Butadiene polymerisation using binary neodymium-based catalyst systems. The effect of catalyst preparation

Butadiene polymerisation using binary neodymium-based catalyst systems. The effect of catalyst preparation

Eur. Pofym. J. Vol. 33, No. 6. pp. 81l-814. 1997 0 1997ElscvierScience Ltd. All rights reserved Printed in Great Britain PII: s0014-3057(%)00289-3 OOW...

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Eur. Pofym. J. Vol. 33, No. 6. pp. 81l-814. 1997 0 1997ElscvierScience Ltd. All rights reserved Printed in Great Britain PII: s0014-3057(%)00289-3 OOW3057/97 517.00+ 0.00

BUTADIENE POLYMERISATION USING BINARY NEODYMIUM-BASED CATALYST SYSTEMS. THE EFFECT OF CATALYST PREPARATION HORIA IOVU’,*, GHEORGHE

HUBCA’, EUGENIA SIMIONESCU’, and JOHN S. HURST’

ELENA BADEA’

‘Polytechnic University, Department of Polymer Technology, Faculty of Industrial Chemistry, Calea Victoriei 149, 71 IOI-Bucharest, Romania *The Manchester Metropolitan University, Dept of Materials Techology, Manchester Ml 5GD, U.K. (Received 24 May 1996; accepted 2 August 1996)

Abstract-The influence pf preparation conditions on the activity of NdC1,.3TBP-TIBA catalysts for the polmerisation of butadiene have been investigated. The highest catalysts activities and resulting polymer molecular masses have been found where the catalyst is “preformed” in the presence of precise and small amounts of butadiene (molar ratio [Butadiene]/[Nd] = 2) and is aged for 1hr at 20°C. Polybutadienes with a 1,4-cis content of 98-99% are readily achieved irrespective of the method of catalyst preparation. The enhanced reactivity of the “preformed” catalyst is explained in terms of a stable n-allylic complex involving the butadiene unit. 0 1997 Elsevier Science Ltd

EXPERIMENTALPROCEDURES

lNTRODUCTlON

Catalysts based on rare earth complexes, especially those based on neodymium, are well known for their ability to polymerise 1,3-butadiene (Bu) to give a polymer of high 1,4-cis content( > 97%) [l]. In particular, two types of neodymium system are used: (1) the binary system consisting of AIR, and a neodymium complex of the type NdC&.nL, where the ligand L can be alcohol, ester of phosphoric acid, hydroxyaldehyde or hydroxyketone [2]; (2) the ternary system Nd(OCOR)X/AIEt2Cl/Al(iBu), (Et = ethyl, iBu = isobutyl) where R is bulky and offers intense steric hindrance (e.g. R = 2-ethyl hexanoate, versatate or naphthenate [l]). The use of the binary system is sometimes preferred because of its ease of handling. Very few authors appear to have undertaken a detailed study of the influence of method of catalyst preparation on such factors as degree of monomer conversion, polybutadiene molecular mass and microstructure. There are some reports on this subject, but only for isoprene polymerisation with a binary [2] or ternary catalyst [3] or for butadiene polymerisation with binary catalysts including Al(iBu)*H as a cocatalyst [4,5]. In this paper, we report on studies of the influence of some aspects of catalyst production (e.g. method of preparation, ageing time, ageing temperature) on monomer conversion, and the intrinsic viscosity and microstructure of the resulting polybutadiene obtained with the NdCla’3TBP(tributylphosphate)TIBA(triisobutylaluminium) catalyst system.

*To whom all correspondence

should be addressed.

Materials

The 1,3-butadiene used was a high purity grade (acetylene content less than SOppm) supplied by CAROM, Onesti, Romania. The monomer was further purified by passing it through columns packed with NaOH and molecular sieves to remove any residual moisture and then through a column packed with copper to remove the last traces of acetylene. Prior to polymerisation the butadiene was dissolved in n-hexane in a separate vessel. n-Hexane used as the polymerisation solvent was supplied by Merck and was distilled onto Na-K alloy and purified according to a method described elsewhere [2]. Tributylphosphate (supplied by Merck) was purified by vacuum distillation and final traces of moisture removed by azeotropic distillation in a special apparatus [2]. Triisobutylaluminium (supplied by Merck) was used as received. The raw lanthanide material NdC13’6Hz0 was used as supplied by the Research Institute for Special Metals, Romania, and NdClj.3TBP complexes in toluene (0.29 mol/ L) were obtained using a method described elsewhere [6]. Polymerisation

