Urethane Chemistry and Applications - American Chemical Society

28 Reactivity Studies and Cast Elastomers Based on trans-Cyclohexane-1,4-Diisocyanate 1,4-Phenylene

and

Diisocyanates

S. W. WONG, W. J. JUANG, V. OLGAC, and K. C. FRISCH Polymer Institute, University of Detroit, Detroit, MI 48221

Downloaded by CORNELL UNIV on May 21, 2017 | http://pubs.acs.org Publication Date: November 30, 1981 | doi: 10.1021/bk-1981-0172.ch028

G. HEINRICHS, and P. HENTSCHEL Research Department, Akzo Corporation, Oburnberg, West Germany p-Phenylene diisocyanate (PPDI) and t r a n s - c y c l o hexane-1,4-diisocyanate (CHDI), produced by the Hofmann degradation of the corresponding acid amides (1) have become available i n developmental quantities for polyurethane production (2). Due to the symmetrical structure of both these molecules and t h e i r r i g i d , r o d - l i k e molecular shape, a very orderly structure i n the build-up of the hard segments will be promoted i n the polyurethane system. These s t r u c t u r a l features could enable the r e s u l t i n g elastomers to perform better under high and low temperature conditions and to achieve high modulus. Previous k i n e t i c studies (3-7) showed that PPDI had a high r e a c t i v i t y , but no k i n e t i c data were a v a i l a b l e for the r e a c t i v i t y of CHDI. Three model isocyanate reactions catalyzed with both t e r t i a r y amine and organotin c a t a l y s t s were c a r r i e d out with PPDI or CHDI and n-butanol (urethane formation) and water (urea formation) as well as c y c l o t r i m e r i z a t i o n (isocyanurate formation) i n s u i t a b l e solvents (toluene, c e l l o s o l v e acetate and butyl acetate). Four widely used commercial diisocyanates, 4,4'-diphenylmethane diisocyanate (MDI), 1,5-naphthalene diisocyanate (NDI), isophorone diisocyanate (IPDI) and 4,4'-methylene b i s (cyclohexyl) diisocyanate (HMDI) were included for comparison. Sample f o r m u l a t i o n s o f c a s t urethane e l a s t o m e r s applicable to conventional industry processing techn i q u e s were d e v e l o p e d , and t h e p h y s i c a l p r o p e r t i e s o f the r e s u l t i n g p r o d u c t s d e t e r m i n e d . Experimental M a t e r i a l s and P u r i f i c a t i o n . The d i i s o c y a n a t e s employed f o r k i n e t i c s t u d i e s were d i s t i l l e d p r i o r t o use. Reagent grade n - b u t a n o l was t r e a t e d w i t h sodium 0097-6156/81/0172-0419$05.00/0 © 1981 American Chemical Society

Edwards et al.; Urethane Chemistry and Applications ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

