l ndi:~ n Joum:il o l' Chemi stry Vo l. 45A. September 2006. pp. l lJ SI - 1987

Papers

Structure investigation of 2-hyclroxy ethyl methacrylate and styrene copolymers by NMR spectroscopy

AS Brar", Sun ita Hoocla" & Ashok Kumar Goya l'1

"Dcp:1rtmcn t o i" Chcm istry . Indian Insti tute oi"Tcchnology Dclhi . Ilauz Khas. New Delhi 11 0 0 16. India Em:1i I: asb t·ar@chcmi stry. i i td. cmct. i n

" IJepartmcnt ol" Chem istt·y. Acha ry:1 N:trc ndra Dcv Collegc. Gov indpuri . K alkaji. New Delhi I I 0 0 19. India

Rcceit·cd /0 Mnr 2006: ncupted I !lugust 2006

2-IIydroxy ethy l mcth acry latc-co-sty rene (1-1/S) copolymers have been prepared by l"rec radi ca l bul k poly meri 7.ation at 70°C an d their compos iti on has bee n de termined !"rom thei1· 111 NM R spcc tr:1. The reac ti vit y rati os o l" I llS copo ly mers l"rnm Kelon Tudos and crmrs in Va ri ables Me thod :1rc l"uund to be r11 = 0.6-1 ± 0.22. r s = OA I ± 0.09 and r11 = 0.62. '\ = 0.-lO. respec ti ve ly . 11-1 and 1.1C( 1ll l NMR spec tra havc been an:il yzed w ith thc hclp ol" d istorti onlcss cnh:mccment by polari zat ion tt·an sl"cr (DEI'T). 2D hcteronuclear singlc quantum coherencc (HSQC) and 2D total corre lated spect roscopy (T OCSY ). T he cat·bony l and methy l carbon ol" !! -unit and methine. qua ternary carbon ol" S- unil ha vc been ass igned up to triad compos it ional sequence. whereas methy le ne ca rbon 1·esonances have been :1ssigncd up to diad composit ion:1 l leve l.

IPC Code: Int. C I.8 C08F2 12!08: C08F220/ I 0: GO I N2-I/OO

Copolymers of hydrophilic an d hydrophob ic monomers ha ve gained ex tensive interes t in vari ous appli cati ons such as hyd roge ls and bioco mpati ble matcrial s 1

-' . 2- Hydroxy eth yl meth acrylate (HEMA) has been widely used as comonomers in des ign and sy nthes is of such material s·'. 2-H ydroxy ethyl methacrylate still represent s th e preferred basic material for the constructi on of so ft co ntact lenses5

and is used for drug deli very sys tems(' and has been proposed for other surgica l appli cati ons7

. So ft contact lens and intraocular lenses based on 2- hydroxy eth yl methacrylate copolymers arc used to replace a damaged natural lenss. The study o r th e arrangement of monomer units in these copolymers will be important , as well as interes ting to understand th e phys ical properties of the co po l y me rs~ . The study of sequence di stri buti on and stereo regularity of the copolymers prov ides import ant in formati on regarding the polymeri za ti on mechani sm and lacti c ity involved. Hi gh reso lution one-dimensional ( I 0 ) 10

'11 al1CI two­

dimensional (2 0)'~·' ' NMR has bee n prove n to be one of the most informati ve tec hniqu es for the in vesti gati on of copolymer mi crostru ctures, as the chemi cal shifts are se nsiti ve to confi gurati onal as well as co mpos iti onal sequences of polymers.

The copolymeri zati ons or 2-hydroxy ethyl methacrylate with other aery I ic monomers ha ve been

I I. ~~~ 16 NMI.., 1· 1· . I reportec ear ter . " stuc tes o styrene wtt 1

vari ous vinyl monomers have al so bee n repo rted 1 7 ~20 .

