Epoxy Resin Chemistry - American Chemical Society

10

Downloaded by UNIV OF CALIFORNIA SAN DIEGO on January 15, 2016 | http://pubs.acs.org Publication Date: December 3, 1979 | doi: 10.1021/bk-1979-0114.ch010

The Effect of Alkyl Substituents on the Properties of Cured Hydantoin Epoxy Resins E. H. CATSIFF, R. E. COULEHAN, J. F. DIPRIMA, D. A. GORDON, and R. SELTZER Research Department, Plastics and Additives Division, CIBA-GEIGY Corporation, Ardsley, NY 10502 Epoxy resins based on glycidylation of bisphenols, cresol and phenol novolacs, polycarboxylic acids, polyols, amines, and aminophenols have been long known. Epoxidized linear and cyclic olefins have also been used as specialty epoxy resins. More recently, glycidylated heterocycles have been introduced, ini tially as specialty resins promising improved resistance to weathering. One heterocycle in particular, the hydantoin ring, has become of particular interest as an epoxy substrate (1). A comprehensive review was given by Habermeier (2) of many types of glycidylated resins based on the hydantoin ring. Much of the emphasis in his account was on the variations possible in the position of the glycidyl groups: direct substitution on either or both of the Ν atoms of the hydantoin ring, glycidoxyalkyl substitution in the same positions, and glycidyl esters and ethers based on substituents in those positions. Also shown were bis(hydantoins) in which the hydantoin rings were linked by methylene or other alkylene groups, diester chains, or the β-glycidoxytrimethylene group derived from epichlorohydrin. Habermeier also pointed out the ready synthesis of hydan toins from aldehydes or ketones; the substituents i n the 5-position of the ring were thus determined by the carbonyl compound used as starting material. Most of the examples cited had methyl, ethyl, or cyclopentamethylene substitution i n the 5-position. Data were presented on the properties of cured resins with these substituents and with a broad variety of the other structural features mentioned. In t h i s paper we report on a s e r i e s of hydantoin r e s i n s derived from a somewhat broader choice of aldehydes and ketones, and show how the 5 - p o s i t i o n s u b s t i t u e n t s i n t e r a c t with s e v e r a l v a r i a n t s of common epoxy c u r i n g systems t o produce the p r o p e r t i e s of the f i n a l cured systems. 0-8412-0525-6/79/47-114-115$05.25/0 © 1979 American Chemical Society

In Epoxy Resin Chemistry; Bauer, Ronald S.; ACS Symposium Series; American Chemical Society: Washington, DC, 1979.

EPOXY

116

RESIN

CHEMISTRY

Hydantoin-Based Epoxy Resins


The simplest c l a s s of hydantoin epoxy r e s i n s are the 1 , 3 - d i g l y c i d y l h y d a n t o i n s of Formula I I . They were r e a d i l y prepared from the 5 , 5 - d i a l k y l or 5-monoalkylhydantoins and e p i c h l o r o h y d r i n . The hydantoins (Formula I) were prepared from ketones or aldehydes v i a the Bucherer r e a c t i o n .

R,-C R

C

R

1~ ~ 2

+

H

C

N

+

N H

3

+

C 0

C

I I

1

' /VN.

2

Conversion o f the hydantoins t o epoxy r e s i n s was s t r a i g h t forward.

Γ o

50%

ι + Λ CH -CH-CH C1 2

2

C

I

I

o

^ /\ A

aq. NaOH

CH -CH-CH 2

,ο

R, -C

2

q

A C

A CH -CH—CH 2

2

0 11 Table I l i s t s t y p i c a l p r o p e r t i e s of a baker's dozen of these r e s i n s , produced by t y p i c a l d i r e c t p r e p a r a t i o n s , without extensive p u r i f i c a t i o n . O v e r a l l , the v i s c o s i t i e s of these r e s i n s were q u i t e low, p a r t i c u l a r l y by comparison t o the w e l l known general purpose epoxy r e s i n s based on the d i g l y c i d y l ether of bisphenol A (DGEBA). The more s h i e l d e d higher a l k y l s u b s t i t u t e d hydantoin r i n g s favored lower v i s c o s i t i e s . Some anomalies i n these v i s c o s i t i e s presumably r e f l e c t e d e i t h e r a tendency of c e r t a i n r e s i n s to c r y s t a l l i z e , or the presence o f some species o f higher molecular weight, formed by r e a c t i o n of the g l y c i d y l group with a second hydantoin r i n g . In some instances a much purer d i g l y c i d y l h y d a n t o i n species has been i s o l a t e d . Pure Resin l i a , 1 , 3 - d i g l y c i d y l - 5 , 5 - d i m e t h y l hydantoin, was a r e a d i l y c r y s t a l l i z a b l e s o l i d , m. 72-73°C ( 2 ) , epoxy content 8.25 eq/kg. The l e s s pure sample described i n Table I tended t o supercool f o r a l i m i t e d time, and could then be handled as a l i q u i d . A d i s t i l l e d grade of Resin l i b ,



10.

117

Cured Hydantoin Epoxy Resins

CATSIFF ET AL.

TABLE 1 1,3-DIGLYC1DYLHYDANTOINS

Hydantoin, Resin

R

*1

0

Y i e l d of I

Resin Viscosity mPa«s

>90%

Solid

7.6

8.32

80%

1400

7.3

7.87

Epoxy/Kg.

