Polymerization Kinetics by Precision Densimetry - American Chemical

21 Polymerization Kinetics by Precision Densimetry K. J. ABBEY

Downloaded by UNIV OF ROCHESTER on June 13, 2013 | http://pubs.acs.org Publication Date: October 7, 1981 | doi: 10.1021/bk-1981-0165.ch021

Glidden Coatings and Resins, Division of SCM Corporation, 16651 Sprague Road, Strongsville, OH 44136

Frequently the extent of conversion in commercial polymer ization reactors can be monitored by measuring the total heat evolved. This is possible because of the large volume-to-sur face area ratio of these reactors. The small scale laboratory preparations become much more difficult to follow by calori metry. Meeks(1) has reported a suitable laboratory scale iso thermal reactor utilizing an analog computer. Many other reac tion calorimeter designs are known. Other methods, such as dilatometry and gravimetric analysis, have been used in the laboratory. A method for monitoring polymerizations was desired which would avoid the restrictions on reactor design, provide rapid response, and allow for automatic data collection and possibly control. The apparatus of Meeks appeared appropriate except that the reaction vessel was an integral part of the instrument. The use of a precision digital density meter as supplied by Mettler Instruments (Anton Paar, Ag.) appeared attractive. Few references on using density measurements to follow polymeriza tion or other reactions appear in the literature. Poehlein and Dougherty (2) mentioned, without elaboration, the occasional use of γ-ray density meters to measure conversion for control purposes in continuous emulsion polymerization. Braun and Disselhoff (3) utilized an instrument by Anton Paar, Ag. but only in a very limited fashion. More recently Rentsch and Schultz(4) also utilized an instrument by Anton Paar, Ag. for the contin uous density measurement of the cationic polymerization of 1,3,6,9-tetraoxacycloundecane. Ray(5) has used a newer model Paar digital density meter to monitor emulsion polymerization in a continuous stirred tank reactor train. Trathnigg(6,7) quite recently considered the solution polymerization of styrene in tetrahydrofuran and discusses the effect of mixing on the reliability of the conversion data calculated. Two other refer ences by Russian authors(8,9) are known citing kinetic measure ments by the density method but their procedures do not fulfill the above stated requirements. 0097-6156/81/0165-0345$05.00/0 © 1981 American Chemical Society

In Emulsion Polymers and Emulsion Polymerization; Bassett, D., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

346

EMULSION POLYMERS AND

EMULSION POLYMERIZATION

T h i s p a p e r i n c l u d e s c r i t i c a l comments on t h e i n s t r u m e n t a t i o n and m e t h o d o l o g y . E x a m p l e s f r o m s o l u t i o n and e m u l s i o n p o l y merization are given f o r i l l u s t r a t i o n .