420

URETHANE CHEMISTRY AND APPLICATIONS


(10% by w e i g h t ) and d i s t i l l e d . D i s t i l l e d w a t e r was used f o r t h e study o f t h e urea f o r m a t i o n . Solvents used were t o l u e n e , c e l l o s o l v e a c e t a t e and b u t y l a c e t a t e . R e a g e n t g r a d e t o l u e n e was p u r i f i e d b y b o i l i n g u n d e r r e f l u x over sodium and d i s t i l l e d . C e l l o s o l v e a c e t a t e was r e f l u x e d o v e r p h o s p h o r u s p e n t o x i d e and d i s t i l l e d . Cata l y s t s employed i n these r e a c t i o n s were d i b u t y l t i n d i l a u r a t e ( T - 1 2 ) , d i a z a b i c y c l o ( 2 , 2 , 2 ) o c t a n e (Dabco) a n d N,N',N"-tris(dimethylaminopropyl) hexahydrotriazine ( P o l y c a t 41) w e r e u s e d d i r e c t l y w i t h o u t a n y f u r t h e r purification. Kinetic Studies. K i n e t i c studies of the three t y p e s o f r e a c t i o n s o f PPDI and CHDI, t o g e t h e r w i t h those o f the four commercially a v a i l a b l e d i i s o c y a n a t e s , M D I , N D I , I P D I a n d HMDI, w i t h c a t a l y s t s w e r e c a r r i e d out i n s o l v e n t s . The r e a c t i o n c o n d i t i o n s f o r t h e k i n e t i c runs are described i n Table I . The r e a c t i o n s w e r e c a r r i e d o u t i n a 300 m l r o u n d bottom f l a s k , equipped w i t h a m a g n e t i c a l l y s t i r r i n g d e v i c e , a r e f l u x condenser, and a n i t r o g e n i n l e t tube. 25 m l o f t h e d i i s o c y a n a t e s o l u t i o n was i n t r o d u c e d i n t o the r e a c t o r and p l a c e d i n a t h e r m o - r e g u l a t e d o i l bath. The s o l u t i o n o f t h e h y d r o x y 1 c o m p o n e n t c o n t a i n i n g t h e c a t a l y s t i n a 25 m l v o l u m e t r i c f l a s k was a l s o k e p t i n t h e same o i l b a t h . A f t e r t h e r e a c t a n t s had reached the d e s i r e d temperature, the hydroxy1 component-catal y s t s o l u t i o n was p o u r e d i n t o t h e r e a c t o r . The t i m e when h a l f o f t h e s o l u t i o n h a d b e e n a d d e d was r e c o r d e d as t h e s t a r t i n g p o i n t o f t h e r e a c t i o n . C o n s t a n t s t i r r i n g a n d f l o w o f n i t r o g e n was m a i n t a i n e d d u r i n g t h e reaction. Samples o f t h e r e a c t i o n m i x t u r e were p i p e t t e d a t measured time i n t e r v a l s and t h e i s o c y a n a t e cont e n t d e t e r m i n e d b y means o f t h e d i - n - b u t y l a m i n e method. Preparation of Cast Elastomers. The c a s t e l a s t o mers were p r e p a r e d i n a t w o - s t e p p r o c e d u r e . First prep o l y m e r s w e r e made f r o m o n e p o l y e t h e r p o l y o l ( p o l y ( o x y tetramethylene) g l y c o l o f 1000 M.W., (POTMG)) a n d t w o p o l y e s t e r p o l y o l s ( a d i p a t e p o l y e s t e r o f 2000 M.W. (PAG) a n d p o l y c a p r o l a c t o n e o f 1250 M.W. (PCL)) by r e a c t i o n w i t h t h e c o r r e s p o n d i n g d i i s o c y a n a t e s (MDI, P P D I , CHDI o r NDI) a t a n NCO/OH r a t i o o f 2 / 1 . The t e m p e r a t u r e was m a i n t a i n e d a t 80°C a n d p e r i o d i c s a m p l e s w e r e w i t h d r a w n to determined the isocyanate content. When t h e i s o c y a n a t e c o n t e n t o f t h e m i x t u r e r e a c h e d w i t h i n 0.3% o f t h e c a l c u l a t e d v a l u e , t h e r e a c t i o n was s t o p p e d b y c o o l i n g . The p r e p o l y m e r c o u l d b e k e p t f o r a p e r i o d o f s i x months i n t h e absence o f m o i s t u r e . The i s o c y a n a t e t e r m i n a t e d p r e p o l y m e r s were t h e n c h a i n - e x t e n d e d with



ί

1

1

f

0.64

0.73

1

26.0

22.8

11.9

3.4

9.2

1.18

min

17.78

11.76

a kcal

ΔΕ

o

1

2

Cellosolve

Dabco

^ H0 R(NC0)

1

;

acetate

0.004 mole l "

1

-1 j Urea 0.12 mole 1 _ i 0.12 mole kg

1

0.001

0.001

0.002 , (1.41 χ 10 )

