Characterisation of glycidylmethacrylate/methacrylonitrile copolymers by NMR spectroscopy
A.S. Brar*, Anil Yadav
Department of Chemistry, Indian Institute of Technology, Delhi, Hauz Khas, New Delhi 110016, India Received 25 December 2000; accepted 24 January 2001
Abstract
Glycidylmethacrylate/methacrylonitrile (G/M) copolymers of different compositions were prepared and a copolymer compo- sition was obtained from quantitative 13C NMR spectroscopy. Reactivity ratios for comonomers were calculated using the Kelen-Tudos (KT) and non linear error in variable (EVM) methods. The reactivity ratios obtained from KT and EVM are TQ = 1.14 ± 0.1, rM = 0.76 ± 0.06 and rG = 1.12, rM = 0.75, respectively. Complete spectral assignment of 13C- and 'H- NMR spectra were done with the help of Distortionless Enhancement by Polarization Transfer (DEPT) and 2D " C - ' H heteronuclear single quantum coherence (HSQC).
Keywords: Glycidylmethacrylate/methacrylonitrile (G/M) copolymers; 2D NMR studies; Sequence distribution
1. Introduction
2D NMR spectroscopy has been used for deter- mining the compositional [1-3] and configurational [4-7] sequence of the polymers. GMA based copoly- mers are receiving great attention due to the presence of reactive epoxide ring, which offers it an opportu- nity to enter into a wide range of chemical reactions [8,9]. The GMA based copolymers have been used for binding drugs, biomolecules [10] and in electronics industries as negative electron beam resists [11].
Microstructure of copolymers of GMA with alkyla- crylate, vinylacetate, A^-vinylpyrrolidone, and acrylo- nitrile have already been reported [12-15]. The microstructure of methacrylonitrile/methylmethacry- late copolymer by ID NMR spectroscopy has also
been reported [16]. To the best of our knowledge the microstructure of glycidylmethacrylate/methacry- lonitrile (G/M) copolymer has not been reported so far. In this article, we report the complete assignment of lH- and 13C{ !H}-NMR spectra of G/M copolymers in terms of compositional and configurational sequences with the help of ID ("Cj'H})- and 2D HSQC-NMR experiments. The vicinal couplings in the copolymer were studied by 2D-1H-1H Total Correlation Spectroscopy (TOCSY). Reactivity ratios for comonomers were calculated using the Kelen- Tudos (KT) [17] and non-linear error in variable (EVM) [18] methods, using compositional data.
2. Experimental section
GMA (Merck) was distilled under reduced pressure and methacrylonitrile(Merck) was distilled by ordinary distillation and both the monomers were then stored below 5°C. A series of G/M copolymers containing different mol% of GMA in feed were
Table 1
The feed in mol fraction and copolymer composition data of G/M copolymers./0 and/M are the mole fractions of G- and M-comono- mers, respectively in feed. FG and FM are the mole fractions of G- and M-comonomers, respectively in the copolymer
Sample
GM1 GM2 GM3 GM4 GM5 GM6
Feed /o
0.20 0.25 0.35 0.40 0.45 0.60
in mol fraction
/ M
0.80 0.75 0.65 0.60 0.55 0.40
Copolymer composition Fa
0.24 0.29 0.41 0.45 0.50 0.64
FM
0.76 0.71 0.59 0.55 0.50 0.36
prepared by bulk polymerisation at 60°C using benzoyl peroxide as an initiator. The conversion was kept below 10% by precipitating the copolymer in methanol. The copolymers were further purified by
using CHCVmethanol system. The copolymer composition was determined experimentally by quantitative ^Cj^H} NMR spectroscopy using the standard pulse program where repetition time was kept at 10s. The various lD^H, 13C{JH}, DEPT), 2D(HSQC, TOCSY) NMR experiments were done in CDC13 on Bruker 300 MHz DPX spectrometer using different standard pulse sequences. The other related details are given in our earlier papers [19-21].
