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propylene copolymers by 13C nuclear magnetic resonance
Note to the Editor
Monomer sequence distribution in butene/propylene copolymers by '3C nuclear magnetic resonance A. Bunn and M. E. A. Cudby ICl Plastics Division, Welwyn Garden City, Hertfordshire, UK (Received 27 January 1976)
We wish to report the determination of monomer sequence distribution in butene/propylene copolymers by 13C nuclear magnetic resonance (13C n.m.r.). This is an established technique for the measurement of stereoregularity in homopolymers ~-~° and the measurement of sequence distributions in copolymers 11-21. However, to our knowledge, the only reports of 13C n.m.r, measurements of a-olefin copolymers concern the systems ethylene/a-olefin~S and propylene/ ethylene 16-18. The proton magnetic resonances in polyolefins are severely overlapped and this limits the structural information obtainable. As the resonances in the 13C n.m.r, spectra of polyolefins occur over a range of about 40 ppm we expect this technique to produce more information than proton magnetic resonance. This is indeed the situation for polypropylene s-7, polyethylene lS,22g.4and propylene/ethylene copolymers ~6-1a. Calculated chemical shifts from Lindeman and Adams data 23 predict that the 13C n.m.r, chemical shifts in butene/propylene copolymers would be sensitive to monomer sequence distribution. In this Note, we report 13C n.m.r, data on butene/propylene copolymers including random and block distributions and a copolymer which has a mixture of block and random distributions. The observed resonances are assigned to dyad, triad and tetrad monomer sequences. The natural abundance 13C n.m.r, spectra of polypropylene, polybutene and butene/propylene copolymers were measured in o-dichlorobenzene solution at 140°C. The 25.2 MHz spectra were recorded on a Varian XL100-15 spectrometer equipped with a proton-noise decoupler and a standard VFT-100X Fourier transform system. A 2 sec acquisition time and a 90 ~tsec pulse width (tip angle ~70 °) were used to acquire data. Field-frequency stabilization was provided by D6-dimethyl sulphoxide contained in a 5 mm o.d.n.m.r, tube held centrally in a 12 mm o.d. tube which contained the copolymer solution. Figure 1 shows 13C n.m.r, spectra of polybutene and polypropylene. The assignments of the resonances are also shown on the Figure. Those for polypropylene are known s-7 and those for polybutene were determined from predicted values (Lindeman and Adams data) and an off-resonance experiment. Our own work on poly(a-olefins) higher than polybutene shows that backbone methine and methylene carbon resonances are the most sensitive to tacticity changes and that in the spectra of non-isotactic polymers these resonances are broader than the remaining resonances. As the resonances in the 13C n.m.r, spectra of butene/propylene copolymers examined were equally sharp and in co-
548
POLYMER, 1976, Vol 17, June
polymers with long propylene sequences the propylene amethyl carbon resonance was a singlet and had a chemical shift the same as that found in isotactic polypropylene we feel justified in making the assumption that only a meso addition of either monomer to the polymer chain is made. Copolymers prepared with a wide range of composition and with differing monomer sequence distributions were examined. Representative spectra of the materials are shown in Figures 2 and 3. The resonances in the 13C n.m.r. spectra of these copolymers were assigned by reference to the spectra of the homopolymers, predicted values from Lindeman and Adam's data 23 and by checking that the relative intensities of the resonances were self consistent. Table 1 lists the chemical shift data of the 13C n.m.r, spectra of these copolymers, our proposed assignments and the monomer sequences characterized by each resonance. The letters P and B denote propylene and butene units with any two forming a meso dyad. Thus a PPB triad would contain a
CH bronchCH 2
choinCH
2H
b
H2
ppm
Figure I
13C n.m.r, spectra of (a) polybutene (b) polypropylene
Note to the Editor
a
b