0.20

0.29

0.43 (5.95 χ 10 )

1

(A)

exp mole "Hn n i

k

k

42

29

19 6.19

8226

8089

mm

0.0006

0.0006

0.0011 , (2.05 χ 10 )

0.045

0.0675 (6.34 χ 10 )

exp min k c a l . 1 mole

AEa

3623 13.12

^

\

(A)

B u t y l acetate

P o l y c a t 41

2

1

6374

6374

3247

79

53

min

\

10.37

12.87

Δ Ε a kcal

0.0025 mole 1

0.28 mole kg

Cyclotrimerization R(NC0)

40 50 _. Reaction Rate and A c t i v a t i o n Energies

.

1

——

T-12 : d i b u t y l t i n d i l a u r a t e Dabco : d i a z a b i c y c l o ( 2 , 2 , 2 ) o c t a n e P o l y c a t 41 : N , N , N " - t r i s ( d i m e t h y l a m i n o p r o p y l ) h e x a n h y d r o t r i a z i n e .

IPDI HMDI

I

1 2

1.40 (1.57 χ 1 0 )

1.81

4.93

j

j

8

CHDI

!

1

MDI

NDI

PPDI

Diisocyanates

"2

0.0002 mole 1

(A) exp 1 . -ι 1 mole mm 9,1?, (8.56 χ 10 )

k

j

Temp., °C

50

; Toluene

Solvent

!

T-12

1

-1 mole 1

1

0.06 mole kg ^~

Catalyst

2

R(NC0)

j

:

Diisocyanate

—

: Urethane 0.12 j n-BuOH

η

REACTION RATES OF CATALYZED DIISOCYANATE REACTIONS. Reaction C o n d i t i o n s

OH Components

TABLE I .


1

422



1,4-butanediol (1,4-BD), 2,2'-p-phenylenedioxydiethanol (HQEE) or a blend of trimethylolpropane (TMP) with 1,4-BD. The f i n a l NCO/OH r a t i o was kept at 1.05/1. The prepolymers were heated to 80-100°C to give a workable v i s c o s i t y and the l i q u i d or molten chain extender was then added to the prepolymer. The respective c a t a l y s t s were used i n CHDI-prepolymers i n order to accelerate the cure. The mixture was then press-molded i n a Carver press at 100°C f o r from 1/2 to 1 hour and postcured f o r 16 hours at the same temperature. Results and Discussion K i n e t i c Studies. Plots of the experimental data are shown i n Figures 1-3, which indicate that both the urethane and urea formations followed second order reaction up to 50% conversion. Although PPDI has two isocyanate groups on the same benzene nucleus, the two isocyanate groups d i d not e x h i b i t a large a c t i v a t i n g influence on the r e a c t i v i t y of each other i n the react i o n with n-butanol catalyzed by T-12. Unlike the study by Burkus and Eckert (4) on the reaction of diisocyanates and 1-butanol catalyzed with t r i e t h y l e n e diamine having a k-^A^ of 8.40, the k i / k of t h i s react i o n was 2. This means that c a t a l y s t T-12 activates the second isocyanate group nearly to the same r e a c t i v i t y l e v e l as the f i r s t isocyanate group. In the case of MDI, the methylene bridge e f f e c t i v e l y i s o l a t e s the two isocyanate functions. In the case of the a l i p h a t i c isocyanates, t h i s e f f e c t was even less apparent. The isocyanate-water reactions (formation of urea) showed the same r e s u l t s . The reaction of the c y c l o t r i m e r i zation of the diisocyanates catalyzed with Polycat 41 i n butyl acetate followed second order up to 30% conversion as shown i n F i g . 3; then the trimer started to p r e c i p i t a t e . I t was also found that the least square f i t t e d s t r a i g h t l i n e d i d not pass through the o r i g i n . This may be due to the mechanism of a complex formed between the diisocyanates with the c a t a l y s t at the beginning of the reaction; then the c y c l o t r i m e r i z a t i o n proceeds at a much slower rate. This has to be proven with more studies. The rates of these three catalyzed reactions of diisocyanates are l i s t e d i n Table I under i d e n t i c a l conditions of reactants and c a t a l y s t concentrations and temperature. The h a l f time, t 1/2, of the reactions was calculated from the reaction constants. The reactions of PPDI and CHDI were c a r r i e d out at three d i f ferent temperatures and the calculated a c t i v a t i o n energies and frequency factors are l i s t e d i n Table I. 2