3. Results and discussion
3.1. Copolymer composition and reactivity ratios determination
The composition of G/M copolymers was deter- mined from quantitative 13C{ !H} NMR spectroscopy.
mr+GGM
ppm 180 160 140 120 100 80 60 40 20 (a)
Fig. 1. (a) The "Cf'H} NMR spectrum of G/M copolymer (FG = 0.50); (b) Expanded nitrile carbon region; (c) Expanded carbonyl carbon region.
A.S. Brar, A. Yadav /Journal of Molecular Structure 602-603 (2002) 29-39 31
ppn
50 40 30T
Fig. 2. The DEPT-135 spectram of G/M copolymer (FG = 0.50) in CDC13.
20
The mole fraction of monomers in feed and copo- lymer are as shown in Table 1. The copolymers composition data were used to determine the term- inal model reactivity ratio (KT method). These initial estimates of reactivity ratios, along with the copolymer composition data were used for the calculation of reactivity ratios by EVM. The errors in determining the monomer composition in feed and in copolymer were estimated to be 3%. The value of reactivity ratios as obtained from KT [17] and EVM method [18] are rG = 1.14 ± 0.1, rM = 0.76 ± 0.06 and rG = 1.12, rM = 0.75 respectively, which are in agreement with each other.
3.2. 13C{'H} NMR and 'H NMR studies
The 13C{ !H} NMR spectrum of G/M copolymer (FG = 0-50 in copolymer) in CDCI3 is shown in Fig.
l(a) along with the complete signal assignments. The extent of overlap of a-methyl group of G- and M- units, epoxy methylene, (3-methylene and epoxy methine carbon signals cannot be ascertained from
" C l ' H } NMR spectrum alone, and so DEPT-135 spectra and 2D HSQC NMR experiments are used to assign them. The carbonyl and nitrile carbon reso- nances are assigned around 8 174.5-178.0 and 122.35-124.3 ppm, respectively. The spectral region around 8 16.0-66.5 ppm is very complex and
«-CH3(G)
°—^_
MmGmM MrGmM
30 28 26 24 22
S(ppm)
20 16
Fig. 3. Expanded "Cf'H} spectrum showing a-methyl carbon signal in (a) poly(glycidylmethacrylate) copolymer with composition FG, (b) 0.64, (c) 0.50, (d) 0.24 and (e) poly(methacrylonitrile).
A.S. Brar, A. Yadav /Journal of Molecular Structure 602-603 (2002) 29-39 33 Table 2
Assignment of resonance signals of 13C NMR spectra recorded in CDC13 to a-CH3 groups of M- and G-centered sequences S. no. Chemical shift (S), ppm Assignment 1
2 3 4 5 6 7 8 9 10 11 12 14 15 16
16.9 18.9 16.65 18.6-19.55 20.6-21.4 17.5-18.6 19.55-20.6 21.4-22.5 23.8-25.0 25.0-25.6 25.8 23.5-24.7 26.75-27.7 22.5-23.5 27.7-29.0
GrGrG GrGmG MrGrG MmGrG MmGmG MrGrM MrGmM MmGmM MrMrM MrMmM MmMmM GrMrM GmMmM GrMrG GmMmG
overlapped and can be assigned to aliphatic carbons in the main and side chain of the copolymer. The over- lapped carbon signals can be resolved by employing the DEPT-135 NMR (Fig. 2) where methylene carbon signals appear in negative phase and methine and methyl carbon signals appear in positive phase. The -OCH2, epoxy methylene and epoxy methine carbon signals appear around 8 66.0, 44.5, 48.8 ppm respec- tively. The (3-methylene carbon of both methacrylo- nitrile and GMA unit resonate around 8 45.5-55.0 ppm.
The signals around 8 32.8 and 49.0 ppm are assigned to quaternary carbons of methacrylonitrile and glycidylmethacrylate, respectively. The signals around 8 16.3-29.0 ppm are assigned to a-methyl carbons of both GMA and methacrylonitrile units in the copolymer.
