Cyclopolymerization and Polymers with Chain-Ring Structures

8 Radical Polymerization of exo and endo N-Phenyl-5-norbornene-2,3-dicarboximides as Models for Addition-Curing Norbornene End-Capped Polyimides 1

NORMAN G. G A Y L O R D and MICHAEL M A R T A N

Downloaded by UNIV LAVAL on July 13, 2016 | http://pubs.acs.org Publication Date: August 12, 1982 | doi: 10.1021/bk-1982-0195.ch008

Gaylord Research Institute Inc., New Providence, NJ 07974

Homopolymerization of exo and endo cyclopentadieneN-phenylmaleimide Diels-Alder adducts in the melt at 150-260°C and in chlorobenzene at 120°C was promoted in the presence of radical catalysts having half -lives of less than 2 hr at reaction temperature. The low molecular weight (< 2000), saturated (H-NMR in CDCl ) homopolymer retained the configuration of the adduct when the polymerization temperature was below 200°C but contained both endo and exo configurations, due to isomerization, when prepared from either isomer at 260°C. The proposed saturated structure with N-phenylnorbornane-2,3-dicarboximide repeating units with 5,7-linkage, is presumably present in the cross -linked products from the high temperature curing of norbornene end-capped addition-type polyimides. 1

3

Aromatic polyimides have achieved considerable success as high temperature-resistant polymers. Since the desired high molecular weight polyimides are not readily processable, they are generated in situ by the thermal ring closure of the processable precursor poly(amic-acids) (2). The use of low molecular weight prepolymers, i.e. poly ( amic-ac ids ), as laminating resins is limited by their conversion to an intractable state before complete elimination of volatile by-products. This problem has been alleviated by the use of low molecular weight polyimide prepolymers end-capped with norbornene rings (3, 4, 5)

1

See Reference 1. 0097-6156/ 82/0195-0097$06.00/0 © 1982 American Chemical Society

Butler and Kresta; Cyclopolymerization and Polymers with Chain-Ring Structures ACS Symposium Series; American Chemical Society: Washington, DC, 1982.

98

POLYMERS WITH CHAIN-RING

STRUCTURES

or monomeric r e a c t a n t s polymerizable t h e r e t o ( 5-É3)

H


OCH

2

N ^ ) . C H

2

^

N H

2

+

n

A t e l e v a t e d temperatures the terminal norbornene r i n g s presumably undergo a d d i t i o n p o l y m e r i z a t i o n t o promote c r o s s l i n k i n g w i t h m i n i mal formation of v o l a t i l e by-products. The mechanism of the c r o s s l i n k i n g r e a c t i o n has been p o s t u l a t e d as (a) d i s s o c i a t i o n of the t e r m i n a l cyclopentadiene-N-arylmaleimide D i e l s - A l d e r adduct t o the monomeric p r e c u r s o r s , which immediately r e a c t t o form an adduct which i n i t i a t e s the homopolymeri z a t i o n of the u n d i s s o c i a t e d terminal norbornene r i n g s t o form a s a t u r a t e d polymer {5),

é

Ο

and as (b) homopolymerization of the norbornene r i n g i n the termi n a l D i e l s - A l d e r adduct through an u n s p e c i f i e d mechanism, although presumably i n v o l v i n g r i n g opening and/or d i s s o c i a t i o n , t o form an unsaturated a l t e r n a t i n g copolymer (8, 9).


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GAYLORD AND MARTAN

W-Vhenyl-5-mrbornene-2 3-d\carboximides

99

t


The r a d i c a l c a t a l y z e d homopolymerization o f the furan-maleic anhydride (F-MAH) D i e l s - A l d e r adduct y i e l d s a s a t u r a t e d homopolymer a t temperatures below 60 C, and an unsaturated equimolar a l t e r n a t i n g copolymer a t e l e v a t e d temperatures, due t o r e t r o g r a d e d i s s o c i a t i o n o f the adduct (10, 11). The c o p o l y m e r i z a t i o n o f monomeric f u r a n and maleic anhydride y i e l d s the same unsaturated a l t e r n a t i n g copolymer, independent o f temperature (10).

