Indian Journal of Chemistry Vol. 45A, July 2006, pp. 1605-1610

NMR and thermal studies of N-acryloylcarbazole/methacrylonitrile copolymers

A S Brar* & Pravin Kumar Singh Department of Chemistry, Indian Institute of Technology, Hauz Khas, New Delhi 110016. India

Email: asbrar@chemistry.iitd.ernet.in

Received 5 April 2006; revised 22 May 2006

Copolymers with different compositions of N-acryloylcarbazole (A) and methacrylonitrile (M) are reported here. Composition of the copolymer has been determined by IH NMR spectrum. The como no mer reactivity ratios , determined by both Kelen-Tudos (KT) and non-linear error-in-variables (EVM) methods are rA= 1.27 ± 0.13, rM= 0 .69 ± 0.06, and rA=

1.30, rM = 0.69, respectively. Complete spectral assignments of the I Hand DC{ IH } NMR spectra of the copolymers is done by Distortionless Enhancement by Polarization Transfer (DEPT) and Heteronuclear Single Quantum Coherence (HSQC) techniques. The methylene carbon signals of both (A and M) units have been found to be sequence sensitive. Thc signals obtained are broad, pertaining to the restricted rotation of bulky carbazole group and the quadrupo lar e ffect o f nitrogen present in carbazole moiety. The thermal stabil ity and glass transition tcmperatures (Tg) of the copolymers are dependant on polymer composition and characteristic of rotat ional rigidity of the polymer chain . Variation in the values of Tg with the copolymer composition has been found to bc in good agreement with theoretical values obtained from Johnston and l3arton equations.

IPC Code: Int. CI.8 C07C255/08; C07D209/82; G03CI/04; GOIN24/08

Organic photosensitive polymer systems have generated a lot of interest in the recent past due to their potential application in recording media for holographic storage and real time optical information processing l-3. Carbazole containing polymers have shown excellent photoconductive, photorefractive and hole transporting properties4

-7

. Methacrylonitrile copolymers have also been a subject of intensive investigations8 mainly because of their industrial applications, especially as photoresist material and in thermal degradation processesl).

Polymer microstructure is one of the most important factors that governs polymer properties, more so in the case of photosensitive polymers. It has been found that polymers containing same type of constituents behave differently due to difference in microstructure 'o. NMR spectroscopy has been proved to be the most effective lechnique to determine the intramolecular (sequence determination and tacticity) and intermolecular (chemical composition) chain structure of the polymers" ·15. Two-dimensional (20) NMR techniques '6- 's, especially the heteronuclear single quantum coherence (HSQC), greatly help in assigning the compositional and configurational sequences of the copolymers . Comonomer sequence and cotactlclty of N-acryloylcarbazole/Methyl methacrylate copolymer have already been reported II). Brar et aI. 20

-22

, Roman el al. 23 and Hill et al. 24 have

reported comonomer sequence and cotacticity of methacrylonitrile copolymers.

Glass transition temperature (Tg), which represents the molecular mobility of polymer chains, is an Important phenomenon that intluences the material properties and potential application of a given polymer25. The thermal studies of poly(N-acryloyl­carbazole)26 and poly(methacrylonitrile)27.28 have

already been reported. To the best of our knowledge, the microstructure

and thermal studies of these copolymers have not been reported so far. We report here the complete assignments of signals obtained from I H, 13C{ I H) NMR, OEPT and 20 HSQC experiments . We also report the analysis of thermal stability and glass transition temperatures of N-acryloyIcarbazole/ methacrylonitrile copolymers.

