Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
1999-01-20
2001-02-06
Seidleck, James J. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S338000, C525S313000, C525S314000, C525S095000, C525S098000
Reexamination Certificate
active
06184307
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to the production of hydrogenated block copolymers made from isoprene and butadiene. More particularly, this invention relates to a process that minimizes the residence time of the hydrogenation step in the production of polyisoprene-polybutadiene block copolymers which are intended to incorporate a small amount of residual unsaturation in the polyisoprene blocks.
BACKGROUND OF THE INVENTION
U.S. Pat. Nos. 5,229,464 and 5,382,604 describe conjugated diene block copolymers which have at least one block each of two different polymerized conjugated dienes. In their preferred embodiments, the conjugated dienes are isoprene and butadiene. The patents describe methods for making such polymers and then hydrogenating them in order to as completely as possible hydrogenate the polybutadiene blocks while leaving a certain amount of residual unsaturation in the polyisoprene blocks. This residual unsaturation may then be reacted to attach epoxy groups to the polymer or some other functionality. Generally, the hydrogenation process described utilizes a nickel-aluminum catalyst as described in U.S. Pat. No. 4,879,349 but other Group VIII metals and titanium catalysts have been used as well as described in U.S. Pat. No. 5,039,755.
Polybutadiene is known to be relatively easy to hydrogenate whereas polyisoprene is more difficult to hydrogenate. The rates of hydrogenation of both of the main microstructure configurations of polybutadiene, 1,2-butadiene and 1,4-butadiene, are higher than the rate of hydrogenation of the main microstructure configuration in polyisoprene, 1,4-isoprene. The rate of hydrogenation of 1,4-butadiene is noticeably faster than that of 1,4-isoprene and the rate of hydrogenation of 1,2-butadiene is noticeably faster than that of 1,4-butadiene. Thus it can be seen that the hydrogenation of the polyisoprene blocks in polybutadiene-polyisoprene block copolymers can be a rate limiting step in the overall process for the production of hydrogenated polybutadiene-polyisoprene block copolymers.
The current mode of hydrogenating such block copolymers involves two stages. In the first stage, the focus is on hydrogenating the polybutadiene blocks as completely as possible, for example to a residual unsaturation of 0.3 meq/g, which for a 4800 number average molecular weight butadiene block is equivalent to a total butadiene double bond conversion of 95% as shown in Example 3 below. Residual unsaturation in this sense means the milliequivalents of unsaturated double bonds per gram of polymer which are left in the polymer block after the hydrogenation step. Residual unsaturation is thus defined once the total conversion of double bonds as a percentage is known and the molecular weight of the polymer or the polymer block is known or chosen. In the second stage, more stringent conditions or more catalyst are utilized to hydrogenate the polyisoprene blocks to the desired level.
The biggest problem with this approach is that the total hydrogenation part of the process can become the rate-limiting step in the process. If a way could be found to reduce the residence time or cycle time of the hydrogenation part of the process, the overall cost of producing such polymers could be significantly decreased. Residence time is the average time the polymer cement spends in a continuous hydrogenation in a batch reactor. Cycle time is the complete time taken to complete the hydrogenation in a batch reactor. These terms are used interchangeably herein.
One obvious way to attempt to speed up the hydrogenation of the polyisoprene blocks is to add more hydrogenation catalyst. Obviously, this increases the cost as the hydrogenation catalyst itself is expensive. Unfortunately, the variability in catalyst activity can make it difficult to target a particular polyisoprene block residual unsaturation. Adding more catalyst to increase the rate of hydrogenation also increases the risk of overshooting the target residual unsaturation. If a narrow specification is required for residual unsaturation, this method is not very effective.
It can be seen that it would be highly advantageous to find a method which would allow one to produce polybutadiene-polyisoprene block copolymers in which the polybutadiene block is almost completely hydrogenated while leaving a specified amount of residual unsaturation within a narrow specification range in the polyisoprene block and doing so at an overall rate that minimizes the residence time of the hydrogenation step. This would allow a cost effective method for producing such hydrogenated polybutadiene-polyisoprene block copolymers.
SUMMARY OF THE INVENTION
The present invention describes such a method for minimizing the hydrogenation residence time during the production of hydrogenated polybutadiene-polyisoprene block copolymers. The method focuses on producing a molecule that contains the desired amount of residual unsaturation in the polybutadiene blocks and also the targeted residual unsaturation in the polyisoprene blocks.
This invention is a method for producing such polymers with a specified amount of residual unsaturation in the polyisoprene blocks utilizing a hydrogenation catalyst wherein the hydrogenation cycle time is minimized. Simply stated, the method adjusts the relative amounts of butadiene and isoprene in the polymer such that the desired level of residual unsaturation in the isoprene block is achieved at the same time the desired degree of butadiene hydrogenation is attained. In other words, the required hydrogenation of the butadiene and isoprene run co-currently and end simultaneously so that no additional time beyond butadiene hydrogenation is required for isoprene hydrogenation. This is obviously the case of minimum cycle or residence time for the hydrogenation.
A more detailed methodology for defining this optimized family of molecules comprises:
a) determining the average relative rates of hydrogenation of 1,2-butadiene to 1,4-butadiene (S1) and 1,4-butadiene to 1,4-isoprene (S2) of the particular batch of hydrogenation catalyst to be used, including whether or not the rates change significantly as the conversion increases,
b) choosing the desired polybutadiene block residual unsaturation (RU
Bd
),
c) choosing the desired polyisoprene block residual unsaturation (RU
Ip
) whereby the desired total residual unsaturation (RU
Tot
) is defined,
d) choosing the desired overall polymer molecular weight or the desired butadiene block molecular weight,
e) determining the relative molecular weight ratio of the polyisoprene blocks to the polybutadiene blocks polymer from the following equation:
RU
Tot
=1000{[F
Bd
((1−V
12
)(1-14BdC)+V
12
(1-14BdC)
S1
)]/54+[F
Ip
(1-14BdC)
1/S2
]/68}
whereby F
Bd
is the weight fraction of polybutadiene in the polymer, F
Ip
is the weight fraction of polyisoprene in the polymer, V
1,2
is the weight fraction of 1,2-butadiene mers in the polybutadiene blocks, and 1,4BdC is the fraction of 1,4-butadiene which is hydrogenated, thereby defining the overall polymer molecular weight and the polybutadiene and polyisoprene block molecular weights,
f) anionically polymerizing butadiene and isoprene to form a block copolymer having the block molecular weights as determined in step e), and
g) hydrogenating the block copolymer to the desired polybutadiene residual unsaturation.
If the relative rates S1 and/or S2 change significantly at any point during the course of the hydrogenation step, i.e., as a function of the amount of conversion of double bonds, then steps a through g are carried out using the first set of rates up to the amount of conversion at which the significant rate change is observed and then steps a through g are repeated using the new values for S1 and S2. This is repeated as many times as there are points at which there are significant changes in the relative rates S1 and/or S2.
REFERENCES:
patent: 3465063 (1969-09-01), Hassell et al.
Asinovsky Olga
Haas Donald F.
Seidleck James J.
Shell Oil Company
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