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
2001-04-05
2003-05-20
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...
C525S338000, C525S191000, C525S088000, C526S093000, C585S273000, C585S275000, C585S277000
Reexamination Certificate
active
06566457
ABSTRACT:
The invention relates to a process for preparing graft rubbers based on (partially) hydrogenated diene-containing dispersions, to a graft rubber which can be prepared by this process, to the use of this graft rubber as impact modifier in thermoplastic blends, to blends comprising this graft rubber, and to a process for their preparation, and also to the use of the blends.
Polymeric materials are used in many different applications, for example in the automotive sector, as a material for pipelines, as insulators for electrical wiring, and as protective coatings. A requirement for applications in these sectors is that the polymeric materials retain their advantageous mechanical and physical properties for a very long period, even when exposed to extreme ambient conditions. Polymeric materials which contain reactive carbon—carbon double bonds are particularly susceptible to oxidative decomposition, leading to structural instability of these polymeric materials.
For example, in the case of what are known as ABS (acrylonitrile-butadiene-styrene) polymers, diene-based graft rubbers are used as impact-modifying rubber. The resultant products have good impact strength but relatively low weathering resistance and aging resistance. If the intention is to obtain polymers which are not only impact-resistant but also at the same time weathering- and aging-resistant, saturated rubbers have to be used as impact-modifying rubber. The elastomeric, preferably crosslinked, acrylate polymers have proven particularly suitable for this purpose. The corresponding molding compositions are called ASA (acrylonitrile-styrene-acrylate) polymers.
When acrylate polymers are compared with diene polymers for use as impact modifiers, disadvantages are that the acrylates used as monomers are more expensive than dienes, and that the low-temperature impact strength is lower. DE-A 31 49 046 relates to weathering-resistant thermoplastic molding compositions built up from a two-part elastomer phase which has a core made from a polybutadiene rubber and a shell made from a polyacrylate rubber. Onto this has been grafted a graft shell made from a hard component based on a styrene copolymer. However, these molding compositions have the expensive polyacrylate rubber alongside a butadiene rubber.
U.S. Pat. No. 4,452,950 relates to a process for preparing a polymeric material which has relatively high resistance to oxidative or thermal degradation. This increased resistance is achieved through hydrogenating unsaturated polymers which have carbon—carbon double bonds, after they have been prepared in aqueous dispersion (latex), using hydrazine or hydrates thereof. However, hydrogenation with hydrazine is problematic since hydrazine is toxic. U.S. Pat. No. 5,068,313 therefore relates to a process for minimizing hydrazine residues in polymer dispersions. Although this method can reduce the amount of hydrazine to a minimum, it necessitates a two-stage process following the hydrogenation.
U.S. Pat. No. 4,469,849 relates to a process for the complete or partial hydrogenation of ABS polymers, using hydrogen, in the presence of a catalyst. For this, a generally aqueous emulsion is first prepared of the ABS polymer to be hydrogenated. This is followed by hydrogenation of the polymer, the hydrogenation catalyst being dissolved in a water-immiscible solvent which at the same time serves to swell the polymer so as to give the catalyst readier access to the double bonds to be hydrogenated. The amount of solvent added is sufficient to give a two-phase mixture, one phase comprising the catalyst and the other phase comprising the (partially) hydrogenated ABS polymer. After separation of the phases, an emulsion of the (partially) hydrogenated ABS polymer is obtained.
DE-A 197 53 302 relates to a process for selectively hydrogenating carbon—carbon double bonds in polymers. For this, the dispersion comprising a polymer and not more than 20% by volume of an organic solvent is reacted with hydrogen in the presence of a hydrogenation catalyst. No disclosure is made of the preparation of graft rubbers which are used as impact modifiers in thermoplastic blends.
It is an object of the present invention to provide a process which is inexpensive and simple to carry out for the preparation of diene-based graft rubbers which are suitable as impact modifiers and have high resistance to environmental influences, and also to provide the corresponding graft rubbers having good mechanical properties and high resistance to environmental influences, e.g. in relation to color changes.
We have found that this object is achieved by means of a process for preparing graft rubbers built up from at least one graft core and from at least one graft shell, comprising
a) preparing an aqueous dispersion of at least one elastomeric polymer built up from
at least one conjugated diene,
where appropriate, at least one monomer copolymerizable with the diene, and
where appropriate, at least one modifying monomer,
b) then, to obtain the graft core, selectively hydrogenating ethylenically unsaturated double bonds in the elastomeric polymer, using hydrogen, in the presence of at least one hydrogenation catalyst selected from salts and complexes of rhodium and/or of ruthenium, where the aqueous dispersion of the elastomeric polymer comprises not more than 20% by volume of an organic solvent, and
c) grafting onto the graft core at least one graft shell built up from
at least one styrene compound of the formula I
where R
1
and R
2
are hydrogen or C
1
-C
8
-alkyl and n is 0, 1, 2 or 3,
where appropriate, at least one monoethylenically unsaturated nitrile compound, and
where appropriate, at least one other monomer.
In the process of the invention, an aqueous dispersion of at least one elastomeric diene polymer is first prepared, and the polymer is (partially) hydrogenated, using hydrogen, on a catalyst. The resultant polymer forms the graft core onto which the graft shell is then grafted. The process is simple to carry out and the graft rubbers obtained are resistant to environmental influences and suitable for use as impact modifiers.
The graft rubber prepared by the process of the invention includes from 30 to 90% by weight, preferably from 40 to 80% by weight, particularly preferably from 50 to 75% by weight, of the elastomeric graft core and from 10 to 70% by weight, preferably from 20 to 60% by weight, particularly preferably from 25 to 50% by weight, of the graft shell, where the entirety of graft core and graft shell gives 100% by weight, based on the graft rubber, and where the graft core and the graft shell may be composed of two or more graft cores and graft shells.
a) Preparation of an Aqueous Dispersion of at Least One Elastomeric Polymer
The elastomeric polymer has the following components
from 10 to 100% by weight, preferably from 20 to 95% by weight, particularly preferably from 50 to 90% by weight, of at least one conjugated diene,
from 0 to 90% by weight, preferably from 5 to 80% by weight, particularly preferably from 10 to 50% by weight, of at least one monomer copolymerizable with the diene, and
from 0 to 20% by weight, preferably from 1 to 15% by weight, particularly preferably from 1 to 10% by weight, of at least one modifying monomer,
where the entirety of the compounds gives 100% by weight, based on the elastomeric polymer.
Suitable aqueous dispersions of elastomeric polymers are either those prepared from aqueous monomer emulsions by free-radical polymerization (primary dispersions) or those whose polymers are prepared in another way and then converted into a n aqueous dispersion (secondary dispersions).
Monomers
Dienes
The dienes used may be any of the usual dienes. Preference is given to the use of dienes selected from butadiene, isoprene, chloroprene, 1-methylbutadiene, 2,3-dimethylbutadiene, 2-(tri-C
1
-C
4
-alkyl)silylbutadiene, such as 2-triethylsilyl-1,3-butadiene, and mixtures of these. Particular preference is given to butadiene and isoprene, and butadiene is very particularly preferred.
Monomers Copolymerizable with the Diene
The elastomer
Barghoorn Peter
Maas Heiko
Niessner Norbert
Schädler Volker
Asinovsky Olga
BASF - Aktiengesellschaft
Keil & Weinkauf
Seidleck James J.
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