EXPERIMENTAL F o r t h e w o r k p r e s e n t e d i n t h i s p a p e r a DMA 60/DMA 601H h i g h p r e c i s i o n , h i g h temperature, d i g i t a l d e n s i t y meter ( M e t t i e r I n s t r u m e n t s C o r p . ) was u s e d . The c o n t i n u o u s l y m o n i t o r e d e m u l sion polymerization reactions u t i l i z e d either a Masterflex p e r i s t a l t i c pump ( C o l e P a l m e r I n s t r u m e n t Co.) e q u i p p e d w i t h v a r i o u s t u b i n g d i s c u s s e d b e l o w o f 1.66 mm I.D. o r a P U L S A f e e d e r M i c r o f l o m e t e r i n g pump ( I n t e r p a c e I n c . ) w i t h a r e m o t e , h e a t t r a c e d , d i a p h r a m pump h e a d . The r e m o t e , h i g h t e m p e r a t u r e d e n s i t y c e l l was e q u i p p e d w i t h a c o n t i n u o u s f l o w a d a p t e r . Teflon t u b i n g o f 1.5 mm I.D. was u s e d f o r t h e i n t e r c o n n e c t i n g p l u m b i n g . F a i l u r e o f t h e pumps was a p e r s i s t e n t p r o b l e m . Viton t u b i n g w o u l d t y p i c a l l y f a i l i n t h e p e r i s t a l t i c pump due t o monomer s w e l l i n g , a c r y l a t e s i n 10-30 m i n u t e s and a f t e r a b o u t 3 hours f o r styrene. K a l r e z t u b i n g (DuPont Co.) was c h e m i c a l l y r e s i s t a n t b u t f a i l e d f r o m m e c h a n i c a l f a t i g u e a f t e r 1-2 h o u r s . S i l i c o n t u b i n g i s r e p o r t e d ( 5 ) t o s u r v i v e 8-10 h o u r s w i t h a s o l u t i o n of methyl methacrylate i n e t h y l acetate. This tubing, h o w e v e r , was o b s e r v e d t o u n d e r g o s w e l l i n g by m e t h y l m e t h a c r y l a t e i n t h i s study. The d i a p h r a m pump f a i l e d a f t e r a c o u p l e h o u r s b e c a u s e a p o l y m e r p l a q u e f o r m e d on t h e c h e c k v a l v e s . This o c c u r r e d f o r b o t h s t a i n l e s s s t e e l and T e f l o n v a l v e s . Plaque f o r m a t i o n was more p r o n o u n c e d w i t h l a t i c e s f o r m u l a t e d f o r l o w Tg. A l l s y n t h e s e s d i s c u s s e d b e l o w u s e d commonly a v a i l a b l e commercial m a t e r i a l s without f u r t h e r p u r i f i c a t i o n . Manually s a m p l e d r e a c t i o n s were a n a l y z e d f o r t h e i r d e n s i t y a t t e m p e r a t u r e s b e t w e e n 20-30°C. C o n t i n u o u s l y s a m p l e d r e a c t i o n s were a n a l y z e d at t h e p o l y m e r i z a t i o n temperature. Temperature c o n t r o l i n t h e d e n s i t y c e l l was b e t t e r t h a n ±0.1°C f o r s t a t i c s a m p l e s . Tempe r a t u r e f l u c t u a t e d more f o r c o n t i n u o u s l y s a m p l e d r e a c t i o n s , sometimes r i s i n g ,1-.3°C b e c a u s e o f t h e e x o t h e r m i c r e a c t i o n continuing i n the density c e l l . Calibration of the density c e l l b e l o w 95°C was a c c o m p l i s h e d u s i n g v a l u e s f o r d e n s i t i e s f o r m o i s t a i r ( 1 0 ) and d e g a s s e d , d i s t i l l e d w a t e r ( 1 1 ) . For measurements a b o v e 95°C a c e r t i f i e d v i s c o s i t y s t a n d a r d o i l (Number S-200 o i l f r o m Cannon I n s t r u m e n t Co.) was u s e d . D e n s i t i e s a t s i x temperatures accurate to four s i g n i f i c a n t f i g u r e s o v e r t h e r a n g e o f 20° t o 100°C f o r t h i s v i s c o s i t y s t a n d a r d was e x t r a p o l a t e d t o h i g h e r t e m p e r a t u r e s u s i n g a n e x c e l l e n t l i n e a r f i t ( c o r r e l a t i o n c o e f f i c i e n t o f 0.999998). The mass f r a c t i o n p o l y m e r , F, a t a g i v e n t i m e , t , i s g i v e n by e q u a t i o n 1. W ( t ) and W ( t ) a r e t h e i n s t a n t a n e o u s masses o f p o l y m e r and monomer, r e s p e c t i v e l y . p

m


21.

ABBEY

347

Precision Densimetry W (t) F

(

t

)

»

W (t) + w (t) p m

(

i>

T h i s e q u a t i o n c a n be p u t i n a more u s a b l e f o r m f o r s e m i c o n t i n u o u s s o l u t i o n o r e m u l s i o n p o l y m e r i z a t i o n by a l g e b r a i c m a n i p u l a t i o n , e q u a t i o n 2.