The expanded " C ^ H } NMR spectrum of the nitrile group carbon resonance of G/M copolymers is shown in Fig. l(b). In this region, the signals around 8 122.4-122.95, 122.95-123.3 and 123.3- 124.25 ppm are assigned to MMM, MMG and GMG compositional triads sequences respectively, by comparing with poly(methacrylonitrile) ^Cj^H}
NMR spectrum. The expanded carbonyl region in the copolymer is shown in Fig. l(c). The three broad signals around 8 174.5-175.75, 175.75-176.7 and 8 176.7-178.0 ppm are assigned to mm, rm and rr configurational sequences by comparing them with
13C{ !H} NMR spectrum of poly (glycidylmethacryl-
ate). These three broad envelopes show variation in intensity with copolymer composition, which shows that resonance signals around 8 174.5-176.7 ppm are not pure configurational but are rather overlapped with compositional sequences. The signals around 8 174.75-175.75 ppm shows increase in intensity with decrease in G-content in the copolymer, while signals around 8 176.7-178.0 ppm shows decrease in inten- sity with decrease in G-content in G/M copolymer.
This shows that signals around 8 174.5-175.75 ppm have predominant concentration of MGM copolymer compositional sequences in the copolymer, while signals around 8 176.7-178.0 ppm does not have the copolymer compositional sequences.
The a-methyl region in 1D(!H and 13C{ !H})-NMR spectrum is quite complex and overlapped. The 13C resonances of the a-methyl groups for several copo- lymer samples of different feed composition and the corresponding homopolymer are as shown in Fig. 3.
The a-methyl resonances of poly(methacrylonitrile) and poly(glycidylmethacrylate) are susceptible to analysis in terms of configurational sequences, and the chemical shift of these two are different. The spectra of copolymers present signals present in homopolymers along with some new signals not present in homopolymers. All the signals could be assigned to G- and M-centered compositional and stereochemical configurational sequences. The assignments to various signals are done by compar- ison with the homopolymer spectrum and by obser- ving the changes in signal intensity with change in the copolymer composition. The a-methyl region can be divided into two broad G- and M-centered envelopes.
The G-centered envelope ranges from 8 16.3-22.5 and M-centered envelope ranges from 8 22.5- 29.0 ppm.
In the G-centered a-methyl region, the signals at 8 16.9 and 18.9 ppm are assigned to GrGrG and GrGmG respectively, by comparing with the assign- ments done in homopolymer 13C{ !H} NMR spectrum.
The signals around 8 16.65, 18.55-19.55 and 20.6- 21.4 ppm, which first shows an increase and then a decrease in intensity with decrease in G-content in the copolymer is assigned to GrGrM, GrGmM and GmGmM, respectively. The signals around 8 17.5- 18.6, 18.6-20.6 and 21.4-22.5 ppm, which shows increase in the intensity with increase in M-content (decrease in G-content) in the copolymer are assigned
Table 3
The compositional and configurational assignments of the G/M copolymers
Peak no.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
from 2D HSQC NMR spectrum
13C (ppm)
16.8 18.9 21.1 16.65 18.5 21.0 18.65 20.3 21.8 25-27 24.0 24.8 26.8 22.5 25.1 28.2 50.0 50.0 50.0 52.0 52.0 52.0 53.4 53.4 53.4
!H (ppm)
0.98 1.1 1.3 0.93 1.3 1.49 1.4 1.67 1.7 1.78-1.9 1.45 1.54 1.62 1.18 1.28 1.43 1.75 1.97 2.18 1.73 2.00 2.19 1.67 1.99 2.19
Assignments a-CH3
GrGrG GrGmG GmGmG MrGrG MmGrG MmGmG MrGrM MrGmM MmGmM MMM GrMrM GrMmM GmMmM GrMrG GrMmG GmMmG (3-CH2
MmM MrM MmM MmG MrG MmG GmG GrG GmG
Table 4 TOCSY Peak no.
