Urethane Chemistry and Applications - American Chemical Society

27 Model Studies of Phenolic-Urethane Polymers J. E. KRESTA, A. GARCIA, and K. C. FRISCH Polymer Institute, University of Detroit, Detroit, MI 48221

Downloaded by FUDAN UNIV on December 8, 2016 | http://pubs.acs.org Publication Date: November 30, 1981 | doi: 10.1021/bk-1981-0172.ch027

G. LINDEN Ashland Chemical Co., Columbus, OH 43216

Phenolic-based urethane foams have been described by various investigators [1-19]. The phenolic resins used were either re soles or novolacs, as well as derivatives of phenol-formaldehyde, or phenol-aniline-formaldehyde condensation products [1-17], in particular poly(oxyalkylene) derivatives [7,9-14] and also Mannich reaction products of phenol with formaldehyde and alkanolamines [15-17]. More recently, new types of phenolic-urethane foams were reported using phenolic resins containing both benzylic ether linkages and methylol groups with polymeric isocyanate (poly meric MDI) [l8]. These foams were characterized by low combusti bility even without the addition of flame retardants, good com pressive strength, and a low Κ factor (0.113). Very recently Papa and Critchfield [19] described the prepara tion of foams based on a resole resin containing a high orthomethylol content and a blend of quasi prepolymer of tolylene diisocyanate, a phosphorus-containing polyol and polymeric isocyanate containing a minor portion of tris-(2-chloro-ethyl) phosphate. The resulting foams had relatively low friability, low combusti bility and smoke evolution. However, the foams were open-celled and the Κ factor was more characteristic of that of phenolic foams (0.254). R e l a t i v e l y l i t t l e b a s i c information has been published r e garding the k i n e t i c s of phenol-formaldehyde intermediates, espe c i a l l y of phenols, methylol phenols, benzyl a l c o h o l and b e n z y l i c ethers with isocyanates. Due to the f a c t that a t y p i c a l r e s o l e contains both phenolic and b e n z y l i c hydroxyl groups, i t was of i n t e r e s t to determine t h e i r r e a c t i v i t y toward isocyanates i n the presence of v a r i o u s c a t a l y s t s , as w e l l as the e f f e c t of s u b s t i t u t i o n on t h e i r r e a c t i v i t y . T h i s i n v e s t i g a t i o n describes the k i n e t i c s of model phenols and model benzyl a l c o h o l s with phenyl isocyanate c a t a l y z e d with e i t h e r a t e r t i a r y amine ( d i m e t h y l c y c l o hexylamine, DMCHA) or an organotin c a t a l y s t , d i b u t y l t i n d i l a u r a t e (DBTDL) i n e i t h e r dioxane or dimethylformamide s o l u t i o n .

0097-6156/81/0172-0403$05.00/0 © 1981 American Chemical Society Edwards et al.; Urethane Chemistry and Applications ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