Theo.

Ia,IIa

CH

lb,lib

C H

Ic,IIc

i-C H

7

H

40%

Solid

7.6

7.87

Id,lid

n-C H

7

H

40%

3300

7.0

7.87

90%

Solid

6.8

7.13

3

2

5

3

3

CH

3

CH

3

- (CH )5 " (a)

Ie,IIe

2

CH

3

80%

1300

6.8

7.08

CH

3

82%

1300

6.9

7.08

52%

2500

5.9

7.08

3

90%

2000

6.6

6.75

3

94%

600

6.7

6.75

93%

1000

6.2

6.44

96%

600

6.3

6.44

40%

900

6.0

6.16

14000

5.3

5.88

If,IIf

i"C H

i g . n g

n

Ih,IIh

n-C H

n

Ii,IIi

i - C H

u

CH

i j . n j

n-C H

n

CH

Ik,Ilk

2-MeBu

C H

11,111

n-C H

CH

Im, Ilm

i"C H

4

c

H

9

4

5

5

5

6

4

(DGEBA)

(a)

~

9

9

1 3

H

2

5

3

i~C H 4

9

—

cyclopentamethylene group forming a s p i r o -

structure.


118

EPOXY RESIN CHEMISTRY

1,3-diglycidyl-5-methyl-5-ethylhydantoin, had v i s c o s i t y 700 mPa.s and epoxy content 7.52 eq./kg., r a t h e r than the values given i n Table I. A d i s t i l l e d grade of Resin l i e , 1 , 3 - d i g l y c i d y l - 5 , 5 cyclopentamethylenehydantoin, was a l s o c r y s t a l l i n e , m. 104-106°C (2), epoxy content 7.07 eq/kg.


P r o p e r t i e s of Cured Hydantoin Epoxy Resins - Glass Temperatures The e f f e c t of a l k y l s u b s t i t u e n t s i n s h i e l d i n g the p o l a r hydantoin r i n g was shown by the g l a s s t r a n s i t i o n temperature Tg achieved a f t e r extensive c r o s s l i n k i n g . As a measure of Tg we used the " i n i t i a l deformation temperature" (IDT) d e f i n e d i n the experimental s e c t i o n . The IDT a l s o depended on the s t o i c h i o metric r a t i o of c u r a t i v e (hardener) to r e s i n , being highest at or near exact equivalence. A l s o , since the r e a c t i o n r a t e f e l l d r a s t i c a l l y when enough c r o s s l i n k i n g had occurred to b r i n g the glass t r a n s i t i o n temperature up to the r e a c t i o n temperature, IDT was e f f e c t i v e l y l i m i t e d by the l a t t e r . In Table I I , the IDT s obtained by c u r i n g v a r i o u s d i g l y c i d y l hydantoins with hexahydrophthalic anhydride (HHPA) are shown. H/R i s the r a t i o of moles HHPA to a c t u a l e q u i v a l e n t s of epoxide; while i t was not kept constant throughout the s e r i e s , experience has shown t h a t , over the range used (H/R = 0.9 to 1.1), the v a r i a t i o n i n IDT was u s u a l l y l e s s than 10°. In a few cases, the f i n a l cure temperature (150°C) may have l i m i t e d the IDT, but with the higher a l k y l s u b s t i t u e n t s , c l e a r l y i t d i d not. Note that the highest IDT was obtained with the c y c l o p e n t a methylenehydantoin r e s i n d e r i v e d from cyclohexanone. It i s tempting to speculate that t h i s i n f l e x i b l e a l k y l e n e moiety was i n e f f e c t i v e i n s h i e l d i n g the hydantoin r i n g , but subsequent comp a r i s o n of the h y d r o p h o b i c - h y d r o p h i l i c balance of amine-cured r e s i n s appeared to r u l e out t h i s explanation; probably the s t i f f s p i r o s t r u c t u r e c o n t r i b u t e d to the high Tg, j u s t as i t c o n t r i buted to the high melting point of the r e s i n i t s e l f ( l i e ) . Aside from t h i s e f f e c t , c l e a r l y the longer a l k y l s u b s t i t uents d i d reduce i n t e r c h a i n i n t e r a c t i o n s so as to lower Tg. Another s t e r i c e f f e c t notable i n Table I I i s that Tg was higher for c l o s e - i n branching of the a l k y l s u b s t i t u e n t s . As shown i n Table I I I , a l l of the anhydride-cured r e s i n s were e s s e n t i a l l y hydrophobic. The amount of water uptake showed l i t t l e or no trend with s i z e or branching of the a l k y l s u b s t i t u e n t s . Water uptake was r e v e r s i b l e , a l s o . 1

Hydrophobic-Hydrophilic

Balance

A somewhat d i f f e r e n t aspect of the hydrophobic s h i e l d i n g e f f e c t of a l k y l s u b s t i t u e n t s was r e f l e c t e d i n the r e l a t i v e h y d r o p h i l i c i t y of a l i p h a t i c amine-cured r e s i n s . A standard room temperature-curing polyamine, t r i e t h y l e n e t e t r a m i n e (TETA), was used to cure a s e r i e s of r e s i n s at room temperature. The


CATSIFF ET AL.

