Indian Journal of Chemistry Vol. 45A, March 2006, pp. 581-586

Synthesis and characterization of poly(N-acryloylcarbazole)

A S Brar* & Pravin Kumar Singh

Department of Chemistry, Indian Insti tute of Technology, Delhi. Hauz K as, New Delhi 1IC 16. India - Email: ashrar@chemistry.ii td.ern t.in

Received 8 Februurl' 2005; rel'ised 27 J OIIU{[/)' 2006

N-acryloylcarbazole was prepared in a two-step syn he. is starling from carbazole, Poly(N-acryioylcarbazolc) was prcpJred by bulk polymerization using benzoy peroxide ( .. PO) as free-radicJI initiator at 100°C. N-acry oylcarbazole was characteri zed by One-dimensional NMR (IH, 13C {'H J and D'stonionless Enhancement by Po\~ iZ:l! iol1 Tran fer (DEPT» experimcnts. Assignments of One-dimcnsional NMR spectrJ were further confirmed by Two-dimensional Heteronuc1car Single QUJntum Coherence (HSQC) experiment and Total Corr lation Spectrusco y (TOCSY). CharacterizJtion of poly( -acryloylcarbazole) was done by I3C {' } and DEPT NMR experimellts. The signals obtained for poly(N-acryloyJcJrbazole) were broad due to the restricted rotat ion of bulky carbazole group and the quadrupolar effect of nitrogen present in carbazole moiety. Assig .ments of One-dimensional NMR spectra were further contlrm~d by HSQC experi ments. The moleculJr weight of poly(N­acryloylcarbazoie) was determined by Gel Permeation Chromatography (GPC). Its thermal st· bility was determined by thermogravimetric Jnalysis (TG/DTA) and Glass tmnsi tion temperature (Tg) \\ as de termined by Di fferenti al Scanning Calorimetry (DSC).

IPC Code: C07D209/82; C08F !26/06

Synthesis of N-acryloylcarbazole has atready been reported 1 having poor yields. Moreover, the direct reaction of carbazole with acryloyl chloride in presence of any base fails mjserably giving back the carbazole. N-acryloy\carbazole contains carbazole moiety. Carbazole is a well known chromophore which has been used in constructi ng polymers, such as, poly(N­vinylcarbazole), poly(N-acroloyl-carbazole). etc. These polymers show photoconductivi ty, photorefractivi ty and hole transporting properties2

-5

. Thus, the synthesis of N-acryloylcarbazoie was undertaken. This alternative route involves condensation of carbazole with 3-chloropropionyl chloride in tolueneD to form N­(3-chloropropionyl)carbazole which was then dehydrohalogenated in the presence of sodium acetate? to give N-acryloylcarbazole.

High resolution NMR spectroscopy is the most powerful technique to determine the intramolecular (sequence determination and tacticity)8-l l and intermolecular (chemical composition) chain structure of the polymer. Two dimensional NMR techniques especially heteronuclear single quantum coherence (HSQC) and total correlation spectrosc py (TOCSY) techniques have the potency to study absolute configuration of polymers 12 and its contribution to the study of homopolymers have already been recognized universa lly 1)-17.

Thermal stabil ity f polymers is an important physical property that conditio! s many applications. 't is important to know the thermal degraciat ion temperature to ensure a safety service temperature which . s possible to maintain their properties. Likewise, polym r glass transltlCI temper~ ture­

representi g the molecular mobiii ty of polymer ch'lins is an important phenomenon that influences the material properties and potentia! application of a given pOlymerl8.

To the be t f our knowledge, the characterization of N-(3-chloropropi nyl)carbazole, N-acryloylcar-bazole and poly(N-acryloylcarbazole) using MR spectroscopy has not been reported so far. We report here the synthesis and characterization of poly(N­acryloylcarbazole) using one- and two-dimensional NMR spectroscopy techniques . Materials and Methods

Toluene was distilled over sodiumlbenzophenone. Carbazole (Aldrich, 96%) was recrystallized from dichloromethane. 3-chloropropi0nyJ chloride (Aldrich, 95%) and sodium acetate (CDH) were used as such. Ethanol was dried over sodium and distilled. Benzoyl peroxide (BPO) was recrystallized from methanol.