In c o n t r a s t , the r a d i c a l c a t a l y z e d homopolymerization of the cyclopentadiene-maleic anhydride (CPD-MAH) D i e l s - A l d e r a d d u c t y i e l d s a s a t u r a t e d homopolymer a t temperatures as h i g h as 220 C, while r e t r o g r a d e d i s s o c i a t i o n occurs a t even h i g h e r temperatures. Nevertheless, the c o p o l y m e r i z a t i o n o f monomeric c y c l o p e n t a d i e n e and maleic anhydride y i e l d s a s a t u r a t e d 1:2 copolymer (12-15). Q


100

POLYMERS WITH CHAIN-RING STRUCTURES

Since the F-MAH and CPD-MAH D i e l s - A l d e r adducts y i e l d unsatur a t e d and s a t u r a t e d polymers, r e s p e c t i v e l y , as a r e s u l t o f r a d i c a l c a t a l y z e d homopolymerization a t e l e v a t e d temperatures, i t was o f i n t e r e s t t o i n v e s t i g a t e the r a d i c a l c a t a l y z e d p o l y m e r i z a t i o n o f the isomeric exo- and endo-cyclopentadiene-N-phenylmaleimide adducts, models f o r the norbornene end-capped p o l y i m i d e s whose thermal p o l y m e r i z a t i o n products have s t r u c t u r e s which have been d i v e r s e l y d e p i c t e d as s a t u r a t e d and unsaturated, without e x p e r i mental v e r i f i c a t i o n .


Experimental The r e c r y s t a l l i z e d CPD-MAH D i e l s - A l d e r adduct, endo-cis-norbornene-2,3-dicarboxylic anhydride, mp 165 C, was maintained a t 2 2 0 C f o r 4 h r t o y i e l d a mixture o f endo and exo anhydrides, mp 101 C. The crude product was r e c r y s t a l l i z e d 3 times from benzene t o i s o l a t e the exo isomer, mp 141 C. The endo- and exo-cis-Nphenyl-5-norbornene-2,3-dicarboximides, mp 144 and 197 C, r e s p e c t i v e l y , were prepared by r e a c t i o n o f the endo- and exo-CPD-MAH adducts w i t h a n i l i n e . The p o l y m e r i z a t i o n o f the adducts was c a r r i e d out by adding 0.2ml o f e i t h e r t - b u t y l p e r a c e t a t e (tBPA), t - b u t y l perbenzoate (tBPB) o r t - b u t y l hydroperoxide (tBHP-70 c o n t a i n i n g 70% tBHP and about 30% d i - t - b u t y l peroxide o r tBHP-90 c o n t a i n i n g 90% tBHP and about 10% t - b u t y l a l c o h o l ) , by s y r i n g e i n f o u r equal p o r t i o n s over a 20 min p e r i o d t o 2g o f the adduct i n a rubber-capped tube immersed i n a c o n s t a n t temperature bath. The mixture was then m a i n t a i n ed a t temperature f o r an a d d i t i o n a l 40 min. Reactions a t 120 C were conducted i n 3ml chlorobenzene. The r e a c t i o n product was d i s s o l v e d i n acetone and p r e c i p i t a t e d w i t h methanol t w i c e . IR s p e c t r a were recorded from f i l m s c a s t on NaCl p l a t e s from acetone s o l u t i o n u s i n g a P e r k i n Elmer Model 21 spectrophotometer. NMR s p e c t r a were o b t a i n e d a t 60MHz i n CDCl^ a t 25 C u s i n g t e t r a m e t h y l s i l a n e as i n t e r n a l standard. q