1
2
3 4 5 6 7 8 9 10 11 12
' H - ' H shift correlations Proton (ppm) O-CH2) in GG dyad in h - t linkage (1.6) O-CH2) in GM dyad in h - t linkage (1.7) (CH2)ed (2.7) (CH2)ed (2.7) (CH2)ed (2.7) (CH2)ed (2.7) (CH2)e° (2.85) (CH2)e° (2.85) (CH2)e° (2.85) (CH)e (3.29) (CH)e (3.29) (OCH2)b (3.86)
Coupled to proton (ppm) 2.15 (geminal)
2.25 (geminal)
(CH2)e° (2.9) (CH)e (3.29) (OCH2)b (3.85) (OCH2)a (4.45) (CH)e (3.29) (OCH2)b (3.85) (OCH2)a (4.45) (OCH2)b (3.85) (OCH2)a (4.45) (OCH2)a (4.45)
assignments done on the basis of 13C NMR are further confirmed by 2D HSQC
shown in Table 3, Fig. 5(a)
3.3. 2D-NMR studies
3.3.1. i The
(rmnn
HSQC studies expanded 2D HSQC
n f hnfh O - a n d M - m
NMR assignments as is and (b).
NMR spectra of a-methyl
nif are, shown in FIST ^i(a\
to MrGrM, MmGrM amd MmGmM respectively. In the M-centered a-methyl region, the signals around 8 23.8-25.0, 25.0-25.6 and 25.8 ppm are assigned to MrMrM, MmMrM and MmMmM, respectively, by comparison with the assignments done in homopo- lymer ^Cj^H} NMR spectrum. The signals around 8 23.5-24.7 and 26.75-27.7 ppm, which first shows a relative increase and then a decrease in intensity with increase in M-content in the copolymer are assigned to MrMrG, and MmMmG respectively.
The resonance signals around 8 22.5-23.5 and 27.7-29.0 ppm which decrease in intensity with increase in M-content in the copolymer are assigned to GrMrG, and GmMmG, respectively. The triad sequences GmMrM and GmMrG are difficult to assign accurately as they overlap with the MmMrM and MrMrM homopolymer region. The chemical shift of main NMR signals along with corresponding assignment is given in Table 2. The various a-CH3
and (b) (FG = 0.64 and 0.24 in copolymer). The a- methyl group in both units shows both compositional and configurational sensitivity. The cross peak at 8 16.8/0.98(1), 18.9/1.1(2) and 21.1/1.3(3) ppm are assigned to GrGrG, GrGmG and GmGmG respec- tively, on basis of the assignments done in poly(gly- cidylmethacrylate) HSQC NMR spectrum. The other cross-peaks in G-centered a-methyl region are assigned on the basis of change in intensity with change in copolymer compositions. The cross peaks at 8 16.65/0.93(4), 18.5/1.3(5) and 21.0/1.49(6) ppm which decrease in intensity with decrease in the G- content in the copolymer are assigned to GrGrM, GrGmM and GmGmM respectively, while the cross peaks around 8 18.65/1.4(7), 20.3/1.67(8) and 21.8/
1.7(9) ppm which increase in intensity with decrease in the G-content (increase in M-content) are assigned to MrGrM, MmGrM amd MmGmM respectively. It is to be noted that the cross peak around 8 17.5-19.9/
1.26-1.4 ppm is assigned collectively to triad
A.S. Brar, A. Yadav / Journal of Molecular Structure 602-603 (2002) 29-39 35
O
Q
-15
-20
30
-15
-20
125
-30
2-0 1.5 1.0 0-5 2.0 1-5 1.0 0-5 S(ppm) 6(ppm)
( a ) (b)
Fig. 5. The expanded methyl region in 2D HSQC NMR spectrum of G/M copolymers of composition FG: (a) 0.64, (b) 0.24.
sequences GrGmM and MrGrM. This assignment is done on the basis of observation that, in Fig. 5(a) (FQ = 0.64), the cross peak is most intense at 8 18.5/1.3 ppm and this is assigned to GrGmM, while in Fig. 5(b) (FG = 0.24), the cross peak is most intense at 8 18.65/1.4 ppm and this is assigned to MrGrM. Similarly, the region around 8 20.0-22.4/
1.58-1.72 ppm is assigned collectively to MrGmM and MmGmM by observing the change in intensity with the change in composition.