2

Figure 1. Second-order plot for reaction between diisocyanates and n-butanol in toluene catalyzed by T-12 at 50°C: [R(NCO) ] = 0.06 g mol/kg; m-BuOH] = 0.12 g mol/L; [T-12] = 0.0002 g mol/L. Key: · , PPDI; O, MDI; |, CHDI; • , IPDI; A, H MDI; and Δ, NDI.


424



0

100

200

300

Time (min) Figure 2. Second-order plot of acetate catalyzed by triethylene [Η,Ο] = 0.12 g mol/L; [Dabco] CHDI; • ,

reaction of diisocyanates and water in cellosolve diamine at 50°C: [R(NCO) ] = 0.12 g mol/kg; = 0.004 g mol/L. Key: ·, PPDI; Ο, MDI; |, 1PD1; Α, Η MDI; Δ, NDI. 2


Edwards et al.; Urethane Chemistry and Applications ACS Symposium Series; American Chemical Society: Washington, DC, 1981. 2

1

1

Figure 3. Second-order plot of trimerization reaction of diisocyanate in butyl acetate catalyzed by polycat 41 at 40°C: [R(NCO) ] : 0.28 mol kg' , [Polycat 41] : 0.0025 mol . Key: · , PPDI; O , MDI; | , CHDI; • , IPDI; A , HMDI.



426


Based on t h e r e a c t i v i t y o f MDI as 1, t h e r e l a t i v e r e a c t i v i t i e s o f the d i i s o c y a n a t e s i n t h e t h r e e c a t a l y z e d r e a c t i o n s were as f o l l o w s : 1. Urethane f o r m a t i o n (with r i - b u t a n o l i n t o l u e n e at 50°C u s i n g d i b u t y l t i n d i l a u r a t e as c a t a l y s t ) PPDI : MDI : NDI : CHDI : IPDI : HMDI = 1 . 8 5 : 0.37 : 1 : 0.28 : 0.15 : 0.13. 2. Urea f o r m a t i o n (with water i n c e l l o s o l v e ace t a t e a t 50°C u s i n g d i a z a b i c y c l o ( 2 , 2 , 2 ) o c t a n e as catalyst PPDI : NDI : MDI : CHDI : IPDI : HMDI = 2.15 : 1.45 : 1 : 0.01: 0.0005 : 0.005. 3. Isocyanurate formation ( c y c l o t r i m e r i z a t i o n c a t a l y z e d w i t h Ν,Ν ,N"-tris(dimethylaminopropyl) hexahydrotriazine) PPDI : MDI : CHDI : IPDI : HMDI = 1.5 : 1 : 0.024 : 0.013 : 0.013. These c o n c l u s i o n s were i n g e n e r a l agreement w i t h the s t u d y c a r r i e d o u t by Akzo Research L a b o r a t o r i e s , Oburnberg, Germany (£), on the r e a c t i o n between d i i s o c y a n a t e s and e x c e s s e t h a n o l o r j i - o c t a n o l a t 80°C. The o r d e r o f r e a c t i v i t i e s o f t h e d i i s o c y a n a t e s were as follows: MDI > TDI > XDI >> HDI > trans-CHDI > IPDI * cis-CHDI > HMDI. 1

