Urethane Chemistry and Applications - American Chemical Society

16 Catalysis of Isocyanate Reactions with Protonic Substrates

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A New Concept for the Catalysis of Polyurethane Formation via Tertiary Amines and Organometallic Compounds GIA HUYNH-BA Experimental Station, Polymer Products Department, Ε.I.Du Pont De Nemours & Co. Inc., Wilmington, DE 19898 R. JERÔME Laboratory of Macromolecular Chemistry and Organic Catalysis, University of Liege, Sart-Tilman, 4000 Liege, Belgium

A survey of the literature indicates that the catalysis of isocyanate-alcohol reactions has produced a variety of mechan istic explanations. The proposed reaction pathways in the literature are often based on limited information and are unable to explain many of the experimental observations well known to scientists and technologists active in the field (1, 2, 3, 4). The catalysis of the polyurethane formation by organo metallic compounds has especially lead to a number of very different interpretations. Entelis assumes the formation of an activated alcohol-isocyanate binary complex during the catalysis of the methanolphenyl isocyanate reaction by dibutyltin dilaurate (DBTDL) (3, 5). Activated alcohol-isocyanate-catalyst ternary complexes have also been proposed by others. However, significant differences can be noted in the structures of either the postulated one (2, 4, 6, 7) or two (8) coordination positions of the isocyanate to the metal. To explain the synergistic effects observed when tertiary amine and organometallic compounds are combined, several authors suggest the formation of an activated quaternary complex: I, II or III (2, 6, 9, 10, 11, 27). 4+

4+ H-0

4+ Sn'

«

NR!tl "3

\ I

II

III

0097-6156/81/0172-0205$05.00/0 © 1981 American Chemical Society Edwards et al.; Urethane Chemistry and Applications ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

206

U R E T H A N E CHEMISTRY AND

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In these schemes, amine and metal are coordinated on separate atoms. In s p i t e of c o n t r a d i c t o r y views of the e l e c t r o n i c d i s t r i b u t i o n of isocyanates (3, 12, 13) the metal i s always shown as i n t e r a c t i n g w i t h the oxygen and never w i t h the n i t r o g e n atom. Furthermore, the o r g a n o m e t a l l i c compound i s noted by M so that the f a t e of the l i g a n d s i s disregarded (6) and c l e a r l y o v e r s i m p l i f i e d s t r u c t u r e s are a c c o r d i n g l y proposed. Thus, s e v e r a l mechanistic pathways based on p o l a r i z a t i o n e f f e c t s have been proposed to e x p l a i n the c a t a l y s i s of the a l c o h o l - i s o c y a n a t e r e a c t i o n . These p r o p o s i t i o n s appear to be o f t e n u n s a t i s f a c t o r y and cannot e x p l a i n even the m a j o r i t y of the experimental r e s u l t s reported i n the l i t e r a t u r e . For an example, why i s the polyurethane formation c a t a l y z e d by potassium acetate (1) and not at a l l by MgC03 nor C s C l (14)? The r o l e played by the nature of the metal remains a l s o unexplained. Robins r e p o r t s the incremental temperature r i s e noted 1 minute a f t e r the mixing of reagents and c a t a l y s t (7, 16). This parameter i s r e l a t e d to the c a t a l y t i c a c t i v i t y and i s an e f f e c t i v e way to show the r o l e played by the o r g a n o m e t a l l i c compound i n i t s i n t e r a c t i o n w i t h the a l c o h o l . A s i m i l a r conc l u s i o n can be drawn from Table I (15) where the Sn+4 d e r i v a t i v e i s much more a c t i v e than the Sn 2 o x i d a t i o n s t a t e or P b . T h i s paper i s an attempt to f u r t h e r evaluate and to suggest a new mechanistic view f o r these important r e a c t i o n s . Knowledge of the complexation between reagents and c a t a l y s t s w i l l be the b a s i c premise.