404

URETHANE CHEMISTRY AND APPLICATIONS

Experimental


M a t e r i a l s . A l l model compounds and dimethylcyclohexylamine (DMCHA) used i n t h i s study were reagent grade and were p u r i f i e d by d i s t i l l a t i o n under n i t r o g e n . D i b u t y l t i n d i l a u r a t e (DBTDL) was used as r e c e i v e d from the s u p p l i e r . Reagent grade 1,4-dioxane was d r i e d by r e f l u x i n g f i r s t w i t h NaOH, then w i t h m e t a l l i c sodium for 24 hours each and then d i s t i l l e d under n i t r o g e n . Toluene was p u r i f i e d by r e f l u x i n g w i t h sodium f o r 24 hours, followed by d i s t i l l a t i o n . Dimethylformamide (DMF) was d r i e d using Linde 4A molec u l a r s i e v e s . Phenyl isocyanate was p u r i f i e d by vacuum d i s t i l l a tion. Measurement of K i n e t i c s . The r e a c t i o n s were c a r r i e d out i n a d r i e d 300 ml three-necked f l a s k , equipped w i t h a n i t r o g e n i n l e t , magnetic s t i r r e r , r e f l u x condenser, and dropping f u n n e l . The r e a c t i o n f l a s k was immersed i n a t h e r m o s t a t i c a l l y c o n t r o l l e d o i l bath. F i f t y ml of 1.0 mole/kg isocyanate s o l u t i o n i n 1,4-dioxane was p i p e t t e d i n t o the f l a s k and was s t i r r e d m a g n e t i c a l l y w h i l e the model compound s o l u t i o n i n dioxane (1 mole/kg) and c o n t a i n i n g v a r i a b l e amounts of c a t a l y s t was placed i n a temperature-controlled dropping f u n n e l . When constant temperature was reached (25oC) i n the f l a s k , as w e l l as i n the dropping f u n n e l , the s o l u t i o n was poured i n t o the f l a s k and the whole mixture was thoroughly mixed. Samples of approximately 2.5 g were withdrawn a t r e g u l a r i n t e r v a l s and the isocyanate content determined by means of the d i - n - b u t y l amine method. C o r r e c t i o n s due to the consumption of the hydroc h l o r i c a c i d by the amine c a t a l y s t were made i n the determination of the isocyanate content. R e s u l t s and D i s c u s s i o n The r e a c t i v i t y of the model phenols and benzyl a l c o h o l s w i t h phenyl isocyanate was determined i n the presence of a t e r t i a r y amine (DMCHA) and a t i n c a t a l y s t (DBTDL) by measurement of the r e a c t i o n k i n e t i c s . The experimental r e s u l t s based on i n i t i a l equal concentrations o f phenyl isocyanate and p r o t i c r e a c t a n t s showed that the c a t a l y z e d r e a c t i o n s f o l l o w e d second order r e a c t i o n w i t h respect t o the disappearance of isocyanate groups (see Figure 1). I t was a l s o found that a l i n e a r r e l a t i o n s h i p e x i s t s between the experimental r a t e constant k , and the i n i t i a l c o n c e n t r a t i o n of the amine c a t a l y s t (see F i g u r e z ) . I n the case of the t i n c a t a l y s t , the r e a c t i o n w i t h respect t o c a t a l y s t c o n c e n t r a t i o n was found t o be one-half order (see F i g u r e s 3-4). A s i m i l a r r e l a t i o n ship f o r the t i n c a t a l y z e d urethane r e a c t i o n was found by Borkent e x p

[203.

In Table I are summarized the k i n e t i c r e s u l t s f o r the model phenols w i t h phenyl isocyanate i n the presence of DMCHA c a t a l y s t i n dioxane s o l u t i o n . I t i s apparent that s u b s t i t u t i o n i n the 2 and 6 p o s i t i o n s decrease s i g n i f i c a n t l y the r e a c t i o n constant k . In the case of model b e n z y l a l c o h o l s using DMCHA c a t a l y s t , the c a t

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

27. KRESTA ET AL.

Phenolic-Ό'rethane Polymers

OH


NCO

Time (min) Figure 1.


405



406

Figure 2.


KRESTA ET AL.

Phenolic-Urethane Polymers


27.

Figure 3.


407



408

Figure 4.



CH

q

lO.

n

.CH

Model Phenol

0.1415

0.0479 0.0786 0.0990

0.015

0.010 0.015 0.020

10.60

0.0464 0.0567

0.010

0.0309

0.0075

0.005

0.0892

9.89

10.20

0.0414

0.005 0.010

pK

χ

^ _ kg mole min

e

Catalyst DMCHA mole/1

k

EFFECT OF SUBSTITUTION ON REACTIVITY OF MODEL PHENOLS WITH PHENYL ISOCYANATE IN DIOXANE AT 25°C

TABLE I


C

5.34

5.28

10.35

ν H ^ kg mole min 2

410


decrease i n the r e a c t i v i t y due t o the s u b s t i t u t i o n i n the 2 p o s i t i o n was r e l a t i v e l y s m a l l as can be seen i n Table I I . A substant i a l increase i n k f o r o-hydroxy b e n z y l a l c o h o l was observed. T h i s increase i n the r e a c t i v i t y can be a t t r i b u t e d t o the formation of i n t e r n a l hydrogen bonding which a c t i v a t e d the phenol group r e s u l t i n g i n the p r e f e r e n t i a l formation of the corresponding o-(hydroxymethyl) phenyl N-phenylcarbamate: c a t

0

C H NC0 Downloaded by FUDAN UNIV on December 8, 2016 | http://pubs.acs.org Publication Date: November 30, 1981 | doi: 10.1021/bk-1981-0172.ch027