Materials and Methods N-acryloylcarbazole was prepared in a two-step

. I' II) 26 syntheSIS as reported in our ear ter paper . . Methacrylonitrile (Merck, Germany, 99%) was distilled under reduced pressure and was then stored below Soc. It was purged with nitrogen gas for 30 min before use. Then, a series of copolymers Elf N­acry loylcarbazole (A) and methacrylonitrile (M), containing different mole fractions , were prepared by bulk polymerization using benzoyl peroxide (BPO) as

1606 INDIAN J CHEM, SEC A, JULY 2006

free radical initiator. The polymeri zation temperature was kept at 70°C. The co nversion was kept below 10% by quenchi ng the reacti on in methanol. The resulting copolymers were puri fied by repeated disso lution in clich loromethane, followed ,by subsequent precipitation in methanol to remove methacrylonitrile. It was further purified by repeated dissolution in dich loromethane, fo llowed by precipitation in ether to remove N-acryloy lcarbazole. The copolymers were dri ed under vacuum at 78°C for 24 h.

The details of recording of NMR spectra and thermal studi es of the copolymer sam ples have been d 'bd' I' bl" 1 !)~6 eSC rI e In our ear ler pu Icatlon '- .

Results and Discussion

IH NMR st udies

The IH NM R spectrum of AIM copolymer (FA= 0.53) in CDCI] is show n in Fig. I. The spectral region around 8 9.0-6.1 ppm is ass igned to aromati c protons of the carbazo le ring. The spectrum region at 84.7-0.5 ppm is found to be complex and overlapping. Nevertheless, the signal s have been resolved with the help of HSQC. The spectra l region around 84.7-3.0 ppm is assigned to methine proton of A unit, the region around 83.0-1.0 ppm is assigned to methylene protO ns of both (M and A) units, and the region around 82.3-0 .5 ppm is assigned to methyl proton of M unit. The compos iti on of the copolymer was calcu lated from the IH NMR spectrum. The relative intensit ies of the aromatic (/1) and aliphatic (/2) proton

eN

I -t- CII - Clt l - C- CIIJ -;-I n

CH, CH,(A) +CII,(M) +CH,(M)

~-

--------I, I ,

q," .... III .. · .... "I'" .... "I' .. "" .. I' " .. ' .. 'I""" .. 'I .. " .... 'I""" .. 'I""" .. 11'''''''''1'' 9.0 8.0 1 D 6.0 5.0 4.0 3.0 2.0 1.0 0.0

ppm

Fig. 1 - IH NMR spectrum of the AIM copolymer (F/\ = 0.53) in CDCI, at 25°C.

reso nances were calculated and then the compositi on of the AIM copo lymer was calculated according to the equation:

F = /I

1/8

1/ 8 + (12 - 3I / 8)/5

where, FA is the mole fracti on of N-acryloy l carbazole (A) mono mer in the copo lymer. The feed mole fraction and copolymer co mposi ti on da ta arc given in Table I .

Determination of reactivity ratios

The initi al es timate of the reactivi ty rati os was done by the Kelen-Tudos2~ method with the help of copo lymer composition data. The va lues of the terminal reac ti vity ratios obtained fro m the plot were: rA= 1.27 ± 0. 13, rM= 0.69 ± 0.06, respectively. These values along with the copolymer com positi on data were used to calculate the reacti vity ratios using the

I· " b I 10 1 1 I d ' I non-mear error-In-varI a es' " metlo uSing tle computer program RR EVM'. The reactivity ratios obtained by thi s method were rA= 1. 30, and rM = 0.69, respectively. The 95 % posterior probability contour for AIM comonomer pa ir is shown in Fi g. 2. The values of reactivity ratios obtained from Kelcn-Tudos and non-l inear error-in-variables melhocls are in good agreef]1ent with each other.

I.Ic {IH} NMR studies

The IJC {I H) NMR spectra of AIM copolymer (FA= 0.61) in CDCl] is shown in Fig. 3a. The carbonyl carbon signals ari sing from A un it resonates around () 176.1-1 72.6 ppm. The aromatic carbons of A unit resonates from 8142- 1 12 ppm . The peaks at 8 117.5, 114.8, 11 9.6, 124.2 and 127.4 ppm are ass igned to C-I ; C-8; CA, 5; C-3, 6 and C-2, 7, respectively. Various assignments of the qu aternary carbons in the DC {IH} NMR spectrurn were done

Table I - Copolymer composition data of the MIA copolymers « I 0% conversion)

Sample No.