n+

+

+

Discussion L i t e r a t u r e data confirm the p o s s i b i l i t i e s of complexation between reagents ( i s o c y a n a t e , a l c o h o l ) and c a t a l y s t ( t e r t i a r y amine, o r g a n o m e t a l l i c compound) considered two by two. The a l c o h o l - t e r t i a r y amine complexation i s w e l l establ i s h e d by NMR (2, 17), cryoscopy (10), UV spectroscopy (2) and other techniques (18-20). According to F r i s c h , 10 to 20% of the amine i s complexed by the a l c o h o l (2) . The evidence f o r the a l c o h o l - m e t a l complexation i s from UV and NMR spectroscopy (2, 5, 17, 21). By cryoscopy, F r i s c h concluded t h a t the metal i s complexed a t about 10-20% by the a l c o h o l (10). NMR measurements agree w i t h the formation of a m e t a l - a l c o h o l - t e r t i a r y amine complex (17). The proton of the a l c o h o l i s indeed s h i f t e d by the a d d i t i o n of a t e r t i a r y amine (0.22 ppm), an o r g a n o m e t a l l i c compound (0.25 ppm) and the combination of these two c a t a l y s t s (0.72 ppm) r e s p e c t i v e l y . S t r u c t u r e IV could account f o r the a l c o h o l a c t i v a t i o n . R-5-H

-

4

NR^

+

XV

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


Oleate

2 +

2 +

Sn

Pb

40,4 32,0

3,5 7,0

2,0

0,9

6,3

[catalyst]

= 10"4 mole/Ζ

C o n d i t i o n s = Solvent s toluene temperature = 30°C

C = methoxy-1-propano1-2

methoxy-3-propanol-l

106,5

68,0

41,4

0,5

1,6

Journal of Applied Polymer Science

0,3

1,0

-

6,9

-

1,2

60,3

3,5

3,4

12,0

48,5

4,9 17,2

3,5

15,2

75,7

262,0

12,0

24,2

290,0

-

2,0 2,5

y

l 2

0,2

0,4

Β - methoxy-2-propanol-l;

Κ - r a t e constant

c K

0,5

h c

3,0

Β

h

A

0,3

A

K

K

0,9

Bu0H-2

A

BuOH-2

C

K

BuOH-1

BuOH-1 = butanο1-1, BuOH-2 = butanol-2; A =

(naphtenate)

Octoate

2 +

Sn

DBTDL

non-catalyzed

Catalyst

K

SuOH-l

Κ X 10 l/equiv.-sec

4

Rate Constant of Phenyl I s o c y a n a t e - A l c o h o l Reactions Catalyzed by Organometallic Compounds (15)

Table I



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UV and IR spectroscopy as w e l l as cryoscopy have been used to assess the i s o c y a n a t e - t e r t i a r y amine complexation (3, 6, 22, 27) . D i - and t r i m e r i z a t i o n of the isocyanate can take p l a c e and complicate the i n t e r p r e t a t i o n ; the occurrence of these s i d e r e a c t i o n s i s of course an i n d i r e c t proof of the isocyanate activation. The isocyanate-metal complexation has a l s o been reported by UV (23, 24, 25, 26, 27) and cryoscopy (10); DBTDL i s proposed to be complexed to the extent of 40-50% by the isocyanate (10). We have i n v e s t i g a t e d the IR s p e c t r a of DBTDL, t r i e t h y l a m i n e and the 1/1 combination of these compounds r e s p e c t i v e l y ( F i g . l ) . When IR-1 and IR-3 are compared s i g n i f i c a n t m o d i f i c a t i o n s i n the r e g i o n of 1700 and 1650 to 1560 cm~l are noted and are c o n s i s t ent w i t h m e t a l - t e r t i a r y amine i n t e r a c t i o n s probably the breaking of the b r i d g e bond between c a r b o x y l a t e and metal and c o o r d i n a t i o n of the amine to the metal v i a the n i t r o g e n . E n t e l i s reported s i m i l a r observations (27) but d i s r e g a r d s them when he proposes the s t r u c t u r e s I I and I I I . On the b a s i s of these r e s u l t s , the polyurethane c a t a l y s i s by o r g a n o m e t a l l i c compounds can h a r d l y be e x p l a i n e d by an a c t i v a t e d b i n a r y complex as proposed by E n t e l i s . Ternary or quaternary complexes are more r e a l i s t i c c a t a l y t i c pathways but t h e i r present d e s c r i p t i o n i s not n e c e s s a r i l y the best one (16). A l l the complexation p o s s i b i l i t i e s are not taken i n t o account. The o r b i t a l i n t e r a c t i o n s between metal ( s , p, d ) , a l c o h o l (ηχ, n2 lone p a i r s of the oxygen) and isocyanate (π, π * ) , f o r example, are not considered a t a l l . What type of i n t e r a c t i o n s can a metal form w i t h an a l c o h o l and an isocyanate r e s p e c t i v e l y ? I t i s u s e f u l to consider the case of DBTDL where 4 d , 5s°, and 5p° l e v e l s of Sn4+ have s i m i l a r energy. A vacant o r b i t a l (5p or 5sp or 5s) of Sn can i n t e r a c t w i t h the η 2 lone p a i r of the a l c o h o l . 1 0