C
I
2734
r
•
nances characteristic of PP, PB and BB dyads show that there are more adjacent butene units than would be predicted for a random copolymer. The presence of three or more adjacent butene units in the copolymer chain is responsible for the 27.00 ppm resonance. The branch-methylene group carbon resonances at 27.00 ppm, 27.18 and 27.34 ppm are characteristic of BBB, BBP and PBP sequences and indicate the blockiness or otherwise of the butene units. Figures 3a-3c show spectra of copolymers E to G. These copolymers contain roughly equal amounts ofbutene and propylene, E and F have spectra with resonance intensities which show that the copolymers are fairly random. The intensities of the resonances in the spectrum of copolymer G (Figure 3c) show that the copolymer does not have a random monomer distribution; this is expected, as its method of preparation would produce long sequence of adjacent propylene units. Features to note in the spectra shown in Figures 3a-3c are the resonances at 27.00 ppm, 27.18 ppm and 27.34 ppm which are characteristic of the three possible butene centred triads, and the three propylene methyl group carbon resonances around 20.7 ppm which are characteristic of the propylene centred triads i.e. PPP, PPB and BPB at 20.96 ppm, 20.74 ppm and 20.60 ppm respectively. Tetrad sequences for propylene/propylene centred units, BPPB, PPPB, PPPP are observed from the backbone methylene carbon resonances at 45.86, 46.10 and 46.40 ppm respectively. The lack of structure on the methine carbon resonances of both butene and propylene units is somewhat surprising, especially as the butene methyl group carbon
d
2734
r
-2718
ppm Figure 2
130 n.m.r, spectra of butene/propylene copolymers (a) 10 molar % propylene as isolated units; (b) 10 molar % propylene as propylene blocks; (c) 10 molar % butene as random copolymer; (d) 10 molar % butene with some butene blocks
b
PP and a PB meso dyad:
-CH2-CH-CH2-CH-CH2-CHI I I CH 3
CH3
c
CH2CH3
Figures 2a-2d show 13C n.m.r, spectra of four copolymers denoted by A-D. Copolymer A is rich in butene and contains isolated propylene units only i.e. BPB. In contrast, copolymer B, although approximately the same overall composition as copolymer A, contains long propylene sequences. The few interchange units give rise to a resonance at 42.76 ppm from the backbone methylene carbon atom. Copolymers C and D are propylene rich and contain approximately 10 molar % butene. Copolymer C has the majority of butene units adjacent to propylene units, i.e. PBP, with the required number of adjacent butene units as is appropriate to a random monomer distribution 2s. For copolymer D, the relative intensities of the methylene carbon reso-
ppm
Figure 3 I3C n.m.r, spectra of butene/propylene copolymers with approximately equal amounts of propylene and butene. Copolymer G (Figure 3c) contains blocks of propylene together with random material
POLYMER, 1976, Vol 17, June 549
Note to the E d i t o r Table I Chemical shift data of the z3C n.m.r, spectra of the copolymers examined Chemical shift from tetramethylsilane (ppm)
REFERENCES 1 2
Assignment, carbon marked with *
Polymer sequences characterized BBB, BBP, PBP BPB BPP PPP BBB BBP PBP PPP, PPB, BPB BBB, BBP, PBP BBBB, BBBP, PBBP
45.86
*CHa-CH2-CH *CH3--CH *CH3-CH *CH3--CH CH3-*CH2-CH CH3-*CH2-CH CH 3--*CH2-CH CHa--*CH CH3-CH2--*CH --CH--*CH2--CH I I Et Et -CH2-CH-*CH2--CH I I Et Me --CH2--CH--*CH--CH I L Et Me --CH--*CH2--CH
46.10
-CH-*CH2--CH--
46.40
--CH--*CH2--CH--
9.92 20.60 20.74 20.96 27.00 27.18 27.34 28.29 34.47 39.64 42.76 43.04
3 4 5 6 7 8 9
PBPP
10 11
BBPB, BBPP and probably also PBPB PPPP
12 13 14 15
Me
PPPB
Me
16 BPPB
17
Me
18 resonances show well def'med shoulders in some of the spectra. These facts indicate to us that the origin of the chemical shift observed on the butene methyl group carbon is not a through bond effect. In conclusion, the above data show that 13C n.m.r. spectroscopy can be used to characterize butene/propylene copolymers in terms of dyad and triad sequences. Well resolved resonances were also observed for propylene/propylene centred tetrads.