2

3

4

5

Mole fraclion in-feed

(lA)

0,05

0.27

0.44

0.55

0 ,85

Molc fracti on in copotymer

(FA)

0.07

0.34

0 .53

0.6 1

0.88

I3RAR & SINGI-I: STUDIES OF N-ACRYlOYlCARI3AZOlE/METI-I ACRYlON ITRllE corOl YMERS 1607

with the help of DEPT-135 NMR spectrum (Fig. 3b). Thus, the peaks at 0140.7-137.4, 137.4-134.4 and 126.3- 124.9 ppm are assigned to C-9; C- 12 and C-l 0, 11 , respectively, of A unit and the peaks at 0122.8 ane! 32.7 ppm are assigned to the nitri le carbon' and the quaternary carbons, respecti vely, of M uni t. The signal s around 027.3-2 1.2 ppm are assigned to u-

1.00

0.95

0.90

0.85

0.80

JO .75

0.65

0.60

0.55

0.50 0.5 01 0 .9 1.1 1.3 1.5 1.7 1.9

RA

Fig. 2 - 95% Posterior probability contour for AIM cOll1onomer pair.

(b)

(a)

175 150 ppm

4 5

ct010 11 ",,: 6

3 I I 2 .&9 12 '& 7

1 N 8 I co CN

I I -t-Cfl- CIl ,-C-CH,-t-I n

3,6 ,)4,5

125 100 75

ell, CH(Al ~

~ CH,(A)+CIl,(M)

>C<

50 25

Fig. 3 - (a) IJC (II-I) NMR spec trum (FA = 0.61); (b) DEPT- 135 NMR spectrum of the AIM copolymcr (FA = 0.61) in CDCI) at 25°C.

methylca'rbon of M unit. The spectra l region around 0 33.5-55 .5 ppm is complex and overlappin g, and thus cou ld not be assigned further with the ' :lC {'H} NMR spectrum. Methine carbon signals of A unit have been di stingui shed from this region with the help of DEPT-90 NMR spectrum and they resonate around 8 42 .1 ~ 37.6 ppm.

The methylene carbon signal s of both, A as well as M, units resonate around 850.2-33.0 ppm and are sensiti ve to compositional sequences. The expanded region of meth ylene carbon resonance signals in the DC . NMR sub-spectra of AIM copo lymers with different mole fractions of A and the corresponding homopolymers is shown in Fig . 4. Due to the bulky pendant group, the spectrum of copolymer is very broad. But assignments can be made up to dyad level on the basis of variation in the :composition of the copolymers, and on comparison with the spectra of corresponding homopolymer. The

AA

9

e

d

e

-------~--- b

A -----_ a

~p~ 50.0 ' I

45.0 I

40.0 I

35.0

Fig. 4 - Expanded methy lene ca rbon signals of both (A and M) units in the I.1C ( II-I) NMR sub-spectra of tile AIM copolymer in CDCI) at 25°C: (a) poly(methaery lon itrile), (b) FM = 0.93, (e) F~ I

= 0.66, (d) FM = 0.47, (e) F,\1 = 0.39, (I) FM = D.12. and (g) poly(N-acryloylcarbazo le),

1608 INDIAN J CHEM, SEC A, J ULY 2006

resonance signals around 850.2-45.4 ppm are assigned to MM dyad, 045.4-40.5 ppm are assigned to MA dyad, and around 040.5-33 .0 ppm are assigned to AA dyad.

Two-dimensional HSQC studies

20 HSQC spectrum further confirms the assignments of the various resonance signals in l3C{lH } and lH NMR spectra. The 20 HSQC NMR spectrum of NM copolymer (FA= 0.61) recorded in COCl) is shown in Fig. 5 along with the complete signal assignments . Various ass ignments of the aromatic region of the lH NMR spectrum were done with the help of HSQC spectrum. The cross-peaks 1, 2, 3, 4 and 5 centered at 8117.5/8.46, 114.817.76, 119.617.9, 124.217.30 and 127.417.34 ppm are assigned to C-1; C-8; C-4, 5; C-3 , 6 and C-2, 7 respecti vel y.

