Polymerization of butadiene

A process for preparing a catalyst for the polymerization of butadiene to obtain a polymer containing a very high content of cis isomer in which a specified neodymium carboxylate, an aluminium hydrocarbyl or aluminium hydrocarbyl hydride and a source of halogen are contacted using a particular procedure.

This relates to a process for preparing a catalyst for the polymerization 
of butadiene capable of producing a polymer containing a very high content 
(98 or more) of cis isomer. 
Polybutadienes containing high contents of cis isomer (e.g. 93-97%) have 
been manufactured for many years by solution polymerization using a 
coordination catalyst, usually one containing a titanium, vanadium or 
nickel compound. Recently polybutadienes containing even higher contents 
of cis isomer (98% or more) have been manufactured using so-called rare 
earth based coordination catalysts. Such catalysts are usually formed from 
a neodymium compound, an organo aluminium cocatalyst and a source of 
halogen. Neodymium carboxylates have proved to be very effective in such 
catalysts. 
We have now found that by careful choice of neodymium component of the 
catalyst and by strictly adhering to a particular procedure for preparing 
the catalyst, improvements in the polymerisation process may be obtained. 
According to the present invention a process for preparing a catalyst for 
the polymerisation of butadiene comprises contacting in hydrocarbon 
solvent (a) an aluminium hydrocarbyl (other than aluminium triethyl) or an 
aluminium hydrocarbyl hydride, (b) neodymium neodecanoate (neodymium 
versatate) or neodymium naphthenate and (c) a source of halogen, the 
contacting and subsequent mixing being carried out at a temperature of 
-15.degree. C. to -60.degree. C., and ageing the catalyst for a period of 
at least 8 hours before use in polymerisation. 
Preferably the preformed catalyst is homogeneous and readily soluble in 
hydrocarbons. Advantageously the catalyst is preformed in the presence of 
a small amount of butadiene monomer. 
Neodymium neodecanoate (neodymium versatate) is the neodymium salt of a 
synthetic acid comprising a mixture of highly branched isomers of ClO 
monocarboxylic acids, (hereinafter called "Versatic Acid"). The acid is 
sold under this trade name by Shell Chemicals. The neodymium salt, 
("versatate"- Nd(C.sub.9 H.sub.19 COO).sub.3), or neodymium naphthenate 
may be obtained from a neodymium compound, conveniently a water soluble 
neodymium salt (e.g. neodymium trichloride) or neodymium oxide (Nd.sub.2 
O.sub.3). 
The aluminium hydrocarbyl or hydrocarbyl hydride (component (a)) preferably 
contains alkyl groups having 3 to 10, more preferably 3 to 5, carbon 
atoms. Preferred examples are diisobutyl aluminium hydride and aluminium 
triisobutyl. 
The source of halogen may be an aluminium alkyldihalide, aluminium dialkyl 
halide, an aluminium alkyl sesquihalide, an organic halogen compound, such 
as benzoyl chloride, t-butyl chloride, methyl chloroformate or benzyl 
chloride or an inorganic compound containing Cl or Br in ionisable form, 
such as HCl or HBr. Examples of aluminium alkyl halides are ethyl 
aluminium dichloride, diethyl aluminium chloride and ethyl aluminium 
sesquichloride. 
The quantities of the various catalyst components are preferably chosen so 
as to give an aluminium:neodymium atomic ratio of at least 10:1, more 
preferably 15:1 to 200:1 and a halogen:neodymium atomic ratio of 0.5:1 to 
5:1. Optimum ratios are readily determined empirically in separate 
experiments. 
Preferably the catalyst is prepared or preformed using the order of 
addition hydrocarbon solvent, component (a), component (b), component (c). 
If prepared in the presence of butadiene monomer, the diene is dissolved 
in hydrocarbon solvent and the components added in the order (a), (b), 
(c). 
The hydrocarbon solvent used in the preparation is preferably a straight 
chain hydrocarbon such as hexane or a cycloalkane such as cyclohexane. 
Mixtures of hydrocarbons may be used. 