Cast Elastomers. T a b l e I I shows t h e e l a s t o m e r s p r e p a r e d from MDI, PPDI, CHDI and NDI w i t h POTMG, M.W. 1000, c h a i n - e x t e n d e d w i t h 1,4-BD. C a t a l y s t T-12 was used i n t h e CHDI-based prepolymer t o a c c e l e r a t e the r e a c t i o n and t o reduce t h e m o l d i n g t i m e . As ex p e c t e d , the PPDI e l a s t o m e r s had a v e r y s h o r t p o t l i f e b u t were s t i l l manageable i n p r o c e s s i n g . The r e s u l t i n g elastomers e x h i b i t e d s u b s t a n t i a l l y b e t t e r p r o p e r t i e s compared t o t h e c o r r e s p o n d i n g MDI-based e l a s t o m e r s , e s p e c i a l l y t h e h i g h temperature r e s i s t a n c e and t h e t e n s i l e s t r e n g t h a t 300% e l o n g a t i o n a t temperatures r a n g i n g from - 2 0 ° t o 150°C, as shown i n F i g . 4. The CHDIbased e l a s t o m e r s e x h i b i t e d lower p h y s i c a l p r o p e r t i e s a t room temperature, b u t e x h i b i t e d a s u r p r i s i n g l y h i g h r e t e n t i o n o f p r o p e r t i e s a t higher temperatures. CHDI a l s o had the advantage o f l i g h t s t a b i l i t y o v e r t h e two a r o m a t i c d i i s o c y a n a t e s . T a b l e I I I shows t h e e l a s t o m e r s p r e p a r e d from MDI, PPDI and CHDI w i t h PAG, M.W. 2000, c h a i n - e x t e n d e d w i t h 1,4-BD, 1,4-HQEE o r b l e n d s o f TMP and 1,4-BD a t a 25/75 r a t i o . C a t a l y s t Dabco 33 LV was used i n a l l t h e c a s e s . A g a i n , t h e PPDI-based e l a s t o mers showed e x c e l l e n t p r o p e r t i e s b o t h a t room and e l e v a t e d temperatures ( F i g . 5 ) . The h i g h v a l u e o f com p r e s s i o n s e t c o u l d be overcome by i n t r o d u c i n g the a r o m a t i c c h a i n - e x t e n d e r HQEE o r c r o s s l i n k e r s such as TMP.


28.

Reactivity

WONG ET AL.

Studies and Cast

427

Elastomers

TABLE I I


COMPOSITION AND PROPERTIES OF POLYURETHANE CAST ELASTOMERS

COMPOSITION: Prepolymer - POTMG 1000: d i i s o c y a n a t e at 111 Extender - 1,4-BD (95% t h e o r e t i c a l ) Diisocyanates

MDI

PPDI

CHDI

NDI

Diisocyanate, %

31.94

23.10

23.76

28.27

NCO Content, %

5.70

6.36

6.34

5.79

-

-

T-12, %

0.0037

PROPERTIES: D e n s i t y , g/ml

1.12

1.14

1.21

1.14

Shore Hardness: A D

78 33

94 48

97 50

95 47

S t r e s s , MPa: At 100% E l o n g a t i o n At 300% E l o n g a t i o n T e n s i l e Strength

5.65 10.04 26.41

13.12 17.31 33.19

12.16 14.53 22.26

8.96 13.69 22.87

Elongation, %

563

512

565

800

64.09 21.36

98.76 20.14

83.35 37.47

55.16 11.38

Bashore Rebound, %

54

58

60

46

Compression S e t , % (70°C, 22 Hrs.)

25

31

37

32

Tear R e s i s t a n c e , Graves Split

KN/m



30

Figure 4.

1 2 3 4 5 NDI

4 = 121; 5 = 150°C.

1 2 3 4 5 CHDI

Stress properties at 300% elongation of poly ether polyol elastomers at various temperatures (NCO/POTMG/1,4-BD = 2/1/0.95).