NMR measurements All the NMR spectra were recorded in CDCI) at

25°C on a Bruker DPX-300 NMR spectrometer

582 INDIAN J r.HEM, SEC A. MARCH 2006

CICH2CH2COCII Toluene

10()<>C, 22 hrs

CARBAZOLE N-(3-CHLOROPROPIONYL)CARBAZOLE

Scheme 1

1. ~

..I j. , '

1. -

I : I , I 1 le __ .. .' \'--~ _________ -"

, 8 0

oom

i 70

i

60 i

50 i

4 0

Fig. 1-300 MHz 'H NMR spectrum of 9-(3-chloropropionyl)carbazole in CDCI] at 25°C.

operating at 300.13 and 75.48 MHz for IH and DC nuclei, respectively using the standard pulse sequences. Gradient Heteronuclear Single Quantum Coherence (HSQC) experiment was performed b .. · using the standard Bruker lnvigptp Pulse sequence. The spectrum was obtained with 512 increments in the FI dimens ion and 2048 data points in the F2 dimension . Total COITelalion Spectroscopy (TOCSY) was carried out using standard pul se sequence. A total 0; 32 scans were accumu lated with a relaxation delay of 2 s for each of the 51 2 11 experiments (where II IS

the increment in evolution time between pulses).

Molecular weight determination The molecular weigh t of the homopolymer was

determined fro m Ge Permeation Chromatography (GPC) using polystyrene as narrow standard. The molecuiar weight was determined on a waters HPLC system equipped with 515 pump, rheodyne injector with 10 J..l1 ioop and Differential Index Detector using a PLgel column. Tetrahydrofuran (THF) was used as mobile phase with flow rate of I mLimin .

Thermal analysis The thermal stability of the po!y(N-

acryioylcarbazole) was determined by recording the TG/DTG on Pyris Diamond (Perki n-Elmer)

TGAIDTA thermogravimetric analyzer on well ground samples in flowing nitrogen (flaw rate 20 cm3/min) atmosphere with a heating rate of 10°C/min. The glass transition temperature (Tg) of the poly(N­acryloylcarbazole) was recorded on di ffe rent ial scanning calorimeter, Pyris Diamond (Perkin-Elmer) DSC, with a water circulating system. The temperature scale was calibrated from the melting point of standard samples (indium and zinc) . DSC scans were recorded in N2 atmosphere at a heating rate of 10°C/min.

Results and Discussion N-(3-chloropropionyl)carbazole

For synthesizing the compound, Carbazole (15 g) was stirred in dry toluene (250 mL) in inert atmosphere of nitrogen for 5 min and heated [ 0

100°e. Then, a solution of 3-chl:oropropionylchloride (17.3 mL) was added via syringe through septum. After 22 h, the reaction mixture was cooled. The solvents were removed under reduced pressure and the slurry obtained was triturated and recrystallized from methanol to obtain N-(3 -chloropropionyl)carbazole (Scheme I). Figure I shows IH NMR spectrum of 9-(3-chloropropionyl) carbazole in CDCI 3 at 25°C at 300 MHz. 83.66 (t, 2H. CH 2), 4 .08 (t, 2H, CH2CI), 7.41 (t, 2H, aromatic {3 ,6)), 7.50 (t, 21-1 , aromatic {2,7) , 8.01 (d, 2H. aromatic {4,5)), 8 .21 (d, 2H, aromatic {I ,8 D. Yield 20.17g (87.23%) m. pt. 124°C.

N-acryloylcarbazole For synthesizing the compound, N-(3-

chloropropionyl)carbazole (14.8 g) and sodium acetate (9.84 g) were taken in absolute ethanol (500 mL) and refluxed for 4 h. Thel!1, the solvents were removed under reduced pressure. The resulting viscous liquid was poured in distilled water (200 mL). which was then extracted with ether (3x I 00 mL) and dried over anhydrous sodium sulfate . Ether was then removed under reduced pressure and resulting product was purified by repeated recrystallization by dissolving in boiling hexane and cooling in liquid nitrogen to obtain N-acryloylcarbazole (Scheme 2) Yield: 9.16 g (71.71 %), m. pt. 52°e.

I H NMR studies

The complete assignment of the resonance signals in IH NMR spectrum of N-acryloyl arbazole in CDCl3 is shown in Fig. 2. The doublet of a doublet at 07.07, doublet at 06.65 and doublet at 86.03 ppm are

BRAR & SINGH: SYNTHESIS AND CHARACTERIZATION OF POLY(N-ACRYLOYLCARBAZOLE) 583

NaOAc/EIOH

Reflux, 4 hrs

N-(3-CHLOROPROPIONYL)CARBAZOLE N-ACRYLOYLCARBAZOLE

1 " .v

J F •• I

~ 'iO 800 OOfn

I -1, 5 I

. - .

