Indian Journal of Chemical Technology Vol. 1 0. March 2003, pp. 1 92- 1 96

Articles

Photoinitiated copolymerization of c i tronellol and methyl methacrylate Prach i Pandey & A K Srivastava*

Department of Chemistry, H B Technological I nstitute, Kanpur 208 002. India

Received 2 Novelllber 200 1 ; revised received 16 Decelllber 2002; accepted 28 Decelllber 2002

Free radical copolymcrization of c itronellol and methyl-mcthacyrlate (MMA) in xylenc . at 30±O.2°C lIsing bcnzoylperoxide (BPO) as the photoinitiator for 2 1 h has been carried out. The system fol lows non- ideal ki netics (Rn

a[BPOjo.62 [ci tronelloljo.87 [MMAjO IJO) due to both primary radical termination and degradati ve chain transfer reaction. Analysis of the copolymer by IR and NMR shows the presence of alcohol ic and acrylate group in the copolymer. The glass transition temperature of copolymer. calculated by di fferential scanning calori metry ( DSC) is 80°e. The nearly alternating nature of the copolymer is confirmed by the product of react iv i ty ratios /"1 ( M M A)=0.062 and /"2 (citrone l lo l)=0.005, calculated by Kelen-Tiidos method. The Alfrey-Price. Q-e parameters for eitronel lol have been calculated as - 1 .09 and 1 .47. The mechani sm has also been explai ned.

Photopolymerizat ion i ncludes the ut i l ization of electromagnetic radiat ion as the energy source for polymerization of functional monomer, which is the bas is of i mportant commerical process w i th broad appl icabi l i ty including photoi maging l , UV curing of

. 2 d ' k 1 coatmgs an m s· . Availabi l i ty of wide range of photo in i tators4 as

well as monomers5 has i ncreased devotion i n the field of free radical photopolymerization. However, the appl ication of photopolymerization of terpenoid class, the derivative of i soprene, is st il l scarce. In 1 983, Tang et at. (, have carried out the photochemical polymerization of isoprene w i th the use of H202 as the photoin i t iator.

Ci tronellol is susceptible to polymerization as i t contains one double bond and one alcohol ic group . Therefore, c i tronel lol is selected to be ph�toco­polymerised with methyl methacrylate as new novel functional monomer. The present paper h ighl igh ts the synthesis, mechanism, kinetics and characterization of functional and optical active copolymers of c i tronel lol and methyl methacrylate (MMA) i n xylene at

30±0.2°C using benzoylperoxide as photoini t iator.

Experimental Procedure Materials

Reagents grade methylmethacrylate ( Merck­schuchardt) and other solvents were purified by usual methods7•8 and dist i l led under vacuum before use.

*For correspondence [E-mai l : akspolym@redi ff.col11; Fax: (05 1 2) 5453 1 2]

Citronel lol!)

was used as . such. Benzoylperoxide

was recrystal l i sed twice from methanol fol lowed by dry ing under vacuum.

Polymerization

Co-monomers were purified and charged to a quartz ampoule i n xylene and photoin i t iator (BPO) for

2 1 h at 30±O.2°C. Thi s was covered wi th a blanket of n itrogen and i rradi ated us ing a Phi l l ips ( 1 25 W) high pressure mercury lamp (path length 1 0 cm, 440 nm

i nterference fi lter) with a l ight i ntensity of 2 .53x I 0-4 Lux. The polymer formed was prec ip i tated with acid i fied methanol and then dried to a constant weight. It was then treated with acetoni tri le to remove polymethyl methacrylate (PMMA) . No detectable

weight loss was observed. Fi nal ly the copolymer was dried to constant weight and percent conversion was calculated. The rate of polymerization (Rp) was calculated from the slope of the percentage versus t i me plots. The polymer was characterised by JR, N M R and DSC techniques. The monomer reactivity ratios were determi ned by Kelen-TUdos method l ()

.

Infrared spectrum The i n frared spectrum was recorded on a Perkin­

E lmer Spectrophotometer (Model 599 B) using KBr pel lets.

Nuclear magnetic resollance spectrum

The N M R spectrum was obtained from varian 1 00 H A Jeol 400 LA spectrophotometer.

Pandey & Sri vastava: Photoinit iated copolymerization of ci tronel lol and methyl methacrylate Articles

Differential scanning calorimetry (DSC)

DSC was carried out on D u Pont V4. I C Model

2000 at the heating rate of l ODC/min under n i trogen atmosphere.

Results and Discussion

It is wel l-establ ished that few monomers l i ke I , 2-disubstituted olefi ns l l , do not undergo homopoly­merization due to steric hindrance l 2 and low stabi l ization energy. Ci tronel lo l too does not homopolymerise under experi mental condi tion . No copolymer was obtained when monomer was alone exposed to light or when was left in dark with B PO. However, copolymerization of ci tronellol with M M A ,

proceeds with a n i nduction period o f about 8-9 h , as i l l ustrated in Fig. I .