3 = 70;

1 2 3 4 5 PPDI

Temp.: 1 = -20; 2 = 25;

1 2 3 4 5 MDI

TS at 275% e l o n g a t i o n TS at 200% e l o n g a t i o n


•a

>

Ό

3 %

H

w g

S3

ο

w

5

S3

H

c m

g

Κ) oo


68.6 47.1 51 33

93.5 58.7 48 21

74.0 36.4 42 36

48 56

46 65

39

57

Bashore Rebound, 0

Compression S e t , % (70OC, 22 Hrs.)

635

730

590

94.6 71.6

713

822

591

7.61 15.13 28.70

86 35

1.14

5.59 11.33 43.29

84 36

1.16

4.73 9.20 34.65

82 33

1.25

82.5 60.8

5.83 11.15 29.87

80 30

4.10 7.57 37.21

80 30

1.13

2.08 3.64 32.70

55 15

1.16

47.8 18.7

Tear R e s i s t a n c e , KN/m: Graves Split

Elongation, %

S t r e s s , MPa: At 100% E l o n g a t i o n At 300% E l o n g a t i o n T e n s i l e Strength

Shore Hardness: A D

1.21

PROPERTIES: D e n s i t y , g/ml

0.024

0.012

0.024

0.025

3.54

0.013

0.025

Dabco 33LV, %

12.92

3.56

0.025

0.025

4.40 9.27 38.56 720 78.6 45.4 48 33

698 49.0 30.5 38 12

577 ί : 38.2 ! 11.6 26 12

78 28 2.63 4.24 39.68

67 20

1.11

3.54

3.56

1.13

13.48

13.06

CHDI

; 1.72 3.18 27.94

55 15

1.19

0.025

3.31

19.01

TMP/1,4-BD PPDI

MDI

CHDI

12.51

3.54

HQEE PPDI

3.31

18.26

13.48

3.56

3.31

NCO Content, %

13.06

19.01

Diisocyanate, %

MDI

CHDI

1,4-BD PPDI

MDI

Diisocyanates

Extender - 95% T h e o r e t i c a l

Prepolymer - PAG : D i i s o c y a n a t e a t 1 : 2

COMPOSITION:

TABLE I I I . COMPOSITION AND PROPERTIES OF POLYURETHANE CAST ELASTOMERS




430

Figure 5. Stress properties at 300% elongation of polyester polyol elastom various temperatures (NCO/PAG/HQEE = 2/1/0.95),


28. WONG ET AL.

Reactivity Studies and Cast Elastomers

431

Both PPDI- and CHDI-based elastomers had high modulus and hardness which resemble those of diamine-cured elastomers. The diol-cured case elastomers of PPDI (CHDI) can be seriously considered as a replacement f o r diamine-cured TDI-based cast elastomers.


Ac know 1 ed gm en t s

The f i n a n c i a l support of t h i s work was granted by the Armak Company and Akzo Chemie and i s g r a t e f u l l y acknowledged.

Literature Cited 1.

2. 3. 4. 5. 6. 7. 8.

H. G. Zengel, International Conference on Cellular and Non-cellular Urethanes, S.P.I. and S.F.K. Strasbourg, France, June, 1980. Preprint Book, Carl Hauser Verlag, pp. 315-325. Technical Data Sheet on PPDI and CHDI, Armak Co. Μ. Ε. Bailey, V. Kirss and R. G. Spaunburgh, Ind. Eng. Chem. 48, 794 (1956). J . Burkus and C. F. Eckert, J . Am. Chem. Soc. 80, 5948 (1958). W. Cooper, R. W. Pearson and S. Darke, The Indus t r i a l Chemist, 36, 121 (1960). T. Yokoyama and T. Iwasa, Kogyo, Kagaku Zasshi, 63, 1835-9 (1960). T. Tanaka, T. Yokoyama and T. Iwasa, Kogyo, Kagaku Zasshi, 66, 158-60 (1963). Akzo Corp., Research Dept., Oburnberg, Germany, private communication.

RECEIVED

April 30, 1981.


Urethane Chemistry and Applications - American Chemical Society

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