Controlled Release Polymeric Formulations

18 Polymers Containing Pendent Herbicide Substituents:

Downloaded by UNIV OF CALIFORNIA SAN DIEGO on July 15, 2016 | http://pubs.acs.org Publication Date: June 1, 1976 | doi: 10.1021/bk-1976-0033.ch018

Preliminary Hydrolysis Studies FRANK W. HARRIS, ANN E . AULABAUGH, ROBERT D. CASE, MARY K. DYKES, and WILLIAM A. F E L D Department of Chemistry, Wright State University, Dayton, Ohio 45431

C o n t r o l l e d - r e l e a s e p e s t i c i d e - p o l y m e r formulations t h a t extend the c o n t r o l o f a wide v a r i e t y o f t a r g e t organisms have been developed ( 1 - 3 ) . For example, h e r b i c i d e - p o l y e t h y l e n e f o r mulations have been prepared and s t u d i e d i n t h i s l a b o r a t o r y ( 4 ) . In these systems the h e r b i c i d e i s p h y s i c a l l y incorporated i n the plastic matrix and r e l e a s e occurs by d i f f u s i o n . Although formu l a t i o n s o f t h i s type have considerable potential, a drawback to their production and use i s the l a r g e amount o f i n e r t polymer carrier (70-90% w/w) t h a t must be employed. The development o f p e s t i c i d e - p o l y m e r formulations t h a t contain a high percentage o f pesticide is highly desirable. One route to such formulations has been the synthesis o f polymers t h a t contain p e s t i c i d e s as pendent s u b s t i t u e n t s ( 5 - 1 8 ) . For example, polymers have been prepared t h a t c o n s i s t o f over 80% 2 , 4 - d i c h l o r o p h e n o x y a c e t i c a c i d (2,4-D) or 2-(2,4,5-trichlorophenoxy)propionic a c i d ( S i l v e x ) as pendent s i d e chains (14-16). T h e o r e t i c a l l y the c o n t r o l l e d r e l e a s e o f p e s t i c i d e i s then achieved by the s l o w , s e q u e n t i a l h y d r o l y s i s o f the p e s t i c i d e -polymer chemical bonds. Bioassay studies conducted i n moist soil, however, i n d i c a t e t h a t homopolymers c o n t a i n i n g p e s t i c i d e residues t h a t are attached directly to a hydrophobic polymer backbone will not undergo h y d r o l y s i s (5). The o b j e c t i v e o f t h i s research was to prepare herbicide-polymer systems t h a t w i l l undergo slow h y d r o l y s i s when immersed i n an aquatic environment. In our i n i t i a l approach to o b t a i n i n g h y d r o l y z a b l e systems, the h e r b i c i d e s 2,4-D and S i 1 vex were incorporated i n the alcohol residues o f a s e r i e s o f a c r y l i c e s t e r s (14-16). In these mono mers the distance between the h e r b i c i d e and the v i n y l group and, hence, the r e s u l t i n g polymer backbone was v a r i e d by v a r y i n g the length o f the u n i t connecting the h e r b i c i d e to the a c r y l i c a c i d . I t was p o s t u l a t e d that i n c r e a s i n g the length o f the pendent s i d e chain would enhance the h y d r o l y s i s o f the herbicide-polymer bond s i n c e the e s t e r l i n k a g e would be removed from the hydrophobic backbone and l e s s s t e r i c a l l y hindered. The monomers, i . e . 2 - a c r y l o y l o x y e t h y l 2,4-dichlorophenoxy222 Paul and Harris; Controlled Release Polymeric Formulations ACS Symposium Series; American Chemical Society: Washington, DC, 1976.


18.

HARRIS E T A L .

