Butyl Acrylate Polymers for Use in Epoxy Resin Toug - American

3

Downloaded by UNIV OF MICHIGAN ANN ARBOR on February 18, 2015 | http://pubs.acs.org Publication Date: June 8, 1983 | doi: 10.1021/bk-1983-0221.ch003

Synthesis and Analysis of Saturated, Reactive n-Butyl Acrylate Polymers for Use in Epoxy Resin Toughening 1

S. GAZIT and JAMES P. BELL University of Connecticut, Storrs, CT 06268 A low molecular weight, carboxyl terminated poly (n-butyl acrylate) rubber was synthesized for evaluation as a toughening agent in epoxy resins. The carboxyl ends were incorporated by initiation with azo bis-cyanovaleric acid and by use of dithiodiglycolic acid as a chain transfer agent to control molecular weight. Bulk polymerization was required to avoid severe chain transfer to solvents, thus providing functionality near 2.0. The molecular weight decreased with increasing chain transfer agent, initiator concentration, and with increasing polymerization temperature.

Epoxy r e s i n s with r e l a t i v e l y high g l a s s t r a n s i t i o n temperature (>100°c) are b r i t t l e , Lee and N e v i l l e (JL) Perez (6.). The toughening o f c r o s s l i n k e d epoxy r e s i n s , such as the d i g l y c i d y l ether of bisphenol A (DGEBA) by Reactive L i q u i d Polymers (RLP) has been the subject of i n t e n s i v e s t u d i e s s i n c e the m i d - s i x t i e s , B u c k n a l l (_7). One method of toughening epoxy by RLP i s based on i n c o r p o r a t i n g a s m a l l p r o p o r t i o n of a low glass t r a n s i t i o n p o l y mer, t y p i c a l l y between 5 and 20%, i n t o the r i g i d matrix. Initia l l y , the rubber i s m i s c i b l e with the mixture of the epoxy monomer and the c u r i n g agent. During the c u r i n g process most of the RLP p r e c i p i t a t e s from the matrix and forms a homogeneously dispersed, rubbery, f i n e p a r t i c l e phase. This two phase morphology improves the toughness o f the host matrix, Manson and S p e r l i n g (3). If the rubbery polymer f a i l s to separate from the epoxy matrix i t serves as a p l a s t i c i z e r r a t h e r than a toughening element, and while toughness may be improved, there i s a major r e d u c t i o n of the sofening temperature. The success of t h i s p r i n c i p l e with 1

Current address: Rogers Corporation, Lurie Research and Development Center, Rogers, CT 06263

0097-6156/83/0221-0055$06.00/0 © 1983 American Chemical Society

In Epoxy Resin Chemistry II; Bauer, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 1983.


