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
2000-07-06
2003-01-14
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...
C525S244000, C525S247000, C525S249000, C525S089000
Reexamination Certificate
active
06506846
ABSTRACT:
The invention relates to a process for preparing impact-modified thermoplastic molding compositions which comprise a soft phase made from a rubber dispersed in a hard matrix composed of vinylaromatic monomers.
There are various known continuous and batch processes, in solution or suspension, for preparing impact-modified polystyrene. In these processes a rubber, usually polybutadiene, is dissolved in monomeric styrene, which is polymerized in a preliminary reaction to a conversion of about 30%. The formation of polystyrene and the associated depletion of monomeric styrene results in a change in the phase coherence. During this process, known as phase inversion, grafting reactions also occur on the polybutadiene and these, together with the intensity of agitation and the viscosity, affect the formulation of the disperse soft phase. The polystyrene matrix is built up in the main polymerization which follows. Processes of this type, carried out in various types of reactor, are described, for example, in A. Echte, Handbuch der technischen Polymerchemie, VCH Verlagsgesellschaft Weinheim, Germany, 1993, pages 484-489 and in U.S. Pat. Nos. 2,727,884 and 3,903,202.
These processes require complicated comminution and dissolving of the separately prepared rubber, and the resultant polybutadiene rubber solution in styrene has to be filtered before the polymerization to remove gel particles.
The required solution of rubber in styrene may also be prepared by anionic polymerization of butadiene or butadiene/styrene in nonpolar solvents, such as cyclohexane or ethylbenzene, followed by addition of styrene (GB 1 013 205 and EP-A-0 334 715) or by incomplete conversion of butadiene in styrene (EP-A 0 059 231 and EP-A 0 304 088) followed by removal of the unconverted butadiene. The rubber solution is then subjected to a free-radical polymerization.
Processes for preparing thermoplastic molding compositions by anionic polymerization of styrene in the presence of a rubber are known, for example, from DE-A-42 35 978 and U.S. Pat. No. 4,153,647. The resultant impact-modified products have lower contents of residual monomers and oligomers, compared with the products obtained via free-radical polymerization.
Anionic polymerization of styrene proceeds very rapidly and gives very high conversions. The high polymerization rate and the heat generation associated with this mean that on an industrial scale these processes are restricted to very dilute solutions, low conversions or low temperatures.
Alkyl compounds of alkaline earth metals, of zinc and of aluminum have therefore been described as retardant additives for anionic polymerization of styrene (WO 97/33923 and WO 98/07765) or butadiene in styrene (WO 98/07766). Controlled anionic polymerization of styrene and butadiene to give homopolymers or styrene-butadiene copolymers is possible with these additives.
WO 98/07766 moreover describes the continuous preparation of impact-modified molding compositions using the styrene-butadiene rubbers which can be obtained by means of the retardant additives in styrenic solution. However, the rubbers obtainable by this process always comprise small amounts of copolymerized styrene in the butadiene blocks.
It is an object of the invention to avoid the disadvantages mentioned and to develop a process which permits the preparation of impact-modified molding compositions which are low in residual monomers and in oligomers. The process should furthermore ensure simple and reliable control of the reaction. It should be suitable for using a very large number of types of rubber, in order to permit a wide range of properties in the impact-modified molding compositions.
Another object was a continuous process for anionic polymerization of impact-modified molding compositions with simple and reliable control of the reaction.
We have found that this object is achieved by means of a process for preparing impact-modified thermoplastic molding compositions which comprise a soft phase made from a rubber dispersed in a hard matrix composed of vinylaromatic monomers, where the hard matrix is prepared by anionic polymerization in the presence of a metal organyl compound of an element of the second or third main group, or of the second subgroup, of the Periodic Table.