, , I

750

Scheme 2

a c H........ _H

.......... C= C ........ b O= c H

1 I 8 N

20·~7 3V--V6

J .o

4 5 b

, I , , • , , • I • • • I Ii' I 700 6 50 6 00

Fig. 2-300 MHz IH NMR spectrum of N-acryloylcarbazole in CDCI) at 25°C.

assigned to vinyl protons P-a, P-b, and P-c, respectively. The aromatic protons resonate from 88.16-7 .30 ppm. The doublet at 88.08, doublet at 87.94, triplet at 7.43 and triplet at 7.34 ppm are assigned to aromatic protons P-l, 8; P-4, 5; P-2, 7 and P-3, 6 respectively . These assignments have been further confirmed with two-dimensional NMR techniques.

/Jc t H} NMR studies

The complete assignment of the resonance signals in the 13C{ IH} NMR spectrum of N-acryloyJcarbazole in CDCl3 is s;1Own in Fig. 3a. The signal at 8165.38 ppm is assigned to carbonyl carbon in the N­acry loyJcarbazole. Despite the fact that the carbazole moiety belongs to C2V symmetry group yet the two benzene rings are magnetically non-equivalent resulting in an asymmetric spectrum. This observation has been attributed to restricted rotation of the bulky carbazole combined with ' the ring current effects of the neighbouring rings l9

. The aromatic carbons resonate from 8127 to 115 ppm. The peaks at

115 .4 1, 119.58,123.25 and 126.70 ppm are assigned to C- l , 8: C-4 . 5: C-3, 6 and C-2, 7, respectively. Various ass ignments of the quaternary carbons of the . ron atic regiQI1 . n the IJC {I H} NMR spectrum were

I i )

I ! i I

"

: I I ! , ,I I~"

I.. ,\ .i to ) ________________________ ~~~ I~

.......... CH =01,

o= c 1 I 8 2Chb9N

"":;7 I . I 3 .610 11 .6 6

.4 5

('=0

I I

I I

:.~ ". , ~ L · 1. '- I ...-:--

T O f, 'I .+ -

(l!~ 1 I ~ i , I' !

. ILl.') ___ ~LI _______________ .~ ____ ~L~~~~ ~

ppm

I ' 160

I 150

! •

140

, I

130 I '

: 20

Fig. 3-75 MHz (a) IJC{IHJ NMR spectrum. (b) DEPT-135 spectrum of N-acryloylcarbazole in CDCI) at 25°C.

done with the help of DEPT-135 NMR spectrum. Figure 3b shows the DEPT-135 NMR spectrum of N­acryloylcarbazole in CDCl3. The peaks at 8138.02 and 125.80 ppm are assigned to quaternary carbons C-9, 12 and C-IO, II, respectively . Methylene and methine carbon signals are also distinguished wi th the help of DEPT-l35 as methylene gives negative signal and methine gives positive signal. Thus, peak at 8130.23 ppm is assigned to the methylene carbon and peak at 8131.38 ppm is assigned to the methine carbon.

2D HSQC studies

2D HSQC NMR spectrum further confirms the assignments of the various resonance signals in I,C{ 'H} and 1H NMR spectra. Figure 4 shows the HSQC spectrum of N-acryloylcarbazole in CDClJ. The methylene carbon should give two resonance signals due to the two non-equivalent protons attached, and the methine carbon should give one resonance. signal. Thus, the crosspeak at 8131.3817.07 ppm is assigned to methi ne carbon and the crosspeaks 2 and 3 at 5130.23/6.65 and 130.23/6.03 ppm are ass igned to methylene carbon resonating with the t ),Io-methylene protons In

584 INDIAN J CHEM, SEC A, MARCH 2006

:1 ' ! _ JJ. JL( J . . _J~ Gi = CH, Ir /' ' Ir

G- ~ ~=1 8 1~ 1 1 5 .0

J G- ' :909: !~[. 1:0.0

ti ---f] J .. 1 125.0

'-=l\ I . -G ,k 8~ ~ ~"o o '====:;=;=:;=;=:;=;=:;=;=:::;::::;::::;::::;:===;'=;'=;'=;r=;'-;=:;:=;' ,l ppm , I I I ' j j I I r

ppm 8 .00 7.50 7.00 6.50 6.00

Fig. 4-20 HSQC NMR spectrum of poly N-acryloylcarbazole in COCl, at 25°C.

l 6.00

6.50

7.00

7.50

8.00

ppm

Fig. 5- 20 TOCSY NMR spectrum of N-acryloy lcarbazole in COCl, wi th low mixing lime at 25°C.

different environments. Various assign ments of the carbons of aromatic regia: in Ihe 13C (I H ) NMR spectrum <:u'e con firmed with the help of HSQC '- pec rum. The crosspeaks 4, 5, 6 and 7 centered at b i 15.4 1/8 .08, 119.58/7.94, 123.2517.34 and ! 26.70/7 .43 ppm are assigned to C-J, 8; C-4, 5; C-3, 6 anci C-2, 7, rcspectiVf'ly.