56

EPOXY RESIN CHEMISTRY

p r e s e n t l y a v a i l a b l e DGEBA/ RLP s y s t e m s h a s n o t y e t r e a c h e d t h e l e v e l s o b s e r v e d w i t h r u b b e r t o u g h e n e d t h e r m o p l a s t i c s s u c h as polystyrene. The t o u g h e n i n g o f e p o x y r e s i n s h a s b e e n a t t e m p t e d w i t h v a r i o u s r u b b e r s . Noshay and R o b e s o n ( 8 ) c o p o l y m e r i z e d DGEBA w i t h l o w m o l e c u l a r w e i g h t p o l y c a p r o l a c t o n e and p o l y p r o p y l e n e o x i d e . S p e r l i n g and F r i e d m a n (9.) i n t r o d u c e d t h e u s e o f S i m u l t a n e o u s I n t e r p e n e t r a t i n g Network (SIN) t o improve t h e i m p a c t s t r e n g t h o f epoxy. I n t h i s method monomers o f DGEBA and η-butyl a c r y l a t e were s i m u l t a n e o u s l y p o l y m e r i z e d i n b u l k . M c G a r r y and W i l l n e r (10) s t u d i e d t h e i n t e r a c t i o n b e t w e e n DGEBA and b u t a d i e n e b a s e d v a r i o u s Hycar rubbery r e s i n s . Most o f t h e r e c e n t s t u d i e s i n t h e f i e l d c o n c e n t r a t e d on t h e s e C a r b o x y l T e r m i n a t e d B u t a d i e n e - A c r y l o N i t r i l e (CTBN) r u b b e r s . A f e w o t h e r l i q u i d , l i n e a r r e a c t i v e m o d i f i e r s have been proposed r e c e n t l y t o toughen epoxy r e s i n s . C a r b o x y l - t e r m i n a t e d p o l y i s o b u t y l e n e ( C T P I B ) was s y n t h e s i z e d and s t u d i e d b y S l y s h ( 1 1 ) . U n i t e d T e c h n o l o g i e s C o r p . h a s a l s o com m e r c i a l i z e d ABAN ( c a r b o x y l a t e d b u t a d i e n e / a c r y l o n i t r i l e c o p o l y m e r s ) f o r t o u g h e n i n g DGEBA. I t i s w e l l known t h a t f o r e f f e c t i v e t o u g h e n i n g o f t h e e p o x y r e s i n t h e r u b b e r y e l e m e n t s h a v e t o be g r a f t e d , t o a c e r t a i n d e g r e e , t o t h e DGEBA m a t r i x ( 1 0 , 1 2 , 1 3 ) . However, an e x c e s s i v e amount o f c h e m i c a l i n t e r a c t i o n b e t w e e n t h e DGEBA and t h e r u b b e r m o d i f i e r might l e a d t o the f o r m a t i o n o f a s i n g l e phase, u n d e s i r a b l e morphology ( 8 ) . V a r i o u s r e a c t i v e groups have been used f o r c h e m i c a l g r a f t i n g b e t w e e n t h e e p o x y r e s i n and t h e r u b b e r y p h a s e ; c a r b o x y l ( 1 0 , 1 1 ) , h y d r o x y 1 ( 1 4 ) , e p o x y ( 1 3 , 1 4 ) , m e r c a p t a n (14) and amine (ATBN, a Hycar r e s i n ) . The r e a c t i v e g r o u p s c a n b e p r e s e n t r a n d o m l y on t h e r u b b e r m o l e c u l e b a c k b o n e o r c a n be l o c a t e d a t t h e ends o f t h e polymeric chain. Most r e s e a r c h e r s suggest t h a t polymers p o s s e s s i n g two r e a c t i v e t e r m i n a l g r o u p s ( t e l e c h e l i c p o l y m e r s ) p r o d u c e s t r o n g e r e l a s t o m e r i c s t r u c t u r e s t h a n r a n d o m l y f u n c t i o n a l RLPs w i t h t h e same m o l e c u l a r w e i g h t ( 1 0 , 1 1 , 1 8 ) . A new RLP, C a r b o x y l T e r m i n a t e d P o l y η-Butyl A c r y l a t e (CTPnBA), reported i n t h i s study, f a l l s i n t o the category of t e l e c h e l i c p o l y m e r s , p o s s e s s i n g on t h e a v e r a g e 1.8-2.0 c a r b o x y l t e r m i n a l groups per c h a i n . The CTPnBA h a s t h e o r e t i c a l l y a h i g h p o t e n t i a l f o r t o u g h e n i n g DGEBA f o r t h e f o l l o w i n g r e a s o n s : Physical—1. 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 PnBA o c c u r s b e t w e e n -40°C and -50°C. I t has a r e l a t i v e l y h i g h m e c h a n i c a l damping p e a k w h i c h i s h e l p f u l f o r t h e t o u g h e n i n g mechanism o f DGEBA/PnBA c o m p o s i t e s . 2. A t room t e m p e r a t u r e PnBA (up t o Mn £ 25,000) i s a viscous l i q u i d . 3. Low m o l e c u l a r w e i g h t l i q u i d PnBA i s s o l u b l e i n DGEBA a t m o d e r a t e t e m p e r a t u r e s . The d i f f e r e n c e i n t h e s o l u b i l i t y p a r a m e t e r s o f PnBA and DGEBA i s r e l a t i v e l y small (2).


3.

GAZIT AND BELL

Epoxy Resin Toughening

57

Chemical—4. PnBA i s more s t a b l e chemically than the butadiene based RLPs, which c o n t a i n r e s i d u a l double bonds. 5. The nBA l i q u i d monomer (b.p. 145°C) i s polymerized r e a d i l y , u s i n g r e l a t i v e l y convenient c o n d i t i o n s .


Experimental The Carboxyl Terminated Poly η-Butyl A c r y l a t e was polymer i z e d i n a g l a s s , 500 ml. batch r e a c t o r . The r e a c t o r was designed f o r s o l u t i o n and bulk p o l y m e r i z a t i o n under atmospheric pressure and v a r i a b l e temperatures, Figure 1. In the s o l u t i o n polymeriza t i o n t e s t s the i n i t i a t o r , 4,4 -azo b i s - ( 4 - c y a n o v a l e r i c acid) (ABCVA), and the chain t r a n s f e r agent, d i t h i o d i g l y c o l i c a c i d (DTDGA), were d i s s o l v e d i n the polymerization s o l v e n t . The mono mers η-butyl a c r y l a t e (nBA) and ethylene d i a c r y l a t e (EDA) were added to the p o l y m e r i z a t i o n media a t a constant flow r a t e through a s y r i n g e pump arrangement. The r e a c t o r was purged with n i t r o g e n at the beginning of the polymerization process, and a n i t r o g e n blanket was maintained over the s o l u t i o n during the e n t i r e r e a c t i o n p e r i o d . In the bulk p o l y m e r i z a t i o n procedure the i n i t i a t o r and the chain t r a n s f e r agent powders were thoroughly mixed and placed (dry) i n the r e a c t o r . A f t e r the r e a c t o r was purged with n i t r o g e n the nBA monomer was poured i n t o the p o l y m e r i z a t i o n container a t once, and r a p i d l y mixed with the powders. The bulk p o l y m e r i z a t i o n was r a p i d and occurred w i t h i n a few minutes between 69 and 120°c. In the a n a l y t i c a l procedure the CTPnBA was separated from the excess i n i t i a t o r , chain t r a n s f e r agent and monomeric nBA i n a c l e a n i n g method which i n c l u d e d s e v e r a l stages, Appendix A. The molecular weight of the p u r i f i e d CTPnBA rubber was measured by a Knauer Vapor Pressure Osmometer i n chloroform s o l u t i o n at 37°C. The carboxyl content of the CTPnBA was determined by a chemical t i t r a t i o n procedure u s i n g a modified p o t e n t i o m e t r i c technique, Appendix B. f