19 20 21 22 23 24 25
Schaefer,J. Macromolecules 1971,4, 110 Carman, C. J., Tarpley Jr. A. R. and Goldstein, J. H. Macromolecules 1971,4,445 Inoue, Y., Nishioka, A. and Chujo, R. Polym. J. 1971, 2, 535 Matsuzaki,K., Kanai, T. and Matsumoto, S. J. Polym. Sci. (Polym. Chem. Edn) 1974, 12, 2377 Randall, J. C..]. Polym. Sci. (Polym. Phys. Edn) 1974, 12, 703 lnoue, Y., Nishioka, A. and Chujo, R. Makromol. Chem. 1972, 152, 15 Zambelli, A., Dorman, D. E., Brewster, A. I. and Bovey, F. A. Macromolecules 1973, 6,925 Inoue, Y., Nishioka, A. and Chujo, R. MakromoL Chem. 1972, 156,207 Lapeyre, W., Cheradame, H., Spassky, N. and Sigwalt, P. J. Chim. Phys. 1973, 70,838 Boileau, S. et al. C. R. Acad. Sci. (C) 1972, 275,535 Whipple,E. B. and Green, P. J. Macromolecules 1973, 6, 38 Schaefer,J. Macromolecules 1969, 2,210 Delfini, M., Seagre, A. L. and Conti, F. Macromolecules 1973,6,456 Schaefer,J. Macromolecules 1971,4, 107 Randall, J. C. J. Polym. ScL (Polym. Phys. Edn) 1973, 11, 275 Crain, W. O., Zambelli, A. and Roberts, J. D. Macromolecules 1971,4, 330 ZambeUi,A., Gabbi, G., Sochi, C., Crain, W. O. and Roberts, J. D. Macromolecules 1971,4,475 Carman, C. J. and Wilkes,C. E. Rubber Chem. Technol. 1971, 781 Cornu, C., Roggaro, A. and Salvation, T. Eur. Polym. J. 1974, 10,525 Wu, T. K., Ovenall, D. W. and Reddy, G. S. J. Polym. Sci. (Polym. Phys. Edn) 1974, 2,901 Stejskal, E. O. and Schaefer, J. Macromolecules 1974, 7, 14 Dorman, D. E., Otocka, E. P. and Bovey, F. A. Macromolecules 1972, 5,574 Linderman, L. P. and Adams, J. Q. Anal. Chem. 1971, 43, 1245 Cudby, M. E. A. and Bunn, A. in press Schaefer,J. J. Phys. Chem. 1966, 70, 1975
ERRATUM
'Sequence distribution of cis-1,4 and trans-1,4 units is polyisoprene' by Yasuyuki Tanaka and Hisaya Sato, Polymer 1976, 17, 1 1 3 - 1 1 6 . Page 113, right hand column, line 6: for 15.0 MHz read 20.0 MHz We apologise for this error.
550
P O L Y M E R , 1976, Vol 17, June
Monomer sequence distribution in butene/propylene copolymers by '3C nuclear magnetic resonance A. Bunn and M. E. A. Cudby ICl Plastics Division, Welwyn Garden City, Hertfordshire, UK (Received 27 January 1976)
We wish to report the determination of monomer sequence distribution in butene/propylene copolymers by 13C nuclear magnetic resonance (13C n.m.r.). This is an established technique for the measurement of stereoregularity in homopolymers ~-~° and the measurement of sequence distributions in copolymers 11-21. However, to our knowledge, the only reports of 13C n.m.r, measurements of a-olefin copolymers concern the systems ethylene/a-olefin~S and propylene/ ethylene 16-18. The proton magnetic resonances in polyolefins are severely overlapped and this limits the structural information obtainable. As the resonances in the 13C n.m.r, spectra of polyolefins occur over a range of about 40 ppm we expect this technique to produce more information than proton magnetic resonance. This is indeed the situation for polypropylene s-7, polyethylene lS,22g.4and propylene/ethylene copolymers ~6-1a. Calculated chemical shifts from Lindeman and Adams data 23 predict that the 13C n.m.r, chemical shifts in butene/propylene copolymers would be sensitive to monomer sequence distribution. In this Note, we report 13C n.m.r, data on butene/propylene copolymers including random and block distributions and a copolymer which has a mixture of block and random distributions. The observed resonances are assigned to dyad, triad and tetrad monomer sequences. The natural abundance 13C n.m.r, spectra of polypropylene, polybutene and butene/propylene copolymers were measured in o-dichlorobenzene solution at 140°C. The 25.2 MHz spectra were recorded on a Varian XL100-15 spectrometer equipped with a proton-noise decoupler and a standard VFT-100X Fourier transform system. A 2 sec acquisition time and a 90 ~tsec pulse width (tip angle ~70 °) were used to acquire data. Field-frequency stabilization was provided by D6-dimethyl sulphoxide contained in a 5 mm o.d.n.m.r, tube