t

4+ R OH + Sn

-·* R'-0: t

->

%

Sn*

+

f

In other words, R 0 i s a hard base (24, 31) i n t e r a c t i n g s i m u l taneously w i t h two hard a c i d s H and S n ^ . H i s harder than Sn^ , the hardness of which depends on the nature of i t s l i g a n d s . More i m p o r t a n t l y the alcohol-Sn^"*" i n t e r a c t i o n and more weakening the 0-H bond should be considered. I n t h i s r e s p e c t , E n t e l i s and T h i e l e ( 3 , 21, 28) r e p o r t that the R L4- Sn organostannic compounds are the most a c t i v e when m = 2 (L = C I " , COO* and R = b u t y l ) . Ph ο +

+

+

+

m

m

I The r e a c t i o n of R3SnOMe + Ph-N=C=0

//

R3Sn-N-C

has been OMe


GIA H U Y N H - B A

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Catalysis of Polyurethane Formation 209


16.


210

U R E T H A N E CHEMISTRY AND

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considered by Davies, who r e p o r t s t h a t Sn becomes l i n k e d to the n i t r o g e n atom of PhNCO (29). The i n t e r a c t i o n between PhNCO and Sn could a c c o r d i n g l y take p l a c e on the C=N double bond. Under these c o n d i t i o n s , F i g . 2 d e s c r i b e s the isocyanate-metal i n t e r a c t i o n by assuming: - a σ donor-type bond between the vacant 5 py o r b i t a l of and the occupied π o r b i t a l of the i s o c y a n a t e . - a π type back bonding between the occupied 4 d orbital of the metal M and the π* antibonding o r b i t a l of the i s o c y a n a t e . This i n t e r a c t i o n decreases the double bonding c h a r a c t e r between the C and Ν atoms of the isocyanate (30). I f the metal, noted Mx, has not an occupied d o r b i t a l w i t h an energy s i m i l a r to that of the vacant py or s type o r b i t a l , the σ c o o r d i n a t i o n ( a , F i g . 2) takes p l a c e whereas the back bonding π type (b, F i g . 2) i s now i m p o s s i b l e ; t h a t i s the case f o r M g and Cs-*- d e r i v a t i v e s . From the above i n t e r a c t i o n s schemes, F i g . 3 i s proposed as a model f o r the s t r u c t u r e of the a c t i v a t e d a l c o h o l - i s o c y a n a t e metal t e r n a r y complex; M and M metals are considered s e p a r a t e l y . 4 +


V z

2 +

+

x

The p o t e n t i a l energy curves d e r i v e d from the angular v i b r a t i o n of both metal-0 ( a l c o h o l ) and metal-j| (isocyanate) bonds are q u a l i t a t i v e l y shown. The curves (1) and ( 1 ) r e l a t i v e to M-0 bond are s i m i l a r (see F i g . 3 ) . On the c o n t r a r y , the curves 1

1

(2) and ( 2 ) are not.