e

Background C a l c u l a t i o n s The k i n e t i c s of d i l u t e s o l u t i o n p o l y m e r i z a t i o n of b u t y l acry l a t e were s t u d i e d by M e l v i l l e and B i c k e l (15). They measured the propagation and termination c o e f f i c i e n t s at 25°c; kp = 13(£/mole sec) and kt 1.8 χ 10 (^/mole s e c ) . M e l v i l l e and B i c k e l a l s o concluded that the termination r e a c t i o n at 25°C occurred mostly through combination, thus t h e o r e t i c a l l y i n c r e a s i n g the p r o b a b i l i t y t o produce a carboxyl terminated PnBA with an i d e a l f u n c t i o n a l i t y of f=2 when the polymerization r e a c t i o n i s i n i t i a t e d with ABCVA. C a l c u l a t i o n of the degree of p o l y m e r i z a t i o n of a f r e e r a d i c a l p o l y m e r i z a t i o n i n very d i l u t e s o l u t i o n , assuming chain t r a n s f e r r e a c t i o n s and termination by combination, i n d i c a t e d Xn = 40-70. 8



58


F i g u r e 1· The r e a c t o r a s s e m b l y f o r t h e p o l y m e r i z a t i o n o f PnBA. Key: a , m i x e r ; b , c o n d e n s e r ; c , s y r i n g e ; d , s y r i n g e d r i v e s y s t e m ; e, r e a c t o r ; f , o i l b a t h ; g, v a p o r t r a p ; and h , n i t r o g e n f l o w m e t e r .


3.

GAZIT AND BELL


59

T h i s i s e q u i v a l e n t to a molecular weight of Mn « 6000-8000, Appendix C. The enthalpy o f mixing o f two l i q u i d s i s expressed by eq. 1, Hildebrand and Scott (4.)


AHm

= Vm

[ δ ^ ]

2

φ φ χ

(1)

2

where δ i s the s o l u b i l i t y parameter, Vm i s the molar volume of the mixture, and φ^, φ^ are volume f r a c t i o n s of s o l v e n t and polymer, r e s p e c t i v e l y . The s o l u b i l i t y parameter δ may be c a l c u l a t e d from the group c o n t r i b u t i o n p r i n c i p l e developed by Small (16). A more complete treatment takes i n t o account secondary e f f e c t s , O l a b i s i et a l . (5.). The enthalpy of mixing c o n t r o l s the m i s c i b i l i t y of two l i q u i d polymers; i f (δ -δ ) = 0, the s o l u t i o n i s assured by the p o s i t i v e entropy term i n the Gibbs Equation AHm - TmASm, making AG negative ( f a v o r a b l e ) . The c a l c u l a t e d s o l u b i l i t y parameters of PnBA an^ ÇGgBA are δ = 9.24 ( c a l / c m ) and δ = 9.70 3

1 / 2

(cal/cm ) respectively. T h i s r e l a t i v e l y small d i f f e r e n c e i n the s o l u b i l i t y parameters o f the two r e s i n s t h e o r e t i c a l l y favors the p r o b a b i l i t y of the spontaneous mixing of PnBA and Epon 828. However, the m i s c i b i l i t y i s a l s o dependent on the molecular weight of the r e s i n s — t h e h i g h e r the molecular weight of the PnBA the lower the δ, and thus the lower the s o l u b i l i t y of the rubber i n the epoxy r e s i n . Results and D i s c u s s i o n P o l y m e r i z a t i o n of CTPnBA i n d i l u t e s o l u t i o n . The s o l u t i o n p o l y m e r i z a t i o n of N-butyl a c r y l a t e i s b e t t e r p r e d i c t e d and simpler to control. The e f f e c t of the molecular weight on the m i s c i b i l i t y of CTPnBA i n Epon 828 was s t u d i e d w i t h a s e r i e s of polymers polymerized i n d i l u t e t-butanol s o l u t i o n s , Table I. As expected, i n c r e a s i n g both d i l u t i o n of the monomer and the p o l y m e r i z a t i o n temperature r e s u l t e d i n decreasing molecular weight of CTPnBA. The s o l u b i l i t y of 10-15 p a r t s of CTPnBA i n 100 p a r t s DGEBA (Epon 828) at 25°C was the m i s c i b i l i t y c r i t e r i o n f o r the two r e s i n s . The c r i t e r i o n was chosen s i n c e the toughening mechanism of CTPnBA/ Epon 828 systems was expected to be e f f e c t i v e w i t h t h i s r e s i n r a t i o range, based on CTBN rubber s t u d i e s (10,14). The r e s u l t s suggested that the upper l i m i t i n g molecular weight f o r the s o l u b i l i t y of CTPnBA i n Epon 828 was around Mn « 4400. The f u n c t i o n a l i t y of polymer 1-b was found to be s u r p r i s i n g l y low f=1.15, apparently a t t r i b u t a b l e to extensive chain t r a n s f e r to the s o l v e n t or due to d i s p r o p o r t i o n a t i o n termination. Tertbutanol was reported to be one of the few s o l v e n t systems i n having an extremely low chain t r a n s f e r p o t e n t i a l i n s i m i l a r f r e e r a d i c a l polymerizations (17). The s o l u b i l i t y of the reagents, the p o l y m e r i z a t i o n temperature and the r e a c t i v i t y c h a r a c t e r i s t i c s r e s t r i c t the choice of s o l v e n t s to only a few, some of which were



