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The initiation of polymerization by organoaluminium amides
European Pol~mt'r Journal Vol. 18, pp. 149 to 150, 1982 Printed in Great Britain. All rights reserved
0014-3057/82 020149-02503.00/0 Copyright © 1982 Pergamon Press Ltd
THE I N I T I A T I O N O F P O L Y M E R I Z A T I O N BY O R G A N O A L U M I N I U M AMIDES A. D. JENKINS, J. Z, NYATHI~ and J. D. SMITH School of Chemistry and Molecular Sciences, University of Sussex, Brighton BN1 9Q J, Sussex, England
(Received 24 June 1981} Abstract--Two organoaluminium amides have been used to initiate the polymerizations of methyl methacrylate, acetaldehyde and n-butyraldehyde. Methyl methacrylate polymerized through the vinyl function to give amorphous products. The aldehydes reacted through the carbonyl group at low temperatures with high degrees of stereospecificity to give polymers with substantial crystallinity. The molecular weight of the polyacetaldehyde is very high.
During an extensive investigation [1] of the chemistry of organoaluminium amides, such us [',AIR2(NR~)',,] and [',AIRz(NHR')I,], compounds were prepared which seemed to be worthy of study as potential initiators for polymerizations; we now report a brief survey of the application to the polymerizations of methyl methacrylate (MMA), acetaldehyde and n-butyraldehyde of [ ',AIEt2(NHPri) ', 3] (I) and [',AIEt2 (NMe2)', 2] (IlL EXPERIMENTAL The preparation of (I) [1] and (II) [2] are described elsewhere. MMA was washed with aqueous Na2CO3 and subsequently with water. After rough drying over Na2SO4, it was treated with calcium hydride from which it was distilled as required. Acetaldehyde was purified by treatment (30 min) with NaHCO 3 followed by overnight contact with CaSO4. Immediately before use, samples were removed by distillation through a 75 cm column packed with Fenske helices under an atmosphere of dry N 2, b.p. 20.5'. n-Butyraldehyde was dried over CaSO4 for several days and fractionally distilled as described for acetyladehyde, b.p. 74.0 °. Hydrocarbon solvents were dried over Na wire for several days. For MMA polymerization, the catalysts were dispensed into fragile glass bulbs from which they could be released by applying pressure. Such bulbs were placed in contact with monomer under an atmosphere of dry N2 and adjusted to the desired temperature; the glass bulb was shattered, and the mixture was stirred magnetically. The polymer was precipitated into methanol, dried, dissolved in benzene and reprecipitated in methanol. With aldehyde monomers, the monomer was transferred into a glass ampoule and degassed. After closing the vessel with a Suba Seal, initiator was added through the seal by means of a hypodermic syringe. The ampoule was then sealed with the reactants cooled in liquid N z. Standard i.r., differential scanning calorimetry, X-ray diffraction and viscosity techniques were employed. RESULTS
1. Polymerization of MMA Reactions were carried out either in bulk monomer or with inert hydrocarbon present, as indicated in Table l. Experiments with both initiators over a wide temperature range establish that polymerization only 149
takes place at significant rate at 3 5 and above, and with a rather small temperature-dependence. The i.r. spectra of the polymers produced are very similar to that of conventional poly(methyl methacrylate) generated by a free-radical mechanism, indicating that polymerization involves the vinyl but not the carbonyl group. The C - - H deformation bands at 1265 c m - a the CH3 deformations at 1435-1485 c m - 1, the C - - O - - - C band at 1060 c m - i and the CH 3 asymmetric stretch at 980-990 c m - 1, as well as the 700 and 735 c m - 1 absorptions, are all consistent with an atactic or syndiotactic structure [3]. Debye-Scherrer X-ray powder photographs of the polymer do not show any patterns corresponding to crystallinity, neither is any melting point discernible in the DSC scan. Evidently, the polymer is amorphous.
2. Polymerization of aldehydes Since the ceiling temperature in acetaldehyde polymerization is - 4 0 4 [4], all attempted polymerizations with this monomer or with n-butyraldehyde were conducted below this temperature. The data for acetaldehyde in Table 1 show that at - 7 8 ° the reaction proceeds at a steady rate, at least over the first 10~o conversion. Increasing temperature is conducive to a small increase in polymerization rate up to - 5 2 . 5 ° but it must necessarily decrease again as the ceiling temperature is approached. The two experiments with n-butyraldehyde clearly demonstrate that II is a much more active initiator than I in this system. For all the aldehyde polymers produced in these experiments, carbonyl absorptions are absent from the i.r. spectrum, although C - - O - - - C stretching modes at 1040, 1083, 1122, 1160 and 1187cm -1 are prominent, confirming that the carbonyl group is the locus of polymerization. The i.r. spectrum of the polyacetaldehyde in the region 1450-900 cm-1 agrees with that reported [5] for the stereoregular crystalline polymer. Following Tani et al. I-6-8] who separated crystalline and amorphous polyacetaldehyde by differential solubility, we found that our samples were not appreciably soluble in chloroform, suggesting a high
150
A.D. JENKINS.J. Z. NYATHIand J. D. SMITH Table I. Polymerization data
Initiator
Monomer Initiator
Temperature (°C)
Methyl Methacrylate* ! 99 !