The effect of [ B PO] on the rate of copoly­merization (Rp) h as been studied by vary ing the

c D .;;; Qj > c D U

1 2 1 5 1 8 2 1

Time (h )

Fig. I-Time conversion plot for the photocopolymerization of citronellol and M MA. [citronel lol]=0.854 mol L-1 , [MMA]= 1 .5 mol L-1 ; copolymerization t ime=2 1 h; copolymerization tempera­

llIre=30±O.2°C [BPO]: 3.4x I O-1 mol L- 1 ; 6.Hx I O-1 mol L- 1 ;

I O.3x I O-1 mol L- 1 ; 1 3.7x I 0-1 mol L- 1 ; 1 7 .2x I 0-1 mol L- 1 ;

20.6x 1 0-' mol L-1

concentration of B PO from 3 .4x l O-3 to 20.6x l O-3 mol L- 1 at a fixed intens i ty of l ight (Table I ) . The Rp increases with increasi n g concentration of B PO. The in i t iator exponent, calcu lated from the s lope of the plot of log Rp versus log [ B PO] i s 0 .62. This value i s

greater than as expected for ideal radical ki netics. The Rp also increases wi th increas ing [ci tronel lo l ]

from 0 .42 to 1 .72 mol L- 1 keepi ng [MMA] and [ B PO]

constant at 1 .5 mol L-1 and 1 3 .77x I 0-3 mol L- 1 res­pect ively (Table 2). The monomer exponent value, calculated from the slope of the l i near plot of log Rp versus log [ci tronello l ] is 0.87.

The value of Rp also increases with increas ing [MMA] from 0.75 to 3 .0 mol L- 1 , keepi ng [c i tronello l ] and [ B PO] constant at 1 .28 mol L- 1 and

1 3 .77x l O-3 mol L- 1 respectively (Table 2). The monomer exponent value, calculated from the s lope of the l inear plot of log Rp versus log [MMA] is 0.90.

The deviated values of in i ti ator and monomer exponents suggest that the system fol lows non-ideal ki netics, which can be explained on the bas is of primary radical termination .

Table I-Effect of i n i ti ator concentration on the rate of photn­copolymerization of citronellol and MMA

[Citronel lnl]=0. 854 mol L- 1 ; I M MA]= 1 .5 mo l L- 1 ; Time=2 I h ; Temperature= 3 0 ± 0.2"C

Sample [BPO]x I O' Conversion Rpx l O6

mol L- 1 % mol L-'s- 1

I 3.4 4 .8 2 .6 1

2 6.8 5 .2 2 .87

3 1 0.3 6.6 3.26

4 1 3 . 7 7.0 4 .30

5 1 7.2 7 .9 4.89

6 20.6 8.6 5 .74

Table 2-Effect of concentration of comonomer 011 the rate of photocopoly merization.

[BPO]= 1 0.3x I 0-1 mol L- ' ; Ti me=2 1 h ; Temperature=30±0.2°C

Sample [Citronel lol ] (MMA] Conversion Rl'x l ot'

( mol L-1 ) ( mol L- ' ) (%) ( mol L-1 s- 1 ) 7 0.42 1 .5 5.7 3 .54

4 0.854 1 .5 7 .0 4.30

8 1 .28 1 .5 H . I 5.0

9 1 .70 1 .5 8.4 5.24

1 0 0.854 0.75 4.9 3.0

4 0.H54 1 .5 7 .0 4.30

I I 0.854 2.25 H.3 5.0

1 2 0.854 3.0 1 0. 1 6.4

1 93

A rticles

To analyse the effect of pri mary termi nation, the fol lowing expression given and MeyerhoffI 2.

! ) have been used.

RI2, 2J, k u kp

2 kPl1 Rp loa log · 0.8684-----ry c

r l l[Mf k l k ; kp [Mr

radical by Deb

where .1i:. represents the fraction of free radical to in i tiate chai n growth ; kd i s the in i t iator decomposition rate constant; kp is the propagation rate constant and kprt is the primary radical termination constant. [M] is the monomer concentration.

I n present study a plot of the left hand side of the above equation versus Rr/[M)" gave a negati ve s lope (Fig. 2) indicating significant primary radical termi ­nation.

