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
2000-05-21
2003-07-08
Seidleck, James J. (Department: 1711)
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...
C524S458000, C524S460000, C528S199000, C528S200000, C528S201000, C528S208000
Reexamination Certificate
active
06590022
ABSTRACT:
BACKGROUND OF THE INVENTION
1) Field of the Invention
The invention relates to a process for preparing protective-colloid-stabilized vinylaromatic-1,3-diene copolymers.
2) Background Art
Protective-colloid-stabilized polymers, especially in the form of their aqueous dispersions or in the form of their water-redispersible polymer powders, are used in a wide variety of applications, for example as coating compositions or adhesives for a very wide variety of substrates. Polymers whose preparation in aqueous media, for example by emulsion polymerization, involves stabilization by emulsifiers, tend to have high water absorption when used, due, to the emulsifier content. When they are used as an adhesive, for example, they have reduced bonding power.
These disadvantages can be overcome by stabilizing the polymerization mixture exclusively with protective colloids. The protective-colloid-stabilized aqueous polymer dispersions and protective-colloid-stabilized polymer powders which have so far become established are especially those based on vinyl ester homopolymers or vinyl ester copolymers, specifically polyvinyl acetate or vinyl acetate-ethylene copolymers. The reason for this is that the stabilizing effect developed by protective colloids is generally lower than that of emulsifiers, so that complete replacement of emulsifiers by protective colloids has hitherto given satisfactory products only with relatively hydrophilic polymers, such as the abovementioned vinyl ester polymers.
However, polymers with any hydrophobic character, such as styrene-butadiene copolymers, are preferred in many applications, and the polymerization of polymers of this type requires effective stabilization. Styrene-butadiene copolymers are therefore generally polymerized in an aqueous phase in the presence of emulsifiers. The hydrophilic character of the emulsifier content present, however, counteracts to some extent the hydrophobic properties of the copolymer when emulsifier-stabilized styrene-butadiene copolymers are used.
In particular when polymers are used in the form of their redispersion powders, for improving mortar properties, a main application sector for redispersion powders, the formulations have to remain stable for a certain time and must not change their working consistency significantly (cement stability). This is because the user cannot be expected to remix at frequent intervals. In the concrete and mortar industry a significant role is played by mechanical properties, such as compressive strength and porosity, and the associated air pore content. If too many air pores are present there is a severe reduction in compressive strength, and if too few or no air pores are present in the mortar or concrete, the building material has insufficient resistance to frost and condensation. In addition, the hydraulically setting systems modified with the dispersion powder should provide adhesion which is even better than that of unmodified systems.
WO-A 96/17891 discloses water-redispersible dispersion powders based on styrene-butadiene copolymers. The powders are obtainable by emulsion polymerization in the presence of emulsifiers. Prior to drying, monosaccharide, polyvinylpyrrolidone and, if desired, emulsifier are then added to the dispersion. WO-A 96/20963 discloses a process for preparing water-redispersible polymer powders based on styrene-butadiene polymers. The polymers here are prepared by two-stage polymerization in the presence of emulsifier to give core-shell polymers, and are spray dried. WO-A 96/41825 likewise relates to dispersion powders based on core-shell polymers. The shell here has saccharide-functional comonomers and crosslinkable comonomers for covalent linking of the shell to the core. In addition to the relatively complicated procedure for preparing the redispersion powders, these powders have the disadvantages discussed above of emulsifier-stabilized styrene-butadiene copolymers, and in addition they have unsatisfactory performance, specifically ease of use with regard to cement stability.
WO-A 97/15603 relates to protective-colloid-stabilized emulsion polymers of conjugated dienes, with mercaptosilanes copolymerized to improve the protective-colloid action. Disadvantages here are that the polymerization uses emulsifiers as well as the protective-colloid and especially that the copolymerization of mercaptosilane, which is an essential requirement, makes the preparation more expensive and is undesirable for many applications since it reduces the degree of crosslinking of the butadiene units.
EP-A 538571 relates to a process for preparing protective-colloid-stabilized polymer dispersions based on polymers having more than 50% content of styrene and/or of (meth)acrylate. All of the polyvinyl alcohol used for stabilization is used as an initial charge, and specific initiator systems are used to adjust hydrophilic properties and viscosity. In the examples, stable dispersions are obtained with styrene, butyl acrylate and acrylamide. A disadvantage is that this process does not give stable dispersions from the copolymerization of styrene and butadiene.
EP-B 62106 discloses a procedure for preparing polyvinyl-alcohol-stabilized polymer dispersions based on styrene units and/or on (meth)acrylate units. The minimum temperature for the procedure is above 65° C., and it is carried out in the presence of organic initiators or peroxosulphur compounds, an by feeding the main portion of the monomers. The preparation of styrene-butadiene copolymers is not dealt with.
U.S. Pat. No. 5,200,459 describes a process for preparing polyvinyl-alcohol-stabilized butadiene copolymers, in the presence of a water-miscible solvent to ensure dispersion stability.
DE-A 4212768 relates to a process for preparing synthetic-polymer dispersions, inter alia styrene-butadiene copolymer dispersions. These are prepared without addition of emulsifier, but instead of this in the presence of a copolymerizable macromonomer based on crosslinking products of polyalkylene glycols and maleic acid or fumaric acid.
U.S. Pat. No. 4,299,903 teaches the preparation of an emulsifier-free toner resin based on styrene-butadiene by copolymerization in the presence of a “charge control agent” selected from the group consisting of quaternary ammonium salts or alkylpyridinium compounds.
The object of the invention was therefore to provide a process which can give access to protective-colloid-stabilized vinylaromatic-1,3-diene copolymers without addition of other auxiliaries to stabilize the polymerization mixture. The products of the process should have entirely satisfactory cement stability, in particular when used with hydraulic binders.
SUMMARY OF THE INVENTION
The invention provides a process for preparing protective-colloid-stabilized vinylaromatic-1,3-diene copolymers in the form of their aqueous polymer dispersions or in the form of their water-redispersible powders, by emulsion polymerization of a mixture comprising at least one vinylaromatic and comprising at least one 1,3-diene in the presence of protective colloid, and, if desired, drying the resultant polymer dispersions, characterized in that some of the protective colloid is used as an initial charge and some of the protective colloid is used as a feed.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Suitable vinylaromatics are styrene and methylstyrene, preferably styrene. Examples of 1,3-dienes are 1,3-butadiene and isoprene, preferably 1,3-butadiene. The polymerization is generally carried out using mixtures with from 20 to 80% by weight of vinylaromatic and from 20 to 80% by weight of 1,3-diene, and the mixtures may, if desired, also comprise further monomers and the per cent by weight data always give a total of 100% by weight.
Based on the total weight of the monomer phase, up to 30% by weight of other monomers copolymerizable with vinylaromatics and with 1,3-dienes may also be polymerized, for example ethylene, vinyl chloride, (meth)acrylates of alcohols having from 1 to 15 carbon atoms or vinyl esters of unbranched or branched carboxylic acids.
Based on the total weight of
Ball Peter
Bastelberger Thomas
Haerzschel Reinhard
Mayer Theo
Weitzel Peter
Brooks & Kushman P.C.
Rajguru U. K
Seidleck James J.
Wacker-Chemie GmbH
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