Due to the π type backbonding, M-| bond 1

i s indeed s h o r t e r than Mx-jj and the p o t e n t i a l energy curve ( 2 ) f

1

i s broader than ( 2 ) . The overlap of the curves ( l ) and ( 2 ) i s a c c o r d i n g l y more important than t h i s one of (1) and (2) and the a c t i v a t i o n energy f o r the r e a c t i o n ( A E R ) i s more f a v o r a b l e f o r metal M than f o r M ( A E R ) . A non-concerted rearrangement can be a n t i c i p a t e d ( F i g . 4 ) : a f t e r complexation there i s formation of an oxygen (RO:alcohol)carbon(isocyanate) bond together w i t h a donor-type bond between n i t r o g e n and metal ( v i a Py); the l a t t e r bond would then hydrol y z e d by the proton (from a l c o h o l ) a l r e a d y present around the c o o r d i n a t i o n sphere of the metal. 1

X

Consequences of the Proposed Reaction Mechanism The mechanism has o n l y q u a l i t a t i v e s i g n i f i c a n c e but i t enables one to e x p l a i n the experimental r e s u l t s more s a t i s f a c t o r i l y than the more o f t e n accepted models. Let us now use t h i s new concept to i n t e r p r e t some of the u n t i l now unexplained observations. -To be v a l i d , the mechanism ( F i g s . 3 and 4) i m p l i e s the p a r t i c i p a t i o n of o r b i t a l s c h a r a c t e r i z e d by a s i m i l a r energy: vacant ρ and occupied d o r b i t a l s of the metal, lone p a i r n£ y z


16.

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HUYNH-BA

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Cb>

ft

2. ( « J The σ bonding between π isocyanate and unoccupied p of the metal (M). (b) The 7Γ back bondings between π* of isocyanate and occupied (or partially)

F/gwre

y

d

yz

o/ //ze me/αϊ

(M).

ft) Figure 3. Potential energy curve of the angular vibration of alcohol-metal (M ) (1) and isocyanate-metal (M ) (2). The rearrangement energy for that system is the collapse region of curves 1 and 2 (ΔΕ ). Similarly, in the case of M we have alcohol-metal (Μ) (Γ), isocyanate-metal (Μ) (2'), and ΔΕ ' < Δ Ε . x

x

Κ/

Κ

Κ

Figure 4. Transition structure during the rearrangement of the alcohol and isocyanate.


212

URETHANE CHEMISTRY AND APPLICATIONS

of the a l c o h o l , π and π* o r b i t a l s of the isocyanate. For a given a l c o h o l - i s o c y a n a t e p a i r , the nature of the metal must p l a y an important r o l e . The i n a c t i v i t y of CsCl and MgCO^ s a l t (M type metals) can be e a s i l y explained by the absence of any a c t i v a t i o n process. -The mechanism assumes a n u c l e o p h i l i c a t t a c k of R 0 on the carbon atom of the isocyanate. The rearrangement i s a c c o r d i n g l y favored by a decrease of the e l e c t r o n i c d e n s i t y of the carbon atom. The polyurethane formation r a t e i s indeed higher f o r an aromatic than f o r an a l i p h a t i c isocyanate ( 1 ) ; the s u b s t i t u e n t R of the isocyanate has a f a v o r a b l e i n d u c t i v e e f f e c t i n the former but an unfavorable e f f e c t i n the l a t t e r . -The nature of the a l c o h o l has a l s o an i n f l u e n c e on the polyurethane formation; the a c t i v i t y i n c r e a s e s from t e r t i a r y , to secondary and f i n a l l y to primary i n the case of non-activated a l c o h o l s (1, 15). The energy of the lone p a i r n£ of these a l c o h o l s i s weakly a f f e c t e d by t h e i r molecular s t r u c t u r e , the a l c o h o l - m e t a l i n t e r a c t i o n should a c c o r d i n g l y be s e n s i t i v e to s t e r i c groups near the h y d r o x y l group ( F i g . 3 ) . -The k i n e t i c r e s u l t s summarized i n Table I can be explained on the b a s i s of the a c t i v a t e d t e r n a r y complex ( F i g . 3 ) . In the presence of DBTDL (R2L2Sn), the r a t e constants r e l a t i v e to d i f f e r e n t a l c o h o l are to be c l a s s i f i e d as f o l l o w s : x