Metal organyl compounds of an element of the second or third main group, or of the second subgroup, of the Periodic Table which may be used are the organyl compounds of the elements Be, Mg, Ca, Sr, Ba, B, Al, Ga, In, Tl, Zn, Cd, Hg. These metal organyl compounds are also termed retarders, due to their effect during anionic polymerization. Preference is given to the magnesium and aluminum organyl compounds. For the purposes of the invention, organyl compounds are the organometallic compounds of the elements mentioned with at least one metal-carbon a bond, in particular the alkyl or aryl compounds. The metal organyl compounds may also contain, on the metal, hydrogen, halogen, or organic radicals bonded via heteroatoms, giving compounds, such as alcoholates or phenolates. The latter are obtained, for example, by complete or partial hydrolysis, alcoholysis or aminolysis. It is also possible to use mixtures of different metal organyl compounds.
Suitable magnesium organyl compounds have the formula R
2
Mg, where R, independently of one another, are hydrogen, halogen, C
1
-C
20
-alkyl or C
6
-C
20
-aryl. Preference is given to dialkylmagnesium compounds, in particular the ethyl, propyl, butyl or octyl compounds which are commercially available products. Particular preference is given to (n-butyl)(sec-butyl)magnesium, which is soluble in hydrocarbons.
Aluminum organyl compounds of the formula R
3
Al may be used, where R, independently of one another, are hydrogen, halogen, C
1-C
20
-alkyl or C
6
-C
20
-aryl. Preferred aluminum organyl compounds are the aluminum trialkyl compounds, such as triethylaluminum, triisobutylaluminum, tri-n-butylaluminum, triisopropylaluminum and tri-n-hexylaluminum. Particular preference is given to triisobutylaluminum. Use may also be made of aluminum organyl compounds produced by partial or complete hydrolysis, alcoholysis, aminolysis or oxidation of aluminum alkyl compounds or of aluminum aryl compounds. Examples of these are diethylaluminum ethoxide, diisobutylaluminum ethoxide, diisobutyl(2,6-di-tert-butyl-4-methylphenoxy)aluminum (CAS No. 56252-56-3), methylaluminoxane, isobutylated methylaluminoxane, isobutylaluminoxane, tetraisobutyldialuminoxane and bis(diisobutyl)aluminum oxide.
The retarders described generally do not act as polymerization initiators. The anionic polymerization initiators used are usually mono-, bi- or polyfunctional alkali metal alkyl compounds, alkali metal aryl compounds or alkali metal aralkyl compounds. It is useful to use organolithium compounds, such as ethyl-, propyl-, isopropyl-, n-butyl-, sec-butyl-, tert-butyl-, phenyl-, diphenylhexyl-, hexamethylenedi-, butadienyl-, isoprenyl- or polystyryllithium, or the polyfunctional compounds 1,4-dilithiobutane, 1,4-dilithio-2-butene or 1,4-dilithiobenzene. The amount of alkali metal organyl compound required depends on the desired molecular weight and on the type and amount of the other metal organyl compounds used, and also on the polymerization temperature. It is generally in the range from 0.002 to 5 mol percent, based on the total amount of monomers.
Preferred vinylaromatic monomers for the hard matrix are styrene, &agr;-methylstyrene, p-methylstyrene, ethylstyrene, tert-butylstyrene, vinyltoluene and 1,1-diphenylethylene, or mixtures. Styrene is particularly preferred.
The rubber used for the soft phase may be any desired diene rubber or acrylate rubber, or mixtures which have a certain compatibility with the vinylaromatic hard matrix. It is therefore advantageous if the rubber comprises a certain proportion of styrene blocks, since the anionic polymerization of the hard matrix does not produce any compatibility of the rubber via grafting of monomers which form the hard matrix.
The rubber used is preferably a styrene-butadiene block copolymer or a mixture of a styrene
Fischer Wolfgang
Gausepohl Hermann
Moors Rainer
Schade Christian
Warzelhan Volker
Asinovsky Olga
BASF - Aktiengesellschaft
Keil & Weinkauf
Seidleck James J.
LandOfFree
Method for producing impact-resistant modified thermoplastic... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method for producing impact-resistant modified thermoplastic..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method for producing impact-resistant modified thermoplastic... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3044823