Pendent Herbicide

223

Substituents

acetate ( l a ) , 2-acryloyloxyethyl 2-(2,4,5-trichlorophenoxy)propionate ( I b ) , 2-methacryloyloxyethyl 2,4-dichlorophenoxyacetate ( H a ) , 2-methacryloyloxyethyl 2 - ( 2 , 4 , 5 - t r i c h l o r o p h e n o x y ) p r o p i o nate ( l i b ) , 4 - a c r y l o y l o x y b u t y l 2,4-dichlorophenoxyacetate ( I l i a ) , 4-acryloyloxybutyl 2-(2,4,5-trichlorophenoxy)propionate ( I l l b ) , 4-methacryloyloxybutyl 2,4-dichlorophenoxyacetate ( I V a ) , and 4-methacryloyloxybutyl 2 - ( 2 , 4 , 5 - t r i c h l o r o p h e n o x y ) p r o p i o n a t e ( I V b ) , were polymerized by b u l k - and s o l u t i o n - f r e e - r a d i c a l techniques t o y i e l d the corresponding polymers ( V - V I I I ) . The p o l y m e r i z a t i o n s were enhanced by low i n i t i a t o r concentrations and m i l d c o n d i t i o n s . Polymeric m a t e r i a l s were obtained t h a t e x h i b i t e d inherent v i s c o s i t i e s as high as 2 . 0 3 . -^ÇH Ο

Ο H » C H ^ C H - C - C H C H ^ O-C-R

>

— C H

2

| -

.

Λ

C

Ο

/ ^ c ^ o - ê - R

lo, b

Vo,b -[-Ç(CH )-CH ^3

2

0 II

CH =Ç-C-0-(CH ) -O-C-R 2

2

-ÏCHfcO-C-R

3*

2

,.o,b

V.o.b -[-ÇH

0 CH =CH-C-0-tCH i 2

2

2 r

0

9-

- C

2

j -

A ft

>

R

— C H

θ ' 0-(CH -Ô-C-R 2

ino,b

Viio.b -[-Ç(CH )-CH -]3

Ρ

.

.

0

CHçFC-C-O-tCHpV-O-C-R I

c - -•

CH 3

2

- -

>

A 0

0

0-{CH ^-O-C-R 2

IVo,b

Vlllo.b /Cl

0)

R^CHÔVqVCI

cr

B

)

R =

_CH-0-(O)-C CH

3

C

|

W

Paul and Harris; Controlled Release Polymeric Formulations ACS Symposium Series; American Chemical Society: Washington, DC, 1976.


224

CONTROLLED RELEASE POLYMERIC FORMULATIONS

This communication describes an a l t e r n a t e approach to en hancing the h y d r o l y s i s o f h e r b i c i d e - p o l y m e r bonds, i . e . the c o p o l y m e r i z a t i o n o f v i n y l d e r i v a t i v e s o f 2,4-D and S i l v e x w i t h v i n y l monomers c o n t a i n i n g h y d r o p h i l i c r e s i d u e s . The r a t e o f h y d r o l y s i s o f e s t e r l i n k a g e s connecting pendent s u b s t i t u e n t s t o a hydrocarbon backbone i s known to be increased by the i n c o r p o r a t i o n o f h y d r o p h i l i c groups along the backbone ( 4 , 1 9 , 2 0 ) . Pre l i m i n a r y s t u d i e s o f the h y d r o l y s i s o f p o l y v i n y l 2 , 4 - d i c h l o r o phenoxyacetate), p o l y ( 2 - a c r y l o y l o x y e t h y l 2,4-dichlorophenoxya c e t a t e ) ( V a ) , p o l y ( 4 - a c r y l o y l o x y b u t y l 2,4-dichlorophenoxya c e t a t e ) ( V i l a ) , and a s e r i e s o f copolymers o f 2 - a c r y l o y l o x y e t h y l 2,4-dichlorophenoxyacetate have a l s o been c a r r i e d out. Results and D i s c u s s i o n Copolymerizations. The 2 - a c r y l o y l o x y e t h y l e s t e r s o f 2,4-D ( l a ) and S i l v e x ( l b ) were copolymerized w i t h trimethylamine methacrylimide ( I X ) , 1,1-dimethyl-2-hydroxypropylamine metha c r y l i m i d e ( X ) , 1,1-dimethyl-(2-hydroxy-3-butoxypropyl)amine methacrylimide ( X I ) , a c r y l i c a c i d ( X I I ) , and m e t h a c r y l i c a c i d ( X I I I ) (Table l ) . The copolymerizations w i t h the aminimides were