99
!
337
1 1 I i 1
117 61 61 148
I I I
61 30.4 20.6 6.2 100 2500
II !I Acetaldeh.wle II 7680 II 7680 II 7680 II 7680 I1"t" 100 !1 7680 11 7680 n-Butyrahlehyde lli" 147 !:~ 375
-22 - 10 20 20
Time (hr) 1
12 24 24
35 50 60
0.5 0.5 3.0
60 60 60 60 79 61.5
0.5 0.5 0.5 0.5 1 0.5
Conversion (%)
Rate of Polymerization Medium (~o hr-l) I~i hydrocarbon)
0 0 0 0
0 0 0 0
1.1
2.2
2.6 22.O 2.7 3.2 3.6 22.0 7.8 0.3
5.2 7.3 5.4 6.4 7.2 44.0 7.8 0.7
0 0 60 60 20 20 0 20 20 20 0 0 0
- 78 - 78 - 78 - 78 -78 - 62.5 -52.5
21 42 66 92 48 48 21
1.6 3.2 5.0 9.3 5.6 8.9 4.2
0.08 0.08 0.08 0.10 0.12 0.19 0.20
0 0 0 0 50 0 0
-78 - 78
48 48
40.0 1.0
0.83 0.02
50 90
Solvents: *benzene; "tn-pentane; ~n-hexane. degree of stereospecificity in the addition process. Although it has been reported that a bulky side-chain enhances stereoregularity [9, 10], the poly(n-butyraldehyde) was about 55% soluble in ethyl acetate so less than half of this material seems to be stereoregular. Deybe-Scherrer X-ray powder examination of the insoluble aldehyde polymers gave the sharp peaks expected for highly crystalline material. According to Natta et al. ['11] crystalline polyacetaldehyde is necessarily isotactic; the unit cell contains sixteen monomer units with the oxygen atoms embedded in a very compact chain, screened by the methyl groups so as to minimise interaction with a potential solvent. Screening by the DSC technique showed that the polyacetaldehyde decomposes between 107 and 167" with the apex of the curve at 145°; similarly, poly(nbutyraldehyde) decomposes between 127 and 217 °. with the apex at 174 ° . Both these polymers degrade below their melting points, 165 and 225 °, respectively. Although the polyacetaldehyde is almost insoluble, it proved possible to dissolve sufficient of the material in N,N-dimethylformamide to determine the intrinsic viscosity of the polymer as 7 dl g - 1; despite the lack of a quantitative correlation with molecular size, it is clear that the polymer is material of very high molecular weight. CONCLUSIONS Organoaluminium amides were shown 20 years ago
to be ineffective catalysts for polymerization of alkenes [12], but, like many other organoaluminium compounds, they appear to initiate the polymerization of M M A . The stereospecific polymerization of aldehydes is similar to that initiated by the derivatives [~R2AIOCR'NPhI2] [6-8,10]; we have, however, been unable to isolate a crystalline complex between organoaluminium amide and acetaldehyde.
REFERENCES
1. S. Amirkhalili, P. B. Hitchcock, A. D. Jenkins, J. Z. Nyathi and J. D. Smith, J.C.S. Dalton Trans. 377 and references therein (1981). 2. K. Ziegler, Br. Pat. 799 823 (1958). 3. U. Baumann, H. Schreiber and K. Tessmar, Makromolek. Chem. 36, 81 (1959). 4. O. Vogl, J. Polym. Sci. 2A, 4591 (1964). 5. J. Furukawa, T. Saegusa, H. Fujii. A. Kawasaki, H. lmai and Y. Fujii, Makromolek. Chem. 37, 149 (1960). 6. H. Tani, T. Aoyagi and T. Araki, J. Polym. Sci. 2B, 921 0964). 7. H. Tani, H. Yasuda and T. Araki, d. Polym. Sci., 2B, 933 (1964). 8. H. Tani and N. Oguni, J. Polym. Sci. 3B, 123 11965). 9. O. Vogl, J. Polym. Sci. (A) 2, 4607 (1964). 10. H. Yasuda and H. Tani, Macromolecules, 6, 17 and references therein (1973). 11. G. Natta, G. Mazzanti. P. Corradini and I. W. Bassi, Makromolek. Chem. 37, 156 (1960}. 12. K. Ziegler and W-R Kroll. Justus Liebigs Annl. Chem. 629, 167 (1960).