2D TOeSY studies

The 20 TOCSY NMR experiment reaffirms tbe assignments made in the proton spectum. The crosspeaks arising in TOCSY spectrum are due to relayed coherence transfer and hence shows correlation among nuclei that are in the same spin system, At a low mixing time, one gets the direct coupling (AM spin type) between the bonded protons. Figure 5 shows the TOCSY spectrum of N­acryloylcarbazoJe in CDCI3 with low mixing time. In this TOCSY spectrum, we can clearly see the three bond correlations between the methylene and methine protons. The cross peaks 8, 9 and J 0 centered at 86.65/6.03, 7.07/6.03 and 7.07/6.65 ppm are assigned to correlation of methylene proton ' b' with methylene proton 'c', methine proton 'a' with methylene proton 'c ' and methine proton 'a' with methylene proton 'b', respectively. The aromatic protons also show three bond correlations. Thus, the cross peaks 11 , 12 and i 3 centered at 88.0817 .43, 7.94/7.34 and '7.43/7 .34 ppm are assigned to correlation of aromatic protons ' I , 8' with aromatic protons '2, 7', aromatic protons '4, 5 ' with aromatic protons '3,6' and aromatic protons '2,7' with aromatic protons '3, 6 ', respectively.

Poly(N-acryloylcarbazole)

Poly(N-acryloylcarbazole) was prepared by bulk polymerization using BPO as initi ator at lOO°e. The monomer (4 g, solid) and BPO (0,9 mg, 0.02 mol % of monomer) were taken in a tube, which was then subjected to three freeze-thaw cycles to remove moi sture and oxygen. Then, the tube was placed in oii bath maintained at lOO°C for 4 h. The resulting polymer was dissolved in dtchloromethane. The dissolved polymer was recovered by precipitation in methanol. The polymer was further purified by repeatedly dissolving it in dichloromethane and preci pitating in ether. The polymer was dried under vacuum at llOoC for 24 h.

He t H} NMR studies

The complete assignment of the resonance signals in the DC{ IH} NMR spectrum of poly(N­acryloyIcarbazole) in CDCb is shown in Fig. 6a. The carbonyl carbon in the poly(N-acryloyIcarbazole) resonates from 8173 ,64 to 175.66 ppm. Despite the fact that the carbazole moiety belongs to C2V symmetry group, the two benzene rings are magnetically non­equivalent resulting in an asymmetric spectrum. This observation has been attributed to restricted rotation of the bulky 'arbazole combined with the ring current effects of the neighboring ri ngs l9

. The aromatic

. ....

BRAR & SINGH : SYNT HES IS AND CHARACTERIZATION OF POL Y(N-ACRYLOYLCARBAZOLE} 585

CO

I 175 ppm

2. -+ CH- CH,+­/" n

o= C I

1 9 N 12 8 2 ~ ",-7

IL 2. - . 10.11

3. 6

1 '\

(TICI) S

(H 9 ~

ft \. J

I , I , I , , I

, I

150 125 100 75 50

r (Hz

V

Fig. 6-75 MHz (a) DC{'H} NMR spectrum. (b) DEPT- 135 spectrum of poly(N-acryloylcarbazole) in CDCl3 at 25°C.

j::CH - CH,-t;; o= C 1 h 8

2(Y~7 3~6

5

50

75

100

~I~ ~ Y .. L :, . ~"-',~: - 21-' - - 19 125

~~=;=;::;, 1=;=' ;=;. ,=;=, ;=;1 ,=;=, ;=;, IT, ;=;, ,=;=, ;=;. 1=;=' ;=;, ,=;=, ;=;1 ,=;=, ;=;, ,T, ;=;, ,T' ;=;, IT' ;=;, ,=;=, ;=;1 ,~, i ppm

aD 7D 6D 5D 4D 3D 2D l D ppm

Fig. 7- 2D HSQC NMR spectrum of poly(N-acry loylcarbazole ) in CDCl) at 25°C.

