Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2002-05-08
2004-03-23
Egwim, Kelechi C. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C524S832000, C526S303100, C526S317100
Reexamination Certificate
active
06710141
ABSTRACT:
The present invention relates to a process for continuous production of crosslinked fine particles of polymer gel.
DE-A-34 32 690 discloses a process for continuous production of crosslinked polymers by polymerizing water-soluble monomers in the presence of a crosslinker and of initiators in a vessel provided with a plurality of parallel rotary stirrer shafts fitted with stirrer blades. The polymerization is carried out continuously in a two-arm kneader or, for example, in a three-shaft kneader. This type of reactor gives rise to pronounced backmixing, so that the monomer solution is applied to the finely divided water-containing gel polymer and the polymerization of the monomer takes place on the surface of the polymer gel. The finely divided polymer gels producible in this way have a relatively high residual monomer content.
EP-A-223 063 teaches a process for continuous production of crosslinked fine particles of polymer gel in a single-screw cylindrical mixer whose mixing segments cause the substances to be conveyed from the upstream to the downstream end of the cylindrical mixer. The polymerization is carried out at from 100 to 800 mbar, so special equipment is needed to regulate the pressure. The monomers have to be metered into the reactor via a pressure maintenance valve, which tends to get clogged up with polymer. In addition, the two processes have an unsatisfactorily broad residence time spectrum and a fluctuating product discharge.
It is an object of the present invention to provide a high space-time yield process which is convenient in terms of equipment and whose product is a uniform polymer gel having a low residual monomer content.
We have found that this object is achieved by a process for continuous production of crosslinked fine particles of polymer gel by copolymerizing
a) water-soluble monoethylenically unsaturated monomers,
b) from 0.001 to mol % based on the monomers (a) of monomers containing at least two ethylenically unsaturated double bonds, and
c) from 0 to 20 mol % based on the monomers (a) of water-insoluble monoethylenically unsaturated monomers in from 20 to 80% by weight aqueous solution in the presence of an initiator at from 0 to 140° C. by feeding the aqueous solution of the monomers together with the initiator and an inert gas continuously into a mixing kneader having at least two axially parallel rotating shafts equipped with a plurality of kneading and transporting elements which convey the substances introduced at the upstream end of the mixing kneader in the axial direction toward the downstream end of the mixer, which comprises the fraction of heat being removed by evaporation of water from the reaction mixture being not less than 5% of the heat of reaction and the fraction of heat being removed by product discharge being not less than 25% of the heat of reaction and the rest of the heat being removed via cooling of the reactor walls.
Water-soluble monoethylenically unsaturated monomers of group (a) include for example ethylenically unsaturated C
3
- to C
6
-carboxylic acids, amides and esters with aminoalcohols of the formula
where R
4
is C
2
to C
5
-alkylene and R
1
, R
2
, R
3
are independently hydrogen, methyl, ethyl or propyl. These compounds include for example acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, the alkali metal and ammonium salts of these acids, acrylamide, methacrylamide, crotonamide, dimethylaminoethyl acrylate, diethylaminoethyl acrylate, dimethylaminopropyl acrylate, dimethylaminobutyl acrylate, diethylaminoethyl methacrylate, dimethylaminoethyl methacrylate, dimethylaminopropyl methacrylate, dimethylaminoneopentyl acrylate and dimethylaminoneopentyl methacrylate. The basic acrylates and methacrylates are used in the form of the salts with strong mineral acids, sulfonic acids or carboxylic acids or in quaternized form. The anion X
−
for the compounds of the formula I is the acid radical of the mineral acids or of the carboxylic acids or methosulfate, ethosulfate or halide from a quaternizing agent.