0014-3057/82 020149-02503.00/0 Copyright © 1982 Pergamon Press Ltd
THE I N I T I A T I O N O F P O L Y M E R I Z A T I O N BY O R G A N O A L U M I N I U M AMIDES A. D. JENKINS, J. Z, NYATHI~ and J. D. SMITH School of Chemistry and Molecular Sciences, University of Sussex, Brighton BN1 9Q J, Sussex, England
(Received 24 June 1981} Abstract--Two organoaluminium amides have been used to initiate the polymerizations of methyl methacrylate, acetaldehyde and n-butyraldehyde. Methyl methacrylate polymerized through the vinyl function to give amorphous products. The aldehydes reacted through the carbonyl group at low temperatures with high degrees of stereospecificity to give polymers with substantial crystallinity. The molecular weight of the polyacetaldehyde is very high.
During an extensive investigation [1] of the chemistry of organoaluminium amides, such us [',AIR2(NR~)',,] and [',AIRz(NHR')I,], compounds were prepared which seemed to be worthy of study as potential initiators for polymerizations; we now report a brief survey of the application to the polymerizations of methyl methacrylate (MMA), acetaldehyde and n-butyraldehyde of [ ',AIEt2(NHPri) ', 3] (I) and [',AIEt2 (NMe2)', 2] (IlL EXPERIMENTAL The preparation of (I) [1] and (II) [2] are described elsewhere. MMA was washed with aqueous Na2CO3 and subsequently with water. After rough drying over Na2SO4, it was treated with calcium hydride from which it was distilled as required. Acetaldehyde was purified by treatment (30 min) with NaHCO 3 followed by overnight contact with CaSO4. Immediately before use, samples were removed by distillation through a 75 cm column packed with Fenske helices under an atmosphere of dry N 2, b.p. 20.5'. n-Butyraldehyde was dried over CaSO4 for several days and fractionally distilled as described for acetyladehyde, b.p. 74.0 °. Hydrocarbon solvents were dried over Na wire for several days. For MMA polymerization, the catalysts were dispensed into fragile glass bulbs from which they could be released by applying pressure. Such bulbs were placed in contact with monomer under an atmosphere of dry N2 and adjusted to the desired temperature; the glass bulb was shattered, and the mixture was stirred magnetically. The polymer was precipitated into methanol, dried, dissolved in benzene and reprecipitated in methanol. With aldehyde monomers, the monomer was transferred into a glass ampoule and degassed. After closing the vessel with a Suba Seal, initiator was added through the seal by means of a hypodermic syringe. The ampoule was then sealed with the reactants cooled in liquid N z. Standard i.r., differential scanning calorimetry, X-ray diffraction and viscosity techniques were employed. RESULTS
1. Polymerization of MMA Reactions were carried out either in bulk monomer or with inert hydrocarbon present, as indicated in Table l. Experiments with both initiators over a wide temperature range establish that polymerization only 149
takes place at significant rate at 3 5 and above, and with a rather small temperature-dependence. The i.r. spectra of the polymers produced are very similar to that of conventional poly(methyl methacrylate) generated by a free-radical mechanism, indicating that polymerization involves the vinyl but not the carbonyl group. The C - - H deformation bands at 1265 c m - a the CH3 deformations at 1435-1485 c m - 1, the C - - O - - - C band at 1060 c m - i and the CH 3 asymmetric stretch at 980-990 c m - 1, as well as the 700 and 735 c m - 1 absorptions, are all consistent with an atactic or syndiotactic structure [3]. Debye-Scherrer X-ray powder photographs of the polymer do not show any patterns corresponding to crystallinity, neither is any melting point discernible in the DSC scan. Evidently, the polymer is amorphous.
2. Polymerization of aldehydes Since the ceiling temperature in acetaldehyde polymerization is - 4 0 4 [4], all attempted polymerizations with this monomer or with n-butyraldehyde were conducted below this temperature. The data for acetaldehyde in Table 1 show that at - 7 8 ° the reaction proceeds at a steady rate, at least over the first 10~o conversion. Increasing temperature is conducive to a small increase in polymerization rate up to - 5 2 . 5 ° but it must necessarily decrease again as the ceiling temperature is approached. The two experiments with n-butyraldehyde clearly demonstrate that II is a much more active initiator than I in this system. For all the aldehyde polymers produced in these experiments, carbonyl absorptions are absent from the i.r. spectrum, although C - - O - - - C stretching modes at 1040, 1083, 1122, 1160 and 1187cm -1 are prominent, confirming that the carbonyl group is the locus of polymerization. The i.r. spectrum of the polyacetaldehyde in the region 1450-900 cm-1 agrees with that reported [5] for the stereoregular crystalline polymer. Following Tani et al. I-6-8] who separated crystalline and amorphous polyacetaldehyde by differential solubility, we found that our samples were not appreciably soluble in chloroform, suggesting a high
150
A.D. JENKINS.J. Z. NYATHIand J. D. SMITH Table I. Polymerization data
Initiator
Monomer Initiator
Temperature (°C)
Methyl Methacrylate* ! 99 !