KM

+

ρ

w

™

( t )

Μ

m


m Ρ W (t) + W (t) ρ m m Ρ

ϋ

> a a Ρ

ν

KM _ _m m Ρ

a a Ρ

W (t) + w (t) ρ m ρ Ρ

W (t) a a Ρ

^)

β

ρ ρ Ρ

(2)

w (t) a a Ρ

The new v a r i a b l e s i n e q u a t i o n 2, pm, pp, pa and W ( t ) , a r e t h e d e n s i t i e s o f t h e monomer, p o l y m e r , and aqueous o r s o l v e n t com p o n e n t s and t h e mass o f s o l v e n t o r a q u e o u s p h a s e . C o l l e c t i n g t e r m s w i t h t h e a s s u m p t i o n t h a t no c h a n g e i n v o l u m e o c c u r s on m i x i n g y i e l d s e q u a t i o n 3. a

v (t) - w (t)/p (t) n

r

r

v (t) - v m

p ( t

)

V ( t ) and V p ( t ) a r e t h e t h e o r e t i c a l v o l u m e s o f t h e e n t i r e r e a c t i o n m i x t u r e a t a n y t i m e a s s u m i n g no p o l y m e r i z a t i o n and c o m p l e t e p o l y m e r i z a t i o n , r e s p e c t i v e l y . W ( t ) and p ( t ) a r e t h e e n t i r e r e a c t i o n mass a t a g i v e n t i m e and t h e m e a s u r e d d e n s i t y o f t h i s mixture. V ( t ) i s c a l c u l a t e d f r o m known masses a n d d e n s i t i e s measured i n i t i a l l y a t t h e o p e r a t i n g t e m p e r a t u r e o f t h e d e n s i meter. The q u a n t i t y V ( t ) r e q u i r e s t h e f u r t h e r k n o w l e d g e o f t h e d e n s i t y o f t h e p o l y m e r b e i n g p r o d u c e d a t any g i v e n i n s t a n t . m

r

r

m

p

RESULTS AND DISCUSSION S e v e r a l c o m p a n i e s s u p p l y d e n s i t y e q u i p m e n t w h i c h was considered s u i t a b l e f o r automatic, continuous operation with s u f f i c i e n t p r e c i s i o n f o r c a l c u l a t i o n of polymerization conver sion. T h e s e b r e a k down i n t o t h r e e c l a s s e s b a s e d o n mode o f operation: γ-ray a b s o r p t i o n , o s c i l l a t o r y f r e q u e n c y o f a s a m p l e f i l l e d t u b e , and mass measurement a t f i x e d v o l u m e . O n l y one o f t h e s e , a n o s c i l l a t o r - b a s e d s y s t e m d i s t r i b u t e d by M e t t l e r I n s t r u m e n t C o r p . ( r e p r e s e n t i n g A n t o n P a a r Ag.) h a s m o d e l s w i t h dead v o l u m e s s m a l l enough f o r l a b o r a t o r y s c a l e e x p e r i m e n t a t i o n . The o t h e r u n i t s g e n e r a l l y a l s o s u f f e r e d f r o m n a r r o w d e n s i t y s p a n s when t h e p r e c i s i o n was s u f f i c i e n t f o r c o n v e r s i o n s t u d i e s . Table

American Chemical Society Library 16th St. N. w . Washington, 0.Polymerization; C. 20036 Bassett, D., et al.; In Emulsion Polymers and Emulsion 1155

ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

EMULSION POLYMERS

348

I represents Mettler-Paar

AND

EMULSION POLYMERIZATION

some c a l c u l a t i o n s b a s e d on s t y r e n e m o d e l s o f t h e instrumentation. TABLE I

S U I T A B I L I T Y OF DENSIMETRY FOR MONITORING POLYMERIZATIONS R e s o l u t i o n (% c o n v e r s i o n ) Δρ 20°C DMA 40 DMA 60/601 (gcm-3) (±1x10-4 gcm-3) (±1x10-6 gcm~3)

Monomer

0.159

6 χ 10

6 χ 10

S t y r e n e (20 w t . % solution)*

0.033

3 χ 10"