60 TABLE I .

t-butanol

#


P o l y m e r i z a t i o n o f nBA i n t-butanol

nBA

Temp.

(g)

Cc)

Mn

Solubility*

(ce)

(g)

1-•a

450

15.75

0.12

1.71

70

6400

No

1-•b

500

25.00

0.17

1.71

83

4400

Yes

1-•c

1000

37.25

0.15

3.42

83

3850

Yes

* +

(cc/min)+

ABCVA

s o l u b i l i t y o f 10 p a r t s o f CTPnBA i n 100 parts DGEBA. flow r a t e of nBA i n t o the r e a c t o r .

TABLE I I .

F u n c t i o n a l i t y o f PnBA i n v a r i o u s s o l v e n t s .

Solvent

# type

nBA

(cc)

(g)

ABCVA (cc/min)

(g)

Temp.

Mn

f*

Cc)

2-•a

t-butanol

500

25.0

0.17

1.71

83

4400

1.15

2--b

acetone

500

25.0

0.19

1.71

56

6900

1.30

2--c

THF

500

14.0

0.34

1.71

65

1350

0.30

*

f - functionality

s t u d i e d , Table I I . The f u n c t i o n a l i t y of CTPnBA was higher i n acetone than i n t-butanol, e i t h e r due to a d i f f e r e n t extent o f chain t r a n s f e r r i n g to the s o l v e n t s , or due to a d i f f e r e n t r a t i o of the termination by combination v s . d i s p r o p o r t i o n a t i o n of the p o l y m e r i z a t i o n i n the two s o l v e n t s . The molecular weight of polymer 2-b (mainly a t t r i b u t a b l e to low p o l y m e r i z a t i o n temperature, l i m i t e d by the b o i l i n g p o i n t ) was too h i g h . E f f i c i e n t toughening by the rubber m o d i f i e r can be obtained, as d i s c u s s e d e a r l i e r , only i f the RLP i s capable of s u f f i c i e n t g r a f t i n g to the epoxy matrix. T h e o r e t i c a l l y , the optimal l i n e a r rubber chain should possess two terminal r e a c t i v e groups. Since t h i s c o n f i g u r a t i o n could not be synthesized i n d i l u t e s o l u t i o n p o l y m e r i z a t i o n , a branched copolymer of nBA and ethylene d i a c r y l a t e (EDA), s t r u c t u r e I, with a p o t e n t i a l l y higher f u n c t i o n a l i t y , was s t u d i e d .

Ethylene d i a c r y l a t e i s used p r i m a r i l y as a c r o s s -


GAZIT AND BELL

3.

CH


0 il = CH - C - 0 - C H

2


I

2

- CH

Ethylene

2

0 I! - 0 - C - CH

61

-

CH

2

diacrylate

l i n k i n g agent i n f r e e r a d i c a l p o l y m e r i z a t i o n s , but i n t h i s study i t was u s e d as a b r a n c h i n g a g e n t . The c o p o l y m e r i z a t i o n o f EDA w i t h nBA was d e s i g n e d t o b u i l d b r a n c h i n g i n t o t h e PnBA c h a i n , and t h u s i n c r e a s e t h e p r o b a b i l i t y o f a f u n c t i o n a l i t y h i g h e r t h a n 2. The a d d i t i o n a l c a r b o x y l g r o u p s t h r o u g h t h i s mechanism can be e x p e c t e d t o be l o c a t e d a t t h e t i p s o f t h e b r a n c h e s . The func t i o n a l i t y o f t h e nBA/EDA c o p o l y m e r s i n c r e a s e d w i t h t h e c o n c e n t r a t i o n o f EDA ( T a b l e I I I ) , b u t e v e n t h i s t e c h n i q u e d i d n o t y i e l d a s u f f i c i e n t i n c r e a s e i n t h e f u n c t i o n a l i t y o f t h e PnBA. The d i f f e r e n c e i n f u n c t i o n a l i t y o f 3-b and 3-c i s i n s i g n i f i c a n t and i t i n d i c a t e s t h a t i n c r e a s e i n EDA c o n c e n t r a t i o n above t h e 3-b f o r m u l a t i o n d o e s n o t l e a d t o an i n c r e a s e i n f u n c t i o n a l i t y .