Polymerisation reactions were carried out according to the method decribed in detail in a previous paper [7]. In brief, a glass, tube-like reactor was evacuated to IO-’ mm Hg and then purged with dry argon. This process was repeated twice and then the reactor evacuated to IO-” mm Hg. At this point the appropriate quantities of solvent (n-hexane) and monomer were run into the reactor and magnetically stirred. Spherical phials, which contained the components of the catalyst system or the whole catalyst system (depending on the method of catalyst preparation) were situated in a side arm to the reactor, were broken with the stirrer contained within the reactor and their contents immediately mixed with the monomer/n-hexane solution. Following careful removal of the top of the polymerisation cell the polybutadiene so obtained was precipitated adding 811

812

H. lovu er al

methanol containing butylated hydroxyl toluene to the contents of the cell. The precipitated polymer/solvent/ monomer/catalyst residue mixture was poured into a glass dish and all volatiles were driven off in an oven. The polybutadiene was analysed to determine the conversion, intrinsic viscosity and microstructure.

Table 2. The influence of the ageing temperature of a “preformed” catalyst of NdCb’3TBP-TIBA on the characteristics of the

Polymer characterisation

IIa IIa IIa IIa IIb IIb IIb IIb

Intrinsic viscosities were determined in toluene at 25°C; solution concentration were 0.25% or less. Microstructures of the polybutadiene produced were deducted from their IR spectra [8]. RESULTS AND DlSCUSSlON

For initial studies the catalyst was prepared either by (I) combining of NdC& with TBP and TIBA in the reactor or (II) separately producing the NdC1,.3TBP complex

and then

bringing

this into contact

Conversion

[YPe

W)

I

17.5 60.7

II

141 Wg)

6.06 8.75

0 IO 20 30 0 IO 20 30

Microstructure (%)

75 84 87 86 90 88 89 89

[q] (dL/g)

I,Ccis

1,4-fans

1.2

11.75 10.85 II.20 13.32 8.86 9.32 9.10 8.61

98.6 99.0 98.7 98.7 98.7 99.0 98.8 98.7

0.7 0.5 0.8 0.7 0.9 0.7 0.6 0.7

0.7 0.5 0.5 0.6 0.4 0.3 0.6 0.6

*[Monomer] = 20% of total mass of reaction mixture; [Nd] = 5.5 x 10e6 mol/g butadiene; [AI]/[Nd] = 30 (molar ratio); [Bu]/[Nd] = 2 (molar ratio in the case of catalysts prepared in the presence of diene); polymn. temp. = 25°C; ageing time = I hr; polymn. time = 2 hr.

Figure 1 illustrates the influence of the ageing time for the “preformed” catalyst on the activity of the catalyst system and the microstructure of the resulting polybutadiene. From the data presented in Fig. 1 it can be seen that “performed” catalyst activity increases with ageing time up to an ageing time of 60 min. After that it remains constant or even slowly decreases. The polymer microstructure appears to change little with catalyst ageing time. Accordingly for all further

72

1 0

40

80

120

160

200

240

&&tg time (lltitl)

1”“““““l

catalytic

Microstructure (%) Catalyst

Catalyst type

with

TIBA in the reactor. The characteristics of the associated polymerisations and resulting polybutadienes are presented in Table 1. From Table 1 it ,is quite apparent that the most active system was that obtained by introducing the NdCI,.3TBP complex to the TIBA in the reactor. Although the catalyst system produced by allowing the three components NdCh, TBP, and TIBA to come into contact in the reactor was significantly less reactive, nevertheless it produced a polybutadiene which was also 99% 1,6cis in character. The molecular mass of the polymer, however, was somewhat less than that for the polymer produced with the Type II catalyst. On the basis of the above results, only Type II catalysts were used in the studies that are reported in the rest of this paper. Three different methods of producing the Type II catalyst have been investigated, namely, (Ha) a “preformed” catalyst prepared in the absence of diene by adding a solution of TIBA in n-hexane to a solution of the NdCh’3TBP complex in toluene followed by an appropriate ageing period at a specific temperature; (IIb) a “preformed” catalyst produced by mixing a solution of the NdCh’3TBP complex in toluene with the precise amount of butadiene necessary to give a Bu/Nd molar ratio of 2, and then adding the resulting solution to the required amount of TIBA in n-hexane and leaving the system to stand for the desired ageing period at a specific temperature; and (11~) an in-situ catalyst where the monomer-solvent mixture was introduced in the reactor first, followed by a solution of TIBA in n-hexane and then by a solution of the NdCl,. 3TBP complex in toluene. A series of butadiene polymerisations were carried out with “preformed” catalysts which had been aged at the temperatures indicated in Table 2.

