7
Indian Journal of Chemistry Vol. 43A, October 2004, pp. 2066-2072 Methacrylonitrile-vinylidene chloride-butyl acrylate terpolymers: Monomer sequence determination by one- and two-dimensional NMR spectroscopy AS Brar *, DR Pradhan & Sunita Hooda # Department of Chemistry , Indian In stitute of T ec hnology, Hauz Khas, New Delhi II 0 016, India Receil •ed 18 June 2004; revised 4 August 2004 Methacrylonitrile-vinylidene chlorid e-b utyl acrylate (M/Y/B) terpolymers of differelll compositio n have been prepared by bulk polyme ri zation us in g benzoyl peroxide as an initiato r. The terpoly mer co mpositions have been determined from quantitative assessment of the respective 13 Cf 1 H} NMR spectra and the obse rved va lu es co mpared with the theoretical val ues ob tained from Alfrey-Goldfin ge r's equation. The over lapping methine a nd methylene carbo n resonances of terpolymers have been differentiated by DEPT experiments. The quaternary ca rbon resonances of M/Y/B terpolymers have been assigned to triad compos itional sequences. The comp le te 1 H and 13 C{ 1 H} NMR spectra of terpoly mers have been assigned without amb iguity with the help of2D HSQC MR spectrosco pi c techniques. !PC Code: Int. CJ. 7 C08F 120/42; GO I R 33/20 The growt h in production of plastic materials durin g the past few years ha s been accompa ni ed by the increased demand for materials with improved physical and mechanical prop erties, grea ter heat and radiation stab ility etc. Only few homopolymers and binary copolyme rs ca n satisfy such demands. The addition of a third monomer component to the so called binary sys tem can yield terpol ymers of desirable chemical, physical and mechanical properties that differ from those of relevant binary copolymers. Therefore multicomponent polymerization have con tinued to evoke much interest not only in academics but also in industry 1.2 . The 20 NMR s pectroscopy has been u sed as the most reliable technique to dete rmine the config urational and conformational str ucture of th e I . 34 I d I copolymers . Vanous co-,vorkers · 1ave repo rte t 1e terpolymerization of maleic anhydride w ith se lected pairs of vinyl monomers. The so rpti on kinetics using viny Iide ne chloride/styrene/aery loni tri le terpol ymers was repot1ed by Wen g et a l. 5 A systemat ic a pproach to study the multi-compon ent polymerization kinetics usi ng various acrylic monomers was reported ear li er 6 - 8 . Mi cros tructural investigation of terpolymers are important to understand the physicochemical properties of the polymers . The study of microstructure of terpolymers require prior knowledge about the co monomer sequences in the copolymers. However, # Depa rtment of Chemistry, Acharya Narendra Dev College, Govindpuri, Kalkaji, New Delhi JJO 019. the prop erties of copolymers and terpolymers depend upon their micro s tructure')-! 1 The studi es of vinylidene c hloride terpolymers 12 - 13 have been reported earli er also. Brar et al. 14 - 16 have repo rt ed the microstructure of acrylonitrile, styrene and methyl methacrylate terpolymers. In this paper, we report the composition of methacrylonitrile/vinylidene ch lor id e/butyl acrylate terpolymers from quantitative assessmen t of 13 C{ 1 H} MR spect ra. Th e complete 1 H and 13 C{ 1 H} MR spec tral assig nment of M/V /8 terpolymers were done with the help of DEPT and 20 HSQC MR expe riments. Materials and Methods The monomers methacrylonitrile (M), vinylidene c hlorid e (V) and butyl ac rylate (B) we re se parately vacuum disti lied and stored below C. The terpo lymers were prepared by bulk po lymeriz atio n using benzoyl peroxide as an initiator under nitro ge n atmosphere in a sea led tube. T he overa ll perc e nt conversion was kept below I 0 % by co ntrolling the time of polymerizat ion and precipitating the terpolymers form ed in benzene. The tcrpolymers were purified by dis so lving in chloroform and reprecipitating in benzene and were dried under vac uum. All 10 ( 1 H, 13 C{ 1 H}, DEPT-13 5) and 20 HSQC NMR s pectra of terpolymers were recorded in CDCI 3 at 25 ° C, on Bruker 300 MHz DPX s pectrometer using different s tandard pulse seq uences. T he conditions for recording of all the NMR spectra have been de sc ribed elsewhere 17 .

