Organic compounds -- part of the class 532-570 series – Organic compounds – Carbonate esters
Reexamination Certificate
1998-07-22
2001-07-03
Powers, Fiona T. (Department: 1626)
Organic compounds -- part of the class 532-570 series
Organic compounds
Carbonate esters
C502S160000
Reexamination Certificate
active
06255520
ABSTRACT:
The present invention relates to organic solutions of dialkyl peroxydicarbonate and to their use in the polymerization of halogenated monomers for the purpose of obtaining polymers with improved properties.
It is known to resort to dialkyl peroxydicarbonates in order to initiate the aqueous suspension polymerization of halogenated monomers. Dialkyl peroxydicarbonates are particularly valued initiators because of their high activity at the usual polymerization temperatures. However, they exhibit the disadvantage of being unstable, so that their storage in the pure state exhibits very serious safety risks.
For the purpose of overcoming this disadvantage, provision has already been made to manufacture these dialkyl peroxydicarbonates in the polymerization reactor (“in situ”). This “in situ” preparation process does not, however, make possible automation of the feeding of the polymerization reactors with initiator. In addition, this process lacks reproducibility due to the lack of accuracy with respect to the amounts of initiator effectively employed in the polymerization. This process also lacks productivity because it is necessary to precede each polymerization cycle by the “in situ” synthesis of the initiator. Furthermore, the by-products and residues from the synthesis of the dialkyl peroxydicarbonate are not removed.
Provision has also already been made to prepare the exact necessary amount of dialkyl peroxydicarbonate outside the polymerization reactor (“ex situ”) and immediately before the polymerization. This preparation is carried out by reaction of an alkyl haloformate with a peroxide compound in the presence of water and of a volatile water-immiscible solvent preferably having a boiling temperature of less than 100° C. The combined reaction mixture in which the dialkyl peroxydicarbonate has been prepared (aqueous phase and organic phase) is then introduced into the polymerization reactor, which is subsequently charged for the purpose of the polymerization (Belgian Patent 822,913 on behalf of Solvay and Co.). The volatile solvent is preferably removed, in all or in part, before the polymerization by applying vacuum.
This process makes it possible to automate the feeding of the polymerization reactors with initiator but still requires that the exact sufficient amount of initiator be produced immediately before the polymerization. A delayed introduction of the initiator, which is an advantageous technique, for example for improving the kinetics of the polymerization, cannot consequently be carried out. Furthermore, this process does not make it possible to have available a dialkyl peroxydicarbonate solution which can be stored in complete safety and which can be used at any time. Furthermore, the water-soluble impurities present in the aqueous phase after the preparation of the dialkyl peroxydicarbonate are not removed before the introduction into the polymerization reactor.
In order to overcome the disadvantages exhibited by the processes of the prior art, the object of the present invention is to provide an organic solution of dialkyl peroxydicarbonate and more particularly of diethyl peroxydicarbonate which is particularly suited to the preparation of halogenated polymers and more particularly of polymers comprising fluorine (including vinylidene fluoride polymers) by aqueous suspension polymerization and an improved process for manufacturing it.
Another subject-matter of the invention is a simple and efficient process for the preparation of halogenated polymers and more particularly of polymers comprising fluorine (including vinylidene fluoride polymers) by aqueous suspension polymerization with the involvement of this organic solution.
Another subject-matter of the invention is the halogenated polymers and more particularly the polymers comprising fluorine (including vinylidene fluoride polymers) thus obtained.
The present invention first of all relates to an improved process for the preparation of an organic solution of dialkyl peroxydicarbonate, which solution is particularly suited for use in the aqueous suspension polymerization of halogenated monomers.
To this end, the invention relates to a process for the preparation of an organic solution of dialkyl peroxydicarbonate according to which an alkyl haloformate is reacted, in water, in appropriate amounts with an inorganic peroxide and the dialkyl peroxydicarbonate obtained is separated by extraction by means of a water-insoluble organic solvent chosen from conventional chain-regulating agents for halogenated polymers, in order to obtain a solution of dialkyl peroxydicarbonate in this solvent.
The water-insoluble organic solvent is preferably chosen from conventional chain-regulating agents for polymers comprising fluorine and, in a more than preferred way, it is chosen from conventional chain-regulating agents for vinylidene fluoride polymers. In a very particularly preferred way, the water-insoluble organic solvent is diethyl carbonate.
The dialkyl peroxydicarbonate is preferably diethyl peroxydicarbonate.
The alkyl haloformate is generally advantageously an alkyl chloroformate. The inorganic peroxide is generally calcium or sodium peroxide or alternatively hydrogen peroxide. In the latter case, it is advisable, in addition, to introduce a base, such as calcium hydroxide or sodium hydroxide, into the aqueous reaction mixture. Preferably, the inorganic peroxide is hydrogen peroxide and sodium hydroxide is then added to the reaction mixture.
The amount of hydrogen peroxide is usually less than or equal to the stoichiometric amount. It is generally greater than or equal to a stoichiometric shortage of 5% with respect to the amount of alkyl haloformate. The amount of sodium hydroxide is usually less than or equal to the stoichiometric amount. It is generally greater than or equal to a stoichiometric shortage of 5% with respect to the amount of alkyl haloformate. The stoichiometric shortage does not necessarily have to be the same for the hydrogen peroxide and the sodium hydroxide. A stoichiometric shortage of 3% for the sodium hydroxide and of 4% for the hydrogen peroxide with respect to the amount of alkyl haloformate usually gives good results.
The reaction between the alkyl haloformate, hydrogen peroxide and sodium hydroxide is usually carried out with vigorous stirring. The temperature of the reaction is generally maintained at a value between −5° C. and +15° C., preferably between 0° C. and +15° C. The total duration of the preparation of the dialkyl peroxydicarbonate is regulated by the duration of the addition of the sodium hydroxide to the aqueous mixture containing the alkyl haloformate and the hydrogen peroxide, which usually varies from a few tens of minutes to a few hours.
The separation by extraction of the dialkyl peroxydicarbonate obtained is carried out in any known and appropriate way. Advantageously, the extraction solvent is added with vigorous stirring to the aqueous reaction mixture from the preparation of the dialkyl peroxydicarbonate, the phases are subsequently allowed to separate by settling, after the stirring has been halted, and the organic phase is separated from the aqueous phase, in order to collect a pure solution of the dialkyl peroxydicarbonate in the extraction solvent.
The extraction solvent can be added to the aqueous reaction mixture at any point in the reaction for formation of the dialkyl peroxydicarbonate, that is to say from the point ranging from the introduction of the main reactants to after the synthesis of the dialkyl peroxydicarbonate. Furthermore, the extraction solvent can be added all at once or in several steps.
The amount of solvent used for the extraction is not critical. It is obvious that it will depend in particular on the degree of solubility of the dialkyl peroxydicarbonate in the chosen solvent. This amount will advantageously be such that the final concentration of dialkyl peroxydicarbonate in the organic solution is comprised between approximately 15 and approximately 40% by weight and more particularly between approximately 20 and between
Bacque Xavier
Bodart Vincent
Declerck Fredy
Lannuzel Thierry
Laurent Guy
Morrison & Foerster / LLP
Murashige Kate H.
Powers Fiona T.
Solvay ( Societe Anonyme)
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