6

5

DMCHA

0-H-NH-C CH 0H 2

S i m i l a r r e s u l t s were obtained by Papa and C r i t c h f i e l d [ 1 9 ] . The e f f e c t of type of c a t a l y s t on the r e a c t i v i t y of phenol and b e n z y l a l c o h o l w i t h phenyl isocyanate can be seen i n Table I I I . In the case o f t e r t i a r y amine (DMCHA), there i s a r e l a t i v e l y small d i f f e r e n c e i n the r e a c t i v i t y of both the phenol and b e n z y l a l c o h o l w i t h phenyl i s o c y a n a t e . Using DBTDL as c a t a l y s t , b e n z y l a l c o h o l was found t o be 26 times more r e a c t i v e than phenol i n the r e a c t i o n w i t h phenyl i s o c y a n a t e . I t i s a l s o of i n t e r e s t t o p o i n t out that DBTDL i s about three times more e f f e c t i v e a c a t a l y s t than DMCHA i n the r e a c t i o n of phenol w i t h phenyl i s o c y a n a t e . Baker and Gaunt [ 2 1 ] found that e t h y l a l c o h o l was 30 times more r e a c t i v e than phenol i n the uncata l y z e d r e a c t i o n w i t h phenyl i s o c y a n a t e . However, i n the presence of a t e r t i a r y amine ( t r i e t h y l a m i n e ) , the r e a c t i v i t y of phenol i n creased s i g n i f i c a n t l y and was found t o be s i m i l a r t o that of e t h y l a l c o h o l (see Table I V ) . The e f f e c t of s o l v e n t s on the k i n e t i c s of the phenol-phenyl isocyanate r e a c t i o n i s seen i n Table V. The r e a c t i v i t y increased i n the f o l l o w i n g order: dioxane < toluene < DMF (1:3.3:92). The d i f f e r e n c e i n r e a c t i v i t y i s due t o the combined e f f e c t s of the r e l a t i v e p e r m i t i v i t y and the s p e c i f i c s o l v a t i o n . Conclusions I t was found that the r e a c t i v i t y o f t y p i c a l f u n c t i o n a l groups present i n r e s o l e type o f p o l y o l s w i t h i s o c y a n a t e s i s a f f e c t e d t o a great extent by the s t r u c t u r a l c o n f i g u a t i o n of the p o l y o l s and the type of c a t a l y s t used. Model s t u d i e s based on s u b s t i t u t e d phenols and b e n z y l a l c o h o l s showed that the presence of s u b s t i t u e n t s i n the ortho p o s i t i o n i n b e n z y l a l c o h o l had a r e l a t i v e l y s m a l l e f f e c t on the r e a c t i v i t y of the h y d r o x y l group w i t h isocyanate i n the presence of t e r t i a r y amine c a t a l y s t (DMCHA). I n c o n t r a s t , s i m i l a r s u b s t i t u t i o n i n phenols s i g n i f i c a n t l y a f f e c t e d the r e a c t i v i t y of the


27.

KRESTA ET AL.

Ρhenolic-Urethane Polymers

411

TABLE I I EFFECT OF SUBSTITUTION ON REACTIVITY OF MODEL BENZYL ALCOHOLS WITH PHENYL ISOCYANATE IN DIOXANE AT 25°C Catalyst DMCHA mole/1


Model Phenol

k

—2 — kg mole min

k —g £S| kg mole min

:

ÇH OH

0.010 0.015 0.020

0.0709 0.1278 0.1664

9.88

CH OH

0.0657 0.1071 0.1459

8.29

0CH„

0.010 0.015 0.020

0.0125** 0.0297** 0.0491**

18.94***

CH 0H

0.001* 0.002* 0.003*

0.005 0.010 0.015

0.0414 0.0892 0.1415

10.35

2

2

2

OH

:o: *equiv 1 ^ **kg equiv ^"min ^ 2 -2 -1 ***kg equiv min



cat

2

^cat^PhOH

^ eaPphCH 0H

k

Relative reactivity:

k

0.95

9.88

10.35

DMCHA 2 -2 -1 (kg mole min ) DBTDL

0.1979 0.3268

0.0002 0.0003

0.0015

0.0918

0.0299 0.0382

0.0010

0.0001

0.0186

kg mole "'"min

0.0005

Dle/1

26.27

32.31

1.23

, 1.5 - -1.5 . -1 kg mole mm

COMPARISON OF TERTIARY AMINE (DMCHA) WITH ORGANOTIN (DBTDL) CATALYSTS IN THE REACTION OF PHENOL AND BENZYL ALCOHOL WITH PHENYL ISOCYANATE IN DIOXANE AT 25°C

TABLE I I I


4^

δ

Η

r ο >

>

α

>

H

GO

w g

Ο

W

>

H

w

to

27.