TABLE I I I .

#

M o l e c u l a r w e i g h t and copolymers.

t-butanol

3-a 3-b 3-c

nBA

(cc)

(g)

500 500 500

25 25 25

(cc/min) 0.23 0.23 0.42

functionality

EDA

ABCVA

(g)

(g)

1.35 3.40 6.81

1.11 1.11 1.65

o f nBA/EDA

Mn

f

6100 6250 6200

1.15 1.27 1.30

A t h e y , M o s h e r and Weston ( 1 9 , 20) s t u d i e d t h e u s e o f symmet r i c a l d i f u n c t i o n a l chain t r a n s f e r agents f o r s y n t h e s i s of t e l e c h e l i c polymers. D i t h i o d i g l y c o l i c a c i d (DTDGA, I I ) was s e l e c t e d i n t h e p r e s e n t w o r k as a c h a i n t r a n s f e r a g e n t t o i n c r e a s e t h e f u n c t i o n a l i t y o f t h e PnBA. T h i s p a r t i c u l a r c h a i n t r a n s f e r a g e n t c l e a v e s a t t h e s u l p h u r - s u l p h u r bond i n t h e p r e s e n c e o f a f r e e r a d i c a l as shown b e l o w : 0 Ρ·

0

0

0

+ 0H-C-CH -S-S-CH -C-0H -> -PSCH -C-0H + 0H-C-CH -S* 2

2

II

2

Dithiodiglycolic

2

(2)

acid

T h i s m e c h a n i s m i n c r e a s e s t h e p r o b a b i l i t y o f o b t a i n i n g an o v e r a l l h i g h e r f u n c t i o n a l i t y o f PnBA by s c a v a n g i n g the free


62


radicals species. i n Table molecular tionality

o f the growing rubber chain with carboxyl c a r r i e r The r e s u l t s o f the chain t r a n s f e r study a r e summarized IV. The e f f e c t s o f the concentration o f DTDGA on the weight o f the polymer were dramatic, however the func o f the PnBA s t i l l d i d not exceed f = 1.30.


TABLE IV. Molecular weight and f u n c t i o n a l i t y o f CTPnBA, e f f e c t of DTDGA c o n c e n t r a t i o n .

# 4-a 4-b 4-c 4-d 4-e *

t-butanol (cc)

nBA*

ABCVA

DTDGA

(g)

(g)

(g)

450 500 500 500 500

16.2 24.7 25.6 25.6 25.2

1.71 1.65 1.65 1.65 1.65

0 0.093 0.468 0.936 1.174

Mn

13200 10100 4200 3800 3850

The monomer was added to the s o l u t i o n at the beginning polymerization.

f

1.15 / 1.23 1.30 1.29 o f the

The r e s u l t s of the d i l u t e s o l u t i o n p o l y m e r i z a t i o n suggested that s o l v e n t chain t r a n s f e r was a governing f a c t o r i n the termina t i o n step. By the same token, the mechanism o f s o l v e n t chain t r a n s f e r termination forms f r e e r a d i c a l s which do not c a r r y carboxyl groups, and serve as potent i n i t i a t o r species i n the p o l y m e r i z a t i o n media. I t was concluded that i n order to o b t a i n higher f u n c t i o n a l i t y o f the PnBA the s o l v e n t had to be e l i m i n a t e d from the p o l y m e r i z a t i o n r e a c t o r . P o l y m e r i z a t i o n o f PnBA i n bulk. The molecular weight o f PnBA i s very dependent on the p o l y m e r i z a t i o n temperature, i n both bulk and s o l u t i o n p o l y m e r i z a t i o n . The e f f e c t o f the p o l y m e r i z a t i o n temperature i n bulk on the molecular weight o f PnBA was s t u d i e d from 69°C to 120°C, Table V. The molecular weight decreased d r a m a t i c a l l y with i n c r e a s i n g p o l y m e r i z a t i o n temperature up to about 105-110°C, where i t reached a p l a t e a u . Due to high mole c u l a r weight, none o f the polymers was m i s c i b l e with Epon 828 a t room temperature. The e f f e c t o f the c o n c e n t r a t i o n o f DTDGA on the molecular weight of CTPnBA was s t u d i e d a t a constant p o l y m e r i z a t i o n tempera t u r e o f Τ = 108°C, Table 6. The r e s u l t s i n d i c a t e that an i n c r e a s e i n the c o n c e n t r a t i o n o f the chain t r a n s f e r agent beyond 10% mole r a t i o o f DTDGA t o nBA may reduce the molecular weight o f the polymer by only a very s m a l l amount.


3.