R e s u l t s and D i s c u s s i o n A f t e r 5 h r a t 170°C, endo-N-phenyl-5-norbornene-2,3-dicarboximide f a i l e d t o undergo i s o m e r i z a t i o n and remained unchanged. S i m i l a r l y , no i s o m e r i z a t i o n o f the exo adduct was d e t e c t i b l e by IR a n a l y s i s a f t e r 5 h r a t 170°C. However, a f t e r 30 min a t 260°C, the exo o r endo adduct was converted t o a 40/60 endo/exo e q u i l i b r i u m mixture, which remained unchanged a f t e r 2 h r a t 260 C. The homopolymerization o f the endo and exo adducts was c a r r i e d out i n the melt a t 150° t o 260°C and i n chlorobenzene a t 120 C (Table I ) . Polymer was obtained when the c a t a l y s t was used a t a temperature where the h a l f - l i f e was s h o r t , e.g. l e s s than 2 h r , c o n d i t i o n s shown t o be e f f e c t i v e i n the homopolymerization o f male i c anhydride (16), norbornene (17, 18) and 5-norbornene-2,3-dic a r b o x y l i c anhydride (CPD-MAH adduct) (12-15), as w e l l as the


8.

N-PhenyU5-norbornene-2,3-dicarboximides

GAYLORD AND MARTAN

101

c o p o l y m e r i z a t i o n o f a c y c l i c dienes (19, 20) and c y c l o p e n t a d i e n e (12-15) w i t h maleic anhydride. TABLE I HOMOPOLYMERIZATION OF CYCLOPENTADIENE-N-PHENYLMALEIMIDE DIELS-ALDER ADDUCTS Catalyst

y

^\/2

m

i

n

Solvent

Temp, °C

Yield, %


endo adduct tBPA tBHP-70 tBPB tBHP-70 tBHP-70

66 720 4 0.8 0.01

CB none none none none

120 150 150 210 260

60 0 20 20 50

120 155 260

46 60 30

exo adduct tBPA tBPA tBHP-90

66 2 1

CB CB none

Elemental and NMR a n a l y s e s i n d i c a t e d t h a t the homopolymers c o n t a i n e d equimolar amounts o f c y c l o p e n t a d i e n e and N-phenylmaleimide, i r r e s p e c t i v e o f p o l y m e r i z a t i o n temperature w i t h i n the 120260 C range. The homopolymers from the exo and endo adducts had s o f t e n i n g p o i n t s o f 240 and 265-280°C, r e s p e c t i v e l y . The polymer from the p o l y m e r i z a t i o n o f the endo adduct a t 120 C had a molecul a r weight o f 1645 (vapor pressure osmometry). The NMR s p e c t r a o f the homopolymers o b t a i n e d from the endo and exo adducts a t temperatures below 200 C i n d i c a t e d t h a t the polymers r e t a i n e d the c o n f i g u r a t i o n o f the monomeric adducts. The spectrum o f the endo adduct homopolymer c o n t a i n e d a peak c e n t e r e d at , not present i n the spectrum o f the exo adduct homopolymer. The endo adduct homopolymer spectrum c o n t a i n e d broad peaks a t 7.0-7.7 and 7.8-8.6^, while the exo adduct homopolymer s p e c t rum had a narrow peak a t 7 . 0 - 7 . 4 f , c e n t e r e d a t 7.25^, and a broader peak a t 8 . 3 - 8 . 9 B o t h s p e c t r a had the peaks o f aromatic hydrogens a t 2.4-3.0 N e i t h e r spectrum c o n t a i n e d peaks a t about 4.0^ a t t r i b u t a b l e t o v i n y l i c hydrogens, i n d i c a t i n g the absence of u n s a t u r a t i o n (Figure 1 ) . The NMR s p e c t r a o f the homopolymers o b t a i n e d from the endo and exo adducts a t 260 C were s i m i l a r t o each o t h e r and d i f f e r e n t from those o b t a i n e d from the homopolymers o f e i t h e r adduct polymeri z e d a t lower temperatures. The s p e c t r a c o n t a i n e d peaks a r i s i n g from both endo and exo isomers, i n d i c a t i n g t h a t the adducts had undergone some endo-exo i s o m e r i z a t i o n . No u n s a t u r a t i o n was shown i n the spectrum o f e i t h e r homopolymer o b t a i n e d a t 260 C (Figure 2 ) .