119



TABLE I I CYCLOALIPHATIC ANHYDRIDE CURING OF 1,3-DIGLYCIDYLHYDANTOINS Resin

-1

lia

CH

lib

C

^2 CH

3

H

C H

Ile

2 5 i-C H

?

3 H

lid

n-C H

?

H

3

3

Ile

- (CH ) 2

3

- (c)

5

H/R

IDT, °C

0.9

140

1.0

148

1.1

148

1.1

139

0.9

153

Ilf

i-C H

9

CH

3

0.9

129

Hg

n-C H

9

CH

3

0.9

118

0.9

115

0.9

112

1.1

123

1.0

115

Ili iij

4

4

i

n

C

H

C H

C

H

C H

" 5 ll

Ilk

~ 5 ll 2-MeBu

III

n-C H

Ilm

^ 4

(DGEBA)

6

Η

3 C H 2

CH

13

i 9

—

3

C

5

3

" 4

H

0.9

(a)

111

1.0

(b)

126

9

A l l were cured with HHPA and 2 phr BDMA. Except where noted, a l l were g e l l e d at 80°C and given a f i n a l cure of 2 hr./150°C (a) g e l l e d at 100°C

(b) f i n a l cure 3 hr./150°C

(c) cyclopentamethylene group forming a

spiro-structure



120


TABLE I I I CYCLOALIPHATIC ANHYDRIDE CURING OF 1,3-DIGLYCIDYLHYDANTOINS Resin Ha lib

CH

CH

3

lie

^2^5 i-C H

lid

n-C H

He

3

3

3

H/R

Water Uptake,

0.9

1.62

0.94

1.49

?

H

1.1

1.58

?

H

1.1

1.80

0.9

1.09

- (CH ) 2

- ( )

5

C

Ilf

i-C H

9

CH

3

0.9

1.45

Ilg

n-C H

9

CH

3

0.9

1.17

Hi

i-C H

n

CH,

0.9

1.28

Hj

n-C H

n

CH

0.9

1.21

Ilk

2-MeBu

C H

1.1

1.47

III

n-C H

CH

1.0

1.50

Hm

i-C H

4

4

5

5

6

4

9

1 3

3

2

5

3

i-C H 4

9

0.9

(a)

0.84

A l l were cured with HHPA and 2 phr BDMA. Except where noted, a l l were g e l l e d at 80°C and given a f i n a l cure of 2 hr/150°C (a) G e l l e d

at 100°C

(b) 4 weeks, room temperature

(c) cyclopentamethylene group forming a s p i r o -

structure



10.

CATSIFF ET AL.


121

stoichiometry chosen was one amine hydrogen/actual epoxide equivalent. In most cases, some specimens were given a mild postcure to see the e f f e c t of increased c r o s s l i n k i n g . The h y d r o p h i l i c i t y of the cured systems was judged by weight gain of small specimens a f t e r immersion at room temperature i n deionized water f o r periods of one day to four weeks. (in some cases, p a r a l l e l specimens were exposed at 35°C i n a 95% R.H. chamber. These data were g e n e r a l l y c l o s e to the room temperature immersion r e s u l t s , and with one exception are not reported here.) The f l e x u r a l modulus of the specimen was a l s o measured at the time of weighing, since the absorbed water acted to p l a s t i c i z e the cured r e s i n . Both weight gain and p l a s t i c i z a t i o n proved to be very sens i t i v e to the a l k y l groups present, as shown i n Table IV. Note that the m i l d postcure somewhat improved the more hydrophobic cured r e s i n s (those with and higher s u b s t i t u e n t s ) , notably p e r m i t t i n g TETA-cured Resin I l k to r e t a i n 95% of i t s f l e x u r a l modulus a f t e r four weeks. M i l d postcure s i g n i f i c a n t l y reduced the r a t e of water uptake of the h y d r o p h i l i c cured r e s i n s . But note a l s o that even with postcure the h y d r o p h i l i c cured r e s i n s u s u a l l y absorbed so much water i n four weeks that the s w e l l i n g s t r e s s e s became greater than the cohesive strength and the specimens broke apart. Even these high water uptakes proved to be r e v e r s i b l e ; i . e . , the water acted only as a s w e l l i n g agent. In general, the hydrophobic TETA-cured r e s i n s were those which, i n Table I I , had low IDT. Both p r o p e r t i e s are a t t r i b u t a b l e to s h i e l d i n g of the hydantoin r i n g by the 5 - p o s i t i o n s u b s t i t u e n t s . The p r i n c i p a l exception to t h i s c o r r e l a t i o n was 1 , 3 - d i g l y c i d y l 5,5-cyclopentamethylenehydantoin ( l i e ) which had a high IDT i n Table I I , but which proved to be q u i t e hydrophobic a f t e r room temperature cure with amines (30. Thus i t appears that the s p i r o j o i n e d c y c l o a l i p h a t i c r i n g was e f f e c t i v e i n s h i e l d i n g the hydantoin r i n g , but i t s r e l a t i v e s t i f f n e s s r a i s e d Tg c o n s i d e r a b l y . Since the h y d r o p h o b i c - h y d r o p h i l i c balance of amine-cured r e s i n s was so s e n s i t i v e to a l k y l s u b s t i t u e n t s on the hydantoin r i n g , i t i s not s u r p r i s i n g that i t was a l s o s e n s i t i v e to the hydrocarbon moieties of the amine c u r a t i v e s . The range of beh a v i o r depended on the r e s i n s u b s t i t u e n t s . For example, the already hydrophobic e t h y l amyl s u b s t i t u t e d Resin I l k showed moderate but s i g n i f i c a n t increases i n h y d r o p h o b i c i t y when cured with c y c l o a l i p h a t i c , h i g h l y branched a l i p h a t i c , or formulated aromatic amines. See Table V. At the other extreme, as shown i n Table VI, a r e s i n mixture c o n t a i n i n g only dimethylhydantoin (DMH) r i n g s was q u i t e h y d r o p h i l i c with a l l room temperature amine c u r a t i v e s except the formulated aromatic amine mixture based on methylenedianiline. (See Table VII f o r i d e n t i f i c a t i o n of the amines i n Table V and subsequent t a b l e s . ) This r e s i n mixture was obtained by hydroxypropylating a p o r t i o n of the DMH, l a .


