Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Treating polymer containing material or treating a solid...
Reexamination Certificate
1999-09-03
2001-02-06
Teskin, Fred (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Treating polymer containing material or treating a solid...
C526S173000, C526S340000
Reexamination Certificate
active
06184341
ABSTRACT:
Applicants claim priority for this application based upon their prior filing of same in Belgium on Oct. 4, 1990, Belgian Patent Application No. 09000942, under the same named inventors and title as herein stated.
FIELD OF THE INVENTION
The invention relates to a process for the decoloration of resinous polymers of the vinyl aromatic/conjugated diene block copolymer type. More particularly the invention relates to a process for the decoloration of such copolymers obtained when starting from a (co)polymerization-initiating stage utilizing alkaline metal based catalysts.
BACKGROUND OF THE INVENTION
French Patent No. 1,149,159 discloses a process for removing the deep color caused by hydrogenation catalysts, from hydrogenated rubber polymers, by means of a mineral acid or of a monocarboxylic or polycarboxylic acid. The resulting polymers are transparent but with a yellowish tinge and have an improved transmittance achieved after a treatment which can take at least one hour on up to 36 hours. However, in the case of copolymers of resinous types, more particularly those disclosed in U.S. Pat. No. 3,639,517 and 4,091,053, the undesirable color is mainly due to the initiating agents used.
Not only for appearance sake, but also for uses in the field of foodstuff containers, it is very important to make this yellowish tinge disappear and to obtain completely colorless, transparent copolymers.
Methods are known for obtaining transparent copolymers by treating solutions of the copolymers with CO
2
and water. However, this requires a distillation of the solvent to separate it from the water and the CO
2
before it is recycled for polymerization, since otherwise these products would act as poisons to the initiator.
However, it must be remembered that in addition to transparency and coloration, the polymer must also maintain all its mechanical and shock-resisting properties, something which is not ensured by the aforementioned processes.
It is also known that an antioxidant additive must be added to these compositions in order to stabilize the butadiene phase during polymer transformation. In fact, the temperatures reached during this stage may cause a degradation of the polybutadiene phase. However, this kind of additive can clearly cause a coloring of the polymeric substance, so that it is desirable to reduce the quantity of antioxidant additive, and even more preferable to not have to add any.
European Patent No. 0084795 also suggests the treatment of polymers with carboxylic diacids. That type of process enables practically all the aforementioned decoloration conditions to be met, but without addressing the problem of the addition of an antioxidant additive.
European Patent No. 0309434 suggests that the copolymers should be treated with monocarboxylic acids containing chemically bonded sulphur. This process enables the amount of antioxidant additive that has to be added to be considerably reduced. Nevertheless, the process is only rarely used on an industrial scale, since the majority of these acids are solid at ambient temperature, having melting points higher than 100° C., and are quasi-insoluble in the majority of usual solvents. This causes considerable difficulties when using the copolymers, the result being the clogging of the ducts or a rapid degradation of the copolymers.
It therefore is desirable to have a process for the treatment of vinyl aromatic/conjugated diene copolymers which ensures that the copolymers remain completely colorless and transparent, retain appropriate shock-resistant properties, are safe and desirable for packaging foodstuffs, are given an antioxidant function without the need for the addition of antioxidant additives, and lastly are readily usable.
SUMMARY OF THE INVENTION
The present invention discloses a process for the decoloration of vinyl aromatic/conjugated diene copolymers so as to meet the aforementioned criteria.
The present invention also discloses a process for the decoloration of vinyl aromatic/conjugated diene copolymers which are transparent, have satisfactory impact-resistant properties, and are advantageous for use in the field of foodstuffs.
The present invention also discloses a process for the decoloration of vinyl aromatic/conjugated diene copolymers which enables the amount of necessary antioxidant additive to be reduced.
The present invention also discloses a process for the decoloration of vinylaromatic/conjugated diene polymers which enables the copolymers to be readily used.
The process according to the present invention for the decoloration of vinyl aromatic/conjugated diene copolymers obtained from alkali-metal based catalysts at the initiation stage is characterized in that the copolymers are treated with a monocarboxylic acid having the general formula R—COOH, where R is a hydrocarbon radical comprising 2 to 4 carbon atoms and is also a linear or branched aliphatic radical, cycloaliphatic radical or alkenic radical.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The monocarboxylic acids utilized in the present invention allow a ready application of the copolymers due to their low melting temperature and/or their outstanding solubility in at least one of the solvents which are useful in the process.
The process of the present invention can be used with copolymers of both the resinous and elastomeric types, prepared by anionic polymerization in a solution of vinyl aromatic monomers and conjugated diene in the presence of initiators of the alkali-metal compound type, polymerization being performed in a sequential manner; it being understood that one or more branches of the sequenced copolymer can be formed as a statistical copolymer.
This type of polymerization is conventionally performed in solution in the presence of a solvent and an initiator of the alkali-metal compound type. Moreover, during polymerization, coupling agents are often used to couple the polymers. The copolymers thus formed are most often found in a linear or radical form, but they have a coloring which is unacceptable for the required uses.
The processes for the polymerization of copolymers for use in the present invention are clearly described in U.S. Pat. Nos. 3,619,537 and 4,091,053, and in European Patents, Nos. 0084795 and 0270515. These polymerization processes can be readily summed up as follows: Polymerization is performed in solution at a temperature of between −100° C. and +150° C., in the presence of a solvent and at a pressure adequate to keep the medium in the liquid phase. The solvents used can be paraffinic, cycloparaffinic or aromatic. Most frequently, cyclohexane or a mixture of hexane and cyclohexane are used as solvents.
If polymerization is performed using coupling agents, first a block of non-elastomeric polymer is formed by charging vinyl aromatic monomer with a certain quantity of organolithium initiator to form long chains of living polymers having a lithium atom on the chain end.
Then the chains of living polymers are brought into contact with monomers of conjugated dienes to form chains or copolymers having elastomeric and non-elastomeric blocks.
Then the copolymers of structure S—B (S=vinyl aromatic,=B=conjugated diene) are brought into contact with coupling agents to form copolymers of structure S—B—X—B—S (in the case of a linear structure), where X is the residue of the coupling agent.
In the case of a polymerization performed without a coupling agent, a sequenced block copolymer is formed by initially charging one of the two monomers, S,B, or a mixture of the two monomers, S/B, with a certain quantity of organolithium initiator in order to initiate polymerization. Then one of the monomers, S or B, or a mixture of the monomers, S/B, is charged successively and in the required order.
Clearly, copolymers of radical or linear structure can be formed, and the blocks can be formed as pure homopolymers or statistical copolymers.
Whatever the copolymers obtained by the various processes of anionic polymerization in solution may be, the process of the present invention can be utilized advantageously for the decol
Lanza Emmanuel
Naveau Jean
Fina Research S.A.
Jackson William T.
Teskin Fred
Wheelington Jim D.
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