KRESTA ET AL.


413

TABLE IV EFFECT OF TERTIARY AMINE CATALYST ON REACTIVITY OF PHENOL AND ETHYL ALCOHOL WITH PHENYL ISOCYANATE Downloaded by FUDAN UNIV on December 8, 2016 | http://pubs.acs.org Publication Date: November 30, 1981 | doi: 10.1021/bk-1981-0172.ch027

21

[PhNCO] = [ROH] =0.24 mole/1 Solvent ;: Temp.:

Bu 0 2

25°C

4

k

χ 10"" -1 -1 1 mole sec

4 k χ 10 -1 -1 1 mole sec C

[Et N] = 3

Catalyst

None

0.03 mole l "

PhOH

0.01

12.0

C H 0H

0.3

12.7

2

5

1

k /k c ο 1200

42.3

Relative reactivity: ^tOH

30

1.06

-

kphOH



Model Phenol

DMF

0.0276 0.0664 0.1082

0.0283 0.0572 0.089

0.002 0.003

0.00004 0.00007 0.00010

0.1415

0.015

0.001

0.0892

0.010

Toluene

0.0414

0.005

Dioxane

exp -1 . -1 kg mole mm τ

Solvent

ι

Catalyst DMCHA mole/1

955.88

34.89

10.35

cat 2 -2 -1 kg mole min

EFFECT OF SOLVENTS ON REACTIVITY OF PHENOL WITH PHENYL ISOCYANATE AT 25°C

TABLE V


Ο 25

Η

r > ο

>

Ο

>

Η

m

g

η

> m

m H Χ


(k)

2

I

!

PhOH

!

i

2

*

Non-Catalyzed

Τ = 25°C; Dioxane

* (21) Τ = 20°C; Bu 0

**

ί

1

(k)

1

PhCH OH :

PhOH

v

;

EtOH

(k)

1

f

! 1

j

1 ;

26.27

DBTDL Catalyzed

0.95

1.06*

Amine Catalyzed

EFFECT OF CATALYSTS ON THE REACTIVITY OF PHENOL BENZYL ALCOHOL AND ETHYL ALCOHOL WITH PHENYL ISOCYANATE

TABLE VI


)

2

cat PhCH OH ^cat^PhOH

(k

^cat^PhOH

^capEtOH

>

H

w

>

H

m

5*

^

Κ)



416

h y d r o x y l groups, which i s presumably due t o e l e c t r o n i c e f f e c t s of the s u b s t i t u e n t s on the p o l a r i z a b i l i t y o f phenols. The e l e c t r o n donating s u b s t i t u e n t (-CH^) i n c r e a s e d the e l e c t r o n d e n s i t y on the h y d r o x y l group of the phenol and consequently decreased the overa l l p o l a r i z a b i l i t y r e s u l t i n g i n lower r e a c t i v i t y . I n t h i s case the e l e c t r o n i c e f f e c t of the s u b s t i t u e n t had a s i g n i f i c a n t l y more pronounced i n f l u e n c e on the r e a c t i v i t y than the s t e r i c hindrance due to the s u b s t i t u e n t . The presence of the e l e c t r o n donor (-0-) i n the v i c i n i t y of the p h e n o l i c h y d r o x y l a c t i v a t e d the -OH group through induced p o l a r i z a t i o n due t o hydrogen bonding and t h e r e f o r e , i n c r e a s e d r e a c t i v i t y was observed. S i m i l a r l y , the p o l a r i z a b i l i t y of the p h e n o l i c h y d r o x y l groups by the t e r t i a r y amine c a t a l y s t i s respons i b l e f o r the m u l t i order (1200 x) i n c r e a s e i n the r e a c t i v i t y compared t o the non-catalyzed r e a c t i o n w i t h isocyanate (see Table I V ) . The a c t i o n o f the t i n c a t a l y s t was found t o be q u i t e d i f f e r ent from the a c t i o n of the t e r t i a r y amine c a t a l y s t . I n the p r e s ence of the amine c a t a l y s t the r e a c t i v i t y of the phenol and b e n z y l a l c o h o l was approximately equal (see Table I V ) . I n the case of DBTDL, the r e a c t i v i t y r a t i o was s i m i l a r t o that of the non-catal y z e d r e a c t i o n , which i n d i c a t e s that the p o l a r i z a t i o n of the i s o cyanate by the t i n c a t a l y s t due t o complex formation presumably played an important r o l e i n the r e a c t i o n c a t a l y s i s (see Table V I ) . The r e a c t i o n of the phenol w i t h i s o c y a n a t e , c a t a l y z e d by the t e r t i a r y amine, was very s e n s i t i v e t o the type of s o l v e n t used. The observed i n c r e a s e i n the r e a c t i v i t y i s due t o the combined e f f e c t s of the r e l a t i v e p e r m i t i v i t y and the s p e c i f i c s o l v a t i o n o f the r e a c t a n t s by the s o l v e n t s .

