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
2002-01-23
2003-04-15
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...
C525S329900, C526S263000, C526S272000
Reexamination Certificate
active
06548606
ABSTRACT:
FIELD OF THE INVENTION
This invention is directed to an improved method of forming grafted copolymers. More specifically, the present invention is directed to a method of grafting nitrogen-containing monomers onto linear, radial or star-shaped copolymers with reduced cross-linking; and to lubricating oil compositions containing the resultant polymers.
BACKGROUND OF THE INVENTION
Lubricating oils for use in crankcase engine oils contain components that are used to improve the viscometric performance of the engine oil, i.e., to provide multigrade oils such as SAE 5W-30, 10W-30 and 10W-40. These viscosity performance enhancers, commonly referred to as viscosity index (VI) improvers include olefin copolymers, polymethacrylates, and styrene/hydrogenated diene block and star copolymers. Such polymeric materials are often referred to as “nondispersant VI improvers” because they do not prevent varnish and/or sludge in the oil from depositing on the internal surfaces of the internal combustion engine.
To prevent the deposition of sludge on engine parts, dispersants, commonly referred to as “ashless dispersants”, are added to motor oils. These dispersants, which commonly have a nitrogen-containing polar head that associates with the sludge in the oil, and a long oil soluble tail portion, keep the sludge and varnish materials suspended in oil and prevent them from forming deposits within the engine. VI improvers can be provided with nitrogen-containing functional groups that impart dispersant capabilities to the VI improver. One trend in the industry has been to use such “multifunctional” VI improvers in lubricants to replace some or all of the dispersant.
Nitrogen-containing functional groups can be added to a polymeric VI improver by grafting a nitrogen-containing moiety onto the polymeric backbone of the VI improver. Processes for the grafting of a nitrogen-containing moiety onto a polymer are known in the art and include, for example, contacting the polymer and nitrogen-containing moiety in the presence of a free radical initiator, either neat, or in the presence of a solvent. The free radical initiator may be generated by shearing (as in an extruder) or heating a free radical initiator precursor, such as hydrogen peroxide.
However, the grafting of a nitrogen-containing moiety onto a polymeric backbone, particularly when extrusion grafting, both degrades the polymer and causes crosslinking between the polymer chains. Crosslinked polymer chains produce a number of undesirable properties in formulated motor oil. Highly crosslinked polymer chains do not dissolve in oil, and the crosslinked polymer must be filtered from the oil soluble polymer before use in the formulation of a lubricating oil. The oil insoluble, filtered material has no commercial value. Also, concentrates containing crosslinked polymers are often gelatinous at room temperature. This causes handling problems as such fluids do not flow, or flow with difficulty, under low shear conditions. Such crosslinked chains are also sensitive to shear and thereby provide lubricating oils in which the viscosity is highly dependent on the intensity of shearing to which the oil is subjected.
U.S. Pat. No. 5,141,996 discloses a process for the preparation of a grafted star polymer in which a nitrogen-containing polymerizable organic polar compound (e.g., 2-vinyl pyridine or 4-vinylpyridine) is contacted with a hydrogenated star polymers comprising a nucleus (e.g., a poly(-polyvinyl aromatic coupling agent) bearing polymeric arms of hydrogenated homopolymers, and copolymers of conjugated dienes; hydrogenated copolymers of conjugated dienes and mono-alkenyl arenes; or mixtures of the foregoing, in a mineral oil solvent, and in the presence of a free radical polymerization initiator and either a chain transfer agent, a pi-electron donor or a comonomer. The chain transfer agent, a pi-electron donor or a comonomer is described as acting as a coupling inhibitor. Suitable chain transfer agents are described as compounds containing an active hydrogen atom, such as long chain alkyl mercaptans. Anisole and N-vinylpyrrolidone are described as suitable pi-electron donors and comonomers, respectively. The presence of the chain transfer agent, pi-electron donor or comonomer was described as leading to a reduction in the degree of cross-linking between nitrogen-containing moieties.
WO 98/13443 describes a multifunctional viscosity index improver for lubricating oil compositions comprising a hydrogenated star-shaped polymer comprising a poly(-polyalkenyl coupling agent) nucleus and at least four polymeric arms linked to the nucleus. Five to ten N-vinyl imidazole functional groups are grafted onto each of the arms, which arms comprise hydrogenated homopolymers and copolymers of conjugated dienes, hydrogenated copolymers of conjugated dienes and monoalkenyl arenes, and mixtures thereof. Said star-shaped polymers are formed by a method in which the nucleus and polymeric arms are contacted, in a solvent, in the presence of a free radical initiator. It is further suggested that cross-linking between the N-vinyl imidazole groups can be minimized if the N-vinylimidazole is introduced prior to the free radical initiator.
WO 99/21902 discloses extruder grafting of N-vinylimidazole to an ethylene/propylene copolymer. One feature of the disclosed process is the use of a polar or non-polar solvent for either the grafting monomer or the initiator employed. It is alleged that the use of a polar solvent (preferably water) suppresses “undesirable side polymerization reactions”.
In the process disclosed in U.S. Pat. No. 4,146,489, crosslinking that results from the grafting of vinylpyridine or vinylimidazole is controlled by post-degradation of the product in a gear pump, an extruder, or preferably, a homogenizer.
U.S. Pat. No. 4,292,414 describes a process for forming maleic anhydride-grafted block copolymers with reduced gelation, wherein grafting is performed in the presence of a “radical inhibitor”, which can be a phenol compound, a phosphorous compound, a naphthol compound, an amine compound, a quinone compound or a sulfur compound. Preferred radical inhibitors are naphthylamine compounds, phenylenediamine compounds, mercaptoalkylamine compounds, N-nitrosoamine compounds, quinoline compounds and phenothiazine compounds.
U.S. Pat. No. 4,506,056 suggests that, in a process for the preparation of carboxyl-containing polymers (specifically methylmethacrylate grafted with maleic anhydride), crosslinking can be reduced by mixing together the methyl methacrylate, maleic anhydride, a free radical initiator and an additive that that inhibits the homopolymerization of maleic anhydride but not that of methyl methacrylate. Suitable “additives” include various nitrogen-, phosphorous- and sulfur-containing compounds. Suitable nitrogen-containing compounds include proprionamide, stearamide, ethylene bis(-stearamide), N-methylacetamide, N,N-dimethylformamide, N,N-dimethylacetamide, N,N-diethyl dodecanamide, N,N-diethyl-m-toluamide, caprolactam, 2-pyrrolidone, N-methylpyrrolidone, N,N-dimethylaniline and 2,6-dimethylpyridine-N-oxide. (See also
J Polymer Science,
Part A: Polymer Chemistry, Vol. 26, 1189-1198 (1988);
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Polymer Letters, Vol. 20, 481-486 (1982) and
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Polymer Letters, Vol. 21, 23-30 (1983), all to Gaylord and Mehta and
Degradation and Cross
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linking of Ethylene
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Propylene Copolymer Rubber on Reaction with Maleic Anhydride and/or Peroxides; J. Applied Polymer Science,
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BRIEF SUMMARY OF THE INVENTION
The invention, in brief summary, is directed to a method of grafting nitrogen-containing grafting monomers to substrate polymers with a reduced occurrence of crosslinking. Specifically, the invention is directed to the discovery that the presence of certain amide compounds during grafting of nitrogen-containing grafting monomer reduces the tendency of the backbones to crosslink. In addition, the presence of certain amides has been found to improve the handling of pellets of t
De Groot Eleanor M.
Hess Martin L.
Rhodes Robert B.
Asinovsky Olga
Infineum International Ltd.
Seidleck James J.
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