Table 1. Butadiene polymerisation with a NdCb-based system*

produced polybutadiene’

Ageing t;_;;. Conversion (%)

0

I ,Ccis

I ,Crrans

I ,2

99.0 99.1

0.6 0.5

0.4 0.4

*[Monomer] = 20% of total mass of reaction mixture; [Nd] = 5.5 x IO-’ mol/g butadicne; [AI]I[Nd] - 30/l (molar ratio); polymn. temperature = 25°C; polymn. time = 30 min.

40

80

120

A#&8

160

200

240

time(mill)

Fig. 1. The influence of the agcing time on the reactivity of the “preformed” catalyst and polybutadiene mircostructure; asing temperature = polymn. temperature = 25°C. The other reaction conditions are identical with those given below Table 2.

Polybutadiene obtained with neodymium catalysts

813

Table 3. The polymerisation of butadiene with a Type Ilb catalyst preformed in the presence of butadiene at different fBul/lNdl molar ratios* Microstructure (%)

~W[W (molar ratio) 0.5 0.5 0.5

2.0 2.0 2.0 5.0 5.0 5.0

Polymerisation time (mix0

Conversion (%f

15 30 120 15 30 120 15 30 120

54 69 87 60 12 89 70 76 93

kl (dL/al

I .4cis

1,4trans

1.2

10.06 9.63 9.06 8.50 8.98 9.35 8.76 8.88 9.02

98.3 98.4 98.6 98.8 98.4 98.8 98.6 98.3 98.7

1.0 0.9 0.8 0.5 0.8 0.6 0.6 0.9 0.4

0.7 0.7 0.8 0.7 0.8 0.6 0.8 0.8 0.9

*Polymerisation conditions: [Monomer] = 20% of total mass of reaction mixture; [Nd] = 5.5 x 1O-6mol/g butadiene; [AI]/[Nd] = 30 (molar ratio); ageing temperature = polymn temperature = 25°C; ageing time = I hr.

polymerisations reported in this paper an ageing time of 1 hour was used. The data in Table 2 and Fig. 1 may be readily explained in terms of the reaction between the NdC11.3TBP complex and the TIBA, to give the alkylated species CbNd(iBu).3TBP which is the active species for polymerisation of the butadiene. [email protected])3

+

being replaced by the much more stable n-allylic complex [9] through reaction with the butadiene:

NdCb.3TBP = Al(iBu)zCl + (iu)Nd(Clh.3l-BP (1)

It is well known that the efficiency of initiation is very low for the NdCl,-based catalyst systems [9] and is regarded as being due to the instability of the o Nd-C bonds or to low degrees of alkylation of the NdC13. In the case of the catalyst system “preformed” in the absence of butadiene, increasing the ageing temperature from 0 to 30°C with the ageing time being kept constant at 1 hr, leads to an increase in conversion probably because this favours reaction (1). Similarly, for a set ageing temperature, it is thought that catalyst activity increases with increasing ageing time as a result of the concentration of butylated species CbNd(iBu) increasing up to an “equilibrium level”; once this is reached the catalyst activity remains constant. The authors have noted a similar effect with Type IIc (in-situ) catalyst. It is interesting to note the enhanced reactivity of the Type IIb “performed” catalyst where a precise and small amount of butadiene was present during the ageing process. We believe that this enhancement results from the unstable NdC bond in the catalyst

To investigate this aspect of the reaction, the activity of the Type IIb “preformed” catalyst has been investigated further. The relevent data are presented in Table 3 and confirm that as the level of butadiene present during the preforming of the catalyst system is increased so does the activity of the catalyst system. Regardless of the molar ratio [Bu]/[Nd] used in the preform stage, the microstructure of the resulting polybutadiene remains at a constant and very high value. It should be noted that the use of higher [Bu]/[Nd] molar ratios in the preform stage was not practical owing to the high viscosity of such systems. To further investigate the influence of method of catalyst formation on catalyst activity three further sets of polymerisations at different catalyst concentrations were performed for each catalyst type (IIa, IIb and 11~). The results are shown in Table 4. As would be expected, % conversion increases and the intrinsic viscosity of the product decreases with increasing catalyst concentration regardless of the method of catalyst preparation. Irrespective of the