3 χ 10

Styrene ( 4 wt. % solution)*

0.006

1.5

-2 1.5 χ 10


Styrene

(bulk)

f C a l c u l a t e d f r o m d a t a i n (12.) ^ * A s s u m i n g i d e a l m i x i n g w i t h s o l v e n t o f d e n s i t y 1.000 gem Under t h e f l o w c o n d i t i o n s o f c o n t i n u o u s l y s a m p l i n g t h e maximum p r e c i s i o n c a n n o t be m a i n t a i n e d f o r t h e DMA 60/DMA 601 instrument. T h i s i s shown by T a b l e I I where a s m a l l s u b s e t o f data i s presented from an emulsion p o l y m e r i z a t i o n o f s t y r e n e f o r w h i c h t h e l a t e x was pumped t h r o u g h t h e d e n s i m e t e r o p e r a t i n g a t 70.0°C. The l a t e x p a s s e d t h r o u g h a n i n t e r n a l h e a t e x c h a n g e r i m m e d i a t e l y b e f o r e e n t e r i n g t h e a c t u a l m e a s u r i n g compartment. I f t h e r a t e o f p o l y m e r i z a t i o n over t h i s s m a l l range o f o v e r a l l c o n v e r s i o n c a n be assumed t o be c o n s t a n t , t h e n t h e a v e r a g e Δρ i s 1.16 χ 10"4 ± 0.10 χ 10-4g/ m3. The s t a n d a r d d e v i a t i o n l e a d s t o a n e r r o r i n t h e p e r c e n t a g e c o n v e r s i o n o f ±0.02% f o r t h e 5 9 % c o n v e r s i o n datum. By c o m p a r i n g t h e e s t i m a t e f o r t h e e r r o r i n the percentage conversion w i t h i n t h ec a l c u l a t e d value i n T a b l e I shows t h a t t h e a c t u a l pumped r e a c t i o n m i x t u r e l e a d s to an order t o magnitude l a r g e r e r r o r . Four p o l y m e r i z a t i o n examples a r e p r e s e n t e d h e r e t o i l l u s t r a t e both a v a i l a b l e s e n s i t i v i t y , experimental d i f f i c u l t i e s , and h o p e f u l l y some i n t e r e s t i n g a s p e c t s o f t h e p o l y m e r i z a t i o n processes. The f i r s t two e x a m p l e s a r e t h e s e m i - c o n t i n u o u s e m u l s i o n p o l y m e r i z a t i o n o f m e t h y l m e t h a c r y l a t e (MMA) a n d s t y r e n e , r e s p e c t i v e l y . The t h i r d e x a m p l e i s a b a t c h c h a r g e d c o p o l y m e r i z a t i o n o f b u t y l a c r y l a t e (BA) w i t h MMA. The f o u r t h example i s a s e m i - c o n t i n u o u s s o l u t i o n p o l y m e r i z a t i o n o f an a c r y l i c system. I n t h i s l a s t e x a m p l e a l i q u o t s were t a k e n m a n u a l l y a n d a n a l y z e d a t 29.7°C u n d e r s t a t i c c o n d i t i o n s . No f u r t h e r p o l y m e r i z a t i o n o c c u r r e d a f t e r t h e s a m p l e s were c o o l e d to t h i s t e m p e r a t u r e . C


21.

Precision

ABBEY

349

Densimetry

TABLE I I EMULSION POLYMERIZATION OF E m u l s i o n ρ 70°C(gcm

)*

F r a c t i o n Conversion

.973906 .974030 .974133 .974251 .974377 .974487


STYRENE Ap

( x l O ) (gem

.5830 .5860 .5885 .5914 .5944 .5971

)

124 103 118 126 110

*22% monomer p l u s p o l y m e r ; d e n s i t y measurements made e v e r y minutes.