122

EPOXY

RESIN

CHEMISTRY


TABLE IV ROOM TEMPERATURE CURED HYDANTOIN EPOXY RESINS

Water Uptake, % Resin Ha

lib

h CH

3

C H 2

R

2

CH

3

CH

5

Hd

n-C H

Hh

η-0

3

Λ

1 Day

4 Wk

(b)

27.7 11.7

(a) (a)

(c,d) 15 (d)

(b)

13.4 5.9

(a) 29.5

10 (d) 10

14.5

(a)

10 (d)

2.6 1.8

12.5 10.6

50 65

2.4

11.5

70

(b)

1.4 1.5

6.8 3.8

80 80 (g)

(b)

1.2 0.8

5.9 4.8

70 95

3

Η

7

ι

Η (b)

Hi

i-C H

III

n-C H

Ilk

n

CH

3

13

CH

3

5

6

2-MeBu

C H 2

% Retention of F l e x Modulus 4 Wk.

5

A l l were cured with TETA at H/R =1.0 amine hydrogen/epoxide. A l l were cured at room temperature; 14-21 days without postcure and at l e a s t 7 days before postcure. Except where noted, expo sure was by immersion i n deionized water at room temperature. (a) (b) (c)

Fragmented Postcured 6 hr./100°C Too s o f t to measure

(d) (g)

At 1 day Exposed to 95% R.H./35°C


10.

CATSiFF

123


ET AL.

TABLE V ROOM TEMPERATURE AMINE CURING OF HYDANTOIN EPOXY RESINS Resin:

I l k [1,3-diglycidyl-5-ethyl-5-(2-methylbutyl)hydantoin]


Water Uptake, % Curative

1 Day

4 Wk

Formulated amine (a) TMDA (a) MMCHA (a) TETA (a)

0.4 0.6 0.6 1.2

1.7 2.7 2.6 5.9

% Retention o f F l e x Modulus 4 Wk 95 90 (b) 70

A l l were cured at H/R = 1.0 amine hydrogen/epoxide. A l l were cured at room temperature 14-21 days. Except where noted, exposure was by immersion i n deionized water at room temperature. (a) (b)

See Table V I I f o r i d e n t i f i c a t i o n . Too b r i t t l e t o c u t . CH

CH„

n

,0 CH -C

CH--C Ν

/ N

H

N

C

Q

J C

+

Ή

/ \ CH -CH-CH 0

2

ft 0

CH^

ι

1

A A

Q

H

3

C

la

CH -CH-0H o

III

As has been pointed out by Habermeier (2_), the non-equiva lence of the 1- and 3- p o s i t i o n s of the hydantoin r i n g r e a d i l y permitted monosubstitution. Subsequent g l y c i d y l a t i o n provided the diepoxide IV. CH

I 0

50%

iii A CH -CH-CH C1 2

2

aq. NaOH

C

I

I

CH

À A

CH "CH-CH 2

#

CH -C 0

>A

+

Q

3

2

0 C

0

Q

I

/\

CH -CH-0-CH -CH-CH 2

IV


2

2


124

TABLE VI


ROOM TEMPERATURE AMINE CURING OF HYDANTOIN EPOXY RESINS Resin:

f70% H a V30% IV

(1,3-diglycidyl-5,5-dimethylhydantoin) [l-glycidyl-3-(2-glycidoxypropyl)5,5-dimethylhydantoin] Water Uptake, % 4 Wk

% Retention of F l e x Modulus 4 Wk

Curative

1 Day

Formulated amine (a) TMDA (a) /30%eq TMDA (a)V I70%eq MCHA ( a ) / /l5%eq TMDAY \85%eq MCHA/ 1,4-BAC (a) 1,3-BAC (a) MXDA (a) IPDA (a) PMDA (a) TETA (a)

0.8 4.7

3.5 16.2

70 5

3.9

11.0

(b)

3.7

10.3

(b)

5.2 5.2 7.4 6.1 (c) 23.4

16.9 17.1 23.1 14.3

35 20 (b) (b) (b) (d,e)

—

(c)

A l l were cured at H/R = 1.0 amine hydrogen/epoxide. A l l were cured at room temperature 14-21 days. Except where noted, exposure was by immersion i n deionized water at room temperature. %eq (a) (b) (c) (d) (e)

= percent o f amine e q u i v a l e n t s See Table V I I f o r i d e n t i f i c a t i o n . Too b r i t t l e t o c u t . Fragmented At 1 day Too s o f t to measure


10.