GAZIT AND BELL

TABLE V.


#

5-a 5-b 5-c 5-d 5-e 5-f

Molecular weight and f u n c t i o n a l i t y of CTPnBA at various p o l y m e r i z a t i o n temperatures, i n bulk p o l y m e r i z a t i o n .

nBA

ABCVA

DTDGA

(8)

(g)

(g)

3.90 3.90 3.90 3.89 3.90 3.91

2.20 2.20 2.20 2.20 2.20 2.20

42.0 42.0 41.9 42.0 42.0 42.1

TABLE VI.

#

6-a 6-b 6-c 6-d

63


Mn

f

13500 12200 9700 7500 7000 6900

/ /

Temp. (°C) 69 80 90 100 110 120

2.06 1.80 1.78 1.82

Molecular weight and f u n c t i o n a l i t y of CTPnBA a t v a r i o u s chain t r a n s f e r concentrations i n bulk polymerization.

nBA

ABCVA

DTDGA

(g)

(g)

(g)

3.90 3.91 3.89 3.88

1.01 3.02 5.99

40.3 39.9 40.9 40.8

/

Mn

10300 8500 7000 6300

f

2.16 2.04 1.96 1.91

The e f f e c t o f the i n i t i a t o r c o n c e n t r a t i o n on the molecular weight o f the CTPnBA was s t u d i e d at p o l y m e r i z a t i o n temperature of 120°C i n the absence of the chain t r a n s f e r agent, Table V I I . As expected, i n c r e a s e i n i n i t i a t o r concentration r e s u l t e d i n a decrease of the molecular weight. The measured f u n c t i o n a l i t y of the CTPnBA rubber i n the bulk p o l y m e r i z a t i o n was i n the range o f f = 1.80-2.16 (Tables V - V I I ) . T h i s value was r e p r o d u c i b l e i n the v a r i o u s experiments and occurred independent of changes i n p o l y m e r i z a t i o n temperature and concentrations of the reagents. The lowest molecular weight of the CTPnBA polymerized i n bulk was i n the range o f Mn = 6000-7000. Carboxyl Terminated Poly η-Butyl A c r y l a t e w i t h t h i s high molecular weight was not s o l u b l e i n Epon 828 a t room temperature, but became m i s c i b l e with the epoxy r e s i n at 120°C. The a d d i t i o n of some amine c u r i n g agents a l s o enhances s o l u b i l i t y ; a s l i g h t l y cloudy mixture of the rubber i n Epon 828 becomes c l e a r when an a l i p h a t i c amine i s added, G a z i t (18).


64


TABLE V I I .


# 7-a 7-b 7-c 7-d

Molecular weight and f u n c t i o n a l i t y of CTPnBA at v a r i o u s i n i t i a t o r concentrations i n b u l k polymerization.

nBA

ABCVA

(g)

(g)

40.5 40.6 40.3 40.2

4.01 5.00 6.00 7.01

Mn

11900 11200 10000 9700

f

1.93 2.03 1.95 1.90

Conclusions 1. The molecular weight o f CTPnBA i s c o n t r o l l e d by the p o l y m e r i z a t i o n temperature, i n i t i a t o r , and the chain t r a n s f e r agent i n both d i l u t e s o l u t i o n and bulk p o l y m e r i z a t i o n . 2. CTPnBA rubber w i t h molecular weight up to Mn ^4400 was m i s c i b l e w i t h Epon 828 at room temperature. 3. Severe chain t r a n s f e r to solvent appeared to cause a l i m i t i n the f u n c t i o n a l i t y of CTPnBA to about f = 1.30 i n d i l u t e s o l u t i o n , free r a d i c a l polymerization. 4. The p o l y m e r i z a t i o n temperature had the strongest e f f e c t on the molecular weight of CTPnBA. T h i s was seen i n both the s o l u t i o n and i n the bulk p o l y m e r i z a t i o n experiments. 5. I n c r e a s i n g concentration of i n i t i a t o r and chain t r a n s f e r agent r e s u l t e d i n decreasing molecular weight of the CTPnBA rubber. 6. F u n c t i o n a l i t y of the CTPnBA rubber d r a m a t i c a l l y i n creased i n the bulk p o l y m e r i z a t i o n experiments, suggesting that chain t r a n s f e r to s o l v e n t was a s i g n i f i c a n t reason f o r the poor f u n c t i o n a l i t y i n d i l u t e s o l u t i o n polymerization. Appendix A The CTPnBA c l e a n i n g procedure. The o b j e c t i v e of the c l e a n i n g procedure was to remove the low molecular weight compounds from the CTPnBA rubber a f t e r the p o l y m e r i z a t i o n had been completed. The l i q u i d s were removed by evaporation under vacuum, and the s o l i d s were separated from the CTPnBA by e x t r a c t i o n i n s o l u t i o n . (a) A f t e r evaporation of the polymerization solvent the mixture o f CTPnBA and the low molecular weight compounds were d i s s o l v e d i n toluene.



3.