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Indian Journal of Chemistry Vol. 43A, October 2004, pp. 2066-2072

Methacrylonitrile-vinylidene chloride-butyl acrylate terpolymers: Monomer sequence determination by one- and two-dimensional NMR spectroscopy

AS Brar*, DR Pradhan & Sunita Hooda #

Department of Chemistry , Indian Institute of Technology, Hauz Khas, New Delhi II 0 016, India

Receil•ed 18 Jun e 2004; revised 4 August 2004

Methacrylonitrile-viny lidene ch loride-butyl acrylate (M/Y/B) terpolymers of differelll composition have been prepared by bulk poly meri zation using benzoyl peroxide as an initiato r. The terpolymer composi tions have been determined from quantitative assessment of the respective 13Cf 1 H} NMR spectra and the observed va lues compared with the theoretical val ues obtained from Alfrey-Goldfinger's equation. The overlapping methine and methylene carbon resonances of terpolymers have been differentiated by DEPT experiments. The quaternary carbon resonances of M/Y/B terpolymers have been ass igned to triad compositional sequences. The complete 1 H and 13C{ 1 H } NMR spectra of terpo lymers have been ass igned without ambigu ity with the he lp of2D HSQC MR spectroscopi c techniques.

!PC Code: Int. CJ.7 C08F 120/42; GO I R 33/20

The growth in production of plastic materials during the past few years has been accompanied by the increased demand for materials with improved physical and mechanical properties, greater heat and radiation stability etc. Only few homopolymers and binary copolymers can sat isfy such demands. The addition of a third monomer component to the so cal led binary system can yield terpolymers of desirable c hemical , phys ical and mechanical properties that differ from those of relevant binary copolymers. Therefore multicomponent polymerization have continued to evoke much interest not only in academics but also in industry 1.2 . The 20 NMR spectroscopy has been used as the most reliable technique to determine the configurational and conformational structure of the

I . 34 I d I copolymers . Vanous co-,vorkers · 1ave reporte t 1e terpolymerization of maleic anhydride with selected pairs of vinyl monomers. The sorption kinetics using vi ny I idene chloride/styrene/aery loni tri le terpol ymers was repot1ed by Weng et al. 5 A systematic approach to study the multi-compone nt polymerization kinetics

usi ng various acrylic monomers was reported earlier6-

8.

Microstructural investigation of terpolymers are important to understand the physicochemical properties of the polymers. The study of microstructure of terpolymers require prior knowledge about the comonomer sequences in the copolymers. However,

# Department of Chemi stry, Acharya Narendra Dev College, Govindpuri, Kalkaji, New Delhi JJO 019.

the properties of copolymers and terpolymers depend

upon their microstructure')-! 1• The studies of vinylidene

chloride terpolymers 12-13 have been reported earli er

also. Brar et al.14-16 have reported the mic rostructure of

ac rylonitril e, styrene and methyl methacrylate terpolymers. In this paper, we report the composition of methacrylonitrile/vinylidene chloride/butyl acrylate terpolymers from quantitative assessmen t of 13C{ 1 H}

MR spectra. The complete 1H and 13C{ 1H} MR spectral ass ignment of M/V /8 terpolymers were done with the help of DEPT and 20 HSQC MR experiments.

Materials and Methods The monomers methacrylonitrile (M), vinylidene

chloride (V) and butyl acrylate (B) were separately

vacuum disti lied and stored below 5°C. The terpo lymers were prepared by bulk polymerization using benzoyl peroxide as an initiator under nitrogen atmosphere in a sealed tube. T he overa ll perce nt conversion was kept below I 0% by controlling the time of polymerization and precipitating the terpolymers fo rmed in benzene. The tcrpolymers were purified by dissolving in chloroform and reprecipitating in benzene and were dried under vacuum. All 10 ( 1H, 13C{ 1H}, DEPT-135) and 20 HSQC NMR spectra of terpolymers were recorded in

CDCI3 a t 25 °C, on Bruker 300 MHz DPX spectrometer using different standard pulse sequences. T he conditions for recording of all the NMR spectra have been described elsewhere 17

.