The IR spectrum of copolymer(s) (Fig. 3) consists of fol lowing groups of bands (i) The range of C-H stretching v ibrations of methy l and methylene group at 2953 .82 and 2929.72 em-I , respecti vely ; ( i i ) The >C=O stretch ing range shows ester carbonyl band at 1 73 1 .77 cm- I for M M A;( i i i ) The C-H deformation range shows bands in the region of 1 383 .90 to 1 45 1 .44 em-I ; (iv) The ester stretch ing band (C-O-C) appears i n the region of 1 1 49.57 to 1 273.83 cm-I ; (v) The alcohol ic group of citronel lo l shows bands at 34 1 4.27 em- I .

The · chemical shifts of protons, attached to elements other than carbon l ike -OH, -NH and -S H , are general ly very sensitive to concentration which affects intermolecular hydrogen bonding. In

I ndian 1 . Chern. Techno! . , March 20m

case where smal l association is not h indered, the hydroxy protons general ly resonate in the region of 3 8 to 5 . 5 8 ppm eq. The signals of -OH group of methanol and ethanol appear at 3.3 and 5 .4 8 respectively i n the N M R sprectra I 4 . However, with large molecu les, the hydroxyl protons often resonate

near 8 = 8 ppm even at relatively "h igh" concen­trations, part ia l ly because the molar concentration is low and partial ly due to steric e ffect .

Therefore, the peaks of -O H group have been

assigned in the range of 7 to 7 .7 B as appeared in the NMR spectra of ci tronel lol as wel l as copolymer of ci tronellol and M M A .

'" + �I� c: � E en .S!

1 .1

1 .0

.9

.8 Ii)

.7

.6

.5

o L-��������_�-L_L-�� 1 00 200 300 400 500 600 700 800 900 1 000

!!.!. x 1 0-5 [M]

Fig. 2-A plot betwecn log Rp�/[I J I Mf and RI/i Mf :

[ci tronel lo l )= 0.854 mol L- 1 : [ M M A j= 1 .5 11101 L- 1 : copolymeri­zation t ime=2 1 h; copolymerization temperature=30±O.2°C

--- - -----_._-_._--------

0.36

0,30 -

� "' u z .. 0.25 t ::;; '" z .. a: I-

0.20

4000 3500 3000 2500 2000 1 500 1000 5Q()

Wavenumber (em·1)

Fig. 3---I R spectrum of the copolymer (sample 3 )

1 94

Pandey & Sri vastava: Photoin i t iated copolymerization of c i tronel l.ol and methyl methacrylate Articles

---- ---- ----------------�--,

7 4 3 8 (ppm)

2 o

Fig. 4--NMR spectrum of (a) pure e i trDnel io l (b) copolymer ( saillp ic :1)

·8

Fig . 5-DSC curve of the copolY l1ler ( sal1lple 3 )

The N M R spectrum o f pure c i trone l lo l ( I ) and those of copoly mers ( I I ) ( Fig . 4) shows the peaks of

( I H . OH) a t 7 -7 .7 i n tr ip let ; ( 3H , C H 1 ) at 0 .9 � i n

tr ip let : ( 2 1-1 , C 1-I 2 ) a t 1 .2-2 .2 0 i n tr ip let and extra peak

at 3 .4-4 .0 0 in s inglet appears in copoly mer. The comparison o/" N M R of monomer (c i t rone l lo l ) and that o /" copolymer con fi rms the format ion of copolymer.

The DSC curve ( Fig . 5) i nd icates the g lass transi t ion temperature (Tg) of c i t rone l lo l -co- M M A as

�W°c.

Copolymer compositioll and values of reactivity

ratios

Determi nation of copolymer microstructure from a high reso lu t ion N M R s tudy has become a matter o/"

Sample

4

7

X

1 0

I I

11

Table }--Composit ion of copolymer

Ti l1le=2 1 h : Temperalllre=30 ± 0. 2"C

Molar ratio i n Conversion Molar ratio i n monomer feed % copolymer composit ion

l M M A l1 I M M A II rCitronel iol 1 IC i tnJnel lol 1

1 .75 7 .0 I .OX

3.57 5.7 1 . 1 7

1 . 1 7 . X . I I ( ))

(UP 4.9 1 . ( )4 2.63 X .3 I . i 3

.04 <!J

.03

.02 @

.01 <!J

0 . 1 .2 .3 .4 .5 .6 .7 .8 .01 >:: '-:: .02

Fig. 6--Kelen-Tlidos plot of citronel lol and MMA fnr determi nation of n:act iv i ty ratios

i ncreas ing concern in these days . However, an attempt for a quan t i tat i ve est i mate of microstructure from these peaks has been made sati sfactori l y . The re lat i ve peak area of resonance peaks at 7-7 .7 f> due to

hydroxyl proton of c i t ronel lo l and at 3 .4-4 8 due to methoxy protons of M M A un i t are used to calcu late the mole fract ion of monomers as we l l as copolymer compos i t ion .

