Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
1999-04-23
2001-07-10
Wu, David W. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S227000, C526S230500, C526S238000, C526S344000, C558S264000, C558S280000
Reexamination Certificate
active
06258906
ABSTRACT:
The present invention relates to a process for the aqueous suspension polymerization of vinyl chloride with the use of dialkyl peroxydicarbonates. It relates more particularly to such a process in which dialkyl peroxydicarbonates with short alkyl chains are used in the form of a solution. The invention also relates to a process for the manufacture of a solution of dialkyl peroxydicarbonate with short alkyl chains.
It is known to make use of dialkyl peroxydicarbonates for initiating the aqueous suspension polymerization of vinyl chloride. Dialkyl peroxydicarbonates with short alkyl chains, such as diethyl and diisopropyl peroxydicarbonates, constitute initiators that are particularly appreciated because of their high activity at the usual temperatures of polymerization of vinyl chloride. However, they have the disadvantage of being unstable, with the result that their storage in the pure state presents very serious hazards.
With a view to overcoming this disadvantage it has already been proposed to manufacture these peroxydicarbonates in the polymerization reactor (“in situ”), for example by reacting alkyl haloformate dissolved in vinyl chloride with a peroxy compound such as hydrogen peroxide, dissolved in alkaline water. This process for “in situ” manufacture of the initiator does not allow an automation of the initiator feed to the polymerization reactors. In addition, it lacks reproducibility (lack of accuracy concerning the quantities of initiator actually introduced into the polymerization) and of production efficiency (need to precede each polymerization cycle with the “in situ” synthesis of the initiator).
It has also been proposed to prepare the quantity of dialkyl peroxydicarbonate which is precisely needed, outside the polymerization reactor (“ex situ”) and immediately before the polymerization.
This preparation is performed by reacting an alkyl haloformate with a peroxy compound in the presence of water and of a water-immiscible volatile solvent which preferably has a boiling temperature lower than 100° C., such as pentane or hexane. The initiator solution thus obtained is then introduced in toto (organic phase and aqueous phase) into the polymerization reactor which is subsequently charged with a view to the polymerization (British Patent 1 484 675 in the name of Solvay & Cie). This process allows the initiator feed to the reactors to be automated but still makes it necessary to produce the sufficient precise quantity of initiator immediately before the polymerization. Besides, it does not allow (either) a delayed introduction of the dialkyl peroxydicarbonates, a technique that is advantageous, for example, in order to improve the polymerization kinetics. In addition, just like the above mentioned process for “in situ” manufacture, it produces vinyl chloride polymers which, after conversion, result in finished articles containing many “fisheyes”.
British Patent Application 2 022 104 and French Patent Application 2 352 839 mention processes for the aqueous suspension polymerization of vinyl chloride with the use of dialkyl peroxydicarbonates with short alkyl chains in the presence of respectively a plasticizer or a diacid higher alcohol ester. The processes described in these documents do however not allow to solve the problems linked with the dialkyl peroxydicarbonate instability during storage, the automated initiator feed to the polymerization reactors and the delayed introduction in the polymerization reactor of these initiators.
The U.S. Pat. No. 3,950,375 relates to a continuous process for the manufacture of pure dialkyl peroxydicarbonates by centrifuging the aqueous reaction phase.
The U.S. Pat. No. 3,377,373 describes a continuous process for the manufacture of a diisopropyl peroxydicarbonate solution in carbon tetrachloride.
The aim of the present invention is to provide a process for the aqueous suspension polymerization of vinyl chloride with the use of dialkyl peroxydicarbonates with short alkyl chains which does not exhibit any of the above mentioned disadvantages. It also aims to provide an improved process for the manufacture of a solution of dialkyl peroxydicarbonates which are particularly suited for use in the aqueous suspension polymerization of vinyl chloride.
To this end, the invention relates to a process for the aqueous suspension polymerization of vinyl chloride with the use of dialkyl peroxydicarbonates with short alkyl chains, characterized in that the dialkyl peroxydicarbonate is used in the form of a solution in a dialkyl alkanedicarboxylate which is liquid and insoluble in water.
The solution of dialkyl peroxydicarbonate with short alkyl chains which is used according to the process of the present invention consists essentially of dialkyl peroxydicarbonate and of solvent (dialkyl alkanedicarboxylate). It is therefore free from other polymerization ingredients such as, for example, monomer.
Dialkyl alkanedicarboxylate (hereinafter referred to briefly as “ester”) which is liquid and insoluble in water is intended to denote the esters which are liquid and insoluble in water in normal conditions, that is to say at ambient temperature and at atmospheric pressure. Insoluble in water is intended more particularly to mean a solubility in water at ambient temperature which is lower than 0.5 g/l. The solubility in water of the esters used as solvent for the peroxydicarbonate in the process of the invention preferably does not exceed 0.3 g/l.
The esters which are liquid and insoluble in water and used in the process of the invention generally have boiling temperatures (in normal conditions) which are appreciably higher than 100° C. In most cases they are higher than 150° C.
By way of examples of esters that can be applied there may be mentioned the liquid and water-insoluble esters as defined above which are derived from C
4
-C
10
alkanedicarboxylic acids and from C
2
-C
12
alkanols (linear or branched saturated aliphatic alcohols). Examples of these that may be mentioned are diethyl and dibutyl butanedicarboxylates (succinates), diethyl, dipropyl, dibutyl, diisobutyl and diethylhexyl hexanedicarboxylates (adipates), diethyl and dibutyl octanedicarboxylates (suberates) and dibutyl, diethylbutyl and diethylhexyl decanedicarboxylates (sebacates).
Esters which are well-suited for carrying out the process of the invention are the alkanedicarboxylates derived from C
4
-C
8
alkanedicarboxylic acids and from C
6
-C
10
alkanols. Esters which are very particularly preferred are chosen from hexanedicarboxylates (adipates) derived from adipic acid and from C
6
-C
10
alkanols. An ester which is very particularly preferred in the process of the invention is diethylhexyl adipate.
The concentration of dialkyl peroxydicarbonate in the solutions used in the polymerization process according to the invention is generally from approximately 15 to 40% by weight. The use of dilute peroxydicarbonate solutions in the polymerization, for example of solutions containing approximately 10% by weight (or less) of dialkyl peroxydicarbonate, introduces the risk of resulting in vinyl chloride polymers whose glass transition temperature, and hence heat resistance, is reduced. In general, approximately 40% by weight is not exceeded because a concentration that is too high reduces the accuracy of the measurement when the reactor is fed with initiator. Good results are obtained with solutions in which the dialkyl peroxydicarbonate concentration is from approximately 25 to 35% by weight.
The solutions of dialkyl peroxydicarbonates with short alkyl chains that are used in the polymerization process according to the invention may be stored without risk at low temperature (below 10° C.) and this may be done for many hours without appreciable loss of activity. They can consequently be prepared in advance in a sufficient quantity to feed a number of polymerization reactors or else to feed a number of polymerization cycles in the same reactor.
For the purpose of the present invention, dialkyl peroxydicarbonates with short alkyl chains are intended to denote the peroxydicarbonates in
Morrison & Foerster / LLP
Solvay
Wu David W.
Zalukaeva Tanya
LandOfFree
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