The temperature at which the catalyst components are brought into contact 
in hydrocarbon solvent is an important part of the catalyst preparation 
procedure. The contacting and subsequent mixing is carried out at a 
temperature of -15.degree. C. to -60.degree. C. Preparation at this 
temperature increases catalyst activity compared with preparation at 
ambient temperatures or above (e.g. +40.degree. C.). 
After contacting and mixing at a temperature of -15.degree. C. to 
-60.degree. C., preferably -20.degree. C. to -40.degree. C., the catalyst 
premix is aged for a period of at least 8 hours. Ageing for several days 
before use, e.g. 7 days, may not be deleterious and may in fact increase 
catalyst activity but beyond about 7 days activity starts to decline. 
Polymer molecular weight may also be increased by ageing for long periods. 
Ageing may be carried out at the same temperatures as used for the 
premixing procedure. Temperatures up to slightly above ambient (e.g. 
+40.degree. C.) may be used for the ageing but the catalyst may become 
unstable so low temperature ageing at below 0.degree. C. is preferred, 
preferably at -20.degree. C. to -40.degree. C. 
Polymerisation is preferably carried out in the same hydrocarbon solvent as 
used in the catalyst preparation. Reaction in the absence or substantial 
absence of solvent is however possible. 
The amount of catalyst component (b) used in the polymerisation is e.g. 
0.05 mMole per Group III Metal/100 g of monomer or more. Usually 0.10 
mMole-0.26 mMole Nd/100 g of monomer is sufficient. 
Polymerisation may be carried out at a temperature of zero (0.degree. C.) 
to moderately elevated temperature (e.g. 200.degree. C.) or above, 
preferably 20.degree. C. to 100.degree. C. Under optimum conditions cis 
contents of 98% or more are attainable. 
By the process of the present invention it is possible to enhance the 
activity of the catalyst, offering opportunities for reduced catalyst 
consumption in the polymer manufacturing process and thus improved process 
economics. Furthermore it is possible to improve the molecular 
weight/molecular weight distribution characteristics of the polybutadiene 
product. In general polybutadienes prepared by the process of the present 
invention have a narrower molecular weight distribution than ones obtained 
using a different neodymium component as component (a) and/or higher 
premixing temperatures. This is particularly important since molecular 
weight distribution is well known to have a significant influence upon the 
processing characteristics of synthetic rubbers. The processing 
characteristics are of crucial importance to the rubber product 
manufacturer, especially tire manufacturers. 
It is important to note that the catalyst of the present invention is 
homogeneous and hydrocarbon soluble and, in one embodiment, is prepared 
from a soluble neodymium component, itself prepared from neodymium oxide. 
Such catalysts are different from heterogeneous catalysts prepared from an 
insoluble rare earth compound, and display quite different reaction 
kinetics/process behaviour. Because of these differences it was quite 
unpredictable that, by following the preparation procedure of the 
invention, enhanced catalyst activity and/or improved molecular 
weight/molecular weight distribution characteristics of the polybutadiene 
product might be obtainable. 
The following Examples illustrate the invention.

EXAMPLES 1-8 
In these Examples neodymium versatate (NdV) or neodymium naphthenate (NdN) 
was used as the neodymium component (b) of the catalyst as 0.2 M [Nd] 
solutions in hexane. The versatate was prepared from Versatic 10 (ex Shell 
Chemicals). 
A series of catalysts was prepared in oven dried (130.degree. C.) crown 
capped half pint bottles using the premixing and ageing conditions shown 
in the table. 
All reagents were dispensed by syringe and the catalyst components were 
added in the following order: 
(i) Hexane, dried by distillation from butyl lithium under nitrogen, to 
give final [Nd] of 0.022 M; 
(ii) Diisobutyl aluminium hydride (ex Aldrich Chemical Co., as supplied). 
The bottle and contents were allowed to equilibrate at the desired 
temperature. 
(iii) NdV or NdN. The bottle was kept at the required temperature for 1 
hour (20.degree. C. or 40.degree. C.) or 2.5 hours (-30.degree. C.) before 
adding: 
(iv) t-Butyl chloride, distilled from freshly dried alumina and diluted to 
0.5 M in hexane. 
Catalyst component molar ratios were such as to give atomic ratios of 
Al:Nd:Cl of 20:1:3 in all cases. 