CATSIFF ET AL.


TABLE V I I IDENTIFICATION OF MATERIALS


Aniline-formaldehyde c u r a t i v e = Jeffamine® AP-22 BAC = bis(aminomethyl)cyclohexane BDMA = benzyldimethylamine DGEBA = d i g l y c i d y l ether of Bisphenol A Formulated amine = L i q u i d amine mixture c o n t a i n i n g MDA, described by Habermeier ( 2 ) . HHPA = hexahydrophthalic anhydride IPDA = isophoronediamine = 3,3 -dimethyl-5-aminomethylcyclohexylamine ,

MCHA = 4,4 -methylenebis(cyclohexylamine) MDA

= 4,4*-methylenedianiline ,

MMCHA = 4,4 -methylenebis(2-methylcyclohexylamine) MXDA = m-xylylenediamine =

1,3-bis(aminomethyl)benzene

PMDA = p-menthanediamine = l-methyl-4-(l-amino-l-methylethyl)cyclohexylamine TETA = t r i e t h y l e n e t e t r a m i n e =

1,4,7,10-tetraazadecane

TMDA = 2,2,4-trimethylhexane-l,6-diamine



126


This r e s i n mixture, which had a low v i s c o s i t y , t y p i c a l l y about 2500 mPa.s, was found to avoid the c r y s t a l l i z a t i o n tendency of pure d i g l y c i d y l DMH, l i a . P a r t i c u l a r u t i l i t y has been found for the r e v e r s i b l e high degree of s w e l l i n g of a room temperature cured v e r s i o n of a DMH-based r e s i n , as a water-permeable topcoat for marine a n t i f o u l i n g paints ( . The methylethylhydantoin-based Resin l i b , as shown i n Table V I I I , gave the g r e a t e s t range of h y d r o p h i l i c i t y when the amine c u r a t i v e was v a r i e d . This i s i n keeping with i t s intermediate degree of a l k y l s u b s t i t u t i o n . A few r e s i n s were given elevated temperature cures with aromatic amines; here the e f f e c t of a l k y l s u b s t i t u e n t s on water uptake could be seen, but the o v e r a l l behavior was intermediate between the elevated-temperature anhydride cures and the room temperature amine cures. Solvent/Chemical Resistance The hydrophobic s h i e l d i n g of the hydantoin r i n g by a l k y l s u b s t i t u e n t s a f f e c t e d a l l the s o l v e n t - s o l u t e i n t e r a c t i o n s of cured r e s i n s . Two of the r e s i n s and the DMH-based r e s i n mixture were cured with a commercially a v a i l a b l e aromatic amine mixture derived from aniline-formaldehyde condensation, ident i f i e d i n Table V I I . Weight gain and solvent p l a s t i c i z a t i o n were followed i n a number of solvents and aqueous media. Some of the exposure was at 60°C as w e l l as at room temperature. For the hydrophobic Resin I l k , the r e s u l t s f o r exposure to v a r i o u s solvents are shown i n Table IX. The s o l v e n t s are l i s t e d i n i n c r e a s i n g order of s o l u b i l i t y parameter £(5). I t i s evident that ( w i t h i n the l i m i t a t i o n s of s o l u b i l i t y parameter theory) t h i s cured r e s i n was l y o p h i l i c i n the range of Î = 9 9.6; there was a l s o a s p e c i f i c i n t e r a c t i o n with methanol. Table X shows the g e n e r a l l y hydrophobic response of t h i s cured r e s i n i n aqueous media ( l i s t e d i n i n c r e a s i n g order of pH). Only strong a c i d had a d e l e t e r i o u s e f f e c t . Again at the other extreme, the DMH-based h y d r o p h i l i c r e s i n mixture was s t u d i e d , with r e s u l t s shown i n Tables XI and X I I . This cured r e s i n was h y d r o p h i l i c (Table X I I ) , though less so than the room temperature amine-cured systems of Table VI, but note i t s general l y o p h o b i c i t y , as shown i n Table XI. Of the non-aqueous media, only methanol and hot t r i c h l o r e t h y l e n e showed much s w e l l i n g or p l a s t i c i z a t i o n i n 16 weeks. Presumably the poorly shielded DMH r i n g s permitted strong i n t e r c h a i n i n t e r a c t i o n s ; t h i s v i r t u a l c r o s s l i n k i n g provided general solvent r e s i s t a n c e . Resin l i b , which proved somewhat l e s s h y d r o p h i l i c than the DMH-based r e s i n mixture (see Table V I I I ) , was studied with c e r t a i n solvents only, as shown i n Table X I I I . I t s l y o p h o b i c i t y was somewhat l e s s than the DMH-based mixture, and i n the two aqueous media i t was somewhat l e s s a f f e c t e d . Thus, again, i t s behavior r e f l e c t e d the intermediate degree of a l k y l s u b s t i t u t i o n .


10.

CATSIFF ET AL.