BRAR et al.: METHACRYLONITRILE-VINYLIDENE CHLORIDE-BUTYL ACRYLATE TERPOLYMERS 2067

Results and Discussion Composition and molecular weight determination

The composition of methacrylonitrile/vinylidene chloride/butyl acrylate (MIV /B) terpolymers were determined from the quantitative 13C{ 1H} NMR spectra and compared with those calculated from Goldfinger's equation 18 using the comonomer reactiv ity ratios: rMv = 2.47 rvM = 0.40; rsM = 2.31, rsM = 0.61; rv13 = 0. 91, r8 v = 0.81. The average molecular wei ghts of the terpolymers with different compositions were determined by GPC in THF at 25°C. The terpolymers composition along with average molecular weights are given in Table 1.

13C{ 1H} NMR studies The complete assignment of carbon resonance

signals in 13C{ 1H} NMR spectrum of M/V/8 terpolymer (M=0.48, Y=0.26, and 8=0.26 mol fraction in the terpolymer) in CDC13 at 25°C is shown in Fig. I. The sharp resonance signals around 813.5 and 8 18.9 ppm are assigned to 4CJ-13 and 3CH2 carbons respectivel y, whereas the multiplet around 829.2-30.8 ppm is assigned to 2CH2 carbon of 8-unit of MIV /8 terpolymers.

The carbon resonance signals of quaternary carbon of M-monomeric unit, ~-methylene carbon resonances of M, V, 8-monomeric units, a methine carbon reso­nances of 8-monomeric unit and oxymethylene carbon resonances of 8-unit of the terpolymer are overlapped and can be assigned with the help of DEPT experiments (Fig. 2 and Fig. 3). The resonance signals around 823.0-27.5 ppm are due to a-CH3

carbon resonances of M-unit in terpolymer. The ~­methylene carbons of M, V and 8 units of the terpolymer resonate around 831 .0-57.0 ppm. The -OCH2 and a-methine carbon signals of 8-unit appear around 860.0-67 .0 and 837 .0-41.5 ppm, respectively. The quaternary carbon signals of M- unit are assigned around 832.0-36.0 ppm, whereas the quaternary carbon of V-unit resonates around 882.0-93.0 ppm. The carbonyl and nitrile · carbon resonances are assigned around 8172.8-175.2 ppm and 8121.2-1 24.2 ppm respective ly. All the resonance signals were assigned by comparing with 13C{ 1 H} NMR spectra of methacrylonitrile-vinylidene chloride (M/V), metha­crylonitrile-butyl methacrylate (M/8) and vinylidene chloride-butyl methacrylate (V/8) copolymers.

Table l- Terpolymer composition for met hacrylonitrile/vinylidene chloride/buty l acrylate (MIV/B) terpo lymers

Monomer Feed Mole Fractio ns

M 0.54 v 0.34 B 0.12

M 0.51 v 0_29 B 0_20

M 0.10 v 0.84 B 0.06 M 0.22 v 0.58 B 0_20

M 0.30 v 0.38 B 0.32

M 0.37 v 0.26 B 0.37

Mole Fractions in Terpolymers

a b

0.72 0.73 0.21 0.20 0.07 O.Q7

0.69 0.70 0.19 0. 18 0_12 0.12

0.16 0.21 0.78 0_73 0.06 0.06 0.40 0.39 0.44 0.45 0_16 0.16

0.48 0.48 0.26 0.28 0.26 0_24

0.58 0.56 0.16 0.18 0.26 0.26

Mw X 10-5 p

7.80 5.70 1.37

7.2 1 5_13 1.4 1

6.70 4.82 1.39

5.20 3.82 1.36

4.82 3.75 L28

4.98 3_77 1.32

aTerpolymer composition using quantitative 13C{ 1H} NMR spectroscopy; bterpolymer composition using statistical model using Alfrey-Goldfinger's equation; Mw and Mn : weight average, number average molecular weights; P:

ol di s ersit .

