r b a t i o n s around t h i s b a s i c p r i n c i p l e . I f t h e r e i s polymer c o i l expansion or c o n t r a c t i o n with temperature due t o ( 1 ) r o t a t i o n a l i s o m e r i c b a c k b o n e e f f e c t s , (2) e x c l u d e d v o l u m e e f f e c t s , ( 3 ) m i c e l l i z a t i o n , ( 4 ) c r y s t a l l i z a t i o n , o r some o t h e r phenomenon, t h e v i s c o s i t y t e m p e r a t u r e c h a r a c t e r i s t i c s w i l l be f u r t h e r m o d i f i e d . G e n e r a l l y t h e s e e f f e c t s are s m a l l , on the o r d e r o f f a c t o r s o f 2, compared t o f a c t o r s o f >10 c h a n g e s due t o d i f f e r e n c e s i n b a s e s t o c k t y p e , o v e r t h e same t e m p e r a t u r e r a n g e . F a c t o r s o f 2 a r e n o t t o be s c o f f e d a t , h o w e v e r . I f one i s t r y i n g t o meet a low t e m p e r a t u r e o i l v i s c o s i t y s p e c i f i c a t i o n ( e . g . , SAE J 3 0 0 ( 1 4 ) ) o f 30,000 cP max a t -25°C, t h e r e i s a b i g d i f f e r e n c e between 35,000 and 17,500 c P . ( T h i s i s r e l a t e d t o o i l p u m p a b i l i t y as m e a s u r e d b y t h e MRV and TP-1 m i n i - r o t a r y v i s c o m e t e r ) ( 1 5 ) . Viscosity Modifier Characteristics. A s F l o r y s a i d l o n g ago ( 1 6 ) , i n c a s e s where s o l v e n t c h a r a c t e r i s n o t c h a n g i n g g r e a t l y w i t h temperature, as i s typical with lube o i l s , d^rel/dT i s c o n t r o l l e d m o s t l y b y d/dT, where rjrel i s t h e r a t i o o f t h e p o l y m e r s o l u t i o n v i s c o s i t y t o t h e b a s e o i l v i s c o s i t y and i s t h e mean square r a d i u s o f g y r a t i o n o f the polymer. There are c u r r e n t l y f i v e polymer types used as commercial viscosity modifiers: p o l y ( e t h e n e - c o - p r o p e n e ) , p o l y a l k y l m e t h a c r y l a t e s (where t h e a l k y l e s t e r s a r e t y p i c a l l y made f r o m C g t o C a l c o h o l s ) , h y d r o g e n ated p o l y ( i s o p r e n e - b - s t y r e n e ) , hydrogenated p o l y ( s t y r e n e - b - ( b u t a diene-r-styrene)), and hydrogenated p o l y i s o p r e n e " s t a r s " . Of these, o n l y t h e m e t h a c r y l a t e s have p o s i t i v e d/dT. Coil d i m e n s i o n s o f t h e o t h e r p o l y m e r b a c k b o n e s a c t u a l l y s h r i n k as Τ i n c r e a s e s ( 1 7 - 1 9 ) , a s shown i n F i g u r e 2. On t h i s b a s i s , t h e a l k y l methacrylates s h o u l d be t h e b e s t p o l y m e r s f o r o b t a i n i n g l o w v i s c o s i t y a t low temperature. N o t i c e t h a t t h e change i n c o i l dimensions i s on the o r d e r o f 50-70% o v e r t h i s temperature range, compared t o more t h a n a n o r d e r o f m a g n i t u d e c h a n g e i n v i s c o s i t y o f an SAE 5W m i n e r a l o i l ( F i g u r e 1 ) . But t h e r e a r e o t h e r p e r f o r m a n c e a n d c o s t c r i t e r i a . S i n c e p o l y m e r s c o s t more t h a n o i l , o n e w o u l d l i k e t o use as l i t t l e polymer as p o s s i b l e . T h i c k e n i n g power i n c r e a s e s w i t h i n c r e a s i n g m o l e c u l a r w e i g h t , and t h e r e f o r e h i g h m o l e c u l a r w e i g h t s y s t e m s w o u l d be p r e f e r r e d . When t h e m o l e c u l e s g e t l o n g enough t h e y c a n b e m e c h a n i c a l l y b r o k e n by t h e s t r e s s e s i n a n e n g i n e ( w h i c h c a n be a t z