CH =C-C^-N(CH ) 2

3

CH =Ç-C-R^-CH

3

2

CH,

CH,

CH C H

3

„

IX

3

2

CH,

Ο ^ CH, OH ι II Θ ffil CH =C-C -Ν — Ν — C H g r C H CH -0-4CH )3CH I CH CH 3

Q

2

2

2

3

3

3

XI

CH =CH—COOH 2

XII

CH I 3 CH =C—COOH 2

XIII

c a r r i e d out without s o l v e n t at 70° w i t h a z o b i s i s o b u t y r o n i t r i l e (AIBN) as the i n i t i a t o r . The aminimides were used as comonomers because o f t h e i r extremely h y d r o p h i l i c nature (21-23). The co p o l y m e r i z a t i o n s w i t h a c r y l i c a c i d and m e t h a c r y l i c a c i d were run i n 2-butanone due to t h e i r tendency to form c r o s s l i n k e d gels when polymerized by bulk techniques. In f a c t , the s o l u t i o n c o p o l y merizations with a c r y l i c acid also resulted in considerable amounts of i n s o l u b l e m a t e r i a l . The presence o f the a p p r o p r i a t e


18.

HARRIS E T A L .

Pendent

Herbicide

225

Substituents

h y d r o p h i l i c residues (aminimide,-0H,-C02H) i n the copolymers was confirmed by i n f r a r e d spectroscopy.

TABLE 1 Copolymer!zation Data


Copolymer

XIV XV

a

Copolymer Composition Monomer 1 Monomer 2

la la

IX IX

Mole % Monomer 1 i n Feed

r

87

b

0.35

75

b

0.44

b

0.20

XVI

la

IX

65

XVII

Ib

IX

50

0.54

XVIII

la

X

50

1.00

XIX

Ib

X

50

0.81

XX

la

XI

50

0.87

XXI

Ib

XI

50

0.78

XXII

Ib

XI

80

1.44

XXIII

Ib

XI

95

1.43

XXIV

la

XII

80

0.70

C

XXV

la

XIII

80

0.38

d

b

I n h e r e n t v i s c o s i t y (0.50 g / d l i n chlorobenzene at 30°C).

Âctual composition as determined by elemental a n a l y s i s . c

I n h e r e n t v i s c o s i t y (0.50 g / d l i n sym-tetrachloroethane

at 30°C).

i n h e r e n t v i s c o s i t y (0.50 g / d l i n 2-butanone at 30°C). H y d r o l y s i s S t u d i e s . The i n i t i a l r e s u l t s o f a study o f the hydrolysis o f p o l y v i n y l 2,4-dichlorophenoxyacetate), poly(2acryloyloxyethyl 2,4-dichlorophenoxyacetate)(Va), poly(4-acryloy l o x y b u t y l 2 , 4 - d i c h l o r o p h e n o x y a c e t a t e ) ( V I I a ) , and the aminimide copolymer XIV i n d i c a t e t h a t only the copolymer i s susceptable to h y d r o l y s i s (Figure 1) (18). This study i s being c a r r i e d out w i t h polymer samples t h a t were ground and sieved to a p a r t i c l e s i z e o f 125-400 μ, and then immersed i n d i s t i l l e d water (pH = 7.2) at 30°C. The amount o f h e r b i c i d e released from each polymer i s determined p e r i o d i c a l l y by spectrophotometric a n a l y s i s . The amounts shown i n Figure 1 are the averages o f three r e p l i c a t e s . This study has now been continued f o r 324 days. The copolymer



polymer

2.0-

mg 4.0' 2,4-D released per gram of

6.0

#

ΙΟ

—Γ

Δ o

± Δ

20

~ι—

ο · ο 30

·

Α

°

Δ

40

50

ο

Figure 1.