Acknowledgments The authors wish t o express t h e i r a p p r e c i a t i o n f o r the f i n a n c i a l support of t h i s i n v e s t i g a t i o n t o the Ashland Chemical Company.

Literature Cited 1. A. Khawam, U. S. Pat. 3,063,964 (to Allied Chemical Corp.), Nov. 13, 1962. 2. R. F. Sterling, U. S. Pat. 2,608,536 (to Westinghouse Electric Corp.), Aug. 26, 1952. 3. H. H. Ender, U. S. Pat. 3,271,313 (to Union Carbide Corp.), Sept. 6, 1966. 4. R. W. Quarles and J. A. Baumann, U. S. Pat. 3,298,973 (to Union Carbide Corp.), Jan. 17, 1967. 5. M. Cenker and P. T. Kan, U. S. Pat. 3,732,187 (to BASF Wyan dotte Corp.), May 8, 1973. Edwards et al.; Urethane Chemistry and Applications ACS Symposium Series; American Chemical Society: Washington, DC, 1981.


27.

KRESTA ET AL.


417

6. Ε. A. Dickert, U. S. Pat. 3,872,034 (to Cook Paint and Var nish Co.), March 18, 1975. 7. D. Β. Davis, Ε. Ε. Jones and R. Ε. Morgan, Jr., U. S. Pat. 3,598,771 (to Dow Chemical Co.), Aug. 10, 1971. 8. A. Heslinga and P. J. Napjus, Ger. Pat. 1,197,614 (to Chemische Fabrik Kalk G.m.b.H.), July 29, 1965. 9. J. S. McFarling, U. S. Pat. 3,770,671 (to Owens-Corning Fiberglass Corp.), Nov. 6, 1973. 10. W. C. Forster, U. S. Pat. 3,470,118 (to Reichhold Chemicals, Inc.,), Sept. 30, 1969. 11. K. D. Longley, F. Park and C. Bernstein, U. S. Pat. 3,682,845 (to Witco Chemical Corp.), Aug. 8, 1972. 12. E. F. Cox, W. H. Cook and F. Hostettler, U. S. Pat. 3,186,969 (to Union Carbide Corp.), June 1, 1965. 13. F. M. Kujawa and J. A. Stone, U. S. Pat. 3,499,961 (to Hooker Chemical Corp.), March 10, 1971. 14. E. F. Cox, W. H. Cook and F. Hostettler, U. S. Pat. 3,245,924 (to Union Carbide Corp.), April 12, 1966. 15. G. D. Edwards, D. M. Rice and R. L. Soulen, U. S. Pat. 3,297,597 (to Jefferson Chemical Co.), Jan. 10, 1967. 16. D. H. Chadwick, Can. Pat. 856,311 (to Mobay Chemical Co.), Nov. 11, 1970. 17. E. F. Cox and R. J. Knopf, U. S. Pat. 3,436,373 (to Union Carbide Corp.), April 1, 1969. 18. R. J. Schafer, L. A. Baker, G. L. Linden, K. C. Frisch and V. Tripathi, J. Cell. Plastics 14, No. 3, 146 (1978). 19. A. J. Papa and F. E. Critchfield, J. Cell. Plastics 15, No. 5, 258 (1979). 20. G. Borkent, Advances in Urethane Science and Technology, edited by K. C. Frisch and S. L. Reegen, Vol. 3, p. 1 (1973), Technomic Publishing Co., Westport, Conn. 21. J. W. Baker and J. Gaunt, J. Chem. Soc. (1949), 9, 19, 27. RECEIVED April 30, 1981.


Urethane Chemistry and Applications - American Chemical Society

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