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
2000-01-07
2001-04-24
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...
C525S316000, C525S098000, C524S504000
Reexamination Certificate
active
06221968
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a process for producing specific tapered block copolymers. More specifically, it relates to a process for producing a specific tapered hydrogenated triblock copolymer of styrene and isoprene.
BACKGROUND OF THE INVENTION
Block copolymers of vinyl aromatic hydrocarbons, such as styrene, and conjugated dienes, such as isoprene and butadiene, are well known. Generally, these are made by polymerizing a polymer block of one of the monomers, for instance, styrene, until all of the monomer is gone, introducing a second monomer and polymerizing it until all of it is gone, and so on. This process would produce block copolymers which have distinct homopolymer blocks. It is also possible to polymerize more than one monomer together to produce random copolymer blocks within the block copolymer.
In some situations, it has been found advantageous to create a random copolymer block within the block copolymer which is “tapered.” A tapered block is a randomly copolymerized block wherein the conditions of polymerization are managed such that the concentration of one of the mers in the block copolymer is highest at one end of the polymer block and generally decreases in the direction of the other end of the polymer block so that the concentration of other mer is greatest at the other end. In these tapered block copolymers, the trend is as described previously but the distribution of the mers is still random.
It has been found that it would be advantageous to be able to produce a tapered polymer block in which the random nature of the distribution of the mers in the polymer block is dramatically decreased in comparison to the prior art tapered block copolymers. The present invention provides a process which allows the production of block copolymers having tapered blocks of styrene and isoprene having a specific taper structure which consists of small segments of variable size of styrene monomer and isoprene monomer wherein the concentration of the isoprene mers at one end of the polymer is high and gradually decreases in the direction of the other end of the polymer block but wherein the random distribution of the mers in the block is substantially decreased.
SUMMARY OF THE INVENTION
The present invention is a process for producing an anionic block polymer which comprises optionally anionically polymerizing styrene to form a homopolymer block of polystyrene, anionically polymerizing isoprene to form a hompolymer block of polyisoprene, and anionically copolymerizing styrene and isoprene to form a tapered copolymer block wherein the charge rate of both styrene and isoprene is from 15% to 75%, preferably 15 to 50%, by weight of the total tapered block monomer charge per minute, and the weight ratio of the styrene to the isoprene is from 0.5:1 to 1.5:1. The process produces a unique polymer containing a tapered polymer block of styrene and isoprene which has a specific taper structure consisting of small segments of variable size of styrene monomers and isoprene monomers.
Although the specification and claims refer to styrene and isoprene only, it is considered within the spirit of the invention to use any vinylaromatic hydrocarbon in the manner of styrene described herein and to use any conjugated diene in the manner of isoprene described herein.
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Atwood Harvey Emerson
Christian Christine Marie
Modic Michael John
Moore Barry Collins
Scheve John Louis
Asinovsky Olga
Haas Donald F.
Seidleck James J.
Shell Oil Company
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