· ο ·

^

70

1—

· ο

Days

Ο

Hydrolysis data

60

Δ

•

2,4-dichlorophenoxyacetate)

80

90

—ι—

Ο·

Δ

100

ι

•

Δ

P o l y ( 2 - a c r y l o y l o x y e t h y l 2,4-dichlorophenoxyacetate (Va)

ο Polyvinyl

•

ο

(Vila)

Copolymer (87:13) o f 2 - a c r y l o y l o x y e t h y l 2 , 4 - d i c h l o r o phenoxyacetate and Trimethyl amine methacrylimide (XIV)

Δ P o l y ( 4 - a c r y l o y l o x y b u t y l 2,4-dichlorophenoxyacetate

•

110

1


ο I

ο

120

Δ

130


18.

HARRIS E T A L .

Pendent Herbicide

Substituents

227

samples have released an average o f 23 mg o f h e r b i c i d e w h i l e the homopolymers have f a i l e d to h y d r o l y z e . An i n v e s t i g a t i o n o f the h y d r o l y s i s o f p o l y ( v i n y l 2 , 4 - d i chlorophenoxyacetate), polymer V a , copolymer XV, copolymer X V I , and copolymer XXV i n a pH 8 buffer has a l s o been i n i t i a t e d . The buffer was used to simulate the pH o f the natural waters i n the South where a q u a t i c weed problems are the most pronounced. The data shown i n Figure 2 were obtained by employing procedures des c r i b e d f o r the previous study. As can be seen from the F i g u r e , the homopolymers are s t i l l r e s i s t a n t to h y d r o l y s i s at pH 8. The r a t e o f h y d r o l y s i s o f copolymer XV which contains 25% t r i m e t h y l amine methacrylimide i s not s i g n i f i c a n t l y d i f f e r e n t than t h a t observed f o r copolymer XIV i n the i n i t i a l h y d r o l y s i s study. Co polymer XVI which contains 35% o f the aminimide, however, releases h e r b i c i d e c o n s i d e r a b l y f a s t e r . This copolymer has r e l e a s e d 20 mg of h e r b i c i d e i n 32 days. The h y d r o l y s i s data f o r the m e t h a c r y l i c a c i d copolymer XXV was not i n c l u d e d i n Figure 2 because the co polymer r e l e a s e d 117 mg o f h e r b i c i d e i n the f i r s t s i x days o f the study. This r a p i d h y d r o l y s i s was accompanied by considerable s w e l l i n g o f the polymer p a r t i c l e s which prevented f u r t h e r s p e c t r o s c o p i c a n a l y s i s o f the sample s o l u t i o n s . Conclusions The homopolymers c o n t a i n i n g h e r b i c i d e s as pendent s u b s t i tuents prepared i n t h i s work w i l l not undergo h y d r o l y s i s under s l i g h t l y a l k a l i n e c o n d i t i o n s at 3 0 ° . Increasing the length of the pendent s i d e chains does not i n i t s e l f s i g n i f i c a n t l y enhance the h y d r o l y s i s o f the herbicide-polymer e s t e r bonds. The i n c o r p o r a t i o n o f h y d r o p h i l i c aminimide residues along the polymer backbone, however, r e s u l t s i n the slow h y d r o l y s i s o f the ester linkages. Increasing the percentage o f aminimide i n the system from 25 to 35% r e s u l t s i n an increase i n the r a t e o f h e r b i c i d e r e l e a s e . The r a t e o f h y d r o l y s i s can be increased dramati c a l l y by i n c o r p o r a t i n g c a r b o x y l i c a c i d groups along the polymer backbone. These groups are very e f f e c t i v e i n c a t a l y z i n g the h y d r o l y s i s o f the herbicide-polymer e s t e r bonds. Experimental U l t r a v i o l e t spectra were obtained w i t h a Cary Model 14 spectrophotometer. Infrared s p e c t r a were obtained on t h i n f i l m s with a Perkin-Elmer Model 457 spectrophotometer. V i s c o s i t i e s were determined w i t h a Cannon Number 75 viscometer. The aminimide monomers were furnished by Ashland Chemicals, Columbus, Ohio. General Bulk Copolymer!zation Procedure. H e r b i c i d e monomer, comonomer, and 0.1% AIBN were thoroughly mixed and s l o w l y heated to 7 0 ° . A f t e r heating at 70° f o r 3 h r , the residue was c o o l e d , d i s s o l v e d i n c h l o r o f o r m , and p r e c i p i t a t e d i n hexane. The polymer