Further water-soluble monomers of group (a) are N-vinylpyrrolidone, acrylamidopropanesulfonic acid, vinylphosphonic acid and alkali metal and ammonium salts of vinylsulfonic acid. The other acids may likewise be used in the polymerization either in non-neutralized form or in partially or up to 100% neutralized form. Useful water-soluble monomers of group (a) also include diallylammonium compounds, such as dimethyldiallylammonium chloride, diethyldiallylammonium chloride or diallylpiperidinium bromide, N-vinylimidazolium compounds, such as salts or quaternization products of N-vinylimidazole and 1-vinyl-2-methylimidazole, and N-vinylimidazolines, such as N-vinylimidazoline, 1-vinyl-2-methylimidazoline, 1-vinyl-2-ethylimidazoline or 1-vinyl-2-n-propylimidazoline, which are likewise used in the polymerization in quaternized form or as salt.
Preferred monomers of group (a) are acrylic acid, methacrylic acid, the alkali metal and ammonium salts of these acids, acrylamide and methacrylamide. These monomers may be copolymerized with each other in any desired proportion.
The monomers of group (a) are polymerized in the presence of crosslinkers (monomers of group (b)). Said crosslinkers contain at least two ethylenically unsaturated double bonds. Useful crosslinkers include for example N,N′-methylenebisacrylamide, polyethylene glycol diacrylates and polyethylene glycol dimethacrylates which are each derived from polyethylene glycols having a molecular weight of from 126 to 8500, preferably from 400 to 2000, trimethylolpropane triacrylate, trimethylolpropane trimethacrylate, ethylene glycol diacrylate, propylene glycol diacrylate, butanediol diacrylate, hexanediol diacrylate, hexanediol dimethacrylate, diacrylates and dimethacrylates of block copolymers of ethylene oxide and propylene oxide, doubly or triply acrylated or methacrylated polyhydric alcohols, such as glycerol or pentaerythritol, triallylamine, tetraallylethylenediamine, divinylbenzene, diallyl phthalate, polyethylene glycol divinyl ether of polyethylene glycols having a molecular weight of from 126 to 4000, trimethylolpropane. diallyl ether, butanediol divinyl ether, pentaerythritol triallyl ether and/or divinylethyleneurea. Preference is given to using water-soluble crosslinkers, for example N,N-methylenebisacrylamide, polyethylene glycol diacrylate, polyethylene glycol dimethacrylates, pentaerythritol triallyl ether and/or divinylurea. The monomers of group (b) are used in the copolymerization in amounts from 0.001 to 5, preferably from 0.005 to 0.5, mol % based on the monomers (a).
The copolymerization of the monomers of groups (a) and (b) may—if a change in the properties of the copolymers is desired—be carried out in the additional presence of monomers of group (c). Useful monomers of group (c) include for example hydroxyethyl acrylate, hydroxypropyl acrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, acrylonitrile and methacrylonitrile.
Also useful are esters of acrylic acid or methacrylic acid with monohydric alcohols containing from 1 to 18 carbon atoms, eg methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, hexyl acrylate, 2-ethylhexyl acrylate, stearyl acrylate, the corresponding esters of methacrylic acid, diethyl fumarate, diethyl maleate, dimethyl maleate, dibutyl maleate, vinyl acetate and vinyl propionate. If the monomers of group (c) are used for modifying the water-soluble polymers, from 0.5 to 20, preferably from 2 to 10, mol % based on monomers (a) are used.
The water-insoluble monomers, if used in the copolymerization, may be finely dispersed in the aqueous solution by means of emulsifiers. Useful emulsifiers include for example ethoxylated nonylphenols, ethoxylated castor oil, alkyl sulfates, sorbitan fatty esters, ethoxylated sorbitols, ethoxylated sorbitan fatty esters and alkylsulfonates. The emulsifiers are used in an amount of from 0 to 3% by weight based on the monomers (a).
The polymerization may be carried out in
Daniel Thomas
Heide Wilfried
Hofmann Jürgen
Nilges Joachim
Wickel Stefan
BASF - Aktiengesellschaft
Egwim Kelechi C.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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