Table 4. The influence of catalyst concentration on the polymerisation of butadiene with Type Ila. Ilb and IIc NdCl;3TBP-TIBA catalyst systems’ Microstructure (%) Catalyst type Ha Ila Ila Ilb Ilb Ilb IIC IIC IIC

lob x [Nd] (moljg monomer)

Conversion (%)

(df-/g)

I ,4-cis

I.Clww

I,2

3.5 5.5 IO 3.5 5.5 IO 3.5 5.5 IO

86 87 93 87 90 94 70 88 92

12.65 Il.23 8.26 9.88 9.35 6.10 I I .21 8.47 6.09

98.5 98.7 98.9 98.7 98.8 99.0 99.0 98.0 99.0

0.8 0.8 0.6 0.7 0.6 0.6 0.5

0.7 0.7 0.5 0.6 0.6 0.4 0.5

ltll

I .o

1.0

0.5

0.5

lPolymerization conditions: [Monomer] = 20% by weight of total polymerisation mixtun; [Bu]/[Nd] = 2 (in the case of Type I ta and Ilb); [AI]/[Nd] = 30 (molar ratio): polymn temp. = 25’C; polymn time = 2 hr; ageing time = I hr.

H. low et al.

814

method of catalyst preparation or catalyst concentration, the polymer microstructure remains unchanged with 98-99% 1,4-cis character. At the same catalyst concentrations, the highest molecular mass polymer was produced by the catalyst “performed” (Type Ha) in the absence of butadiene. The catalyst “preformed” in the presence of butadiene (Type Ilb) produced the lowest molecular mass polymer. Not surprisingly, the activity of catalysts prepared in-&u (Type IIc) were lower than for Types IIa and Ilb. As the monomer concentration and the [Al]/[Nd] molar ratio were constant, the differences between the activity of the three catalysts type (IIa, IIb and 11~) may be explained by the different global concentration of the organoaluminium compound in the moment of obtaining the catalyst system, namely a higher concentration for the “preformed” catalyst than for the in-situ prepared one, in the later the total mass consisting also of monomer and solvent. A higher concentration of TIBA determines a higher rate of the alkylation reaction (1) so a higher catalyst activity. CONCLUSIONS 1. The activity of the NdC1,‘3TBP-TIBA catalyst system in the polymerisation of butadiene is increased if prior to polymerisation the NdCh.3TBP complex is prepared. 2. The highest catalyst activity has been found with a “preformed” catalyst particularly where the preforming was carried out in the presence of a precise and small amount of butadiene which is believed to replace the weak Nd-C bonds in

(iBu)NdCl,.3TBP with stronger n-allylic complexes according to reaction (2). 3. With “preformed” catalysts, ageing time and temperature are considered to be critical in determining the activity of the system. The optimum ageing time and temperature are considered to be 1 hr and 20°C. 4. With catalysts “preformed” in the presence of butadiene, the value of the molar ratio [Bu]/[Nd] should not exceed 2 if the viscosity of the catayst system is not too high. REFERENCES

I. Marina, N. G., Monakov, Y. B., Sabirov, 2. M. and Tolstikov, G. A., Vysokomol. Soedin., 1991, A33, 467. 2. Dimonie, M., Fieroiu, V., Hubca, G., Gruber, V.,

Badea. E. G.. Vladulescu. M.. Verestoi. A.. Iovu. H. and Vasile, 1.1 Rev. Roum’. Chim., 1989,’34,’ 5. 3. Cabassi, F., Italia, S. and Ricci, G., Transition Metal Catalyzed Polymerisation. Cambridge University Press, Cambridge, 1988, p. 655. 4. Monakov, Y. B., Marina, N. G. and Tolstikov, G. A., Polymery-Tworzywa 263.

Wielkoczasteczkowe,

1989,

34,

5. Marina, N. G., Gadeleva, K. K. and Monakov, Y. B., Dokl. Akad. Nauk. SSSR 1984, 274, 641. 6. Dimonie, M., Hubca, G., Badea, E. G., Gruber, E., Simionescu, E., Vladulescu, M., Iovu, H., Stan, S., Vasile, I. and Munteanu, R., Synthetic Polym. J. 1994, 1, I. 7. Dimonie, M., Hubca, G., Badea, E., Simionescu, E. and Iovu, H., Rev. Roum. Chim. 1995, 40, 83. 8. Ciampelli, F., Morero, D. and Cambini, M., Mukromol. Chem. 1963, 61, 250. 9. Ricci, G., Italia, S. and Cabassi, F., Polym. Commun. 1987, 28, 223.