The catalyst was then kept at the same temperature for 1 hour and aged as 
indicated before use. 
Polymerisations were carried out in 1 pint crown capped bottles at 
60.degree. C. for 240 minutes using a standard recipe: 
______________________________________ 
Hexane 350 ml 
1,3 Butadiene 45 g 
Catalyst 0.15 mM Nd/100 g monomer 
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Reaction was stopped by venting off excess butadiene, adding hexane 
containing antioxidant and coagulating with methanol. Polymers were dried 
at 50.degree. C. under vacuum and the conversion calculated from the 
weight of polymer obtained. In all cases substantially 100% conversion of 
polymer was obtained after 240 minutes reaction. 
The Intrinsic Viscosity (IV) of each polymer was measured on 0.1% (w/v) 
solutions in toluene at 30.degree. C., and using GPC, the weight average 
molecular weight (Mw), number average molecular weight (Mn) and the 
molecular weight distribution (MWD) characteristics for each were 
determined. 
The results are indicated in the table. By comparison of the Examples 
according to the invention (Examples 2, 4 and 6) with the control Examples 
(Examples 1, 3 & 5), the advantages of using the low temperature premixing 
process of the present invention can be seen from the lower values for 
I.V., Mw and MWD for the products obtained in Examples 2, 4 & 6. 
In addition separate experiments showed that the catalyst preparation 
procedure of Examples 2, 4 & 6, (premixes made at -30.degree. C. and aged 
at -20.degree. C.) gave catalysts of increased activity, especially after 
ageing for 7 days. Premixes made at -30.degree. C. but aged at +20.degree. 
C. were all more active than comparison premixes made at +20.degree. C. 
and the activity increased with ageing time. In general, versatate 
catalysts were more active than naphthenate catalysts, when prepared at 
-30.degree. C. 
Comparison Examples 7 and 8 show that premixing at +40.degree. C. and aging 
at 20.degree. C. gives very high weight average molecular weights (Mw) 
and, in the case of Example 7, a broader molecular weight distribution. In 
addition the catalysts were less active than the control examples. 
Thus, in general, catalysts prepared by premixing at -30.degree. C. and 
aging at -20.degree. C. give lower overall molecular weights and the 
narrowest molecular weight distributions, and exhibit increased activity 
compared with catalysts prepared at ambient temperature (20.degree. C.) or 
slightly above (40.degree. C.). 
It should be noted that neodymium naphthenate is not very soluble in hexane 
at -30.degree. C., but neodymium versatate gives a clear solution at this 
temperature. This, coupled with the advantage of much increased activity 
which is obtained with neodymium versatate, by preforming at low 
temperature and aging, offers the possibility of a particularly 
advantageous polymerisation process. 
______________________________________ 
Nd Preparation Mw Mn 
Ex salt Conditions IV .times. 10.sup.-3 
.times. 10.sup.-3 
MWD 
______________________________________ 
1* NdV Premix 20.degree. C. 
2.36 328 110 3.25 
Aged at 20.degree. C. 
for 20 hrs. 
2 NdV Premix -30.degree. C. 
1.77 207 77 2.68 
Aged at -20.degree. C. 
for 20 hrs. 
3* NdV Premix 20.degree. C. 
3.08 417 124 3.37 
Aged at 20.degree. C. 
for 7 days 
4 NdV Premix -30.degree. C. 
1.98 311 101 3.07 
Aged at -20.degree. C. 
for 7 days. 
5* NdN Premix 20.degree. C. 
3.30 465 113 4.10 
Aged at 20.degree. C. 
for 7 days. 
6 NdN Premix -30.degree. C. 
2.77 368 121 3.05 
Aged at -20.degree. C. 
for 7 days. 
7* NdV Premix 40.degree. C. 
2.64 389 103 3.78 
Aged at 20.degree. C. 
for 20 hrs. 
8* NdV Premix 40.degree. C. 
2.40 415 138 3.01 
Aged at 20.degree. C. 
for 7 days. 
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*comparison Examples.