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l e a s t on t h e o r d e r o f (10' s e c " ) ( . 0 3 p o i s e ) = 3 x l O dynes/ crrr shear s t r e s s , i n flows t h a t c a n a l s o i n c l u d e complex s q u e e z i n g o r e x t e n s i o n a l c o m p o n e n t s ) . Two b a s i c s h e a r s t a b i l i t y g r a d e s a r e s o l d w i t h e i t h e r 2 0 % o r 10% maximum v i s c o s i t y l o s s i n a b e n c h t e s t ( t h e " K u r t O r b a h n " d i e s e l f u e l i n j e c t o r ) ( 2 0 ) . In t h i s t e s t , a formulated o i l i s c i r c u l a t e d repeatedly through a d i e s e l f u e l i n j e c t o r , f o r a t o t a l o f 30 p a s s e s . The p o l y m e r m o l e c u l e s u n d e r g o some c o m p l i c a t e d e x t e n s i o n a l f l o w t h e s o l u t i o n e n t e r s a n o z z l e a n d upon e x i t a s o i l d r o p l e t s a r e f o r m e d , and b r e a k n e a r the c e n t e r o f each c h a i n . Some p o l y m e r s a r e i n h e r e n t l y more s t a b l e t h a n o t h e r s f o r a g i v e n t h i c k e n i n g power. F o r a l l c a r b o n - c a r b o n bond t y p e p o l y m e r s , i n h e r e n t bond s t r e n g t h s a r e n o t t o o d i f f e r e n t f r o m one p o l y m e r t o the next (21,22). T h i c k e n i n g g o e s a s [η] ~ < S * > ' V M (Zimm m o d e l ) , w h i l e s h e a r s t r e s s p e r p o l y m e r m o l e c u l e g o e s a s [t?]M»y a t c o n s t a n t s h e a r r a t e . The i n t r i n s i c v i s c o s i t y , [η], f o r a g i v e n M, i n c r e a s e s t h e f e w e r t h e number and s i z e o f s i d e g r o u p s and t h e s t i f f e r t h e c h a i n ( i . e . , l a r g e c h a r a c t e r i s t i c r a t i o , C^) a s > C l , where η i s t h e number o f b a c k b o n e bonds and 1 t h e bond l e n g t h . By t h i s m e a s u r e p o l y ( e t h e n e - c o - p r o p e n e ) i s b e s t , followed by styrene-b-HPI or styrene-b-(HPB-r-styrene) f o l l o w e d by polyalkyl methacrylates. The data i n Figure 3 agree reasonably w e l l w i t h t h e s e p r e d i c t i o n s , w i t h t h e e x c e p t i o n o f t h e HPI s t a r s and t h e p o l y ( s t y r e n e - b - H P I ) , w h i c h a r e more s t a b l e t h a n e x p e c t e d f o r t h e i r [η]. T h e y w i l l be d i s c u s s e d i n g r e a t e r d e t a i l b e l o w . P o l y i s o b u t y l e n e i s now e s s e n t i a l l y o f f t h e m a r k e t due t o p o o r mechanical and o x i d a t i v e s t a b i l i t y . Polymethacrylates, while not t e r r i b l y c o s t - e f f e c t i v e , have a d e s i r a b l e v i s c o s i t y - t e m p e r a t u r e relationship and therefore low zero-shear v i s c o s i t y a t low temperatures, a n d s u r v i v e m a i n l y i n m a r k e t s where o u t s t a n d i n g low t e m p e r a t u r e p e r f o r m a n c e a t low s h e a r s t r e s s e s i s d e s i r e d . J