f

where BuOHl = 1-butanol and BuOH2 = 2-butanol are non-activated a l c o h o l , A = CH3-O-CH2-CH2-CH2-OH, Β = CH3-CH(OCH3)-CH20H and C = CH3-O-CH2-CHOH-CH3 are a c t i v a t e d a l c o h o l s . DBTDL i s described as an o c t a h e d r a l complex (31, 32); four of i t s c o o r d i n a t i o n vacancies are occupied by the l i g a n d s where as the a l c o h o l and the isocyanate can occupy the two l a s t p o s i t i o n s . The methoxy group of the a c t i v a t e d a l c o h o l s i s unable to p a r t i c i p a t e to the c r y s t a l l i n e f i e l d and has only a s t e r i c and t h e r e f o r e , negative e f f e c t on the r a t e . With Sn2+ and P b ^ based c a t a l y s t s , two l i g a n d s are coordinated and the methoxy group of the a c t i v a t e d a l c o h o l can be i n v o l v e d i n the c r y s t a l l i n e f i e l d (ether-metal bond) and be r e s p o n s i b l e f o r a donor-type e f f e c t on the metal. The r e a c t i v i t y sequence i s now reversed (Table I ) : +

S

n

2

+

K

>K

A BuOHl K

P b 2 +

>K

C BuOH2

V A K

K

> K

BuOHl

>K

C BuOH2



16.

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S i m i l a r l y , Robins r e p o r t s an i n c r e a s i n g a c t i v i t y (17x) when 1butanol i s replaced by 3-dimethylaminoethanol i n the presence of Pb2+ (7, 16). I t i s w e l l known that the lone p a i r of n i t r o g e n i s more donor than that of oxygen ( e t h e r ) ; i t could t h e r e f o r e be concluded that the amino group e x e r t s i t s donor e f f e c t through c o o r d i n a t i o n w i t h the metal. This view i s non-consistent w i t h the s t r u c t u r e of the a c t i v a t e d quaternary complexes reported elsewhere ( I , I I , I I I ) . With DBTDL as a c a t a l y s t , the replacement of a nona c t i v a t e d a l c o h o l (1 or 2-butanol) by an a c t i v a t e d one (Α, B, or C) has a depressive k i n e t i c e f f e c t . S u r p r i s i n g l y , the same behavior i s not observed when 1-butanol i s s u b s t i t u t e d by 3dimethylaminoethanol. T h i s apparent c o n t r a d i c t i o n can be e x p l a i n e d by the c o o r d i n a t i o n of the amine i n s t e a d of the i s o c y a n a t e . Two arguments can be forwarded that a r e i n favor of t h i s hypothesis. -The donor c h a r a c t e r of the t e r t i a r y amine i s higher than that of an i s o c y a n a t e . T e r t i a r y amines a r e indeed recognized as powerful donor l i g a n d s f o r metals such as Cu2+, S n , Sn2+ (24, 31, 32). -Outside the c o o r d i n a t i o n sphere of the metal, the i s o cyanate can be a c t i v a t e d by the c a r b o x y l a t e group of l a u r a t e or acetate l i g a n d s . I t i s to be r e c a l l e d that c a r b o x y l a t e s a l t s are e f f i c i e n t c a t a l y s t s i n the t r i m e r i z a t i o n of isocyanate (1) as w e l l as i n polyurethane formation ( 4 ) . The i n t e r a c t i o n probably takes p l a c e through the lone p a i r of c a r b o x y l a t e and π* o r b i t a l s of the i s o c y a n a t e . Figure 5 i s proposed to e x p l a i n the a c t i v a t i o n e f f e c t observed i n the systems: i s o c y a n a t e - o r g a n o m e t a l l i c compound-^ amino a l c o h o l . This phenomenon i s c o n c l u s i v e l y r e l a t e d t o the donor e f f e c t of the amine onto the metal and not t o the a c t i v a t i o n of the isocyanate by the metal [ s t r u c t u r e s I and I I (2, 6, 2 7 ) ] . 4 +