0.95

F i g u r e 1 shows t h e c o n v e r s i o n h i s t o r y f o r t h e MAA l a t e x , t h e r e c i p e f o r w h i c h i s g i v e n i n T a b l e I I I . The p o l y m e r i z a t i o n was c o n d u c t e d e s s e n t i a l l y i s o t h e r m a l l y a t 82-84°C. The d e n s i t y c e l l was s e t a t 83.0°C f o r a s t a t i c s a m p l e . C u r v e A i s t h e c a l c u l a t e d r e s p o n s e when t h e d e l a y b e t w e e n r e a c t o r and d e n s i t y c e l l i s ignored. C u r v e Β was c a l c u l a t e d c o n s i d e r i n g a f i x e d d e l a y o f 2.7 m i n u t e s . TKe d e l a y was i n f a c t n o t c o n s t a n t and t e n d e d t o i n c r e a s e as t h e r e a c t i o n p r o g r e s s e d . This i s believed t o be r e l a t e d t o t h e p r o b l e m s m e n t i o n e d above w i t h t h e s a m p l i n g pumps, b u t c o u l d a l s o be r e l a t e d t o a v i s c o s i t y change i n t h e r e a c t i o n medium. F u r t h e r , t h e r e s p o n s e s m e a s u r e d i n t h e d e n s i t y c e l l are not e x a c t l y those o c c u r r i n g i n the r e a c t o r s i n c e r e a c t i o n c o n t i n u e s i n t h e c i r c u l a t i o n l i n e s and d e n s i t y c e l l . T h u s , c u r v e Β i s an u p p e r l i m i t t o t h e t r u e r e a c t o r b e h a v i o r . T h e s e o b s e r v a t i o n s s u g g e s t t h e use o f t h e l o w e s t dead v o l u m e and l a g time p o s s i b l e i n the sampling l o o p . TABLE I I I MMA Initial

LATEX RECIPE FOR

2

Charge

Deionized water Surfactant Buffer. K S 0 o

FIGURES 1 AND

o

Q

400.Og 4.0g 0.8g 0.3g

MMA

+

modifier

20.Og

MMA

+

modifier

380.8g

Feed



350

EMULSION POLYMERS AND EMULSION POLYMERIZATION

if" A

gs < Figure 1. Conversion representation of MMA semicontinuous emulsion polym erization. Curve A results from neglect ing lag in sampling while curve Β is cor rected for 2.7 min of lag.

D

0

40 80 120 TIME, MINUTES

5 Ο

z> ζ ο

Figure 2. Rate representation for MMA semicontinuous emulsion polymerization (( ) the monomer feed rate (right or dinate); (O) the polymerization rate with out correction for the lag in sampling (left ordinate); (+) the most significantly changed points when the 2.7-min lag is used)

< Ο

î • 40 TIME,

ο

"d

80

120

MINUTES


ABBEY

21.