The a-methyl group of M-unit is further assigned to compositional and configurational sequences. The cross peaks region around 8 25.0-27.0/1.78- 1.9(10) ppm are assigned to the MMM triad sequence by comparing with the poly(methacrylonitrile) 2D HSQC NMR spectrum. The other cross-peaks in M- centered a-methyl region are assigned on the basis of change in intensity with change in the copolymer composition. The cross peaks at 8 24.0/1.45(11), 24.8/1.54(12) and 26.8/1.62(13) ppm are assigned to MrMrG, MrMmG and MmMmG respectively, while the cross peaks at 8 22.5/1.18(14), 25.3/1.28(15) and 28.2/1.43(16) ppm which shows increase in intensity with G-content in the copolymer are assigned to GrMrG, GrMmG and GmMmG respectively. The
cross peak intensities in 2D HSQC NMR spectra show that, triad sequences in the copolymers with greater M-content shows more preference for mm configuration. The various a-CH3 assignments done on the basis of 2D HSQC NMR, are shown in Table 3.
The (3-CH2 region, due to its symmetry is sensitive to dyad, tetrad, etc. This region is divided into broad MM, MG and GG dyads on the basis of change in intensity of signals with change in the copolymer composition. These three dyads are assigned around 8 48.0-51.0, 51.0-52.5 and 52.5-54.5 ppm respec- tively. These dyads show further splittings into three cross peaks along the proton axis due to stereoche- mical configurations. The meso-configuration gives two peaks because the two methylene protons lie in different environment and racemic gives one cross peak lying in between the two cross peaks corre- sponding to meso configurations. The two cross peaks at 8 50.0/1.75(17) and 50.0/2.18(19) ppm in MM dyad are due to meso configuration and the cross peak at 8 50.0/1.97(18) ppm is due to racemic configuration. Similarly, the cross peaks at 8 52.0/
1.73(20) and 52.0/2.19(22) ppm in MG dyad and that at 8 53.4/1.67(23) and 53.4/2.19(25) ppm in GG dyad corresponds to meso configuration and the cross
A.S. Brar, A. Yadav / Journal of Molecular Structure 602-603 (2002) 29-39 37
CH3
-fOH2-C
I Hb H
Ha
,Hd
CH3
-H-CH2-C
CN
« - C H3( G + M )
'—I—'
1.5 5.0 4-5 U.Q 3-5 3-0 2.5
6(ppm)
2.0 1.0 0-5
Fig. 6. The !H NMR spectrum of G/M copolymer (FG — 0.50) in CDC13.
peaks at 8 52.0/2.19(22) and 53.4/1.99(24) ppm are due to MrG and GrG respectively. All these assign- ments are shown in 2D HSQC NMR spectrum (FG = 0.50 in copolymer), Fig. 4 (Table 3).
The cross peak at 8 49.0/3.28 ppm is assigned to the epoxy methine group of the copolymer. The - OCH2 methylene protons that are adjacent to the chiral centre in G/M copolymer shows diastereo- merism and gives two crosspeaks at 8 66.0/3.89 and 66.0/4.5 ppm. Similarly, the epoxy methylene proton signal also gives two cross peaks at 8 44.5/2.7 and 44.5/2.9 ppm respectively as shown in Fig. 4.
3.3.2. 2D TOCSY studies
The proton spectrum along with complete assign- ments is shown in Fig. 6 (FG = 0.50). Once " C ^ H } NMR spectrum is assigned completely, the various overlapped resonance signals in !H NMR spectrum are assigned by one to one correlation between carbon and proton with the help of 2D HSQC NMR spectra.
In order to understand the connectivity and confirm the various couplings in the polymer chain, the TOCSY spectrum was recorded. Three and four bond couplings between the protons of different directly coupled groups in G/M copolymer can be clearly seen in TOCSY experiments in the long mixing time (80 ms) as shown in Fig. 7 (FG = 0.50) (Table 4). The crosspeaks at 8 1.6/2.15 (1) and 1.7/
2.25(2) ppm are due to geminal coupling of (3-CH2
protons in GG and GM dyads in head to tail linkage.
The cross peaks at 8 2.7/2.9(3), 2.7/3.29(4), 2.7/
3.85(5) and 2.7/4.45(6) ppm are assigned to couplings between protons 'd' with 'c', 'd' with epoxymethine, 'd' with 'b' and 'd' with 'a' protons, respectively.