The styrene and methyl methacrylate copo lymers I I b . . I b I "I~'\ 1ave a so een tn ves ti gatec y many rese~u·c 1ers- -· . Brar el a/. have reported th e mi crostructure o r various vinyl copolymers using one- and two-dimensiona l

'"~-J. "'6 . MR spectra- - . Vanous coworkers ha ve reported

the co polymeri zati on of 2-hyd roxy ethyl meth ac rylate . '17-"" tJ • with styrene- - (H/S); but to the best ol ou r

kn owledge, NMR studi es of 2- hydroxy ethyl methacrylate and styrene copolymer ha ve not been reported so far. We report here th e micros tructure of H/S copolymers. The reactt vtty rati os o r the co monomers have been cal culated usin !.! a li near Kelen Tuclos meth ocJ ·' 11 and non-linear l; ast sq uare error-in- variables method·" . The complete sequence ass ignment s in 1H ancl '-'C{ 1H} NMR spec tra of H/S copolymers have been clone with the help of OEPT-135, and 20 (HSQC and TOCSY) NMR ex periments.

Matcl"ials and Methods 2-H ydroxy ethyl meth acrylate and styrene

monomers were vacuum di still ed and stored below soc. A se ri es of H/S copolymers o r cli rrere nt co mpos iti ons were prepared by free radi cal bu lk polymeri zati on using azobi sisobutyronitril e as an initiator at 70°C under nitrogen atmos phere. The percent converston was kept below I 00'c by prec ipttating the copolymers tn wate r. The co polymers were furth er puriri ecl by crys tall ization meth od using methan ol/water for hi gher co mpos iti on

1982 INDIAN J CI-IEM. SEC A. SEPTEMBER 2006

rH, r 1 r +c-c-c-c1; I 161 /c~ Her

12H

HOCH,CH,O 0 5 :::,. 3 4

ppm 6 5 2 0

Fig. !- The 111 NM I{ spec trum o i" II/S copolymc 1· (F11 = 0.-17) in DM SO-dr, at X0°C.

Tabl e !-Copolymer compos iti on d;lla or 11 /S copol y mers (!i 1 = ked in composition or 11 -unit: F11= I-ced nut composition or 11 -unil in copol y mer)

S No.

2 3 -1 .'i 6 7

Copo ly mer sy mbol

I-lSI I-I S2 I-ISJ Il S-I HS.'i II S6 I-I S7

.Iii F11

0.10 0.20 0.20 0.2X 0-10 0.-17 O . .'iO O . .'iCJ 0. (l() 0.61 0.70 0.67 O.XO 0.7)

or H-un it and chl oroform/waf er for lower co mpos iti on o r H-unit in copolyme r. The va ri ous types or 1MR spectra have been reported by di sso lving the copo lymer in DMSO-dr, ~~t ~W°C12 .

Results and Discussion The composition of H/S copoly mers was

determi ned from 1 H NMR spect rum as show n in Fig. I. The comonomcr mole fraction s in ked and in the copo lymer arc show n in Table I. The termin al mode l reac ti vity ratios were ca lculated from composition data using Kc lcn Tudos method ( KT)2 1

.

The reactivity rati o from KT method along with copo lymer compos iti on data was then used to calcu late reactivity ratio from non-linear error- in­variables method (EVM)22

. The va lues or reac ti vity ratio obtained from KT and EVM method arc ~'11 = 0.64 ± 0.22, rs = 0.41 ± O.OSJ and r11 = 0.62. ' 's = 0.40, respectively. The intensit y of - CH1 protons

or H-unit and -Cr,H5 protons of S-unit was used to c~tlc ulat e copo lymer :.:o mpos iti on using the relation:

L'C{ 111) NM R studi es

The 11Cl 1Hl NM R spect rum of H/S copolymer (F11= 0.47) in DMSO-cl 6 at 80°C is shown in Fig. 2. The resonance signa ls around 8 17.50-21. 75 ppm were clue to a-CI-I, carbon resona nces or H-unit in copo lymer. The region around 0 36.5- 52.5 ppm was ass igned to th e overlap of methylene ca rbon of both H- ~llld S-unit , mcth ine carbon of S-unit and quate rn ary carbon of H-unit in H/S copolymer. The ca rbonyl carbon region of H-unit of H/S copolymer appeared aro und 8 174.5 -1 77.0 PJDl . whereas the signals around o 65.5 ppm and 8 58.57 ppm we re assigned to - OCH 2 and -C H20 carbo ns of H-unit. respectively. The reso nance signals a:·o und 0 125 K 8 127.97 and o 144.5 ppm were ass igned to C-2. C-6: C-3, C-4, C-5 and C- 1 aromatic carbo ns or styrene unit, respective ly. The overlap of 0-mcth ylcnc. mcthinc and quaternary carbon resonance signa ls around 8 36.5-52.5 ppm can be reso lved with the hel p of DEPT- 135 NMR spectrum. In DEPT-135 NMR spectru m, methinc and meth yl carbl)ns appea red as pos iti ve signa ls wh il e methylene e<,rbo n appeared as negat ive signal and quaternary carbn t~ docs not appear in spectrum. Resonan ce signal aro u1 1d o 39.45 ppm. which appeared as a pos iti ve signa l w~t s assigned tn

Brar eta/.: STUDIES ON 2-1-IYDROXY ETHYL METHACRYLATE A 10 STYRENE COPOLYMERS 1 t) 83

r, I I I + e-c-c-e-}:

I I 61 n /~'\, H 6 r 1

2 H

HOCH2CH 20 0 5 ::,.. 3

4

' ~ ~(C-3

DMSO

(-CH 20),.

ppm 160 140 120 100 80 60 40 20

J-i g. 2- Thc 13C{ 111} NMR spectru m along with ex paneled quaternary c 11·bon or aromatic regi on or I liS copolymer (F11 = 0. -17) in DMSO-d6 at ~;ooc.

J ~ .

-v~V\~

.---,-----,-~--,---.--~~.--~....---------r---

23 22 21 20 19 18 17 16

ppm

Fig. }- T he expa nded a-methyl region in "C{ 1 ll} NMR spcctmm or (a) !'I-lEMA and 1-1 /S copo lymers with co mpositions (1- 11 =): (b) 0.7'l . (c) 0.67. (d) 0.-17 and (c) 0. 20 in DMSO-dr, at sooc.

- CH carbon of S-unit and DMSO-d(, sol vent. while th e negati ve signal around o 41.0-52 .5 ppm \\'as assigned to - CH2 carbon which spread over 12 ppm range, and because of its symmetry. it is sen siti ve to compos iti onal sequences.

The ~-methy l e n e carbon reg ions of H- and S-unit s of H/S copo lymer are sens iti ve to the compositi onal sequences. Three broad enve lopes around o 49.0, o 5 1.5 and o 53.5 ppm have been assigned to - C H2

carbon resonance signal in SS , SH/HS and HH cliads. respectively on the basis or change in intensity o f siQnals w ith the copo lymer composttt on. The quaternary carbon of H-unit appeared around o 4-L5 ppm in PHEMA, while thi s resonance signa l overlaps w ith SS diad of 0-methylcne reg ion in copol ymer w ith higher composition of S- unit (Fig. 2) .

The a-methyl carbon region of 1-1 -unit of , H/S copolymers along with poly(2-hyclroxy ethy l methacrylate) is shown in Fig. 3. The a-methyl carbon region spread over a wide range of chemical shirt s clue to tacti city effects of poly(2-hyclroxy ethy l methacrylate) and compositional sequences. The assignments to variou s signal s were done w ith the help of spectrum of poly(2-hyclroxy ethy l methacrylate) and by observ! ng change in inten sity of signals w ith change in composi ti on of copolymers.

1984 INDI AN J CI IEM. SEC i\. SE I'TEM13EI ~ 2006

(d J -""·

(CJ

178 177 176 ppm

175

.... _...,. · ~··

174

Fi g. +--The c:xpamkd carbnny l c;1rhon rcg iuns or (;1) I)II [Mi\ ;1nd I llS copo lymers with con1pos iti uns (1: 11 =) : (b) 0.75 . (c) 0.67. (d) 0.47 and (c) 0.20 in DMSO-d1, ;1t XO"C.