TABLE VIII ROOM TEMPERATURE AMINE CURING OF HYDANTOIN EPOXY RESINS Resin:

l i b (1,3-diglycidyl-5-methyl-5-ethylhydantoin) Water Uptake, %

% Retention ο F l e x Modulus 4 Wk

Curative

1 Day

Formulated amine (a) ΤMDA (a) f30%eq TMDA ( a ) \ l70%eq MCHA (a); fl5%eq TMDÀV \85%eq MCHA/ MMCHA (a) 1,4-BAC (a) 1,3-BAC (a) MXDA (a) IPDA (a) TETA (a)

0.5 1.4

2.4 5.3

80 80

1.5

6.0

(b)

1.5

6.0

(b)

1.1 2.4 1.9 2.4 (c) 13.4

4.3 11.4 10.4 9.6

4 Wk

— (c)

(b) (b) (b) (b) (b) 10 (d)

A l l were cured at H/R =1.0 amine hydrogen/epoxide. A l l were cured at room temperature 14-21 days. Except where noted, exposure was by immersion i n d e i o n i z e d water at room temperature. %eq = percent of amine equivalents (a) (b) (c) (d)

See Table V I I f o r i d e n t i f i c a t i o n . Too b r i t t l e to c u t . Fragmented At 1 day



128

TABLE IX


SOLVENT RESISTANCE OF AROMATIC AMINE-CURED HYDANTOIN EPOXY RESIN Resin: I l k [ 1 , 3 - d i g l y c i d y l - 5 - e t h y l - 5 - ( 2 - m e t h y l b u t y l ) h y d a n t o i n ] IDT = 128°C Solvent Uptake, % Solubility Temp. Parameter(5) °C

Solvent

7.50

Heptane Kerosene


1 Wk.

16 Wk.

25

0.03

0.54

100

25 60

0.02 0.3

0.10 0.9

110 95

0.8 5.3

100 85

Xylene

8.9

25 60

0.08 0.5

E t h y l Acetate

8.91

25

1.9

Benzene

9.16

25

0.1

1.2

25 60

3.5 (a)

55.1

9.16

—

——

Chloroform

9.16

25

(a)

—

—

Acetone

9.62

25

(a)

—

—

Isopropyl A l c o h o l 11.44

25

-0.08

Methanol

25

11.1

Trichlorethylene

14.50

29.8 (b)

0.43

15 100 30 (g)

100

20.7

25

A l l were cured with aniline-formaldehyde c u r a t i v e . See Table V I I . H/R = 1 amine hydrogen/epoxide equivalent G e l l e d 16 hr./65°C. Postcured 2 hr./150°C (a)

Fragmented

(b) Cracked

(g) At 8 weeks



CATSiFF ET AL.


129

TABLE X CHEMICAL RESISTANCE OF AROMATIC AMINE-CURED HYDANTOIN EPOXY RESIN Resin: H k

[1,3-diglycidyl-5-ethyl-5-(2-methylbutyl)hydantoin] IDT = 128°C L i q u i d Uptake, % Temp. °C

Aqueous Medium

1 Wk.

16 Wk. 38

25% HC1

25

8.5

5% A c e t i c A c i d

25 60

1.3 2.9

3.6 4.8

Water

25 60

1.2 2.9

3.5 4.4

25 60

1.1 2.4

3.1 3.5

25

1.2

4.3

25 60

-0.04 0.05

10% NaCl

10% NH

3

50% NaOH

% Retent: F l e x Modi 16 \

0.01 0.14

A l l were cured with aniline-formaldehyde c u r a t i v e . Table V I I . H/R = 1 amine hydrogen/epoxide equivalent G e l l e d 16 hr./65°C. Postcured 2 hr./150°C

40 105 95

— 95

— 95 95 105 90 See


130


TABLE XI


SOLVENT RESISTANCE OF AROMATIC AMINE-CURED HYDANTOIN EPOXY RESIN Resin: 1*70% H a \30% IV

[1,3-diglycidyl-5,5-dimethylhydantoin] [l-glycidyl-3-(2-glycidoxypropyl)5,5-dimethylhydantoin] IDT = 125°C Solvent Uptake, %

Solubility Temp. Parameter(5) °C.

Solvent Heptane

7.50

Kerosene

Xylene

8.9

% Retention of F l e x Modulus 16 Wk

1 Wk.

16 Wk.

25

0..12

0.84

100

25 60

0..09 0,.5

0.29 1.7

100 105

25 60

0,.04 0..2

1.1 2.2

— 95

E t h y l Acetate

8.91

25

0..06

0.6

100

Benzene

9.16

25

0,.07

1.0

100

9.16

25 60

0 .15 0 .4

1.1 6.8

95 80

Chloroform

9.16

25

0 .1

1.25

100

Acetone

9.62

25

0 .11

0.96

95

Isopropyl A l c o h o l 11.44

25

0 .00

0.13

105

Methanol

25

6 .9

T r i c h l o r e t h y l ene

14.50

21.0

15

A l l were cured with aniline-formaldehyde c u r a t i v e . See Table V I I . H/R = 1 amine hydrogen/epoxide equivalent G e l l e d 16 hr./65°C. Postcured 2 hr./150°C



CATSIFF ET AL.


TABLE XII CHEMICAL RESISTANCE OF AROMATIC AMINE-CURED HYDANTOIN EPOXY RESIN Resin:/70% H a \30% IV

[1,3-diglycidyl-5,5-dimethylhydantoin] [l-glycidyl-3-(2-glycidoxypropyl)5,5-dimethylhydantoin] IDT = 125°C L i q u i d Uptake, % Temp. °C.