GAZIT AND BELL


65

(b) The ABCVA and DTDGA p r e c i p i t a t e d o v e r n i g h t w e r e f i l t e r e d s e v e r a l t i m e s u n t i l t h e s o l u t i o n became c l e a r . ( c ) The p o l y m e r s o l u t i o n i n t o l u e n e was m i x e d w i t h d i s t i l l e d w a t e r i n a r a t i o o f a b o u t 1 p a r t o f H«0 t o 3 p a r t s o f toluene solution. The f l a s k was s h a k e n f o r aïïout 1 h o u r , d u r i n g w h i c h time t h e r e m a i n i n g d i s s o l v e d s o l i d s i n t h e t o l u e n e were e x t r a c t e d by t h e water. The o r g a n i c p o l y m e r r e m a i n e d i n t h e o r g a n i c phase. (d) The s o l u t i o n was c e n t r i f u g e d f o r a b o u t 1 h o u r a t 2800 rpm, i n a l a b - b e n c h c e n t r i f u g e , and t h e two p h a s e s s e p a r a t e d , t h e upper f r a c t i o n c o n t a i n i n g t h e c l e a n polymer i n t o l u e n e . (e) The t o l u e n e was e v a p o r a t e d i n a r o t a r y e v a p o r a t o r , and t h e n p l a c e d i n a vacuum o v e n a t 80°C f o r a b o u t 12 h o u r s u n t i l c o n s t a n t w e i g h t was o b t a i n e d . S t e p s ( c ) and (d) w e r e r e p e a t e d 3-4 t i m e s u n t i l t h e c h e m i c a l t i t r a t i o n showed no s i g n i f i c a n t c h a n g e i n t h e a c i d c o n t e n t . Appendix Β The d e t e r m i n a t i o n o f t h e c a r b o x y l c o n t e n t i n t h e CTPnBA. The method i s b a s e d on a p o t e n t i o m e t r i c a c i d - b a s e t i t r a t i o n t e c h n i q u e i n organic solution. r e a g e n t s = 1. R e a g e n t a b s o l u t e m e t h a n o l 2. R e a g e n t a c e t o n e 3. S t a n d a r d i z e d 0.5N KOH s o l u t i o n i n m e t h a n o l An amount o f 2-3 g o f t h e c l e a n e d and d r i e d CTPnBA r e s i n s a m p l e was t i t r a t e d . The p o l y m e r s a m p l e was a c c u r a t e l y w e i g h e d i n a 300 c c r o u n d b o t t o m f l a s k . 50 c c o f m e t h a n o l and 100 c c o f acetone were p i p e t t e d i n t o the f l a s k . The s o l u t i o n was s t i r r e d f o r a b o u t 20-30 m i n u t e s . The s t a r t i n g pE o f t h e s o l u t i o n was i n t h e r a n g e o f 4-6. S t a n d a r d i z e d 0.5N KOH s o l u t i o n was t h e n c o n t i n u o u s l y added t o t h e s a m p l e s o l u t i o n a t a r a t e o f a b o u t 0.1 c c / m i n b y u s e o f a s y r i n g e pump. The i n f l e c t i o n e n d p o i n t o c c u r r e d a t a b o u t pH 10.5. The a c i d - b a s e t i t r a t i o n p r o c e d u r e was c h e c k e d w i t h ABCVA and a c r y l i c a c i d , and was f o u n d a c c u r a t e and r e p r o d u c i b l e . Functionality. The number o f c a r b o x y l e q u i v a l e n t s was d e t e r m i n e d from the p o t e n t i o m e t r i c acid-base t i t r a t i o n . The number m o l e c u l a r w e i g h t Mn o f t h e CTPnBA was d e t e r m i n e d b y t h e V a p o r P r e s s u r e Osmometer measurement. The p r o d u c t o f t h e number o f a c i d e q u i v a l e n t s by t h e m o l e c u l a r w e i g h t d i v i d e d by t h e w e i g h t o f the t i t r a t e d PnBA s a m p l e i s t h e c a l c u l a t e d a v e r a g e number o f c a r b o x y l g r o u p s p e r c h a i n o f t h e p o l y η-butyl a c r y l a t e . Appendix C The c a l c u l a t i o n e x a m p l e o f t h e d e g r e e o f p o l y m e r i z a t i o n o f η-butyl a c r y l a t e . The c a l c u l a t i o n assumes c h a i n t r a n s f e r t o monomer, s o l v e n t and c h a i n t r a n s f e r a g e n t f o r a t y p i c a l b a t c h .