STRUCTURES


102

Figure 2. NMR spectra of homopolymer from peroxide catalyzed polymerization of the exo adduct at 260°C (a), and the endo adduct at 260°C (b).


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N-Phenyl-5-norbomene-2,3-dicarboximides

103


The s a t u r a t e d s t r u c t u r e s o f the homopolymers obtained both a t temperatures below 200°C w i t h r e t e n t i o n o f the endo o r exo conf i g u r a t i o n o f the monomeric adduct, and a t 260 C w i t h both endo and exo c o n f i g u r a t i o n s , suggests a simple double bond a d d i t i o n .

I t has p r e v i o u s l y been proposed t h a t the s a t u r a t e d products from the homopolymerization o f norbornene (3/7) and the CPD-MAH D i e l s - A l d e r adduct (12-15), and probably from the furan-maleic anhydride D i e l s - A l d e r adduct (11), have rearranged s t r u c t u r e s . An analogous s t r u c t u r e would a r i s e from the homopolymerization o f the cyclopentadiene-N-phenylmaleimide CPD-NPMI adduct, as f o l l o w s :

The r e t r o g r a d e d i s s o c i a t i o n o f the D i e l s - A l d e r adduct t o gene r a t e the diene and d i e n o p h i l e , f o l l o w e d by the p o l y m e r i z a t i o n o f the comonomer charge t r a n s f e r complex, has p r e v i o u s l y been p r o posed (12-15) i n the p o l y m e r i z a t i o n o f the CPD-MAH adduct, i n the presence o f peroxides having s h o r t h a l f - l i v e s a t the e l e v a t e d p o l y m e r i z a t i o n temperatures. Under these c o n d i t i o n s , the ground s t a t e complex, presumably i n v o l v e d i n endo-exo i s o m e r i z a t i o n , i s converted t o the e x c i t e d s t a t e complex which undergoes the i n d i cated polymerization. The c r o s s l i n k e d products r e s u l t i n g from the h i g h temperature " p y r o l y t i c p o l y m e r i z a t i o n " (_5) c u r i n g o f the norbornene end-capped


104


STRUCTURES

"addition-type" polyimide prepolymers, such as P13N, P10P, etc., as well as those prepared by means of in situ polymerization of monomeric reactants (PMR), at least those obtained at temperatures up to 260 C, may be presumed to have saturated structures similar to those obtained from the polymerization of the isomeric N-phenyl5-norbornene-2,3-dicarboximides at elevated temperatures. The weight loss or volatilization noted during curing has been attrib uted to the escape of volatile by-products, e.g. cyclopentadiene, which are formed by dissociation of the norbornene end-caps (_3, £3). This is consistent with our proposed polymerization mechanism and polymer structure. Subsequent to the presentation of the results reported here in (21),^C and 270 MHz H-NMR studies of the thermally induced polymerization of the N-phenyl-5-norbornene-2,3-dicarboximides (22) and C-NMR studies of norbornene end-capped polyimide pre polymers (23) were reported. Endo-exo isomerization of the adducts takes place at 200 C and above. Retrograde dissociation of the CPD-NPMI adduct occurs above 275 C and the saturated poly mers obtained at temperatures of 285 C and above contain units derived from the exo and endo CPD-NPMI adducts as well as units derived from N-phenylmaleimide and the Diels-Alder adducts of liberated cyclopentadiene and the CPD-NPMI adducts. The proposed saturated structures suggest simple addition across the norbor nene (CPD-NPMI and CPD-CPD-NPMI) and maleimide (NPMI) double bonds, in the absence of concrete evidence to support the rearranged structures postulated herein and in the products of earlier cat alytic polymerizations. The proposed copolymerization of the norbornene and maleimide double bonds is in agreement with our finding that the peroxyester-catalyzed copolymerization of mono meric cyclopentadiene and N-phenylmaleimide at 85 C and 155 C yields saturated copolymers containing the NPMI and CPD in 2/1 mole ratio (24). o


