Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2002-05-30
2004-03-02
Seidleck, James J. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S197000, C526S184000, C525S251000, C525S285000, C525S284000, C525S263000, C525S064000
Reexamination Certificate
active
06699949
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a solution process for preparing maleic anhydride modified polyolefins with controllable polymer structure (high polymer molecular weight and desirable maleic anhydride content). More particularly, the present invention relates to a post-reactor process for grafting maleic anhydride molecules to a polyolefin chain with little or no side reactions that usually dramatically change polymer molecular weight and molecular weight distribution. The chemistry involves an in situ controlled oxidation reaction of trialkylborane (BR
3
) in the presence of polyolefin (e.g., polyethylene (PE), polypropylene (PP), ethylene-propylene copolymer (EP), etc.) and maleic anhydride. Under certain reaction conditions, this process produces very desirable mono-oxidized trialkylborane adducts, i.e., peroxyldialkylborane (R—O—O—BR
2
), that can undergo homolytic cleavage to form [R—O* *O—BR
2
] and activate the saturated polyolefin chain by alkoxyl radical (R—O*) hydrogen-abstraction at ambient temperature. The formed polymeric radical (C*), associated with the oxidized borane moiety (*O—BR
2
), then reacts with maleic anhydride by addition reaction without side reactions. The resulting functional polyolefins, which contain incorporated maleic anhydride side groups, are very effective interfacial materials for improving the interaction between polyolefins and other materials, such as glass fiber, nano-size clay particles, fillers, nylon, etc., in polyolefin blends and composites.
BACKGROUND OF THE INVENTION
Although useful in many commercial applications, polyolefins suffer a major deficiency in that they interact poorly with other materials. The inert nature of polyolefins significantly limits their end uses, particularly those in which adhesion, dyeability, paintability, or compatibility with other materials is paramount. Moreover, attempts to blend polyolefins with other polymers have been unsuccessful for much the same reason, i.e., the incompatibility of the polyolefins with the other polymers.
It has been demonstrated that addition of polar groups to polyolefin can improve the adhesion of polyolefin to many substrates, such as metals and glass (W. Chinisirikul et al, J. Thermoplastic Composite Materials 6, 18-28, 1993). In polymer blends, the incompatible polymers can be improved by adding a suitable compatibilizer that alters the morphology of these blends (U.S. Pat. No. 4,174,358). To be successful it is necessary to reduce the domain sizes for both of the polymers and to increase the interaction between domains.
In general, polyolefins have been the most difficult materials to chemical modify. In direct polymerization processes (in-reactor), it is difficult to incorporate functional group-containing monomers into polyolefins using the early transition metal catalysts (both Ziegler-Natta and Metallocene) because the functional groups tend to poison the catalysts. In post-reactor processes, the inert nature and crystallinity of the olefin polymers usually makes the material very difficult to chemically modify under mild reaction conditions. In many cases, post reaction modification of polyolefins, such as polyethylene and polypropylene, results in serious side reactions, such as crosslinking and degradation (G. Ruggeri et al, Eur. Polymer J. 19, 863-866, 1983). Accordingly, it is very challenging to develop a new chemistry that can prepare functionalized polyolefins having a controlled molecular structure.
In earlier work (U.S. Pat. Nos. 5,286,800 and 5,401,805), systematic investigations were made of borane-containing polyolefins that were prepared either by direct polymerization of organoborane-substituted monomers and &agr;-olefins in Ziegler-Natta and metallocene polymerization processes or by hydroboration of the unsaturated polyolefins (Chung et al, Macromolecules 27, 26-31, 1994; Macromolecules 27, 7533-7537, 1994; Polymer 38, 1495-1502, 1997). The borane-containing polyolefins are very useful intermediates for preparing a series of functionalized polyolefins (Chung et al, Macromolecules 32, 2525-2533, 1999; Macromolecules 31, 5943-5946, 1998) and polyolefin graft copolymers, which showed very effective interfacial activity for improving polyolefin blends by reducing the domain sizes and increasing the interaction between domains. (Chung et al, Macromolecules 26, 3467-3471, 1993; Macromolecules, 27, 1313-1319, 1994).
An alternative route was described in U.S. Pat. No. 3,141,862. In that patent, graft copolymers were prepared via borane-containing polyolefin. The process was carried out by first treating a solid hydrocarbon polymer, in the presence of an inert organic diluent, with a boron alkyl (BR
3
) and an oxygen-containing gas (e.g., air) at a temperature in the range of 20 to 150° C. The treated polymer was washed and then contacted with polar monomers (including 4-vinylpyridine and acrylonitrile) to form the graft copolymer. Apparently, the graft reaction was very inefficient, and all reactions required high concentration of organoborane and monomers to result in low yield graft copolymer and some homopolymers. Moreover, no information about the molecular structure of resulting copolymers was given. The estimated overall graft efficiency (graft density vs. borane) was very low (less than a few percent). Excess oxygen may cause over-oxidization of trialkylborane to form inactive bororate, borate, etc., as will be apparent from the discussion hereinbelow of the trialkylborane oxidation mechanism. Oxygen is also known to be a powerful inhibitor of free radical reactions by forming a relatively stable peroxyl radical. In addition, moisture in air can easily hydrolyze the oxidized borane moieties and prevent the graft reaction with the polymer.
In the prior art, it also has been disclosed that trialkyborane in an oxidized state becomes an initiator for the polymerization of vinyl monomers. (J. Furukawa et al, J. Polymer Sci., 26, 234-236, 1957; J. Polymer Sci. 28, 227-229, 1958; F. S. Arimoto, J. Polymer Sci.: Part A-1, 4, 275-282, 1966; F. J. Welch, J. Polymer Sci. 61, 243-252, 1962 and U.S. Pat. No. 3,476,727). The polymerization involves a free radical addition mechanism. A major advantage of using borane initiators is their ability to initiate the polymerization at low temperature. Traditional peroxides and azo initiators usually require considerable heat input to decompose and thereby to generate free radicals. Elevation of the temperature often causes significant reduction in molecular weight of a polymer accompanied by the loss of important properties of the polymer.
Despite the advantage of borane initiators, organoborane-initiated polymerizations tend to be unduly sensitive to the concentration of oxygen in the polymerization system. Too little or too much oxygen results in little or no polymerization. High oxygen concentration causes organoborane to be transformed rapidly to borinates, boronates and borates, which are poor initiators at low temperature. Moreover, polymerization is often inhibited by oxygen. To facilitate the formation of free radicals, some borane-containing oligomers and polymers were used as initiators in free radical polymerization reactions (See, e.g., U.S. Pat. Nos. 4,167,616 and 4,638,092). These organoboranes are prepared by the hydroboration of diene monomers or polymers or copolymers. Similar polymeric organoborane adducts, prepared by the hydroboration of 1,4-polybutadiene and 9-borabicyclo(3,3,1)-nonane (9-BBN), have been reported by S. Ramakrishnan in Macromolecules 24, 3753-3579, 1991. However, no information was provided about the application of organoborane-containing polyolefin polymers in the preparation of polyolefin graft copolymers.
Due to their unique combination of low cost, high activity and good processiblity, maleic anhydride (MA) modified polyolefins are, by far, the most important class of functionalized polyolefins in commercial applications. They are the general choice of material for improving compatibility, adhesion, and paintability of polyolefins. Among them, MA modifi
Asinovsky Olga
DeLaurentis Anthony J.
Penn State Research Foundation
Seidleck James J.
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