66


monomer - nBA 30.0 gr, 33 cc (MW - 128) i n i t i a t o r - ABCVA 1.7 gr, (MW = 280) chain t r a n s f e r agent = DTDGA 2.2 gr, (MW - 182) s o l v e n t = t-butanol 393 gr, 500 cc (MW - 74) The f o l l o w i n g r a t e constants were c o l l e c t e d from Brandrup and Immergut (2), and M e l v i l l e and B i c k e l (15), f o r the polymer i z a t i o n of n - b u t y l a c r y l a t e a t 25°C. C, = 2.5

χ 10"

C

χ 10

g

C

T

- 6.8 = 6.5

kd - 1.55 kp = 1.3 kt = 1.8 f = 0.6

χ 10"

5

(/)

2

χ 10"

4

(/)

(t-butanol)

(/)

(DTDGA)

(1/sec)

χ 10

1

(%/mol sec)

χ 10

4

(%/mol sec)

(assumed)

I t i s assumed that there i s a c a n c e l l a t i o n of the tempera t u r e e f f e c t s on the r a t e constants, t h e r e f o r e they can be used f o r an estimated c a l c u l a t i o n of the degree of p o l y m e r i z a t i o n nBA at 80°C. The r a t e o f propagation i s c a l c u l a t e d by eq. C - l

= kp ( 0 0 1 1 ) 1 / 2

R Ρ R

* = 4.3

[ M ]

( ( W L )

t

χ 10"

5

(mole/ϋ

sec)

Ρ The degree o f p o l y m e r i z a t i o n , Xn = 36, i s c a l c u l a t e d by the eq. below (Ref 21), and t h i s value i s e q u i l v a l e n t to an average molecular weight of Mn = 4600 f o r PnBA.

^X Ρ where

R R k

1\ K

+ c + c 181

[M]

m

S

[M]

+

-El

c C

[M]

Ρ = r a t e of p o l y m e r i z a t i o n mols/A-sec

t

= termination r a t e const., A/mol. sec. = propagation

r a t e const. Jl/mol. sec.

[β] = monomer c o n c e n t r a t i o n , mol/1 [S] = s o l v e n t c o n c e n t r a t i o n , mol/I [T] = chain t r a n s f e r agent c o n c e n t r a t i o n , mollI C , C , C^. - chain t r a n s f e r constants -m* s' t X = degree o f p o l y m e r i z a t i o n , number s t r u c t u r a l units/chain


3.

GAZIT AND BELL


67

Acknow1e dgmeη t The authors express t h e i r a p p r e c i a t i o n to S h e l l Development Company f o r support o f t h i s r e s e a r c h .


Literature Cited 1. Lee, H.; Neville, K. "Handbook of Epoxy Resins"; McGrawH i l l , New York, 1967. 2. Brandrup, J.; Immergut, Ε. H. "Polymer Handbook"; John Wiley, New York, 1975. 3. Manson, J. Α.; Sperling, L. H. "Polymer Blends and Compos ites"; Plenum Press, New York, 1976. 4. Hildebrand, J.; Scott, R. "The Solubility of Non Electro lytes"; Reinhold Publishing Corp., New York, 1949. 5. Olabisi, O.; Robeson, L. M.; Shaw, M. T. "Polymer-Polymer Miscibility"; Academic Press, New York, 1979, p. 52. 6. Perez, R. J. in "Epoxy Resin Technology"; Polymer Engineer ing and Technology, 1968, p. 45. 7. Bucknall, C. B. "Toughened Plastics"; Applied Science Publishers, London, 1977. 8. Noshay, Α.; Robeson, L. H. J. Polymer Sci., Chem. Ed., 1974, 12, 689. 9. Sperling, L. H.; Friedman, D. W. J. Polymer Sci., part A-2, 1969, 7, 425. 10. McGarry, F. J.; Willner, A. M. "Toughening of an Epoxy Resin by an Elastomeric Second Phase"; R68-8, Massachusetts Institute of Technology, March, 1968. 11. Slysh, R. "Epoxy Resins"; ADVANCES IN CHEMISTRY SERIES No. 92, ACS: Washington, D. C., 1970; p. 108. 12. Bucknall, C. B.; Yoshii, T. The British Polym. J., 1978, 10, 53. 13. Scarito, P. R.; Sperling,L. H. Poly. Eng. and Sci., 1979, 19, 297. 14. Riew, C. K.; Rose, Ε. H.; Siebert, A. R. ADVANCES IN CHEM ISTRY SERIES No. 154, ACS: Washington, D. C., 1976; p. 326. 15. Melville, H. W.; Bickel, A. F. Trans. Faraday Soc., 1949, 45, 1049. 16. Small, P. A. J. Appl. Chem. 1953, 3. 17. Siebert, A. R.; U. S. Patent, 3,285,949, 1966. 18. Gazit, S. "Toughening of Epoxy Resin by Acrylic Elastomer," Ph.D. Dissertation, University of Connecticut, Sept. 1980. 19. Athey, R. D.; Mosher, W. Α.; Weston, N. W. J. Polym. Sci., 1977, 15, 1423. 20. Athey, R. D.; Mosher, W. Α.; Weston, N. W. ACS Polymer Preprints, 20, No. 2, 1979. 21. Henrici-Olive, G.; Olive, S. Fortschr. Hochpolymer Forsch. 1961, 2, 496. RECEIVED December 16, 1982


Butyl Acrylate Polymers for Use in Epoxy Resin Toug - American

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