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
2000-08-28
2002-05-14
Wu, David W. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C526S065000, C526S090000, C526S201000, C526S348200, C526S348500, C526S348600, C526S943000
Reexamination Certificate
active
06388016
ABSTRACT:
FIELD OF INVENTION
Background of the Invention
This invention relates to a method of making polymer blends using series reactors and a metallocene catalyst. Monomers used by the invention are ethylene, a higher alpha-olefin (propylene most preferred), and optionally, a non-conjugated diene (ethylidene norbornene, i.e., ENB, most preferred). More specifically, this invention relates to making blends of EP (ethylene-propylene) copolymers in which the blend components differ in any of the following characteristics: 1) composition 2) molecular weight, and 3) crystallinity. We use the terminology EP copolymer to also include terpolymers that contain varying amounts of non-conjugated diene. Such terpolymers are commonly known as EPDM.
There are various advantages for making the aforementioned blends. For example, EP (ethylene propylene copolymer) and EPDM (ethylene propylene diene terpolymer) polymers are often used as blends of two or more polymers to obtain optinum polymer properties for a given application. High molecular weight and low molecular weight polymers are blended yielding a broadened molecular weight distribution (MWD) and therefore better processibillity than a narrow MWD polymer with the same average molecular weight. A semicrystalline polymer may be blended with an amorphous polymer to improve the toughness (green strength) of the amorphous component at temperatures below the semicrystalline polymer melting point. Higher green strength polymers are less likely to cold flow and give improved handling characteristics in processing operations such as calendering and extrusion.
One method of making the aforementioned blends is by mixing two different polymers after they have been polymerized to achieve a target set of properties. Such a method is expensive making it much more desirable to make blends by direct polymerization. Blends by direct polymerization are well known in the prior art such as EPDM manufacture with soluble vanadium based Ziegler-Natta catalysts by using reactors in series and making a polymer with different properties in each reactor. Patents which show vanadium in series reactor operation are U.S. Pat. Nos. 3,629,212, 4,016,342, and 4,306,041, all of which are incorporated by reference for purposes of U.S. patent practice.
Although polymer blending may be performed by vanadium based Ziegler-Natta catalysts in series reactors, there are severe limitations on the amount and characteristics of the polymers that can be made in each reactor, especially in the second reactor. Due to economical considerations, the most preferred method of reactor operation is to add catalyst only to the first reactor to minimize the use of the expensive catalyst components. Because of the rapid deactivation rate of the active vanadium species, catalyst concentration is very low in the second reactor in the series and would be even lower in succeeding reactors. As a result, it is very difficult to make more than about 35 wt % of the total polymer in the second reactor. Also, the low catalyst concentration may put limits on the composition or molecular weight of the polymer. To cure this problem, catalyst activators or additional catalyst can be added to the second and later reactors; however, this raises manufacturing costs. Furthermore, vanadium catalysts are limited in their ability to produce polymers containing less than about 35 wt % ethylene since they much more readily polymerize ethylene than propylene or higher alpha-olefins. In addition, soluble vanadium catalysts are incapable of producing copolymers and terpolymers that contain crystallinity due to the presence of long sequences of isotactic polypropylene.
SUMMARY OF THE INVENTION
This invention departs from the prior art by providing a process for producing polymer blends in series reactors that cures the problems of prior art processes associated with property limits. Note that the terms “multi-stage reactor” and “series reactor” are used interchangeably herein. By employing metallocene catalysts, which enjoy a long catalyst lifetime, polymer blends can be made that vary in the amount of the components, the composition of the components, and the molecular weight of the components over much wider ranges than obtainable with prior art vanadium catalysts. In particular, it is the objective of this invention to use a series reactor process and produce the following types of blends: a) blends in which the ethylene content of the polymer made in the first and second reactors differ by 3-75 wt % ethylene, and b) blends in which the MWD of the blend is characterized by Mw/Mn =2.5-20 and Mw/Mn for the individual blend components is 1.7-2.5, and c) blends in which both the polymer composition and MWD meet the criteria in items a) and b) above, and d) blends in which one component contains 0 to 20 wt % ethylene, is semicrystalline due to the presence of isotactic propylene sequences in the chain, and has a melting point of 40-160° C., and the other component is amorphous, and e) blends in which one component contains 60 to 85 wt % ethylene, is semicrystalline due to the presence of long ethylene sequences in the chain, and has a melting point of 40-120° C., and the other component is amorphous.
This series reactor polymer blend is used in the dynamic vulcanization process to provide improved thermoplastic elastomer products.
Polymerization is preferably homogeneous solution polymerization. The catalyst is a cyclopentadienyl metallocene complex which have two Cp ring systems for ligands or monocyclopentadienyl metallocene catalyst. The metallocene complexes are activated with an alumoxane, eg methylalumoxane (MAO) or a non-coordinating anion (NCA) described further below. Optionally, a trialkyl aluminum scavenger may be added to the reactor feed(s) to prevent deactivation of catalyst by poisons. The reactors are preferably liquid filled, continuous flow, stirred tank reactors. The method employs two or more continuous flow, stirred tank reactors in series with two reactors as a preferred embodiment. Solvent and monomers are fed to each reactor, and preferably catalyst is fed only to the first reactor. Reactors are cooled by reactor jackets or cooling coils, autorefrigeration, prechilled feeds or combinations of all three. Autorefrigerated reactor cooling requires the presence of a vapor phase in the reactor. Adiabatic reactors with prechilled feeds are preferred. This gives rise to a temperature difference between reactors which is helpful for controlling polymer molecular weight. Monomers used in the process are ethylene and a C3-C8 higher alpha-olefin. Propylene is the most preferred as a higher alpha-olefin. Monomers may also optionally include a non-conjugated diene in which case ENB (5-ethylidene-2-norbornene) is the most preferred diene. Reactor temperature depends upon the effect of temperature on catalyst deactivation rate and polymer properties. For economic reasons, it is desirable to operate at as high a temperature as possible; however, temperatures should not exceed the point at which the concentration of catalyst in the second reactor is insufficient to make the desired polymer component in the desired amount. Therefore, temperature will be determined by the details of the catalyst system. In general, the first reactor temperature can vary between 0-110° C. with 10-90° C. preferred and 20-70° C. most preferred. Second reactor temperatures will vary from 40-160° C. with 50-140° C. preferred and 60-120° C. most preferred.
When two reactors are used in series, the composition of the polymer made in the first reactor is 0-85 wt % ethylene while the composition of the polymer made in the second reactor polymer is 0-85 wt % ethylene. The average composition of the polymer blend is 6-85 wt % ethylene.
If Mw/Mn for the blend is less than 2.5, then the difference in composition between the polymer produced in the first and second reactors is 3-75% ethylene, preferably 5-60% ethylene, and most preferably, 7-50% ethylene. If Mw/Mn for the blend is equal to or greater than 2.5, then the composition of the blend
Abdou-Sabet Sabet
Rosenbaum Barry M.
Advanced Elastomer Systems L.P.
Cheung William K
Skinner Williiam A.
Wu David W.
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