The resonance signal I (o 16.25 ppm) was ass igned to 1-lrl-lrl-l triad on compari so n with poly(2-hydroxy et hy l meth acry late). The additi onal signal 2 (b 17.50 ppm) that appeared in co polymer spec trum unl y, was ass igned to HrHrS tri ad. The signal 3 (b 18.20 ppm) was ass igned to Hrl-lml-1 triad . The reso n ~ tn ce signals at 4 (8 19.80 ppm) and 5 (0 20 .75 ppm) appeared in th e copolymer on increasin g the co mpos iti on o l' S-unit and the ir intensity in creased with In crease tn com pos iti on o l' S-unit. So. th e signal s were ~ t ss i g ned

to 1-lrl-lmS and Sri-IrS tri~td s, res pecti ve ly. On co mpari so n with poly(2-hydroxy eth yl methacry late) , the reso nan ce signal at 6 (8 2 1.20 ppm) was ass igned to Srl-lmS triad.

The ex panded carbo nyl ca rbon resonance signal o l' 1-1 -unit in copolymer along with poly(2- hydroxy ethy l meth acrylate) is shown in Fig . ...J.. The vari ous resonance signal s we re ass ig ned on compari so n with spectrum o l' po ly(2-hydroxy eth yl methacry late) and on th e basis o l' variati on in int ensit y o l' signa ls with copo lymer compos iti o n. On co mpan son with spectrum o l' poly(2-h ydroxy eth yl methacry late). th e signals at I (o 177 .40 ppm) and 3 (<S 176.4 0 ppm) were ass igned to Hrl-lrl-1 and 1-lrl-lml-1 triads. respec ti ve ly, whil e the resonance s i g n ~li at 2 (0 176.60 pp m) was ass igned to 1-lrl-lrS tri ad. The resonan ce signal at 4 (0 175 .75 ppm) was ass igned to th e ove rl ~ tp

_) i (a) ----) .) ~

'] I ) -

&

\ I / ~

l l II 10

\ ~ __:__ ~

-~ L ----- -·· - --------.... , .. .. ... .......... ....... ...... .... .. ... , .............. ..... , ~·(• fTI J

_ _.---· -

,1\ / \ .. _

---..

) (b)

\ l

! ' _ _j I

~--. I

,-~ I l .

! J - - -J

~ .J

I )

~

I

2

{~-~

9 & I

~ 12 11 I 0

\ '6d <((tV

•• • • • • ••• • ~ · 1 . ...... .. ... .. ..... . . ... .. . . . .... . . . .. . .

(c)

9 8 I / I ,

~ 12 (

c::o

~

.) '~~1 I

""''' I' • • • ' '' '' ' '' ,...-,' ' ' 1' '''' ' . • _....., ·~ · '' · • ' ', . , •'' ' •·· ' • ' ~~· ·

GO

GC

;.opm

Fig. 5- Thc expanded 2D IISQC spectra o r f~-lllcth) knc carbon regions al ong with - C I I,O ;1nd - OCII , regions or 11 /S copo lymers wi th CO ill jlOSiti on (/: I I =) : (a) 0.20. (b) 0.47 and (c) 0.7) in DMSO-d,, ;1t ~\DoC.

13r:Jr e1 a!.: STUDIES ON 2- II YDROXY ETHY L METHACRYLATE AND STYRENE COPOLYMERS 1985

_/' -c---/----- ,_'-----..___ _ _--- ------ -'----._

( 0.5

\ ) 1. 0

I 1 " I

) 2 .0

ppm ..,._...,~~

ppm 2 0 1. 5 1. 0 0 5

\ (c) )

I j

/ I 3 .0

-3.5

4.0

6

I_ 4 . 5 7' ----tP ,t:/

ppm

ppn 4 . ~ 4 0 3.5 3.0

2 . 0

·----- ppm

ppm 2. 0 1 . 5 1 0 0. 5

'\ ! \. (\I I

_)~ ___ j\J v \__ ____ ) -! --(d)-- ---··--·-·--- ·--

/

,---'1 ; ~ __ .r·

--> ~- - -

)