Conclusions The main experimental r e s u l t s r e l a t i v e to the c a t a l y s i s of the polyurethane formation by o r g a n o m e t a l l i c compounds can be e x p l a i n e d by t a k i n g i n t o account the s t r u c t u r e of the c a t a l y s t s and of c o o r d i n a t i o n v a c a n c i e s . S e v e r a l cases a r e to be con sidered. Case 1. The a l c o h o l i s n o n - a c t i v a t e d (no donor group i n 3 or γ p o s i t i o n of the a l c o h o l ) and the metal has a t l e a s t two vacancies. The l a t t e r a r e occupied by the a l c o h o l and the i s o cyanate r e s p e c t i v e l y and the process takes p l a c e i n accordance to F i g . 6. This mechanism i m p l i e s metals c h a r a c t e r i z e d by a t l e a s t p a r t i a l l y or completely occupied d o r b i t a l s w i t h an energy s i m i l a r t o the one of the f i r s t unoccupied s, ρ l e v e l s (Sn2+, Cu + ). 2



214


L^*

9s"

COO

Figure 5. (a) Structure of an octahedral complex of the metal carrying fo ligands. The two remaining vacancies will be occupied by an alcohol and a (isocyanate, alcohol, amine, and metal present simultaneously); (b) Same sit as in (a) but the metal carries only two ligands.

1

J/'V°

' 1

RNCO

i

«V/ ^

'Ι

Ν

Figure 6. Proposed mechanism for the methane formation catalyzed by orga metallic compounds.


16.

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Catalysis of Polyurethane Formation

Case 2. The same system as i n Case 1 i s now added w i t h a t e r t i a r y amine. The amine occupies a vacancy on the metal i n s t e a d of the i s o c y a n a t e . I f the isocyanate i s a c t i v a t e d o u t s i d e the c o o r d i n a t i o n sphere of the m e t a l , i . e . by a c a r b o x y l i c l i g a n d , the process takes p l a c e ( F i g . 5a). Case 3. Case 2 but the metal has more than two v a c a n c i e s . A l l these components ( a l c o h o l , isocyanate and amine) are coor dinated onto the metal ( F i g . 5b). The r e s u l t s of Frisai (15) (Pb2+ and S n i n Table I ) , Smith ( 6 ) , and Robins (7) are now accordingly explained.


2 +

Case 4. When a (3-amine o r e t h e r o - a l c o h o l i s used, Cases 2 o r 3 are encountered. I n the Case 2, the isocyanate can however be coordinated onto the metal i n preference t o the ether group. Under these c o n d i t i o n s , a s t e r i c hindrance due to the ether group can e x e r t a depressive e f f e c t on the k i n e t i c s of the process. Further r e s e a r c h , of course, i s needed t o support the new concepts developed i n t h i s paper. Recently we found i n the l i t e r a t u r e t h a t the r e s u l t s obtained by Bechara (33) supported our concepts. Acknowledgements The authors want t o express t h e i r g r a t i t u d e t o P r o f e s s o r s : K. C. F r i s c h ( U n i v e r s i t y of D e t r o i t , Michigan - 48221), J . E. McGrath ( V i r g i n i a P o l y t e c h n i c I n s t i t u t e and State U n i v e r s i t y , Blacksburg, VA 24061), P. Teyssie ( U n i v e r s i t y of L i e g e , S a r t Tilman, 4000 L i e g e , Belgium) f o r very f r u i t f u l d i s c u s s i o n s and comments.

Literature Cited 1) Saunders, J. Η., Frisch, K. C., "Polyurethanes, Chemistry, and Technology" Part I Chemistry Interscience, New York (1962) 2) Frisch, K. C., Rumao, L. P., Jour. Macromol. Sci. Revs. Macromol. Chem. (1970) (1), C5, 103 3) Entelis, S. G., IUPAC International Symposium on Macromolecular Chemistry, Budapest (1969), 89 4) Farkas, Α., Mills, G.A., Adv. Catalysis, (1962), 13, 393 5) a) Nesterov, O.V., Zabrodin, V.B., Chirkov, Yu. Ν., Entelis, S. G., Kinetic Cat. (1974), 15, 1183 b) ibid; Kinetic Cat. (1972), 13, 200 c) Zabrodin, V. B., Nesterov, O. V., Entelis, S. G., Kinetic Cat. (1970), 11, 877 d) ibid; Kinetic Cat., (1970), 11, 91 e) ibid; Kinetic Cat., (1969), 10, 544 Edwards et al.; Urethane Chemistry and Applications ACS Symposium Series; American Chemical Society: Washington, DC, 1981.