The a -methyl region of the M unit shows compositional sensitivity along proton ax is and conformational sensitivity towards carbon axis . The cross-peaks 6, 7 and 8 centered at 826.3/\.77, 24.711 .32 and 23.5/ \.07 are assigned to triad compositional sequences MMM, MMA and AMA, respectively on the basis of change in intensity with the change in copolymer composition. The cross­peaks 9 centered at 839.9/4.06 ppm is assigned to the methine carbon of the A unit.

The methylene groups of both (M and A) units show dyad compositional sensitivity along carbon

6~ 25

jr ' 8 .,... ,

9 10 'r' 50

11 t2

4 5 75 3QJ)6

2 • 7

2 1 1 8 CO CN

11;" -.JH-CHr .t-CH2 .... 100

I 3

CH3 .. , 4 125 . 5 pm

r-T"'T"1 ..... iil i ii •• iii. j . " i l' i i. j ji •• j •• i.jii i.

>' . 0.0 7.0 B.O 5.0 4.0 3.0 2.0 1.0 ,! .!', . ppm

.fj'g: . 5 2b, I-isQc NMR spectrulJl of AIM copolymer (FA == 0.53) in CDCI3 at 25°C.

axis. The region is quite complex and overlapped and can only be assigned with the help of 2D HSQC spectra. On the basis of variation in intensity of signals with the change in copolymer composition, various dyad compositional sequences in the methylene region are ass igned to AA, AM and MM. The cross-peaks 10, 11 and 12 centered at 836.7/2.45, 43.4/2.02 and 48.3/ 1.71 ppm are assigned to AA, AM and MM, respectively. These dyads could not be assigned further due to the restricted rotation of bulky carbazole group and the quaternary effect of nitrogen present in carbazole moiety, which make the signals broad.

DSC studies

Physical properties of a copolymer are determined by its glass trans ition temperature (Tg). Out of various theoretical model s32

-36 to obtain Tg, the one derived by

Johnston35 and Barton36, which correlate Tg to the

dyad distribution in the copolymers, exhi bit better agreement with experimental T/ 7

. The dependence of the Tg on composition in these copolymers has been analyzed by us ing Johnston and Barton equations as reported in our earlier publication l

'). The value of TgAM of the copolymer system was determined by computerized multiple regress ion analysis usi ng Tg of the homopolymers and the series of copolymers.

The Tg of the M/ A copolymers and the homopolymers are shown 111 Table 2. The copolymerization of N-acryloylcarbazole with methacrylonitri le leads to the lowering of Tg• Figure 6 shows the comparison of the experimental and theoretical Tg values calcul ated using Johnston equation with the weight fraction of monomer A

Table 2 - Glass transi tion and thermal degradation temperatures of MIA copolymers

Sample N-acryloyl- N-acryloyl- Decompo- Glass No. carbazole carbazole mole siticon transition

mole fract ion fraction in temperature temperature in-feed (fA) copolymer (Ttl) (K)

(FA) (KJ

I I(A) 1.00 639 430.4

2 ' 0.85(A I) 0.88 637 426.1

3' 6.5?(A2) 0.6 1 617 416.7 ,

4 ' 0.44(A3) 0.53 603 406.7 "

5 0.27(A4) 0.34 599 372.8

6 0.05(A5) 0.07 347.5

7 O.OO(M) 0.00 58X 341.5

BRAR & SINGH: STUDIES OF N-ACRYLOYLCARBAZOLE/METHACRYLONITRILE COPOLYMERS 1609

"0.---------------------,

~o

~ .ao

I-

300

2'0 +--~~~-~-__r_-~-..,__-~-~~--l

o 0.1 0.2 03 0.4 0.' O~ 0.7 OJ 09

WA

Fig. 6 - Variation of T~ (experimental and theoretical values calculated from Johnston equation for AIM copolymers) with weight fraction (WA ) of monomer A.