2068

0 I !<

INDIAN 1 CHEM, SEC A, OCTOBER 2004

z u I

r--1

> I

-u-I

.!:' u 0 u

r---1

ID

X u I 'II + ID

+ > + :l: ....

X u I 1!!.

+ Ill

.... :r u 0 I

.... X

.... ..,u X m u ... ,..., X

u ... ...,...,

~ ~ £

I u -y- I ~

r-1 r-"j

l"'"''"''''''''' 'l'"'''"'''''''''''i'''''''''''" ''''''l '''''''''''''''''' 'l' '''' '' '' '''''' ''''l'''''''''''''' '''''l'''''' '''''''''''''l'''''''''''''''' '''l'''"r'""'"TTTTnTr 1.60 t..o 120 too eo 60 40 20

GCppmJ

Fig. 1- The 1' C{ 11-1)-NM R spectrum of methacry lonitrile/ vinylidene chloride/butyl acry late (M/V/8 ) terpolymer (M=0.48, Y=0.26 and

B= 0.26 mol % in terpolymer) in CDCI3 at 25°C.

10 60

..__ CH(BJ r-----1

40

5(ppm)

' 30 20 10

Fig. 2- The DEPT-135 NMR spectrum of methacrylonitrile/ viny lidene chloride/butyl acrylate (MIV/B) terpolymer (M=0.48, Y=0.26

and B= 0.26 mol % in teroolvmer) in CDC!, at 25°C.

BRAR eta/.: METHACRYLONITRlLE-VINYLIDENE CHLORIDE-BUTYL ACRYLATE TERPOLYMERS 2069

«-CH (8)

43 42 41 40 39

S(ppm)

38 37 36 35

Fig. }- The DEPT-90 NMR spectrum of methacrylonitrile/ vinylidene chloride/butyl acrylate (MIV/B) terpolymer (M=0.48, V=0.26 and B= 0.26 mol %in terpolymer) in CDCJ3 at 25°C.

1H and 2D HSQC NMR studies

The expanded methyl regions of HSQC NMR spectra of three different compositions of MIV /B terpolymer are shown in Fig. 4, [4a (M=0.16, Y=0.78 and M=0.06 mol % in the terpolymer) , 4b (M=0.48, Y=0.26 and B=0.26 Mol% in the terpolymer) and 4 c (M=0.72, Y=0.21 and B=0.07 mol % in the terpolymer) respectively]. The a-CH 3 region in 10 (

1H and 13C { 1H}) NMR spectra of the terpolymers is quite complex and overlapped. This region can be assigned with the help of 20 HSQC NMR spectra. The cross peaks at 826.2/1.82 (1), 824.9/1.62 (2) and 823.5/1.35 (3) are assigned to MMM + MMY, MMB and BMB triads respectively while other cross-peaks at 825.7/1.72 (4) and 827.4/1.95 (5) ppm are assigned to BMY and YMY triads (Figs 4a, 4b and 4c). All the assignments were done with the help of HSQC spectra of poly(methacrylonitrile), methacrylonitrile/ butyl acrylate and methacrylonitrile/vinylidene chloride copolymers and by observing the change in intensity of the signals with the terpolymer composition.

The methine carbon resonances of B-unit of M/Y/B terpolymer are assigned to triad compositional sequences. The cross-peaks at 841.0/2.38 (6), 839.5/2.58 (7) and 837.0/2.80 (8) ppm are assigned to BBB, MBB and MBM triads, respectively on the basis of change in intensity of the signals with change in terpolymer composition and by comparing with HSQC spectrum of M/B copolymer. Similarly, the

cross-peaks at 840.5/2.90 (9) 837.8/3.12 (10) and 839.5/3.48 (11) ppm are assigned to BBY, MBY and \' BY triads (Fig. 5) respectively by comparing with HSQC spectra of Y/B copolymer and by observing change in intensity of the signals with change in terpolymer composition.