Precision

Densimetry

351

Figure 2 i s the rate of polymerization corresponding to c u r v e A i n F i g u r e 1. The o n l y s i g n i f i c a n t a l t e r a t i o n c a u s e d by i n c l u d i n g t h e 2.7 m i n u t e d e l a y i n r e s p o n s e i s a f l a t t e n i n g o f t h e minimum t h a t o c c u r s a t a b o u t 10 m i n u t e s ( r e p r e s e n t e d by + s i n t h e f i g u r e ) . The r a t e r e p r e s e n t a t i o n h a s s e v e r a l a d v a n t a g e s , one o f w h i c h i s g r e a t e r s e n s i t i v i t y t o p r o c e s s p e r t u r b a t i o n s e s p e c i a l l y a t h i g h c o n c e n t r a t i o n and h i g h conversion. The r a p i d r a t e i s p o s s i b l e b e c a u s e o f t h e f i f t h s i g n i f i c a n t d i g i t a v a i l a b l e when t h e DMA 60/DMA 601 i n s t r u m e n t combination i s used. The s t y r e n e p o l y m e r i z a t i o n i s shown i n F i g u r e s 3 and 4. As w i t h t h e MMA l a t e x , t h e s t y r e n e l a t e x began w i t h a s m a l l p o r t i o n o f t h e monomer added i n i t i a l l y . The r e m a i n i n g monomer was added a s shown i n F i g u r e 4. A p p a r e n t " n e g a t i v e " c o n v e r s i o n was c a u s e d by t h e c o l l e c t i o n o f a s e p a r a t e d monomer p h a s e on t h e glass walls of the density c e l l . T h i s b e h a v i o r was o n l y n o t e d w i t h s t y r e n e and was a f u n c t i o n o f t h e p r o p o r t i o n o f monomer to s u r f a c t a n t i n t h e i n i t i a l charge. The s e p a r a t e d monomer was s l o w l y a b s o r b e d i n t o t h e c i r c u l a t i n g r e a c t i o n medium. A f t e r a b o u t 70 m i n u t e s , o r above 5 0 % c o n v e r s i o n , t h e r e s p o n s e s a r e reliable. The s h a r p r a t e a c c e l e r a t i o n due t o t h e T r o m m s d o r f f g e l e f f e c t c a n be s e e n i n b o t h f i g u r e s a t a b o u t 100 m i n u t e s . The l a g b e t w e e n d e n s i t y c e l l r e s p o n s e and r e a c t o r e v e n t s were c o n s i d e r a b l y l e s s f o r t h i s example and t h e f i g u r e s i g n o r e a n y correction. A f t e r e s t a b l i s h i n g a "steady s t a t e " response t o t h e monomer f e e d ( a b o u t 160 m i n u t e s i n t o t h e r e a c t i o n ) , t h e i n c r e m e n t a l i n c r e a s e o f t h e feed r a t e i s seen n o t t o a l t e r t h e o v e r a l l f r a c t i o n a l conversion since the r a t e of polymerization i n c r e a s e s t o p a r a l l e l t h e monomer f e e d r a t e . A t t h e end o f t h i s s e t o f d a t a t h e r a t e i s 2-3 t i m e s t h a t o b s e r v e d e a r l i e r b e f o r e the feed.


T

The b a t c h c h a r g e d e m u l s i o n c o p o l y m e r i z a t i o n o f BA and MMA i s shown i n F i g u r e s 5 and 6. The r e a c t i o n p r o c e e d e d more s l o w l y t h a n t h e a b o v e MMA l a t e x and t h e l a g t i m e was a l s o l e s s ( i g n o r e d i n these p l o t s ) . The r a t e a c c e l e r a t i o n a t a b o u t 4 0 % c o n v e r s i o n i s b e l i e v e d t o be t h e T r o m m s d o r f f e f f e c t . The much l o w e r s l o p e o f t h e c o n v e r s i o n c u r v e above 90% c o n v e r s i o n i n F i g u r e 5 i s b e l i e v e d t o be a n a r t i f a c t o f t h e s i m p l e m o d e l u s e d i n t h e calculations. The m o d e l assumed t h a t t h e c o m p o s i t i o n o f t h e p o l y m e r p r o d u c e d was t h e same a s t h e i n i t i a l monomer m i x . T h i s , of course, i s not the case. Given an i n i t i a l composition o f 25 m o l e % BA, t h e p o l y m e r p r o d u c e d c a n be c a l c u l a t e d u s i n g l i t e r a t u r e r e a c t i v i t y r a t i o s (12) t o v a r y i n c o m p o s i t i o n from a b o u t 15 m o l e % BA e a r l y i n t h e r e a c t i o n t o a b o u t 50 m o l e % d u r i n g t h e l a s t 1 0 % o f t h e r e a c t i o n . The e n t i r e p l o t i s t h u s skewed, w i t h t h e c o m p o s i t i o n c h a n g i n g most r a p i d l y l a t e i n t h e polymerization. The u s e o f d e n s i m e t r y p r o v i d e s a r a p i d a n d , w i t h p r o p e r c a r e , p r e c i s e measure o f t h e p o l y m e r i z a t i o n p r o c e s s . By u s i n g a s e c o n d i n d e p e n d e n t method o f m e a s u r i n g t h e same p r o c e s s , t h e


352



Q.

