Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Statutory Invention Registration
1997-10-29
2001-04-03
Jordan, Charles T. (Department: 3641)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S083000, C526S085000
Statutory Invention Registration
active
H0001957
ABSTRACT:
The present invention relates to a process for the immediate termination of free radical polymerizations. Once initiated, free radical polymerizations are usually highly exothermic, ie. take place with considerable evolution of heat, the heat of polymerization, unless removed, additionally accelerating the free radical polymerization.
If the abovementioned heat removal takes place in an inadequate manner in intentional free radical polymerizations, there is a danger that the polymerization will be so vigorous that the vessel containing the polymerization mixture will explode if the runaway polymerization (for example, free radical mass, solution, emulsion or suspension polymerization of compounds (monomers) having at least one ethylenically unsaturated group) is not counteracted. However, such an effective countermeasure is also required in particular in the case of unintentionally initiated free radical polymerizations. Unintentionally initiated free radical polymerizations may occur, for example, during the storage and/or transport of substances containing monomers, since both heat and light or undesired free radicals can initiate the free radical polymerization of monomers. It is true that an attempt is usually made to prevent such unintentional free radical polymerizations by adding small amounts (as a rule up to 1000 ppm by weight) of free radical polymerization inhibitors (free radical acceptors, polymerization inhibitors) to the monomers. However, their inhibiting effect must not be too pronounced since otherwise they would have to be separated off before subsequent use of the monomers for free radical polymerization purposes. However, free radical polymerization initiators can usually predominate over a moderately inhibiting effect, as possessed, for example, by the monomethyl ether of hydroquinone (MEHQ), and it is for this reason that MEHQ is a storage and/or transport stabilizer particularly frequently used for monomers. However, experience has shown that, even in the case of monomers stabilized with storage and/or transport stabilizers, an unintentional free radical polymerization of said monomers cannot be completely ruled out. The latter applies in particular when the monomers are (meth)acrylic monomers and/or styrene, which particularly readily undergo free radical polymerization.
The term (meth)acrylic monomers is to be understood here as meaning substances which comprise acrolein, methacrolein, acrylic acid, methacrylic acid and/or esters of the two abovementioned acids. In this publication, (meth)acrylic is generally used as an abbreviation for acrylic and/or methacrylic.
Especially substances which comprise at least 90% by weight of (meth)acrylic monomers and/or styrene are at risk with regard to an unintentional free radical polymerization (this also applies when polymerization inhibitors are added as a preventive measure). This applies in particular when such substances are exposed to extreme external conditions during transport and/or during storage (for example, extremely, high temperatures during transport by ship through various climatic zones (eg. across the equator), as is the case, for example, for transport from Europe to Southeast Asia, or extremely low temperatures, as in the case of storage in outdoor tanks in northern countries). In particular, low temperatures are not without risks since they can in extreme cases lead to partial or complete crystallization of the monomers. The latter usually results in separation of monomers and stabilizer (purification by crystallization), which may lead to the presence of unstabilized regions of monomers and subsequent melting for a certain duration, which regions can with high probability be the starting point of an unintentional free radical polymerization.
For safe transport and/or safe storage of monomer-containing substances, there is therefore a need for a process which is capable of very rapidly terminating an unintentionally initiated free radical polymerization of the monomers. Such a process is also required, however, for stopping runaway unintentional free radical polymerizations immediately.
It is an object of the present invention to provide such a process in a very advantageous and very broadly applicable manner.
We have found that this object is achieved by a process for immediately terminating free radical polymerizations by adding a phenothiazine-containing inhibitor solution to the system undergoing free radical polymerization, wherein the solvent of the inhibitor solution comprises at least 50% of its weight of an N-alkylpyrrolidone.
The advantageous nature of the novel process is a result of intensive and extensive research activity, as follows:
compared with the recommendation of EP-B 64628 and EP-A 200181 to add a polymerization inhibitor solution based on hydroquinone or butylpyrocatechol or derivatives thereof for immediately terminating a free radical polymerization, the inhibitor solution to be added according to the invention containing phenothiazine contains a substantially more efficient and more broadly applicable free radical polymerization inhibitor;
compared with the recommendation of Res. Dicl. 1989, 300, 245 (Eng.) to add an aqueous Cu(II) salt solution for immediately terminating an unintentional free radical polymerization of acrylic acid, inhibitor solutions based on N-alkylpyrrolidone are as a rule, on the one hand, miscible both with aqueous and with nonaqueous systems and, on the other hand, also subsequently readily separable from such systems;
Process Saf. Prog. 12(2) (1993), 112-114 recommends, for immediately terminating an unintentional free radical polymerization of acrylic acid, adding thereto an inhibitor solution based on phenothiazine, but this prior art contains no indication that the phenothiazine is to be added in solution in a solvent comprising mainly N-alkylpyrrolidone.
Further advantages of the novel procedure are that N-alkylpyrrolidones are inert to most substances. Furthermore, the boiling point of N-alkylpyrrolidones is above the boiling point of most monomers, facilitating subsequent separation from the monomers and permitting subsequent further use of the monomers. Moreover, the high boiling point of the N-alkylpyrrolidones prevents the formation of explosive vapor/oxygen mixtures in hot climatic zones. Furthermore, N-alkylpyrrolidones generally have a low melting point, which permits their use even in northern countries. Another advantage is the low flashpoint of N-alkylpyrrolidones and their low toxicity, if they are toxic at all. However, the fact that phenothiazine has high solubility in N-alkylpyrrolidone at room temperature (25° C.) is very particularly advantageous for the novel process. This permits the novel use of phenothiazine solutions having a high phenothiazine content without the risk of the phenothiazine being immediately partially or completely precipitated from the solution with a change of outdoor temperature.
The addition of phenothiazine as such for immediately terminating free radical polymerizations is a disadvantage in that the low degree of division of the phenothiazine as such is not appropriate for the required immediate termination.
N-alkylpyrrolidones preferred according to the invention are those with alkyl groups of 1 to 8 carbon atoms. Particularly preferred among these are the N-alkylpyrrolidones whose alkyl group is of 1 to 6 carbon atoms. Very particularly preferred N-alkylpyrrolidones are N-methylpyrrolidone and N-ethylpyrrolidone.
In addition to N-alkylpyrrolidones, the phenothiazine solution to be added according to the invention may also contain other solvents. Suitable solvents of this type are all those which are miscible with N-alkylpyrrolidones. Examples of such solvents are biphenyl, diphenyl ether, toluene, xylene, dimethyl phthalate, butyl acetate and 2-ethylhexyl acetate. N,N-dialkylcarboxamides whose alkyl groups are preferably of 1 to 8 carbon atoms are furthermore suitable as such other solvents. Particularly advantageous alkyl groups are methyl, ethyl and n-butyl. N,N-dialkylcarboxamides of C
1
Fried Michael
James Lawrence Edwin
Kageler Paul Leon
Nestler Gerhard
Baker Aileen J.
BASF - Aktiengesellschaft
Jordan Charles T.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
LandOfFree
Immediate termination of free radical polymerizations does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Immediate termination of free radical polymerizations, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Immediate termination of free radical polymerizations will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2442647