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Recent V i s c o s i t y M o d i f i e r Developments. A g a i n s t t h i s b a s i c s e t o f c o n c e p t s , t h e r e h a v e emerged " h i g h t e c h " v i s c o s i t y m o d i f i e r s . E x a m p l e s a r e shown i n F i g u r e 4. A l t h o u g h t h e S h e l l K r a t o n - t y p e S-b-HPI d i b l o c k p o l y m e r s have been a r o u n d f o r many y e a r s t h e y p r e s e n t an i n t e r e s t i n g case (23). These polymers have m o l e c u l a r w e i g h t f r o m 80,000 t o 120,000, and c o n t a i n a r o u n d 3 0 wt% s t y r e n e . They have extremely narrow m o l e c u l a r weight d i s t r i b u t i o n s , w i t h M /M r f 7 ) M , i . e . a s c/M f o r our s o l u t i o n s ( 3 4 ) . β i s a dimensionless shear r a t e l o c a t i n g t h e o n s e t o f s h e a r r a t e d e p e n d e n c e o f v i s c o s i t y , and i s t y p i c a l l y n e a r 1.5 i n t h i s c o n c e n t r a t i o n r a n g e . T h e s l o p e o f t h e v i s c o s i t y shear r a t e curve i n t h e non-Newtonian r e g i o n s h o u l d be s i m i l a r a t constant c|>]. The f a c t t h a t t h e CCS i s a c t u a l l y r u n a t c o n s t a n t s h e a r s t r e s s s h o u l d make t h e d i f f e r e n c e s even l a r g e r . The S-HPI-1 a n d -2 p o l y m e r s a g a i n have E P - 1 i k e "arms" i n s o l u t i o n extending from t h e s t y r e n e m i c e l l e c e n t e r s . Thus, »? ] v s . Τ i s s i m i l a r a t h i g h t e m p e r a t u r e s t o EP-1, EP-3, o r HPI s t a r 250. T h e MRV o f 9,000 c P i s n e a r l y t h e same a s 200 o r 250, s i g n i f i c a n t l y h i g h e r t h a n E P - 3 o r - 4 . T h e CCS v i s c o s i t y i s measurably b e l o w a l l o t h e r p o l y m e r t y p e s . r;(CCS)/»?(MRV) = 0.27 i s c l o s e t o HPI 200 o r EP-3, b u t t h e a b s o l u t e v i s c o s i t y i s 300 c P lower. T h i s v a l u e c o u l d r e s u l t f r o m one o r b o t h o f t h e f o l l o w i n g reasons. P e r h a p s t h e p o l y s t y r e n e m i c e l l e c o r e becomes somewhat s m a l l e r a t l o w Τ a n d h e l p s keep »7 -| s l i g h t l y s m a l l e r t h a n f o r f r e e EP chains. T h u s t h e 9,000 c P MRV v a l u e i s r e a l l y b e l o w t h e s t a r HPI a t 9,500 and t h e EP-1 a t 12,000 c P . P e r h a p s t h e r e a l s t a r d o e s n o t s h e a r t h i n as much as EP-1 o r t h e S-b-HPI m i c e l l e . A l t e r n a t i v e l y , i t seems r e a s o n a b l e t h a t s t r e s s c o u l d p u l l t h e m i c e l l e s a p a r t t o some e x t e n t . V i s c o s i t y f a l l s o f f d r a m a t i c a l l y f o r S-b-HPI p o l y m e r s above 110°C, where t h e m i c e l l e s a p p e a r t o d i s s o c i a t e . Why c o u l d n ' t t h i s happen t o some e x t e n t u n d e r s t r e s s a t - 2 0 ° C ? P e r h a p s s c a t t e r i n g e x p e r i m e n t s on s h e a r e d s o l u t i o n s , t h e a d d i t i o n o f s m a l l re

r e

o

o

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re

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Formulated to Same cM

[Viscosity)


270

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Lower M, Higher c J Viscosity J 1

I I

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1

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ι Higher M, Lower c

J

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I I

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Solvent vis

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6

Shear Stress F i g u r e 10. Schematic R e p r e s e n t a t i o n o f the Shear Rate Dependence of Viscosity f o r O i l s F o r m u l a t e d t o t h e Same Z e r o - S h e a r V i s c o s i t y , C o n t a i n i n g Polymers With D i f f e r e n t M o l e c u l a r Weights. The " S o l v e n t V i s c o s i t y " C o u l d be P e r t u r b e d b y t h e P o l y m e r T h u s C o n f u s i n g an "Upper N e w t o n i a n L i m i t . "


15.

V E R STRATE & S T R U G U N S K I

Lubricating-OU Viscosity Modifiers

271

amounts o f s o l v e n t t o " s o f t e n " t h e s t y r e n e d o m a i n s , o r e v e n " h y s t e r e s i s " i n s t r a i n r a t e c y c l e h i s t o r y c o u l d help t o answer t h i s question. The S - b - ( S - r - H P B ) h a s a good c o m b i n a t i o n o f CCS and MRV. P e r h a p s t h e r e i s enough s t y r e n e i n t h e S-r-HPB b l o c k t o c a u s e t h o s e s e g m e n t s t o come o u t o f s o l u t i o n as compared t o t h e HPI s e g m e n t s i n t h e S-b-HPI p o l y m e r . The S-r-HPB segment may f u r t h e r c o l l a p s e i n t o a c e n t e r m i c e l l e a s Τ d r o p s g i v i n g good drç -j/dT, due t o a r e a l s o l v e n t q u a l i t y e f f e c t a n d not r o t a t i o n a l i s o m e r i c e f f e c t s . T h e s h e a r t h i n n i n g o f t h i s s t r u c t u r e i s n o t as g o o d as t h e S-b-HPI s t r u c t u r e , however. F u r t h e r m o r e , we d o n o t know d/dT f o r t h i s polymer. re