1

Literature Cited 1. 2. 3. 4. 5. 6. 7. 8. 9. 10.

Donor-Acceptor Complexes in Copolymerization. LXI. Sroog, C. E. Macromol. Revs. 1976, 11, 161. Lubowitz, H. R. (to TRW Inc.) 1970, U. S. Patent 3,528,950. Lubowitz, H. R. Polymer Preprints 1971, 12, 329. Serafini, T. T.; Delvigs, P.; Lightsey, G. R. Applied Polymer Symposium 1973, 22, 89; and other references cited therein. Serafini, T. T.; Delvigs, P.; Lightsey, G. R. J . Appl. Polym. Sci. 1972, 16, 905. Serafini, T. T. in May, C. Α., Ed. "Resins for Aerospace"; ACS Symposium Series 1980, 132, 15. Dynes, P. J.; Panos, R. M.; Hamermesh, C. L. J . Appl. Polym. Sci. 1980, 25, 1059. Dokoshi, N. Kobunshi 1974, 23, 125. Gaylord, N. G.; Maiti, S.; Patnaik, Β. K.; Takahashi, A. J. Macromol. Sci.-Chem. 1972, A6, 1459.



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'S-Pheny U5-norbornene^ ,3-dicarboximides

105

11. Gaylord, N. G.; Martan, M.; Deshpande, A. B. J . Polym. Sci., Polym. Chem. Ed. 1978, 16, 1527. 12. Gaylord, N. G.; Solomon, O.; Stolka, M.; Patnaik, Β. K. J. Polym. Sci., Polym. Lett. Ed. 1974, 12, 261. 13. Gaylord, N. G.; Solomon, O.; Stolka, M.; Patnaik, Β. K. J. Macromol. Sci.-Chem. 1974, A8, 981. 14. Gaylord, N. G. Polymer Preprints 1976, 17, 666. 15. Gaylord, N. G.; Deshpande, A. B.; Martan, M. J . Polym. Sci., Polym. Lett. Ed. 1976, 14, 679. 16. Gaylord, N. G.; Maiti, S. J . Polym. Sci., Polym. Lett. Ed. 1973, 11, 253. 17. Gaylord, N. G.; Mandal, Β. M.; Martan, M. J . Polym. Sci., Polym. Lett. Ed. 1976, 14, 555. 18. Gaylord, N. G.; Deshpande, A. B.; Mandal, Β. M.; Martan, M. J. Macromol. Sci.-Chem. 1977, A l l , 1053. 19. Gaylord, N. G.; Stolka, M.; Takahashi, A.; Maiti, S. J. Macromol. Sci.-Chem. 1971, A5, 867. 20. Gaylord, N. G.; Stolka, M.; Patnaik, B. K. J . Macromol. Sci.Chem. 1972, A6, 1435. 21. Gaylord, N. G.; Martan, M. Polymer Preprints 1981, 22, 11. 22. Wong, A. C.; Ritchey, W. M. Macromolecules 1981, 14, 825. 23. Wong, A. C.; Garroway, A. N.; Ritchey, W. M. Macromolecules 1981, 14, 832. 24. Gaylord, N. G.; Martan, M.; Deshpande, A. B. Polym. Bulletin 1981, 5, 623. RECEIVED

February 25, 1982.


Cyclopolymerization and Polymers with Chain-Ring Structures

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