Similarly, the coupling between proton 'c' with epoxy- methine, 'c' with 'b' and 'c' with 'a' protons are assigned at 8 2.85/3.29(7), 2.85/3.85(8) and 2.85/
4.45(9) ppm respectively. The cross peak at 8 3.29/
3.85(10) and 3.29/4.45(11) ppm are due to coupling of epoxymethine proton with proton 'b' and with proton
UQ U
o
•z
inU
o
A.S. Brar, A. Yadav /Journal of Molecular Structure 602-603 (2002) 29-39 39
'a', respectively. The cross peak at 8 3.86/
4.45(12) ppm is due to the coupling between diastereo- meric protons 'b' and 'a'.
4. Conclusions
The reactivity ratios of GMA/methacrylonitrile copolymer system are rG = 1.12 and rs = 0.75. The various lDC'H, 13CCR}, DEPT) and 2D(HSQC, TOCSY) NMR spectroscopic techniques are used to resolve the broad and overlapped signals in !H and
^Cj'H} NMR spectra. Carbonyl and nitrile carbon resonance are assigned to triad sequences, a-methyl to triad pentad compositional and configurational sequence and the methylene carbon resonances were assigned to dyad sequence with the help of 2D HSQC NMR spectrum.
Acknowledgements
The authors wish to thank the Council of Scientific and Industrial Research for providing the financial support to carry out this work.
References
[1] J.M.J. Frechet, E. Bald, F. Svec, React. Polym. 1 (1985) 21.
[2] D. Lindsay, D.C. Sherrington, React. Polym. 3 (1985) 27.
[3] P.K. Dhal, G.N. Babu, S. Sudhakaran, P.S. Borkar, J.Polym.
Sci., Polym. Chem. Ed. 23 (1985) 319.
[4] P.K. Dhal, G.N. Babu, S. Sudhakaran, S.P.S. Borkar, Makromol. Chem., Rapid Commun. 6 (1985) 91.
[5] F.L. Thomson, L. Yau, E.M. Doerries, J. Electrochem. Soc.
126 (1979) 1703.
[6] P.K. Dhal, G.N. Babu, A. Steigel, Polymer 30 (1989) 1530.
[7] F.A. Bovey, L. Jelinski, P.A. Mirau, Nuclear Magnetic Reso- nance spectrum, Academic Press, New York, 1988.
[8] J. Kalal, F. Svec, V. Marousek, J. Polym. Sci. Symp. 47 (1974) 155.
[9] D.A. Tomalia, in: R.H. Yocum, E.B. Nuquist (Eds.), Func- tional Monomers, vol. 2, Dekker, New York, 1974.
[10] J. Kalal, J. Polymer Sci. Polym. Symp. 62 (1978) 251.
[11] E.D. Feit, M.E. Wurtz, G.W. Kammlott, J. Vac. Sci. Technol.
15 (1978) 944.
[12] T.C. Hunter, G. Price, J. Polymer 35 (1994) 3530.
[13] P.K. Dhal, G.N. Babu, R.K. Nanda, Macromolecules 17 (1984) 1131.
[14] A.S. Brar, Shiv Charan, J. Polym. Sci., Part A: Polym. Chem.
34 (1996) 333.
[15] A.S. Brar, K. Dutta, Macromolcules 31 (1998) 4695.
[16] Julio San Roman, Blanca Vazquez, Migel Valero, Gonzalo Martin Guzman, Macromolecules 24 (1991) 6089.
[17] T. Kelen, F.J. Tudos, Macromol. Chem. A9 (1975) 1.
[18] M. Dube, R.A. Sanyel, A. Penlidis, K.F. O'Driscoll, P.M.
Reilly, J. Polym. Sci., Polym. Chem. Ed. 29 (1991) 703.
[19] A.S. Brar, K. Dutta, Macromol. Chem. Phy. 199 (1998) 2005.
[20] A.S. Brar, K. Dutta, G.S. Kapur, Macromolecules 28 (1995) 8735.
[21] K. Dutta, A.S. Brar, J. Polym. Sci., Polym. Chem. 28 (1999) 3922.