z

Conclusions Lube o i l t e c h n o l o g y p r o v i d e s a n i n t e r e s t i n g o p p o r t u n i t y t o work c r e a t i v e s c i e n c e from molecule s y n t h e s i s to s e m i d i l u t e s o l u t i o n behavior o f polymers. T h e r e a r e many o p p o r t u n i t i e s r e m a i n i n g t o p r o d u c e an optimum s t r u c t u r e t h a t i s b e s t f o r m e c h a n i c a l s t a b i l i t y , low temperature viscometric properties, fuel economy a n d dispersancy.

Literature Cited (1) Muller, H.G. Tribology International 1978, 11, 189. (2) Bartz, W.J. SAE Technical Paper, 890728, February 1989. (3) Fein, R.S. Ind. Eng. Chem. Fundam 1986, 25, 518. (4) Candau, F.; Heatley, F.; Price, C.; Stubbersfield, R. Eur. Pol. J. 1984, 20, 685. (5) Spiess, G.; Johnston, J . ; Ver Strate, G. in Additives for Lubricants and Operational Fluids; Bartz, K., Ed.; Technische Akademie Esslingen 1987; p. 8.10-1. (6) Ramesh, K.; Clifton, R. J. Tribology 1987, 107, 215. (7) Marui, E. et al. Trans ASME 1987, 109, 696. (8) Klamann, D. Lubricants and Related Products, Verlag Chemie Weinheim (1984) p. 185. (9) Spearot, J . ; Murphy, C. SAE Technical Paper, 880680, 1988. (10) Watson, R.; McDonnell, T. SAE Technical Paper, 841208, 1984. (11) Ver Strate, G. Rolduc Meeting, April 22, 1989 in press. (12) Kapuscinski, M.; Sen, Α.; Rubin, I. SAE Technical Paper, 892152, September 1989. Sen, Α., Rubin, I. Macromolecules, 23, 2519 (1990).


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(13)

Rozeanu, L.; Shavit, Α.; Maayan, M. SAE Technical Paper 850545, 1985.

(14)

Society of Automotive Engineers Specification J300.


(15) ASTM D3829 and D4684 test methods. (16)

Flory, P. J. Statistical Mechanics of Chain Molecules; Wiley, 1969; p. 37.

(17)

Kurata, M.; Tsunashima, Y.; Iwama, M.; Kamada, K. In Polymer Handbook; Brandrup, J . ; Immergut, E., Eds.; John Wiley, NY, 1975.

(18)

Mark, J. Rubber Chem. Tech. 1973, 46, 593.

(19)

Mark, J. J. Chem. Phys. 1972, 57, 2541.

(20)

DIN 51382.

(21)

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(22)

Odell, J . ; Keller, A. J. Poly. Sci. Β Physics 1986, 1899.

(23)

St. Clair, D.; Evans, D. U.S. Patent 3 772 196, 1973.

(24)

Schouten, M.; Dorrepaal, J . ; Stassen, W.; Vlak, W.; Mortensen, K. Polymer 1989, 30, 2038.

(25)

Eckert, R., U.S. Patent 4 116 917, 1978.

(26)

Ver Strate, G.; Graessley, W. Polymer Preprints 1979 20 149.

(27)

Ver Strate, G.; Graessley, W.; Kresge, Ε. U.S. Patent 4 620 048, 1986.

(28)

Trepka, W., U.S. Patent 4 412 087, 1983.

(29)

Schiff, 1971.

(30)

Ver Strate, G.; Ju, S.; Cozewith, C. Macromolecules 1988, 21, 3360.

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Ver Strate, G.; Bloch, R.; Struglinski, M.; Johnston, J.E.; West, R.; U.S. Patent 4 804 794, 1988. Rangel-Nafaile, C.; Metzner, Α.; Wissbrun, K. Macromolecules 1984 17, 1187.

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S.; Johnson, M.; Streets, W. U.S. Patent 3 554 911,

(34) Graessley, W.W. Adv. Polymer Sci. 1974, 16, 1. Received July 18, 1990 In Polymers as Rheology Modifiers; Schulz, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1991.

Polymers as Lubricating-Oil Viscosity Modifiers - American Chemical

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