Aqueous Medium

1 Wk.

16

Wk.


25% HC1

25

(a)

—

—

5% A c e t i c A c i d

25 60

1.8 8.0

10.1 15.9

75 50

Water

25 60

1.9 7.7

10.6 12.7

25 60

1.3 4.8

6.5 9.5

25

1.8

13.7

55

25 60

0.005 0.2

0.25 -0.15

110 85

10% NaCl

10%

NH

3

50% NaOH

— 60

— 70


Fragmented



132


TABLE XIII SOLVENT/CHEMICAL RESISTANCE OF AROMATIC AMINE-CURED HYDANTOIN EPOXY RESIN Resin:

l i b [1,3-diglycidyl-5-methyl-5-ethylhydantoin] IDT = 149°C Solvent Uptake, % Solubility Temp. Parameter(5) °C.

Solvent

1 Wk.

16 Wk.

% Retention of F l e x Modulus 16

8.91

25

0.01

1.0

105

9.16

25 60

0.3 2.7

1.4 6.5

105 90

Chloroform

9.16

25

0.3

2.2

100

Acetone

9.62

25

0.12

3.3

85

(a)

~

8.5

90

E t h y l Acetate T r i c h l o r e t h y l (ene

25% HC1

25

10% NH

25

18.7 1.3


Fragmented


10.

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133


Conclusions By v a r y i n g the s u b s t i t u e n t s at the 5 - p o s i t i o n on the hydantoin r i n g , i t i s p o s s i b l e to c o n t r o l the i n t e r m o l e c u l a r forces of hydantoin-based epoxy r e s i n s . T h i s c o n t r o l i s manifested to some extent i n the monomeric r e s i n s , but i s f a r more evident i n the g l a s s t r a n s i t i o n temperature of h i g h l y c r o s s l i n k e d r e s i n - c u r a t i v e systems, and p a r t i c u l a r l y i n the h y d r o p h i l i c hydrophobic balance of amine-cured systems. Within l i m i t s p r e s c r i b e d by the s u b s t i t u e n t s on the hydantoin r i n g , the hydrop h i l i c - h y d r o p h o b i c balance i s a l s o g r e a t l y a f f e c t e d by the organic moieties introduced by the amine c u r a t i v e . Analogous p r i n c i p l e s may be invoked i n c o n s i d e r i n g the l y o p h i l i c - l y o p h o b i c balance of aromatic amine-cured hydantoin epoxy r e s i n s . Experimental

Procedures

Mold C o n s t r u c t i o n . C a s t i n g molds were prepared from precleaned mold-release-coated g l a s s p l a t e s and square-angled U-shaped s i l i c o n e rubber gaskets. The gasket sheets were about 1.6 mm t h i c k and two or more were p l i e d t o the c a s t i n g t h i c k ness d e s i r e d , and spring-clamped between p l a t e s . The molds were set v e r t i c a l l y with the top edge open f o r pouring, and u s u a l l y were preheated i n an oven to keep the v i s c o u s c a s t i n g mixture as f l u i d as p o s s i b l e . The most common p l a t e s i z e used was about 20 cm square. Specimen P r e p a r a t i o n . The demolded c a s t i n g s were cut using a c i r c u l a r saw with a diamond c u t t i n g wheel to provide specimens f o r the v a r i o u s t e s t s . Casting. Castings of l i q u i d epoxy r e s i n s cured with hexah y d r o p h t h a l i c anhydride (HHPA) were prepared by h e a t i n g the l i q u i d r e s i n i n a s t i r r e d 3-necked f l a s k to which the c a l c u l a t e d amount of premelted HHPA was added. A vacuum was drawn t o p a r t i a l l y degas the mixture; then 2 phr benzyldimethylamine (BDMA) was added as a c c e l e r a t o r . A f t e r f u r t h e r degassing, the mixture was poured i n t o c a s t i n g molds prepared as d e s c r i b e d above. The f i l l e d molds were put i n t o an oven at the d e s i r e d g e l l i n g temperature; subsequently, e i t h e r the oven was reset t o the f i n a l cure temperature or the molds were t r a n s f e r r e d to a second oven, as convenient. Castings o f s o l i d epoxy r e s i n s cured with HHPA were prepared s i m i l a r l y , except that the r e s i n a l s o had t o be premelted. Except where noted i n Table I I , HHPA-cured c a s t i n g s were g e l l e d at 80°C ( a t l e a s t 3 hours and u s u a l l y overnight) and then cured 2 hr./150°C. Castings cured with the commercial aromatic amine d e r i v e d from aniline-formaldehyde were prepared l i k e the HHPA-cured c a s t i n g s , but without a c c e l e r a t o r . The aromatic amine mixture was about 90% m e t h y l e n e d i a n i l i n e (MDA) and tended to p a r t i a l l y