(WA ). Figure 7 shows the comparison of the experimental and theoretical Tg values calculated using Barton equation with the mole fraction of monomer A (FA). These models show good agreement with the experimental data.

TGA studies

The decomposition temperatures of (Td) of copolymers are shown in Table 2. The decomposition of poly (N-acryloylcarbazole) takes place in a single step. It shows that the thermal decomposition temperature is principally produced by random scission of the chain. It can also be concluded that the termination by disproportionation is negligible and the termination by combination does not produce higher steric effect that could induce instability at lower temperatures. The second analogy is somewhat expected in the way that the species produced by the termination by recombination has bulky carbazole moieties farther apart and hence will have lesser strain. Moreover, the thermal decomposition temperature (Td) is high even for copolymers having low content of N-acryloylcarbazole. Moreover, as the FA increases the decomposition of copolymer is produced in a single step akin to that produced in poly (N-acryloylcarbazole). This shows that an increase of A content decreases the amount of growing radicals ending in M unit and the termination step is mainly produced by combination. In other words, termination by disproportionation, as in case of polymethacrylo­nitrile28

, is absent.

Conclusions

The reactivity ratios of monomers are rA= 1.27 ± 0.13, rM = 0.69 ± 0.06 and rA= 1.30, rM = 0.69, respectively, by KT and EVM methods respectively

550.-------------------,

500

450

300

250~-.__,-~-__r_-._-._-.__.-~-~

o 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9

WA

Fig. 7 - Variation of Tg (experimental and theoretical values calculated from Barton equation for AIM copolymers) with mole fraction (FA) of monomer A.

The a-methyl carbon resonances of M unit are assigned to triad compositional sequences. The complex 'H NMR spectrum of copolymer is assigned with the help of HSQC. The complex DC NMR spectrum is resolved with the help of DEPT and HSQC. The DSC studies are used to study the rigidity of the chain. The value of Tg varies with the variation in copolymer composition. As the amount of N­acryloylcarbazole increases, the Tg increases from 341 K for poly(methacrylonitrile) to 430 K for poly(N­acryloylcarbazole). The dependence of the Tg on the composition of the copolymers is analyzed by using different theories that take into account the sequence distribution in the copolymer. The copolymers were found to be thermally stable. The termination by disproportionation is absent in the copolymers.

Acknowledgement The authors wish to thank the University Grants

Commission (UGC), India for providing the financial support to carry out this work.

References 1 Patrikios S C & Krasia T, Polymer, 43 (2002) 2917. 2 Hwang J, Moon H, Seo J, Park S Y, Aoyama T & Sabase H,

Polymer. 42 (2001) 3023. 3 Yu L, J PolYIll Sci Part A: Polym Chem, 39 (2001) 2557. 4 Sanetra J, Bogdal 0 , Warzala M & Boron A, Chem Mater,

14 (2002) 89. 5 Turner S R & Pai 0 M, Macromolecules , 12 (1979) I. 6 Lee J H, Park J W & Choi S K, Synthetic Met, 88 (1997) 31. 7 Zhang Q, Hu Y, F, Cheng Y X, Su G P, Ma 0 G, Wang L X,

Jing X B & Wang F S, Synthetic Met, 137 (2003) 1111. 8 Mark H F, Bikales N M & Overger C G, Encyclopedia of

Polymer Science and Engineering (Wiley Interscience, New York), Vol. 1,1985, pp. 461.

16 10 , l . I i T . . ,INDIAN J CI-IEM, SEC A, JULY 2006

9 110 13 C Chin W K & LeL: Y D, J ApI'/ PO/YIII Sci , 42 ( 199 1) 99, .

10 Misurkinl A, Clielll PIi),s RepoJ'/s, 15 ( 1996) 12 1.

II Bovey F A & Mi rau I' A, NMR of Po/mleJ".I' (Academ ic Prt~Ss, New York), 1996.