--~

I

J 'i

7'

~ 'y --------- -·---

ppm 4 . 5 4 . 0 3 5 3. 0

3 . 0

~3 5

4.0

4 .5

ppm

Fig. 6- Thc 2D TOCS Y spectrum or P-mcth ylcnc carbon region with compos ition (F 11 =):(a) 0.47. (b) 0.75 and - CII 20 and - OCI I2

regions or 1-1 /S copolymers wi th composition (F11 =): (c) 0.47 ;111J ( J ) 0.75 in DMSO-d1, at80°C.

of SrHrS + HmHmH triads whil e th e reso nance signals at 5 (o 175.45 ppm) and 6 (o 175. 15 ppm) vvere ass igned to H rH mS and SrH mS triad s, respec ti vely.

The ex panded quaternary carbon reso nance signa l (C-1 ) or S-unit in copolymer is show n in Fig. 2. The vanous resonance signal s were assigned 0 11

compari son with spectrum of polystyrene and on th e basis of change in intensity of signals with co pol ymer compos iti on. The resonance signal I was ass igned to SSS triad on compari son with polystyrene. As the intensity of reso nance signal 3 increases with increase in co mpos iti on of 1-1-unit, it was ass igned to HSI-1 triad. The intensit y of resonance signal at 2 first increases with increase in composition o r H-unit , passes through the ma ximum value and then decreases with increase in co mpos ition of H- unit ; so it was ass igned to SSH triad.

2D IISQC ami TOCS Y NMR studies

The expanded B-methylene region along with -OC H2 and - CH20 region in 2 D HSQC spectra is given in Fig. 5. The cross peaks I, 2 and 3 were assigned to HH , HS/SH and SS diads, respect ively. The protons of HH diad coupl ed with protons o r SS diad, resulted in cross co rrelati on peak I' in 2D TOCSY spectrum (Figs Ga and Gb). The cross peaks centered around o 38 .5/2.18 ppm were ass igned to methine reg ion of S-unil in copolymer. The cross peaks 4, 5 and 6 were ass igned to SSS, SSII and HSH triads, respectively based on the variation in intensity o r cross peaks with composition of copolymer. 2D TOCSY studi es were used to ascertain these ass ignment s by assigning I ,3-bond order co upli ngs bet ween methylene protons and met hi ne protons o r S-un it. The cross correlati on peaks I' were al. o ass igned to the coupling of - C H proton in SSS lri ;td

1986 INDIAN J CI-IEM. SEC A, SEPTEMI3ER 2006

(a)

16

18

20

22

6 ppm

~··-r

ppm 0.8 0.5 0.4 0 . 2

(b)

15 2 J

18

5 20

22 6

ppm

ppm 0.8 0.5 0.4 0.2

(c)

2 16

18

J 20

22

ppm

ppm 0. 8 0. 5 0 . 4 0 . 2

Fig. 7------Thc ex panded a -meth y l c;u·bon reg ions o f 2D 1-ISQC spec tra o f HIS copoly mers w ith compos iti ons (F 11 =): (a) 0.20. (b) 0.47 and (c) 0.75 in DMSO-d1, at XOOC.

Table 2- J\ ss ignmcnt o f P-methy lcne ca rbon n;~;o nancc o f 1-1/S copo lymers fro m 20 1-ISQC spcc:ra

S.No A ssignment 2D 1-I SQC 1'C( 11-I } (ppm)

fl-lllelln·/ene region I I-III 51.51)1 1.75 2 liS 4761)1 1.60 3 ss 45.51) I 1.45

M ethine region 4 sss 39 .5•) I 1.80 5 SS I-I 38.57 I 2.30 (i I-lSI-I 3X.:'i< J I 2.45

-CIIcO reg ion 7 SS (-CI-1 ,0 ) 58.2'1 I 3.0:'i R SI-1 I l-I S (-CI-IcO) 58.2J I 3.30 9 1111 (-C II ~O) 5iU:J I 3. -!8