held centrally in a 12 mm o.d. tube which contained the copolymer solution. Figure 1 shows 13C n.m.r, spectra of polybutene and polypropylene. The assignments of the resonances are also shown on the Figure. Those for polypropylene are known s-7 and those for polybutene were determined from predicted values (Lindeman and Adams data) and an off-resonance experiment. Our own work on poly(a-olefins) higher than polybutene shows that backbone methine and methylene carbon resonances are the most sensitive to tacticity changes and that in the spectra of non-isotactic polymers these resonances are broader than the remaining resonances. As the resonances in the 13C n.m.r, spectra of butene/propylene copolymers examined were equally sharp and in co-
548
POLYMER, 1976, Vol 17, June
polymers with long propylene sequences the propylene amethyl carbon resonance was a singlet and had a chemical shift the same as that found in isotactic polypropylene we feel justified in making the assumption that only a meso addition of either monomer to the polymer chain is made. Copolymers prepared with a wide range of composition and with differing monomer sequence distributions were examined. Representative spectra of the materials are shown in Figures 2 and 3. The resonances in the 13C n.m.r. spectra of these copolymers were assigned by reference to the spectra of the homopolymers, predicted values from Lindeman and Adam's data 23 and by checking that the relative intensities of the resonances were self consistent. Table 1 lists the chemical shift data of the 13C n.m.r, spectra of these copolymers, our proposed assignments and the monomer sequences characterized by each resonance. The letters P and B denote propylene and butene units with any two forming a meso dyad. Thus a PPB triad would contain a
CH bronchCH 2
choinCH
2H
b
H2
ppm
Figure I
13C n.m.r, spectra of (a) polybutene (b) polypropylene
Note to the Editor
a
b
C
I
2734
r
•
nances characteristic of PP, PB and BB dyads show that there are more adjacent butene units than would be predicted for a random copolymer. The presence of three or more adjacent butene units in the copolymer chain is responsible for the 27.00 ppm resonance. The branch-methylene group carbon resonances at 27.00 ppm, 27.18 and 27.34 ppm are characteristic of BBB, BBP and PBP sequences and indicate the blockiness or otherwise of the butene units. Figures 3a-3c show spectra of copolymers E to G. These copolymers contain roughly equal amounts ofbutene and propylene, E and F have spectra with resonance intensities which show that the copolymers are fairly random. The intensities of the resonances in the spectrum of copolymer G (Figure 3c) show that the copolymer does not have a random monomer distribution; this is expected, as its method of preparation would produce long sequence of adjacent propylene units. Features to note in the spectra shown in Figures 3a-3c are the resonances at 27.00 ppm, 27.18 ppm and 27.34 ppm which are characteristic of the three possible butene centred triads, and the three propylene methyl group carbon resonances around 20.7 ppm which are characteristic of the propylene centred triads i.e. PPP, PPB and BPB at 20.96 ppm, 20.74 ppm and 20.60 ppm respectively. Tetrad sequences for propylene/propylene centred units, BPPB, PPPB, PPPP are observed from the backbone methylene carbon resonances at 45.86, 46.10 and 46.40 ppm respectively. The lack of structure on the methine carbon resonances of both butene and propylene units is somewhat surprising, especially as the butene methyl group carbon
d
2734
r
-2718
ppm Figure 2
130 n.m.r, spectra of butene/propylene copolymers (a) 10 molar % propylene as isolated units; (b) 10 molar % propylene as propylene blocks; (c) 10 molar % butene as random copolymer; (d) 10 molar % butene with some butene blocks
b
PP and a PB meso dyad:
-CH2-CH-CH2-CH-CH2-CHI I I CH 3
CH3
c
CH2CH3