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6) Smith, Η. Α., Jour. Appl. Polym. Sci. (1963) 7, 85 7) Robins, J., Jour. Appl. Polym. Sci. (1965) 9, 821 8) Williams, F., Ulrich, H., Jour. Appl. Polym. Sci. (1969) 13, 1929 9) Willeboorse, F. C., Critchfield, F. Ε., Meeker, R. L . , Jour. Cellular Plast. (1965), 1, 76 10) Reegan, S. L . , Frisch, K. C., Jour. Polym. Sci. (1970) A1, 8, 2883 11) Smith, Η. A., Jour. Poly. Sci. (1968) A1, 6, 1299 12) Entelis, S. G., Nesterov, O. V. Russ. Chem. Revs., (1966) 35, (12) 917 13) Zabrodin, V. B., Zhur. Phys. Khim. (1971) N3, 45 14) Anzuino, G. Pirro, A., Rossi, G., Polofriz, L . , Jour. Polym. Sci. Polym. Chem. Ed. (1975) 13, 1667 15) Rand, L. Thir, B. Reegan, S. L . , Frisch, K. C., Jour. Appl. Polym. Sci. (1965) 9, 1787 16) Huynh-ba, G. Teyssie, Ph. Jerome, R., Polym. Preprint, (1980) 21 (2) 307 17) Frisch, K. C., Reegan, S. L . , Floutz, W. V., Silver, J. P., Jour. Polym. Sci. (1967) A1, 5, 35 18) Farkas, A., Strohm, P. F., Industr. and Eng. Chem. Funda mental (1965) 4, 32 19) Oberth, Α. Ε., Βrunner, R. S., Jour. Phys. Chem. (1968) 72, 845 20) Zharkov, U. V., Zhitinlainer, Α. V., Zhokhova, F. A., Zh. Fiz. Khimie. (1970) 44, 223 21) a) Entelis, S. G., Nesterov, O.V., Kinet. Kataliz. (1966) 7, 464 b) ibid., Kinet. Kataliz.(1966), 7, 627 c) ibid., Kinet. Kataliz. (1966) 7, 805 22) Pestemer, H., Lauerer, D., Angew Chem. (1960) 72, 612 23) Frisch, K. C., "Polyurethane Technology", Bruins, P. F., ed. Wiley Inters., New York (1969) 24) Dyer, Ε., Pinterton, R. Β., Jour. Appl. Polym. Sci. (1965) 9, 1713 25) Bloodsworth, A. J., Davies, A. G., Proc. Chem. Soc. (1963) 264 26) Lipatova, Τ. Ε., Bakalo, L. A., Niselsky, Yu. Ν., Sirotinskaya, A. L . , Jour. Macromol. Sci. Chem. (1970) A4, (8) 1743 27) Chirkov, Y.N., Nesterov, O. V., Entelis, S. G., Kinetic Cat. (1973), 14, 798 28) Thiele, L . , Becker, R. Frommelt, Η., Faserforch Tesiltech. (1977) 28 (7), 343 29) Bloodworth, A. J., Davies, A. G., Jour. Chem. Soc., (1965) 5328


16.

GIA HUYNH-BA AND JEROME


30) Teyssie, Ph. Private Communication: structure type double is valid only for very "soft" metals with low


4+

oxidation stage. Our example on Sn is "hard" type and high oxidation stage. 31) Okawara, R., Wada, Μ., Adv. Organomet. Chemistry, (1967) 5,137 32) Zubieta, J. Α., Zuckerman, J. J., Progress in Inorganic Chemistry, Lippard, S. J. Ed., Interscience, New York (1978) 24, 251 33) Bechera, S., Org. Coat. and Plast. Chem., (1980) 43, 914 RECEIVED May 14, 1981.


Urethane Chemistry and Applications - American Chemical Society

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