6

ζ Ο

Figure 3. Conversion representation for styrene semicontinuous emulsion polym erization ((· - ·) zero conversion axis)

60 120 180 TIME, M I N U T E S

z^

Ο Lli

52 < ο Q£

1

Ο Figure 4. Rate representation for sty rene semicontinuous emulsion polymeri zation (( ) the monomer feed rate (right ordinate); the scatter plot is the polymerization rate (left ordinate))

Ω O u_

To

60 120 180 TIME, M I N U T E S



21. ABBEY

353

Precision Densimetry

8

16 24 TIME, MINUTES

~l

S

24~~

TIME, M I N U T E S

Figure 5. Conversion representation for α ΒAI MM A (30/70 by weight) batch emulsion polymerization

Figure 6. Rate representation for a Β A/MMA (30/70 by weight) batch emulsion polymerization



354

EMULSION POLYMERS

Figure 7. Conversion representation for a multicomponent acrylic, semicontinuous solution polymerization

AND EMULSION POLYMERIZATION

Q. °0

80 160 2 4 0 TIME, MINUTES



21.

ABBEY

Precision Densimetry

355

copolymer reactivity ratios could be determined as a function of conversion. The study of the copolymerization of styrene and methyl methacrylate at high conversion (13,14) has shown that the reactivity ratios do deviate from the values reported from dilute solution measurements. The last example, for which Figure 7 shows the running fractional conversion as a function of time, was conducted by feeding a catalyzed acrylic monomer mixture into a hot solvent mixture. The control on monomer feed rate was not as good as in the previous examples. This accounts for much of the scatter in the data as the calculations assume a constant feed rate. Unlike the semi-continuous emulsion polymerizations, the fractional conversion did not remain constant during the monomer feed, but increased throughout. Indeed, the actual weight of free monomer remained remarkably constant irrespective of the running total reaction mass or conversion, Table IV. TABLE IV WEIGH UNREACTED MONOMER IN SOLUTION ACRYLIC DURING FEED Time (min.)

Monomer (g)

15 30 45 60 75 90

5.2 9.6 9.1 12.7 11.8 15.1

Time (min.) 105 120 135 150 165 180

Monomer (g) 11.2 9.7 10.3 9.6 11.1 12.7

CONCLUSIONS The use of precision density measurements for monitoring polymerization reactions can be done rapidly and automatically using commercially available instrumentation. The method is independent of the reactor size and design but suffers from sampling difficulties. The examples of this paper show the rapidity of data collection and three distinct sampling problems; pump failure from either monomer attack or polymer scale formation, monomer phase separation in the density cell, and the lag time for rapid polymerizations. Techniques have or can be devised to avoid or reduce the influence of these problems. LITERATURE CITED 1. 2. 3.

Meeks, M. R., Polym. Eng. Sci. 1969, 9(2), 141. Poehlein, G. W. and Dougherty, D. J., Rubber Chem. Techn. 1977, 50(3), 601. Braun, D. and Disselhoff, G., Polymer 1977, 18(9), 963.



356 4. 5. 6. 7. 8. 9. 10. 11.


12. 13. 14.

Rentsch, C. and Schultz, R. C., Makrom. Chem. 1978, 179, 1131. Ray, W. Η., private communication 1980. Trathnigg, Β., Makrom. Chem. 1978, 181, 1979-1986. Trathnigg, Β., Angew. Makrom. Chem. 1980, 88, 127-133. Pugachevich, P. P. and Toknev, A. G., Zavod. Lab. 1970, 36(7), 817. Zotov, L. I. and Sedov, L. N., Plast. Massy 1969(9), 68. Weast, R. C. (ed.), "CRC Handbook of Chemistry and Physics, 57th Edition", p. F-9, CRC Press, Cleveland, 1976. Weast, R. C. (ed.), "CRC Handbook of Chemistry and Physics, 53rd Edition", p. F-5, CRC Press, Cleveland, 1972. Brandrup, J. and Immergut, Ε. Η., "Polymer Handbook, 2nd Edition", John Wiley and Sons, New York, 1975. Johnson, M., Karmo, T. S., and Smith, S. S., European Polym. J. 1978, 14, 409-14. Dionisio, J. M. and O'Driscoll, K. F., J. Polymer Sci., Polymer Letters Ed. 1979, 17(11), 701-7.

RECEIVED

April 6, 1981.


Polymerization Kinetics by Precision Densimetry - American Chemical

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