Figures 2a-2d show 13C n.m.r, spectra of four copolymers denoted by A-D. Copolymer A is rich in butene and contains isolated propylene units only i.e. BPB. In contrast, copolymer B, although approximately the same overall composition as copolymer A, contains long propylene sequences. The few interchange units give rise to a resonance at 42.76 ppm from the backbone methylene carbon atom. Copolymers C and D are propylene rich and contain approximately 10 molar % butene. Copolymer C has the majority of butene units adjacent to propylene units, i.e. PBP, with the required number of adjacent butene units as is appropriate to a random monomer distribution 2s. For copolymer D, the relative intensities of the methylene carbon reso-
ppm
Figure 3 I3C n.m.r, spectra of butene/propylene copolymers with approximately equal amounts of propylene and butene. Copolymer G (Figure 3c) contains blocks of propylene together with random material
POLYMER, 1976, Vol 17, June 549
Note to the E d i t o r Table I Chemical shift data of the z3C n.m.r, spectra of the copolymers examined Chemical shift from tetramethylsilane (ppm)
REFERENCES 1 2
Assignment, carbon marked with *
Polymer sequences characterized BBB, BBP, PBP BPB BPP PPP BBB BBP PBP PPP, PPB, BPB BBB, BBP, PBP BBBB, BBBP, PBBP
45.86
*CHa-CH2-CH *CH3--CH *CH3-CH *CH3--CH CH3-*CH2-CH CH3-*CH2-CH CH 3--*CH2-CH CHa--*CH CH3-CH2--*CH --CH--*CH2--CH I I Et Et -CH2-CH-*CH2--CH I I Et Me --CH2--CH--*CH--CH I L Et Me --CH--*CH2--CH
46.10
-CH-*CH2--CH--
46.40
--CH--*CH2--CH--
9.92 20.60 20.74 20.96 27.00 27.18 27.34 28.29 34.47 39.64 42.76 43.04
3 4 5 6 7 8 9
PBPP
10 11
BBPB, BBPP and probably also PBPB PPPP
12 13 14 15
Me
PPPB
Me
16 BPPB
17
Me
18 resonances show well def'med shoulders in some of the spectra. These facts indicate to us that the origin of the chemical shift observed on the butene methyl group carbon is not a through bond effect. In conclusion, the above data show that 13C n.m.r. spectroscopy can be used to characterize butene/propylene copolymers in terms of dyad and triad sequences. Well resolved resonances were also observed for propylene/propylene centred tetrads.
19 20 21 22 23 24 25
Schaefer,J. Macromolecules 1971,4, 110 Carman, C. J., Tarpley Jr. A. R. and Goldstein, J. H. Macromolecules 1971,4,445 Inoue, Y., Nishioka, A. and Chujo, R. Polym. J. 1971, 2, 535 Matsuzaki,K., Kanai, T. and Matsumoto, S. J. Polym. Sci. (Polym. Chem. Edn) 1974, 12, 2377 Randall, J. C..]. Polym. Sci. (Polym. Phys. Edn) 1974, 12, 703 lnoue, Y., Nishioka, A. and Chujo, R. Makromol. Chem. 1972, 152, 15 Zambelli, A., Dorman, D. E., Brewster, A. I. and Bovey, F. A. Macromolecules 1973, 6,925 Inoue, Y., Nishioka, A. and Chujo, R. MakromoL Chem. 1972, 156,207 Lapeyre, W., Cheradame, H., Spassky, N. and Sigwalt, P. J. Chim. Phys. 1973, 70,838 Boileau, S. et al. C. R. Acad. Sci. (C) 1972, 275,535 Whipple,E. B. and Green, P. J. Macromolecules 1973, 6, 38 Schaefer,J. Macromolecules 1969, 2,210 Delfini, M., Seagre, A. L. and Conti, F. Macromolecules 1973,6,456 Schaefer,J. Macromolecules 1971,4, 107 Randall, J. C. J. Polym. ScL (Polym. Phys. Edn) 1973, 11, 275 Crain, W. O., Zambelli, A. and Roberts, J. D. Macromolecules 1971,4, 330 ZambeUi,A., Gabbi, G., Sochi, C., Crain, W. O. and Roberts, J. D. Macromolecules 1971,4,475 Carman, C. J. and Wilkes,C. E. Rubber Chem. Technol. 1971, 781 Cornu, C., Roggaro, A. and Salvation, T. Eur. Polym. J. 1974, 10,525 Wu, T. K., Ovenall, D. W. and Reddy, G. S. J. Polym. Sci. (Polym. Phys. Edn) 1974, 2,901 Stejskal, E. O. and Schaefer, J. Macromolecules 1974, 7, 14 Dorman, D. E., Otocka, E. P. and Bovey, F. A. Macromolecules 1972, 5,574 Linderman, L. P. and Adams, J. Q. Anal. Chem. 1971, 43, 1245 Cudby, M. E. A. and Bunn, A. in press Schaefer,J. J. Phys. Chem. 1966, 70, 1975
ERRATUM
'Sequence distribution of cis-1,4 and trans-1,4 units is polyisoprene' by Yasuyuki Tanaka and Hisaya Sato, Polymer 1976, 17, 1 1 3 - 1 1 6 . Page 113, right hand column, line 6: for 15.0 MHz read 20.0 MHz We apologise for this error.
550
P O L Y M E R , 1976, Vol 17, June