The methylene carbon resonances of M/Y/B terpolymer show dyad, tetrad compositional and configurational sequences, due to its symmetry. The cross-peaks region around 837.011.65-2.18, 843.5/1.62-2.52 and 848.5/1.80-2.40 ppm are assigned to BB, MB and MM dyads, while the cross­peaks at 850.0-51.0/1.88-3.25 , 854.0-56.0/2.40-3.30 and 862.0.65 .0/3.40-3.80 ppm are assigned to BY, MY and YY dyads, respectively (Fig. 5). Further splitting within BB, MB and MM dyads are due to configurational sensitivity. In these BB and MM dyad regions, three cross-peaks along the proton axis are assigned due to configurational sequences. The meso (m) configuration gives two cross-peaks due to the presence of two methylene protons in different environment and racemic (r) gives one cross-peak between two cross-peaks of the meso configuration. The cross-peaks at 837.0/1.63 (12) and 837.0/2.10 (12') ppm are assigned to BmB dyad whereas the cross-peak at 837.0/1.87 (13) ppm is assigned to BrB dyads, respectively. Due to two non-equivalent protons of B-unit in MB dyad, the cross-peaks at 843 .5/1.65 (14) and 843.5/2.12 (14') ppm are assigned

2070 INDIAN J CHEM, SEC A, OCTOBER 2004

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

c

1.5

6(ppm)

1.5

6 (ppm)

3

L21

t~: 24

25

26

27

28

ppm

21

22

23

24

25

26

27

28

ppm

21

22

23

24 .. ~~~~~~2 25

1.5 6(ppm)

26

27

28

ppm

Fig. 4-The expanded a-methy l region of 20 HSQC NMR spectra of methacrylonitrile/vinylidene chloride/butyl acrylate (M/V/8) terpolymer. (a) M=0.72, V=0.21 and B= 0.07 mol % in terpolymer) (b) M=0.48, V=0.26 and B= 0.26 mol % (c) M=0.16, V=0.78 and B= 0.06 mol % recorded in COCI3 at 25°C.

40

45

50

55

24 27 60

"W-" }· 1 1 . 26 65

PP•

3.5 3 . 0 2 .5 ' 0 1.5

6 (ppm)

Fig. 5-The expanded a -mcthine and ~-meth y l e ne regions of 20 HSQC NMR spectrum of methacrylonitrile/vi nylidene chloride/ butyl acrylate (M/V/B) terpolymer (M=0.48. V=0.26 and B= 0.26 mol % in terpolymer) in COCI3 at 25°C.

to MmB dyad . Similarly, the cross-peaks at 843.5/L.90 (15) and 843 .5/2.45 (15') ppm are assigned to two protons of M-unit in different environment in MrB dyad. ln MM dyad region , the cross-peaks at 848.0/2.0 (16) and 848.0/2.20 (16') are assigned to MmM dyad, whereas the cross-peak at 848.0/2.10 ( 17) ppm is assigned to MrM dyad.

Further splitting within VB , MY and VV dyads are due to compositional sensitivity . In VB dyad, the cross-peaks at 850.0/2.40 (18), 851.0/2.82 (19) and 850.5/3.08 (20) ppm are assigned to BVBB, VVBB (BVBV) and VVBV tetrads respectively. The cross­peaks at 855 .5/2.70 (21), 854.7/2.95 (22) and 854.0/3.22 (23) ppm in the MY dyad region are due to MMVM, VMVM (MMVV) and VMVM tetrads respectively . Similarly, in VV dyad region, the cross­peaks at 862.5/3.78 (24), 863 .5/3.68 (25) and 864.8/3.58 (26) ppm are assigned to VVVV, MVVV and MVVM tetrads, whereas, the cross-peaks at 862.7/3.60 (27) and 864.0/3.50 (28) ppm are assigned to BVVV and BVVB tetrads. All the assignments (Figs 4 and 5) are shown in Table 2.

