Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2000-04-28
2002-10-22
Wu, David W. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S505000, C524S552000, C524S567000, C524S575000, C526S227000, C526S229000
Reexamination Certificate
active
06469094
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention is generally directed to a processes for the preparation of polymeric particulate materials with narrow particle size distribution properties and containing polymeric resin with narrow molecular weight distribution properties. More specifically, the present invention relates to processes for the preparation of polymeric particulate materials with improved reliability and yield, that is conversion of monomers to polymers, that provide highly stable latexes(latices) and to improved control over the resulting latex particle size and latex particle size distribution properties.
The present invention also relates to processes for the preparation of polymers, and more specifically to a two stage semi-emulsion process that includes a first bulk polymerization where controlled initiation and limited or partial monomer polymerization is accomplished for the purpose of preparing a prepolymer mixture followed by a second stage mini-emulsion polymerization where substantially complete monomer polymerization is accomplished. The present invention also relates to the polymeric resins, highly stable and versatile latices containing the polymeric resins, and useful latex particulate materials formed by the aforementioned processes.
Emulsion polymerization processes are known in the art, as illustrated hereinafter. Conventional emulsion polymerization processes proceed by a free radical mechanism providing resins of broad polydispersities and generally high molecular weights. The present invention relates to a semi-emulsion polymerization process that proceeds via a pseudoliving free radical mechanism and provides resins of high, intermediate, or low molecular weights and with narrow polydispersities. The present invention provides product resins with a latent thermally reactive functional group on at least one end which can be used for further reaction to prepare other resins with complex architectures. The present invention, in embodiments, provides for control of the emulsion droplet size and the resultant polymer resin bead or particle size, for example, as disclosed in the aforementioned commonly owned and assigned U.S. Pat. No. 5,852,140.
Emulsion polymerization processes are industrially important, and are the predominant process for the synthesis of a number of copolymers, such as for example styrene/butadiene. However, resins prepared by emulsion polymerization processes typically have broad polydispersities and high molecular weights. When low molecular weight resins are desired, a chain transfer agent is typically added to limit the extent of chain growth by way of premature chain termination events and which agent is, for example, an unpleasant smelling thiol compound. Polymers prepared by thiol type chain transfer mediated emulsion polymerization processes are terminated at either end with functional groups which preclude further free radical reactions and therefore limit the utility of the polymer resin products produced therefrom.
The present invention is directed to semi-emulsion polymerization processes which permit the economic preparation of high stability polymer particle latices containing narrow polydispersity resins with operator selectable low, intermediate, or high molecular weights. The low molecular weight polymer resins can be prepared without a chain transfer agent or molecular weight modifier and thereby provides several advantages over conventional emulsion polymerization processes as illustrated herein.
PRIOR ART
In U.S. Pat. No. 5,686,518, issued Nov. 11, 1997, Fontenot, et al., there is disclosed an essentially stable monomer miniemulsion characterized by small monomer droplet size is prepared and is then polymerized to a polymer latex under free radical polymerization conditions. The monomer miniemulsions herein include, in addition to water, a surfactant, and a monomer or mixture thereof, one or more polymers which function as a polymeric co-surfactant. The monomer miniemulsions are characterized by average monomer droplet size of 10 to 500 nanometers, preferably 80 to 150 nanometers. The amount of polymer added as a co-surfactant is about 0.5 to about 5 percent by weight based on monomer weight. The monomer emulsion may contain either a single monomer or a monomer mixture. The monomer emulsion is polymerized under conventional emulsion polymerization conditions yielding a polymer latex having an average polymer particle size of 10 to 500 nanometers, preferably 80 to 150 nanometers, and a narrow particle size distribution, i.e., a polydispersity index of about 1.05 to about 1.40. A representative monomer is methyl methacrylate and a representative polymer as co-surfactant is polymethyl methacrylate.
In U.S. Pat. No. 5,852,140, issued Dec. 22, 1998, to Georges, et al., there is disclosed a process for the preparation of a polymer which comprises effecting bulk polymerization of a mixture of at least one monomer, a free radical polymerization initiator, and a stable free radical agent until from about 10 to about 50 weight percent of the monomer has been polymerized(i.e. latomer mixture); optionally adding additional free radical initiator; optionally adding a colorant; dispersing with a high shear mixer the aforementioned partially polymerized mixture in water containing a stabilizing component selected from the group consisting of non-ionic and ionic water soluble polymeric stabilizers to obtain a suspension of particles with an average diameter of from about 0.1 to about 10 microns; and polymerizing the resulting suspension to form the polymer.
U.S. Pat. No. 5,006,617 issued Apr. 9, 1991, and U.S. Pat. No. 4,665,142 issued May 12, 1987, both to Engel et al., disclose the preparations of polymers free from emulsifiers and protective colloids by the free-radical initiated emulsion polymerization of ethylenically unsaturated copolymerizable monomers, wherein the emulsion polymerization is carried out in the absence of emulsifiers and protective colloids, using water-soluble, free-radical forming initiators and with the addition, at least at the start of the polymerization, of at least 0.01% by weight, based on the total amount of monomers, of poly-(ethylenically unsaturated) monomers, and the polymers can be obtained in the form of aqueous or non-aqueous dispersions or in the form of powder. The use of the polymers in the form of dispersions or powders is for modifying polymer materials and polymer raw materials and for the production of shaped articles and films.
U.S. Pat. No. 4,385,157 issued May 24, 1983, to Auclair et al., discloses a novel emulsion polymerization process for preparing a latex of rubber particles having a bimodal rubber particle size distribution of large and small particles followed by grafting said rubber particles with a monomer mixture forming a poly-blend of said grafted rubber particles and a matrix phase polymer of said monomers.
Bon et al., disclose a controlled radical polymerization process using a conventional emulsion system. Latex particles are prepared by a conventional emulsion polymerization process, and the resultant latex particles are then selected as a host for the SFR polymerization, see
Macromolecules,
1997, 30, 324-326.
The following references are also of interest: U.S. Pat. Nos. 3,682,875; 3,879,360; 3,954,722; 4,201,848; 4,542,182; 4,581,429; 4,777,230; 5,059,657; 5,173,551; 5,191,008; 5,191,009; 5,194,496; 5,216,096; and 5,247,024. All the aforementioned prior art references are incorporated herein in their entirety by reference.
In emulsion polymerization reaction processes of the prior art, various significant problems exist, for example difficulties in predicting or controlling both the polydispersity and modality of the polymers produced. These emulsion polymerization processes produce polymers with high weight average molecular weights (Mw) and low number average molecular weights (Mn) resulting in broad polydispersities or low molecular weight (Mn) and low conversion. Further, emulsion polymerization processes of the prior art are prone to generating exce
Georges Michael K.
Keoshkerian Barkev
MacLeod Paula J.
Odell Peter G.
Cheung William K.
Thompson Robert
Wu David W.
Xerox Corporation
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