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
1998-09-18
2001-07-03
Teskin, Fred (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S087000, C525S256000, C525S259000, C525S331900, C525S333200, C525S375000, C525S376000, C525S377000, C525S904000
Reexamination Certificate
active
06255402
ABSTRACT:
BACKGROUND OF THE PRESENT INVENTION
1. Technical Field
The invention relates to a process for preparing a high-impact vinylaromatic polymer composition, in other words a composition comprising a matrix of vinylaromatic polymer and particles of rubber.
According to the prior art, the particles of rubber can be in various morphologies. The following morphologies may be obtained:
the “salami”-type morphology, which means that the rubber particle contains a number of occlusions, generally substantially spherical but not concentric, of vinylaromatic polymer,
the “labyrinth”-type morphology, which means that the rubber particle contains a number of elongated, curved, generally aspherical and generally asymmetric occlusions of vinylaromatic polymer,
the “onion”-type morphology, which means that the rubber particle is substantially spherical and contains, concentrically with respect to itself, a number of occlusions of vinylaromatic polymer contained within one another,
the “capsule”-type morphology, which means that the rubber particle, which is generally substantially spherical, contains a single occlusion of vinylaromatic polymer.
The salami, labyrinth and onion morphologies can be termed “multi-occlusion” morphologies. They are generally substantially larger than is the capsules.
These morphologies affect the impact properties and the gloss of vinylaromatic polymer compositions. The influence of this morphology on the gloss, in increasing order of gloss, is as follows: salami, then labyrinth or onion, then capsule.
In general, the greater the occlusion content of a particle the larger it is. This is why the rubber particles generally increase in size in the following order: capsule, then labyrinth or onion, then salami. It is for this reason that it is possible to consider the possibility of enhancing the gloss of a high-impact vinylaromatic polymer composition by reducing the size of the particles of rubber it contains.
Depending on the target properties of the material, especially its impact resistance and gloss, one may be led to combine within the same material particles having different morphologies and, for example, to adjust the capsules/multi-occlusions ratio. In particular, a material whose mass of rubber particles consists predominantly of capsules and in which the remainder of the mass of particles, for example from 5 to 40%, consists of multi-occlusions exhibits a good tradeoff between impact and gloss.
If the desire is to obtain a particularly glossy high-impact vinylaromatic copolymer or polymer, one may be led to research the preparation conditions which lead exclusively to the capsule morphology.
2. Description of Related Art
According to the prior art, the morphologies other than the salami morphology, in other words the labyrinth, onion or capsule morphologies, cannot be obtained by making use of a conventional polydiene but only by polymerizing the vinylaromatic monomer in the presence of a styrenebutadiene copolymer. In particular, in accordance with the prior art, the capsule morphology would only be obtainable by polymerizing styrene in the presence of a styrene-butadiene copolymer comprising at least 15 and 15 preferably 40% styrene. This teaching results in particular from the following documents:
Echte et al., J. Sci. Ind. Res. 40, 659 (1981),
EP 48389
Echte, Rubber Toughened Plastics, C. Keith Riew Editor, American Chemical Society, Washington, 1989.
However, such copolymers are expensive and, moreover, must be introduced into the polymerization medium in higher concentrations than a conventional polydiene for a given level of polydiene in the final high-impact vinylaromatic composition. Such amounts of copolymer are, moreover, liable to require longer periods of solubilization within the styrene prior to polymerization. For this reason it is desirable to know how to obtain a capsule, onion or labyrinth morphology while making use of a conventional, less expensive rubber which can be introduced in a smaller quantity into the polymerization medium.
The desired capsules/multi-occlusions ratio for a given material can, for example, be obtained by mixing defined amounts of a high-impact vinylaromatic polymer containing only capsules and a high-impact vinylaromatic polymer containing only particles of the multi-occlusion type.
The patent application EP 0726280 teaches that it is possible to prepare a high-impact polystyrene by polymerizing styrene in the presence of a rubber and a stable free radical. However, in the practical examples of this document, the final material does not include any capsule particles. The practical examples of that document teach that the presence of the stable free radical during polymerization may lead to an increase in the size of the rubber particles within the end material.
SUMMARY OF THE INVENTION
The present invention relates to a process for preparing a composition comprising a vinylaromatic polymer matrix and particles of rubber, the said process comprising a step of polymerizing at least one vinylaromatic monomer in the presence of a rubber comprising a group which generates a stable free radical.
The process according to the invention makes it possible to obtain morphologies other than salami morphologies, such as the labyrinth, onion or capsule morphology, with the aim, for example, of enhancing the gloss of the high-impact vinylaromatic polymer.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The process according to the invention provides a solution for obtaining morphologies different from the salami morphology with the aim, for example, of increasing the gloss of the high-impact vinylaromatic polymer without it being necessary to employ a styrene-butadiene copolymer, by employing a homopolybutadiene. However, the use of a styrene-butadiene copolymer is not ruled out since there may be a desire to combine the advantage of the use of such a copolymer and the advantage of the fact that such a copolymer carries a group which generates a stable free radical. Such a combination makes it possible to use a rubber which carries fewer groups which generate a stable free radical than if the rubber were to be derived from a polybutadiene devoid of units of styrene as comonomer.
By morphology other than the salami morphology is meant at least one of the labyrinth, onion or capsule morphologies, or their combinations, also including if appropriate their combination within the same material with particles of the salami type. The process according to the invention may lead to a composition comprising a high proportion of capsules.
The process according to the invention comprises a step of polymerizing at least one vinylaromatic monomer in the presence of a rubber comprising a group which generates a stable free radical, referred to hereinafter as carrier rubber.
The carrier rubber is prepared prior to the polymerization of the vinylaromatic monomer.
In general, the process according to the invention leads to an end material whose rubber particles have a lower average size in comparison with a process which employs a conventional rubber which does not carry a group which generates stable free radicals, under otherwise comparable operating conditions.
The carrier rubber may be obtained, for example, by a process including a step of heat treatment of an elastomer conventionally used for the preparation of high-impact vinylaromatic polymers, in the presence of a stable free radical, of a free-radical initiator which is capable of withdrawing a proton from the elastomer, and of a solvent and in the absence of vinylaromatic monomer. Such an initiator can be selected, for example, from the list of polymerization initiators proposed below for use in the polymerization according to the invention. The initiator is preferably selected from the following list:
tert-butyl isopropyl monoperoxycarbonate,
tert-butyl 2-ethylhexyl monoperoxycarbonate,
dicumyl peroxide,
di-tert-butyl peroxide,
1, 1-di (ttert-butylperoxy) cyclohexane,
1, 1 -di (tert-butylperoxy)-3,3, 5-trimethyl- cyclohexane,
tert-butyl peroxyacetate,
cumyl tert-butyl peroxide,
tert-butyl per
Boutillier Jean-Marc
Forges Nathalie
Atofina
Pennie & Edmonds LLP
Teskin Fred
LandOfFree
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