The monomer react i v i ty rat ios of c i trone l lo l and M M A have been esti mated by Kelen-Ti.idos method (Table 3) . The val ues of r l ( M M A ) and 1",

(c i t ronel lo l ) , caleu lated from Kelen-Tlidos p lot of 11 vs � (F ig . 6) are 0 .062 and 0.005 respect ive ly . The product of r l r2 i s nearly zero which i s a s ign of a l ternati ng copolymerizat ion .

The e2 and Q2 val ues for c i tronel lol were ca lcu lated us ing e t =0.40 and Q I =0.74 for M M A by fol lowing equation t 5- t 6 (Tabl e 4) .

( I )o.:i e2=el ± og 1" 1 1"2

1 95

Articles

0.062

Mechallism

Table 4---React i v i ty parameters

rl r�

(l.005 0.0003 1

Q�

1 .47 -0. 1 09

d ' 7 C C . I t has been reporte , that > = < I S more suscept i ble than alcohol i c O-H bond and, therefore,

IT bond takes part in polymerizat ion. Therefore, the fol lowing reaction mechan ism is suggested :

In i t iat ion o ° 0 r::::::\ II II� h" � II , ,r;::::\ &-r. - o - o - c &-- 2 &- C - O -- & · + co2

Propagation

Termination

1 96

rOI CH Y 1 3 H2C - C I COOCII3

n

I nd ian J. Chem. Techno! . , March 2003

Conclusion

From the above d iscussions, it is conc luded that c i tronel lo! can be successfu l ly photocopolymerized w i th M M A, resu l t i ng in the formation of an a l tern at i ng and fu nct ional copolymer. The rate equation of photocopol y merization in the c i tronel lo l ­a l t-MMA system can be s i mply expressed by :

Rp a [ B P010 62 I ci tronc l lol ]o X7 [MMA 111 1)11

Acknowledgements

Authors are thankfu l to the Director, Harcourt But ler Technological I ns t i tute, Kanpur for providing necessary fac i l i t ies . One of the authors Ihank DST, New Delhi for the sanction of the research project "synthesis and characterization of copoly mers of terpenes with v i nyl monomers" .

f{efcrences I Green G E. Stark B P & Zah i r S A, J M({Cmlllll/ Sci Rev

Mtlcrolllo/ ehem Part-c' 2 1 ( 1 9X 1 - 1 9X2) I X7. 2 Senich G A & Flori n R E, J M{IITOIIIO/ Sci Nl'v /V/({Cmlllo/

ChI'lli Part, 24 ( J 9X4) 2:W. :1 Went ink S G & Koch S D, ( Eds) U V Cllrillg ill Scrall

4 5

7

9 1 0 I I

1 2 l:l 1 4

1 5

1 6

1 7

Prilllillg ./i,,· prillled Circllils tllld Ihl' Graphic A rts. (Technology Marketi ng Corp, Norwalk, Conn ) , 1 9X I . Gruber H F, Prog PO/VIII Sci, 1 7 ( 1 992) 95:1. [3outev in B & Transanta F Guiclapie, J /'O/.\'III Sci p({rt- A PO/VIII Chelll. :1X, 20 ( 2000) :1722 . Tang D K & Ho S y , J 1'0/.1'111 Sci. /YO/VIII Ch('lll r;dll. 22 ( 1 9X4) U57 . Overberger C G & Yamamoto , J PO/VIII Sc: A- L 4. ( 1 %6 ) :1 1 0 1 . Vogel A L A Text /look {�r PJ"({ctim/ Org({lIic Chelllistrl', ( Longmans, London) , 1 966, :195. I noue S, J ChI'lli Soc ChI'lli COlIllIIlIII, ( 1 9X7) 1 0:16. Kelen T & Tlidos F, J M(Jcrolllo/ Sci ChI'lli r;dll 9, ( 1 975) I . M i l ler M L. Till' StJ"/lctllrr of" PO/Viii 1'''.1 , (Re i nhold Publ i sh i ng Corporat ion, London) , 1 96R. 450. Deb P C & Meyerhoff, G, Ell,. Po/v J, I (l ( 1 9X9) 709. Deb p c, ElIr Po/y J. I I ( 1 975) :1 1 . John R Dyer, Ilpp/icatiolls of" Ahsorptioll Spectm.I"ClJ/)V ot Orgallic COIIII}()lJlltl .... ( I 'relllice Hal l , New Delh i ), 1 997. Gronowski A & Woj lezak Z, Makrolllo/ Chrlll, 1 90 ( 1 9R5) 206:1. Woj tczak Z & Gronowski A, MakrolllO/ Chml. I X6 ( 1 9X5) 1 :19. Pandey P & Srivastava A K , PO/VIII 1111. 50 ( 200 I ) 9:17.