-OCH2 reg irm 10 SS ( -OC II ~) 6o.O I 3.05 II SI-1 I l-I S (-OCI-1 2) 66.0 I 340 12 1111 (-OC J-1 2) (j(. (I I 3.85

Tabl e }------1 1-1 -111 cross :.:orrelat ion between l:<'n-cqu ivalcnt geminal protons in IllS copoly mers ob,crvcd

from 20 TOCSY spectra

Coupled protons

Corrcb - Pro ton I Proton II l'c;1k posit ion tion peak /TOCSY. No. 111 / II . ppm/

I' -CII o f (SSS). -C II2 of SS -C II ,of llll -CII , of SS I X'i I 1.30

2' -C II in SS II -C I-1 , o f li S 2. :\2 I 1.55 T -C II in SS I-I -CII2 of III-I 2.35 I I. X5 4' -C II ini-ISII -C II 2 o f 1111 2.50 I 1.90 :)' -C II 20 ( I I a ~ -C II ,O (II b) :1 .90 I 3_:)(, (,' -O il -CI-1,0 ( l-I b) 4_:)(, I 3.n

7' -O il -C II ,O( II ;!) -UQ I 3.55

vvith methylene proton tn SS wn ile the cross corre lation peaks 2' and 3' \VC rc ~; s~ i g nccl to the coup ling or ---C J-1 proton in SS H triad with methy lene protons in HS and HI-I diads, respec ti ·,rn /y. The cross­correlati on peak at 4' was ass igned to the coupling of ---CJ-1 proton in I-ISH triad w ith methy lene proton in HH respectively. A ll th e assignments of ---C J-1 ~ region in 2D HSQC spectra arc given in Tabk 2.

The cross peaks centered on o 58 .5/3.30 ppm and o 66 .0/3.45 ppm were ass igned to - C:HcO and -OCH ~

group, respect ive ly (Fig. 5). On the bas is of variation in intensity of cross peaks vv i lh copo lymer compositi on, the cross peaks 7, 8 and 9 were ass igned

Brar et a/. : STUDI ES ON 2- HYDROXY ETHYL METH AC RYLATE AN D STYREN E COPOLYM ERS 1987

to SS , SH/HS and HH diads of - CH20 region, respectively , whil e the cross peaks 10, II and 12 were ass igned to SS , SH/ HS and HH diads of - OCH2

reg ion, res pecti vely. In 2D TOCSY spectrum (Fi gs 6c and 6d) , the cross correlation peak 5' was assigned to geminal coupling of -CH20 protons, whil e the cross correlation peaks 6' and 7' were ass igned to the coupling of proton of - OH group with Hb and Ha protons of -CH20 group respecti vely, as shown in Table 3.

The expanded a-methyl reg ion in 2D-HSQC spectra is shown in Fig. 7. The cross peaks l , 2 and 3 were ass igned to HrHrH , HrHrS and HrHmH triads res pectively (Fig.7a), whil e the cross peaks at 4,5 and 6 (Figs 7c and 7d) were ass igned to HrHmS , SrHrS and SrHmS triads, respecti vely.

Conclusions The reacti vity rati o of comonomers 111 H/S

copolymers arc r 11 = 0.62 and rs = 0.40. The complex and overlapped 1 H and uc { 1 H} M R spectra of the copolymers were reso lved with the help of DEPT-1 35 and 2D HSQC spectra . The carbonyl carbon and methyl carbon of H-unit were ass igned up to triad compos itional and confi gurati onal sequ ences in I\ I · C{ H} NMR spectrum, whereas methylene carbon resonances were assi gned up to diad compositi onal sequences (HH , HS/SH and SS). The methine carbon of S-unit was assigned up to triad compositional sequences, i. e. SSS , SSH and HSH.

Acknowledgement One of the authors, Sunita Hooda, wants to thanks

Department or Science and Technology (DST), CW

Delhi , India, for prov iding financial support.

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