After the complete assignment of 13C{ 1H} NMR spectra of M/V /B terpolymer with the help of 20 HSQC spectra, the 1 H NMR spectrum of MIV/B

BRAR eta/.: METHACRYLONITRI LE-VINYLIDENE CHLORIDE-BUTYL ACRYLATE TERPOL YMERS 2071

v B

BB

VB

c<- CH (B)

MV

vv

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

~ .0 3 . 5 3 . 0 2 . 5 2 . 0 1. 5 1.0 0 .5

6 (ppm)

Fig. 6---The 11-! -NMR spectrum of methacry lonitrilc/vinyli dene chloride/butyl acrylate (MIY/B) terpolymer (M=0.48. V=0.26 and B= 0.26 mol % in terpolymer) in CDCI .l at 25°C.

Table 2-- Thc composi ti onal ~nd configurational assignments of methyl, m~thine and met hylene c·arbon resonances from HSQC spectra

of MIV/B tcrpolymcrs

Peak No 'JC (ppm) 111 (pp m) Ass ignments

a-CI-1, I 26.2 1.82 MMM + MMV 2 24.9 1.62 MMB 3 23.5 1.35 BMB 4 25.7 1.72 v 18 5 27.-l 1.95 VMV

a-Ci l 6 .:11.0 2.38 BBB 7 39.5 2.58 MBB 8 37 .0 2.80 MB M 9 40.5 2.90 BBV 10 37.8 3. 12 M13 V II 39.5 3.4R VBV

~CH , 12.12' 37.0 1.63.2. 10 BmB 13 37.0 1.87 BrB 14. 14' -!3.5 1.65,2 .1 2 Mmfl 15.15' 43.5 1.90,2 .45 MrB 16, 16' 48.0 2.00,2.20 MrnM 17 48.0 2.10 MrM 18 50.0 2.40 BVBB 19 5 1.0 2.80 VVBB/BVBV 20 50.5 3.08 VVBV 2 1 55 .5 2.70 MM VM 22 54 .7 2.95 MMVV!VMVM 23 54 .0 3.22 VMVV 24 62.5 3.78 vvvv 25 63.5 3.68 VVV M 26 04.8 3.58 MVVM 27 62.7 3.60 VVV B 28 64.0 3.50 BVVB

' m' stands fo r meso configu ration and 'r' ;tands for racemic confinuration.

terpolymer is assigned. Figure 6 shows the complete ass ignment of 1 H NMR spectrum of MIV /8 terpolymer (M=0.48, V=0.26 and 8=0.26 mol % in the terpolymer) in CDC b . The a -methyl protons in the terpolymer resonate around 81.20-2.00 ppm, while the ~-methy lene protons resona te around 81.60-3.90 pp m. T he spectral region around 82.25-3.60 ppm is ass igned to a -methine proton s of 1H NMR spectrum of M/V /8 terpolymer. The M/V /B terpolymer compos1t1on was determined fro m the quantitati ve 13C{ 1 H} NMR spectra. The terpolymers composition are in good agreement with the calculated values obtained from Goldfinger's eq uation. The co mplex and overlapped 1 H and 13C { 1 H} NMR spectra of terpolymers were resolved without ambi guity with the help of DEPT, 20 HSQC NMR experiments. The 20 HSQC spectra gave correct ass ignment for 1H NMR spectrum of the terpolymer. The methyl , methine and methylene carbon resonances of M/V /8 terpo lymer were assigned up to triad and tetrad co mpos itional and configurational sequences.

Acknowledgement One of the authors, DRP is thankful to the CS IR fo r

providing financial support.

References a) Bovey F A & Mirau P A, NMR of Polymers (Academic Press, New York) 1996.

2072 INDIAN J CHEM, SEC A, OCTOBER 2004

b) Matsuzaki K, Uryu T & Asakura T, NMR Spectroscopy and Stereoregularity of Polymers (Japan Scientific Society Press, Tokyo) 1996. c) Hatada K & Kitayama T, NMR of Polymers (Springer­Verlag-Berlin Heidelberg). 2004.

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9 Odian J L J, Principle r~j" Polymerization (Wiley. New York) 1981.

10 Tonelli A E & Shilling C F. Ace Chem Res, 14 (1981) 233. II Dong L, Hill D J T, 0' Donnell J H & Whittaker A K.

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