134


s o l i d i f y on standing, so i t had to be prewarmed and w e l l mixed before use. In the work reported here, the degassed c a s t i n g s were g e l l e d 16 hr./65°C and given a f i n a l cure of 2 hr./150°C. For room temperature c u r i n g , preheating was used only when a b s o l u t e l y necessary to reduce v i s c o s i t y and f a c i l i t a t e mixing. For t h i s reason, Resin l i e was not considered s u i t a b l e f o r room temperature c u r i n g , and Resin l i a was so cured on only a few occasions, a f t e r premelting. Such r e s i n s could be used i n l i q u i d mixtures, as noted i n Tables VI, XI, and X I I . In a s i m i l a r way, s o l i d amines, such as MDA and methylenebis(cyclohexylamine), MCHA, could only be used i n l i q u i d mixtures. With a l l the amine c u r a t i v e s , the stoichiometry used was one amine hydrogen/epoxide; e.g., TETA, having two primary and two secondary amines/molecule, would have s i x equivalents/mole. The mixture of l i q u i d r e s i n and l i q u i d amine was s t i r r e d and degassed i n a 3-necked f l a s k , j u s t as f o r the thermal c a s t i n g s , but an i c e bath was used to c o n t r o l any exotherm i n the f l a s k , so that r a p i d v i s c o s i t y increase due to r e a c t i o n would not occur to i n t e r f e r e with degassing. A f t e r pouring i n t o the mold, the c a s t i n g was kept at room temperature f o r at l e a s t 14 days before demolding. When a mild postcure was d e s i r e d , at l e a s t 7 days/room temperature c u r i n g preceded i t ; the postcure was 6 hr./100°C. Weight Gain and F l e x u r a l Modulus. Weight gain and p l a s t i c i z a t i o n by absorbed l i q u i d were measured on small f l e x bar specimens (7.62 cm χ 2.54 cm χ 0.32 cm). Most exposure was by immersion at room temperature, but some specimens were immersed at 60°C, and some specimens were exposed to 95% R.H. at 35°C i n a c o n t r o l l e d - h u m i d i t y chamber i n p a r a l l e l to t h e i r immersion i n water. Deionized water, ten organic s o l v e n t s , and f i v e aqueous s o l u t i o n s were used as immersion media, as noted i n the appro p r i a t e t a b l e s . Exposure times ranged from 24 hours to 4 weeks f o r the water- or humidity chamber-exposed samples, and from 1 to 16 weeks f o r the s o l v e n t - or aqueous media-exposed samples. At the d e s i r e d i n t e r v a l s , each specimen was removed from i t s environment, r i n s e d i f necessary f o r safe handling, wiped dry, and weighed. Then the f l e x u r a l modulus was measured, to a max imum o u t e r - l a y e r s t r a i n of 0.5%. Thus, the f l e x measurement was e s s e n t i a l l y non-destructive and the specimen could be returned to i t s exposure. I n i t i a l Deformation Temperature (IDT). IDT was determined as the temperature at which a standard t e s t bar (1.27 cm wide χ 0.635 cm deep), c e n t r a l l y loaded on a 100 mm span, d e f l e c t e d an a d d i t i o n a l 0.25 mm under a load that gave a maximum (outerl a y e r ) s t r e s s of 1.82 MPa, while being heated at a r a t e of 2°C/min. The operating procedure followed ASTM Method D648-72 for " D e f l e c t i o n Temperature of P l a s t i c s Under F l e x u r a l Load" (6), but the maximum s t r a i n reached at the IDT was h a l f that at the " d e f l e c t i o n temperature under l o a d " (DTUL), so IDT was


10.

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135

s e v e r a l degrees lower than DTUL.


Abstract Hydantoin epoxy resins having glycidyl groups in the 1- and 3-positions and one or two alkyl groups in the 5-position were prepared by the Bücherer reaction, followed by treatment with epichlorohydrin. These resins were crosslinked with hexahydrophthalic anhydride to examine the effect of alkyl substituents on the glass transition temperatures of the cured systems. Higher alkyl substituents shielded the hydantoin rings and gave lower glass temperatures. The same shielding effect was observed in the reduced hydrophilicity of higher alkyl-substituted hydantoin epoxy resins cured with triethylenetetramine. Steric factors - branching at or close to the hydantoin ring - raised the glass transition temperature while maintaining the shielding effect. Amines of different structures were used as room temperature curatives with a few representative resins, to observe the effect on hydrophilic-hydrophobic balance. Solvent effects were examined on aromatic amine-cured resins; the most hydrophilic cured system proved to have the broadest range of lyophobicity. Acknowledgement This work could not have been c a r r i e d out without the techn i c a l a s s i s t a n c e and support o f many c o l l e a g u e s . Particular thanks go to Dr. J . H. Bateman and Messrs. L. A l t e r , H. B. Dee, A. T. Doyle, D. N e i d i t c h , and J . V e l t e n .

Literature Cited 1. Catsiff, Ε. H.; Dee, H. B.; Seltzer, R. Modern Plastics, 1978, 55 (7), 54. 2. Habermeier, J . Angew. Makromol. Chem., 1977, 63 (921), 63. 3. Eldin, S., private communication. 4. Weiss, J . Organic Coatings and Plastic Chemistry, 1978, 39, 567. 5. Hoy, K. L. J. Paint Technol., 1970, 42 (541), 76. 6. Lukens, R.P., Ed. "Annual Book of ASTM Standards;" Am. Soc. for Testing and Materials: Philadelphia, PA, 1976, Part 35, p. 219. RECEIVED May 21, 1979.


Epoxy Resin Chemistry - American Chemical Society

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