A

16

A

Δ

A

24

ο Λ

32

.

θ

2,4-dichlorophenoxyacetate)

Δ

Figure 2.

40

56

64

ο

Hydrolysis data

Days

48

Φ ο ο ·

Δ

Δ

72

#

Δ

° 80

88

96~

ο P o l y ( 2 - a c r y l o y l o x y e t h y l 2,4-dichlorophenoxyacetate

• Polyvinyl

(Va)

Δ Copolymer (75:25) o f 2 - a c r y l o y l o x y e t h y l 2,4-dichlorophenoxy acetate and Trimethylamine methacrylimide (XV)

A Copolymer (65:35) o f 2 - a c r y l o y l o x y e t h y l 2,4-dichlorophenoxy acetate and Trimethylamine methacrylimide (XVI)


18.

HARRIS E T A L .

Pendent Herbicide

Substituents

229

was c o l l e c t e d by f i l t r a t i o n and d r i e d under vacuum at 60° f o r 24 h r .


General S o l u t i o n Copolymerization Procedure. H e r b i c i d e monomer, comonomer, 2-butanone (4 m l / g o f monomers), and 0.05% AIBN were thoroughly mixed and s l o w l y heated under n i t r o g e n to 75°. A f t e r heating at 75° f o r 3 h r , the mixture was c o o l e d , d i l u t e d with 2-butanone, and p r e c i p i t a t e d i n hexane. The c o p o l y mer was c o l l e c t e d by f i l t r a t i o n and d r i e d under vacuum at 60° for 3 h r . H y d r o l y s i s S t u d i e s . The copolymers were e x t r a c t e d w i t h methanol f o r 18 hr to remove unreacted monomer, d r i e d under vacuum, and then ground and sieved to a p a r t i c l e s i z e o f 125400 y . Three one-gram samples of each copolymer were placed i n 500-ml erlenmeyer f l a s k s c o n t a i n i n g 300 ml o f a b o r i c acid-sodium hydroxide buffer (pH = 8 . 0 8 ) . The f l a s k s were a g i t a t e d i n a constant temperature bath at 3 0 ± 0 . 1 ° . The amount o f h e r b i c i d e released from each copolymer was determined p e r i o d i c a l l y by s p e c t r o p h o t o m e t r y a n a l y s i s a t 198 nm. Acknowledgement Support o f t h i s research by the Department o f the Army, U. S. Army Engineer Waterways Experiment S t a t i o n under Contract DACW39-76-C-0016 (Neg.) i s g r a t e f u l l y acknowledged. A p p r e c i a t i o n i s a l s o expressed to AmChem Products, Inc. f o r f u r n i s h i n g the h e r b i c i d e s and to Ashland Chemicals Company f o r f u r n i s h i n g the aminimides used i n t h i s study. Literature Cited 1.

