Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
1999-02-17
2001-01-23
Wu, David W. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S088000, C526S201000, C526S202000, C524S458000, C524S459000
Reexamination Certificate
active
06177525
ABSTRACT:
The present invention relates to a novel process for the preparation of a particulate polymer P having an average particle diameter d
50
of from 0.1 to 50 &mgr;m, in which an emulsion E is prepared from
one or more monomers M, which are polymerizable by free radical polymerization to give the polymer P,
water, and
at least one protective colloid PC
by the action of high shear forces, and the emulsion E is subjected to polymerization in a reactor with the use of a free radical polymerization initiator RI.
The present invention furthermore relates to special embodiments of the process as well as to particulate polymers P prepared by the process and the use of the polymers P as additives for thermoplastic molding materials or as toners for copiers.
Processes for the preparation of particulate polymers are, for example, emulsion polymerization and suspension polymerization. In emulsion polymerization, as a rule the monomers are emulsified in water and polymerized with the use of a polymerization initiator soluble in the aqueous phase and of an emulsifier, comparatively small polymer particles of, usually, from 30 to 1000 nm in diameter being formed. In suspension polymerization, the monomers are usually suspended in water with the use of a protective colloid which prevents the monomer droplets or polymer particles from aggregating and sticking together, and polymerization is carried out by means of an initiator which is soluble in the monomers, comparatively large particles of usually, from 50 to 500 &mgr;m in diameter being obtained.
A variant of suspension polymerization is microsuspension polymerization. Here, the mixture of monomers, water and protective colloid is exposed to high shear forces generated, for example, by very rapid and thorough stirring, resulting in monomer droplets—and from these polymer particles—their diameter of, usually, 0.1 to 50 &mgr;m is substantially smaller than in the case of the usual suspension polymerization.
A process of this type for the microsuspension polymerization of styrene divinylbenzene mixtures is described, for example, by L. Danicher et al. in Reactive Polymers 20 (1993), p. 111-121, and that for the microsuspension polymerization of styrene-n-butyl acrylate mixtures is described by M. Kamiyama in Journal of Applied Polymer Science, 50 (1993), p. 107-113.
German Patent, 2,618,761 discloses such a process for the polymerization of vinyl chloride.
EP-B 38 208 describes a corresponding process for the preparation of (pigment-containing) copier toner particles from a vinyl monomer.
EP-B 443 609 and U.S Pat. No. 4,071,670 disclose a microsuspension process for the polymerization of vinyl monomers with the use of a special high-speed stirrer.
Common to all these processes is that the total amount of the monomer emulsion is first initially taken in a stirred kettle reactor and early thereafter the polymerization is begun. The polymerization is accordingly carried out by a batchwise procedure.
In this procedure, controlling the temperature during the reaction presents problems since—particularly in the case of stirred kettles of relatively large volume—the heat of reaction evolved as a result of the exothermic polymerization can be removed only to an insufficient extent. In spite of stirring of the reaction mixture, hot spots may form in the kettle, leading to a nonuniform degree of crosslinking of the polymer particles and a nonuniform molecular weight distribution of the resulting polymer, ie. to undesired fluctuations in the product properties.
This problem cannot always be overcome, even when the kettle is equipped with—large-dimensioned and therefore expensive—cooling apparatuses, for example heat exchangers.
Moreover, the poorly controllable heat removal may result in the polymerization reaction going out of control (runaway of the reactor), which constitutes a considerable safety risk.
It is an object of the present invention to provide a process which does not have the disadvantages described. In particular, it is intended to provide a process which permits the preparation of a particulate polymer P of constant product quality.
It is a further object of the present invention to provide a technically simple and therefore economically advantageous process for the preparation of polymers P.
It is a further object of the present invention to provide a process which permits a particularly safe polymerization procedure.
We have found that this object is achieved by the process defined at the outset, wherein, based on the emulsion E, not more than 35% by weight of the emulsion E (referred to hereinafter as initially taken portion of E) are initially taken in the reactor at the beginning of the polymerization and at least 65% by weight of the emulsion E (referred to hereinafter as feed portion of E) are not fed to the reactor until after the beginning of the polymerization.
We have also found preferred embodiments for the process with regard to the period of addition of the feed portion and the type of monomers and protective colloids used.
Further preferred embodiments found relate to the addition of additives, the addition and polymerization of further monomers M*, the type of monomers M* and finally the particulate polymers P prepared by the process and their use as additives for thermoplastic molding materials or as toners for copiers.
The novel process and the preferred embodiments are described in more detail below.
Suitable as monomers M are all monomers, which are capable of free radical polymerization, ie. polymerize in the presence of free radicals. Preferred monomers M1) to M9) are the following:
M1) C
1
-C
12
-alkyl esters of acrylic acid or of methacrylic acid
Particularly suitable alkyl acrylates are those which are derived from ethanol, from 2-ethylhexanol and in particular from n-butanol. 2-Ethylhexyl acrylate and very particularly n-butyl acrylate are preferred. Mixtures of different alkyl acrylates which differ in their alkyl radical may also be used.
The alkyl acrylates are preferably crosslinked, for which purpose a polyfunctional, crosslinking monomer is present in amounts of up to 10% by weight, based on the monomers M. Crosslinking monomers are bi- or polyfunctional comonomers having at least two olefinic, nonconjugated double bonds, for example butadiene and isoprene, divinyl esters of dicarboxylic acids, such as those of succinic acid and adipic acid, diallyl and divinyl ethers of bifunctional alcohols, such as those of ethylene glycol and of butane-1,4-diol, diesters of acrylic acid and methacrylic acid with the stated bifunctional alcohols, 1,4-divinylbenzene and triallyl cyanurate. The acrylates of tricyclodecenyl alcohol of the following formula
which is known under the name dihydrodicyclopentadienyl acrylate, and the allyl esters of acrylic acid and of methacrylic acid are particularly preferred.
A particularly suitable alkyl methacrylate is methyl methacrylate.
M2) conjugated dienes, such as butadiene, isoprene and chloroprene, as well as norbornene and dicyclopentadiene.
M3) vinyl aromatic monomers, such as styrene and styrene derivatives of the general formula
where R
1
and R
2
are each hydrogen or C
1
-C
8
-alkyl.
M4) acrylonitrile and methacrylonitrile.
M5) the glycidyl esters glycidyl acrylate and methacrylate.
M6) N-substituted maleinimides such as N-methyl-, N-phenyl- and N-cyclohexylmaleinimide.
M7) acrylic acid, methacrylic acid, and dicarboxylic acids, such as maleic acid, fumaric acid and itaconic acid, and the anhydrides thereof, such as maleic anhydride.
M8) monomers having nitrogen functional groups, such as dimethylaminoethyl acrylate, diethylaminoethyl acrylate, vinylimidazole, vinylpyrrolidone, vinylcaprolactam, vinylcarbazole, vinylaniline, acrylamide and methacrylamide.
M9) aromatic and araliphatic esters of acrylic acid and methacrylic acid such as phenyl acrylate, phenyl methacrylate, benzyl acrylate, benzyl methacrylate, 2-phenylethyl acrylate, 2-phenylethyl methacrylate, 2-phenoxyethyl acrylate and 2-phenoxyethyl methacrylate.
M10) unsaturated ethers, such as vinyl methyl ether.
The
Jahns Ekkehard
Kastenhuber Walter
McKee Graham Edmund
Renz G{umlaut over (u)}nter
BASF - Aktiengesellschaft
Egwim Kelechi C.
Keil & Weinkauf
Wu David W.
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