carbons resonate from 8142.63 to 109.87 ppm. The peaks at 8117.25, 114.12, 118.92, 123.27 and 126.79 ppm are assigned to C-I : C-8; C-4, 5; C-3, 6 and C-2, 7. respe::- tively . Various assignments of the quaternary carbons of the aromatic region in the 13C { I H} NMR spectrum were done with the help of DEPT-135 NMR spectrum. Figure 6b shows the DEPT-135 NMR spectrum of the homopolymer. The peaks at 8138.87, 136.37 and 126.18 ppm are assigned to C-9, C-1 2 and C-IO, 11 , respectively . Methylene and methine carbon signals are also distinguished with the help of DEPT-135. The methylene carbon resonates from 834.2 to 37 .0 ppm and methine carbon resonates from 838.9 to 41 .8 ppm.

2D HSQC studies 2D HSQC NMR spectrum further confirms the

assignments of the various resonance signals in 13C{ I H} and I H NMR spectra. Figure 7 shows the HSQC spectrum of poly(N-acryloylcarbazole) in CDCI3. Due to the bulky pendant group and quadrupolar effect of nitrogen in carbazole moiety, the signals are very broad. The crosspeaks 14 and 15 centered at 835.8/1 .78 and 39.9/3.29 ppm are assigned to the methylene carbon and the methine carbon , respectively. Various assignments of the carbons of aromatic region in the I3C {'H} NMR 'spectrum are confirmed with the help of HSQC spectrum. The crosspeaks 16,0 17, 18, 19 and 20 centered at 8117 .25/8.34, 114.1217.14, 118.9217.29, 123.2717.0 and 126.7917.03 ppm are assigned to C-l ; C-8 ; C-4, 5; C-3, 6 and C-2, 7, respectively.

Molecular weight studies

The number average molecular weight ( M n) of

poly(N-acryloylcarbazole) was found out to be 69,000

and weigh t average molecular weight ( M w) of

poly(N-acryloylcarbazole) was found out to be

13 1,000 with polydi spersity ( ( M w ) / ( M n ) to

be 1.90.

TGA studies The knowledge of mechani sm of termination and

propagation is indispensable to the understandi ng of thermal stability of polymers obtained by free rad ical polymerization . The decomposition of po!y(N­acry loylcarbazole) is produced in a single step (Td= 638.5 K). It shows that the thermal decomposition

586 INDIAN J CHEM. SEC A. MARC H 2006

temperature is principally produced by random sciss ion of the chain. It can be concl uded thal the termination by disproportionation is neglig ible and the termination by combin ati on does not produce higher steric effect which could . nduce instability at :ower tempera ures. T he second analogy is somewhat .:X· ected in the way that the species produced by the . ~nnination by recombination has bulky carbazoie :noieties farther apart and hence will have lesser .~tra in .

DS C .I'll/dies

Physical properties of a po lymer are determined by its glass transition temperature (T,J . It represents the molecu lar mobility of polymer chains. Hence, its ~: nc\viedge is indls iensable in polymer app icat ion . 'l'he glass t ran~lllon temperature of poly(N­acryloylcarbazoie) was obtained from d ifferenti al .'canning calorimetry (DSC). Tg of the poly(N­acry!oylcarbazoJe) was fo und to be 430.4 K which is almost ; 55 K higher than its alkyl homologue (pol) vinylketone)2l! . it indicates that the rigid c .l rbazo le ring hi nders the rotation around the bond in the chain. ~v!oreover. th is val ue is about 70 K lower than POIY (1 ' -vi 1 lcarbazoie), wn ich makes it easier to process.

Conclusi ns , -acry!oy;carbazoie w~s syn thesized a .d

c 1::r2c te~'i zed with t:le he l of One-dimensional NM R ( IH, I.'C {IHI and DEPT-i35 ) experiments. Ac;sigl ments or O ne-oi mensionai NM R spectra were ~'::rther confi '1 1ed by Two-dimensional HSQC and TOCS Y ex,.,erimenrs. Poly(N-acry loylcarbazole) was at. 0 ~ynti1esized and characterized with the help of NM R '':'.cbniques. Assi gnments f IJC{ IH } and DEPT- i ~5 1 M spectrum were further confi rmed by HSQC experi ment. Poly(N-acry!oylcarbazole) was

also found to be thermal ly stable and casi iy processable.

Acknowledgements The authors wi sh to thank the University Grants

Commi ssion (UGC), India and the Department of Science and Technology, India fo r prov iding the inancial support to carry out thi s work .

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