Cardarelli, Nate F., Ed., "Proceedings 1974 I n t e r n a t i o n a l C o n t r o l l e d Release P e s t i c i d e Symposium," The U n i v e r s i t y o f Akron, Akron, Ohio, 1974. 2. H a r r i s , Frank W., Ed., "Proceedings 1975 I n t e r n a t i o n a l Con trolled Release P e s t i c i d e Symposium," Wright State Univer sity, Dayton, Ohio, 1975. 3. Cardarelli, Nate F., " C o n t r o l l e d Release P e s t i c i d e s , " Chemical Rubber P u b l i s h i n g Company, C l e v e l a n d , Ohio, 1976. 4. H a r r i s , Frank W., N o r r i s , Steve O., and P o s t , Larry Κ., Weed S c i e n c e , (1973), 21 ( 4 ) , 318. 5. Neogi, A. N., "Polymer S e l e c t i o n f o r C o n t r o l l e d Release P e s t i c i d e s , " Ph.D. T h e s i s , U n i v e r s i t y o f Washington, Seat tle, Washington, 1970. 6. A l l a n , G. G., Chopra C. S., Neogi, A. N., and W i l k i n s , R. Μ., Nature, (1971), 234, 349. 7. Jakubka, H. D. and Busch, Ε., N. Chem., (1973), 13 ( 3 ) , 105. 8. Akagane, K. and Allan, G. G., Shikizai K y o k a i s h i , (1973), 46, 437; Chem. A b s t r . , (1974), 80, 61104k.


230 9. 10. 11.

12.


13.

14.

15. 16. 17.

18. 19. 20. 21. 22. 23.

CONTROLLED RELEASE POLYMERIC FORMULATIONS Montemarano, J. Α., and Dyckman, E. J., Am. Chem.Soc.,D i v . Org. Coat. P l a s t . , P r e p r i n t s , (1974), 34 ( 1 ) , 607. B a l t a z z i , E., U. S. Patent 3,343,941 (1967); Chem. A b s t r . , (1968), 68, 50730 n. M e h l t r e t t e r , C. L., Roth, W. B., Weakley, F. Β., McGuire, Τ. Α., and Russell, C. R., Weed S c i e n c e , (1974), 22 ( 5 ) , 415. A l l a n , G. G., Chopra, C. S., and Russell, R. Μ., I n t . Pest Contr., (1972), 14 ( 2 ) , 15. A l l a n , G. G., Chopra, C. S., F r i e d h o f f , J. F., Gara, R. I., Maggi, M. W., Neogi, A. N., Roberts, S. C., and W i l k i n s , R. W., Chem. Tech., (1973), March, 171. H a r r i s , Frank W. and P o s t , L a r r y K. in "Proceedings 1974 I n t e r n a t i o n a l C o n t r o l l e d Release P e s t i c i d e Symposium," Cardarelli, Nate F., Ed., The U n i v e r s i t y o f Akron, Ohio, 1974. H a r r i s , Frank W., and P o s t , L a r r y Κ., Am. Chem. Soc., Polym. Div., P r e p r i n t s , (1975), 16 ( 2 ) , 622. H a r r i s , Frank W. and P o s t , Larry K., J. Polym. Sci., Polym. Sci., Polymer L e t t e r s ed., (1975), 13, 225. F e l d , W i l l i a m Α., P o s t , L a r r y Κ., and Harris, Frank W. i n "Proceedings 1975 I n t e r n a t i o n a l C o n t r o l l e d Release P e s t i c i d e Symposium," p. 113, Harris, F. W., Ed., Wright State Univer sity, Dayton, Ohio, 1975. H a r r i s , Frank W., F e l d , W i l l i a m Α., and Bowen, Bonnie, ibid, p. 334.. Morawetz, H. and Gaetjens, E., J. Polym. Sci., (1958), 32, 526. Davies, R. F. B., and Reynolds, G. E. J., J. Appl. Polym. Sci., (1968), 12, 47. M c K i l l o p , W. J., Sedor, Ε. Α., C u l b e r t s o n , Β. Μ., and Wowzonek S., Chem. Rev., (1973), 73, 255. C u l b e r t s o n , Β. Μ., Sedor, Ε. Α., and Slagel, R. C., Macromolecules, (1968), 1 , 254. C u l b e r t s o n , Β. Μ., and Slagel, R. C., J. Polym. Sci., P a r t A-1, (1968), 6, 363.


Controlled Release Polymeric Formulations

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