99
!
337
1 1 I i 1
117 61 61 148
I I I
61 30.4 20.6 6.2 100 2500
II !I Acetaldeh.wle II 7680 II 7680 II 7680 II 7680 I1"t" 100 !1 7680 11 7680 n-Butyrahlehyde lli" 147 !:~ 375
-22 - 10 20 20
Time (hr) 1
12 24 24
35 50 60
0.5 0.5 3.0
60 60 60 60 79 61.5
0.5 0.5 0.5 0.5 1 0.5
Conversion (%)
Rate of Polymerization Medium (~o hr-l) I~i hydrocarbon)
0 0 0 0
0 0 0 0
1.1
2.2
2.6 22.O 2.7 3.2 3.6 22.0 7.8 0.3
5.2 7.3 5.4 6.4 7.2 44.0 7.8 0.7
0 0 60 60 20 20 0 20 20 20 0 0 0
- 78 - 78 - 78 - 78 -78 - 62.5 -52.5
21 42 66 92 48 48 21
1.6 3.2 5.0 9.3 5.6 8.9 4.2
0.08 0.08 0.08 0.10 0.12 0.19 0.20
0 0 0 0 50 0 0
-78 - 78
48 48
40.0 1.0
0.83 0.02
50 90
Solvents: *benzene; "tn-pentane; ~n-hexane. degree of stereospecificity in the addition process. Although it has been reported that a bulky side-chain enhances stereoregularity [9, 10], the poly(n-butyraldehyde) was about 55% soluble in ethyl acetate so less than half of this material seems to be stereoregular. Deybe-Scherrer X-ray powder examination of the insoluble aldehyde polymers gave the sharp peaks expected for highly crystalline material. According to Natta et al. ['11] crystalline polyacetaldehyde is necessarily isotactic; the unit cell contains sixteen monomer units with the oxygen atoms embedded in a very compact chain, screened by the methyl groups so as to minimise interaction with a potential solvent. Screening by the DSC technique showed that the polyacetaldehyde decomposes between 107 and 167" with the apex of the curve at 145°; similarly, poly(nbutyraldehyde) decomposes between 127 and 217 °. with the apex at 174 ° . Both these polymers degrade below their melting points, 165 and 225 °, respectively. Although the polyacetaldehyde is almost insoluble, it proved possible to dissolve sufficient of the material in N,N-dimethylformamide to determine the intrinsic viscosity of the polymer as 7 dl g - 1; despite the lack of a quantitative correlation with molecular size, it is clear that the polymer is material of very high molecular weight. CONCLUSIONS Organoaluminium amides were shown 20 years ago
to be ineffective catalysts for polymerization of alkenes [12], but, like many other organoaluminium compounds, they appear to initiate the polymerization of M M A . The stereospecific polymerization of aldehydes is similar to that initiated by the derivatives [~R2AIOCR'NPhI2] [6-8,10]; we have, however, been unable to isolate a crystalline complex between organoaluminium amide and acetaldehyde.
REFERENCES
1. S. Amirkhalili, P. B. Hitchcock, A. D. Jenkins, J. Z. Nyathi and J. D. Smith, J.C.S. Dalton Trans. 377 and references therein (1981). 2. K. Ziegler, Br. Pat. 799 823 (1958). 3. U. Baumann, H. Schreiber and K. Tessmar, Makromolek. Chem. 36, 81 (1959). 4. O. Vogl, J. Polym. Sci. 2A, 4591 (1964). 5. J. Furukawa, T. Saegusa, H. Fujii. A. Kawasaki, H. lmai and Y. Fujii, Makromolek. Chem. 37, 149 (1960). 6. H. Tani, T. Aoyagi and T. Araki, J. Polym. Sci. 2B, 921 0964). 7. H. Tani, H. Yasuda and T. Araki, d. Polym. Sci., 2B, 933 (1964). 8. H. Tani and N. Oguni, J. Polym. Sci. 3B, 123 11965). 9. O. Vogl, J. Polym. Sci. (A) 2, 4607 (1964). 10. H. Yasuda and H. Tani, Macromolecules, 6, 17 and references therein (1973). 11. G. Natta, G. Mazzanti. P. Corradini and I. W. Bassi, Makromolek. Chem. 37, 156 (1960}. 12. K. Ziegler and W-R Kroll. Justus Liebigs Annl. Chem. 629, 167 (1960).