12 M atsuzaki K, Uryu T & A sakura T . NMR Speclroscopy alld Sll'I"eoreg ll /arily of Po/mlers (Japan Sci Soc Press, Tokyo), 1996, .

13 I-Iatada K & Kitaya ll1<1 T. NMR Spectroscopy. of PO/YllleJ',I' (Springer-Verl ag, Berlin/Heidelbcrg. GermHIJY). 2004.

14 Ibbell R N. NMR SpeClI'IJ,ICOpV of J'O/YlIIl'I"S (Chapman tf;.. lIill , Glasgow). 1993. . '

15 Chcng H N & Engli sh A D. NMN SfI('cll'IJscojJv ofPo/Ylliers ill SII/lIlioll {/lId Solid Slm!.! ACS Snll.posi/JIII Ser ies 834 (A meri can Chem ica l Socicty. Washington. DC). 2003.

16 Kotyk J J, l3erger P A & Remson E E. Macrollio /ecIIJes. 23 ' ( 1990) 5 107.

17 Asakura T, ' Nakayailla 'N. DCJ1lura M & ' Asano A, Macrollio/eclI/es. 25 ( 1992) 4X76.

I X DUlla K, Mukheljee M & Brar A S. J Po/nil Sci 1"111'1 Il: ' Po/vlIIC/lelll , 15{ 1999)5S I , ' 1

19 Singh r K & I3rar AS. J Allpll'o/YIII Sci. 100 (200G) 2667,

20 Brar A S, Pradhan D ,R & Hooda S. J ApI'/ 1"0/)'111 Sci, 96 (20()5) 1865: . i , "

2 1 Ilooda S & I3rar A S.) API" Po/nil Sci. 8X (2003) 3232.

I ' ,

. . ,'!

" ,-;

/ ,1!. I .'. , I i

. ; ! I

, ! . ,

) J ,

I !

22 I3rar A S, KUJ1lar R & Kaur M, J Mo/ I/mclllre. 650 (2003) 85.

23 Roman J S, Vanqucz B, Valero M & Guzman G M. MaCl'IJlllo/eclI /es, 24 ( 199 1) 6089.

24 Hi ll D J T , Dong L & O'Donnell J H. J PO/VIII Sci. ParI A: PO/VlII l'I" Clielllislr\" 3 1 ( 1993) 2951 .

25 Garcia M F, Fuen te J L & Madruga E L. PO/WII fllIlI . 45 (2000) 397.

26 I3rar A S & Singh r K, Illdiall J Gelli . 4S/\ (2000).58 1. 27 Katirciog lu T Y & Guven O. J App/ PO/VIII Sci. X2 (200 I )

1936. 28 Nakamur;l S, Otake T & Matsuzaki K, J App/ Po/nil Sci . 16

( 1972) 18 17. 29 Kelen T & T udos F J, Macrolli o/ Sci Clieil i. A9 ( 1975) I , 30 Harris S H & Gil bert R D, J PO/VIII Sci PO/ylll Clielll Ed. 20

( 1982) 1653. 31 Schneider H A & Neto H N. PO/V/II 8ull . I} ( 1983) 457. 32 DiMarzio E A & Gibbs J H, J PO/VIII Sci. 40 ( 1959) 121. 33 Fox T G, 81111 A/II PIi."s Soc, I ( 1956) , 23 34 Couchman P R & Karas7. F R. Macrolliolecllies. II ( 1971:\)

117, ' 35 Johnston N W, J M({c/"{)lIIo/ Sci ReI' Mac/"IJlllo/ Clielli . C I4

( 1976) 2 15. 36 Barton J M , J 1'0 /.1'/11 Sci PaJ'/ C: PO/YIII Lel/ . 30 ( 1970) 537, 37 MacEwen I J & Johnson A J, ill Allenlll l illg Copolrllll'I"S,

ed ited by J M G Cowie. (P len um Press. :"Jew York ). I <)X5,

':i

I,

' , j