METHOD FOR POLYMERISING AN AQUEOUS SUSPENSION OF STYRENE USING AT LEAST ONE ORGANIC HEMIPEROXYACETAL PEROXIDE

Abstract

The present invention relates to a method for polymerising an aqueous suspension of styrene using at least one organic hemiperoxyacetal peroxide, the method comprising a step a) of keeping the aqueous suspension of styrene comprising the organic hemiperoxyacetal peroxide at a temperature below the 1-hour half-life temperature of the organic hemiperoxyacetal peroxide, preferably at 5 to 25° C. below the 1-hour half-life temperature of the organic peroxide, for at least 30 minutes.

Claims

1-15. (canceled)

16. A process for the polymerization of an aqueous styrene suspension using at least one organic hemiperoxyacetal peroxide, said process comprising a stage a) of maintenance of said aqueous styrene suspension comprising said organic hemiperoxyacetal peroxide at a temperature lower than the half-life temperature for 1 h of said organic hemiperoxyacetal peroxide, for at least 30 minutes.

17. The polymerization process as claimed in claim 16, comprising a stage b), subsequent to stage a), of maintenance of said suspension at a temperature greater than or equal to the half-life temperature for 1 h of said organic hemiperoxyacetal peroxide, for at least 30 minutes.

18. The polymerization process as claimed in claim 16, in which the half-life temperature for 1 h of said organic hemiperoxyacetal peroxide is of between 100° C. and 120° C.

19. The polymerization process as claimed in claim 16, in which stage a) is carried out at a temperature lower by 6 to 25° C. than the half-life temperature for 1 h of said organic hemiperoxyacetal peroxide.

20. The polymerization process as claimed in claim 16, in which stage a) is carried out at a temperature ranging from 80° C. to 100° C.

21. The polymerization process as claimed in claim 16, in which stage a) is carried out at a temperature ranging from 80° C. to less than 100° C.

22. The polymerization process as claimed in claim 17, in which stage b) is carried out at a temperature ranging from 105° C. to 140° C.

23. The polymerization process as claimed in claim 16, wherein the organic peroxide is selected from the group consisting of the hemiperoxyacetals corresponding to the following general formula (I): ##STR00002## in which formula (I): R.sub.1 represents a linear or branched C.sub.1-C.sub.4, R.sub.2 represents a branched C.sub.4-C.sub.12, R.sub.3 represents a linear or branched C.sub.1-C.sub.4, and n denotes zero or is an integer varying from 1 to 3.

24. The polymerization process as claimed in claim 16, wherein the organic hemiperoxyacetal peroxide(s) is or are selected from the group consisting of 1-methoxy-1-(tert-amylperoxy)cyclohexane (TAPMC), 1-methoxy-1-(t-butylperoxy)cyclohexane (TBPMC), 1-methoxy-1-(t-amylperoxy)-3,3,5 -trimethylcyclohexane, 1-ethoxy-1-(t -amylperoxy)cyclohexane, 1-ethoxy-1-(t-butylperoxy)cyclohexane, 1-ethoxy-1-(t-butyl -3,3,5-peroxycyclohexane and their mixtures.

25. The polymerization process as claimed in claim 16, wherein the organic peroxide is 1-methoxy-1-(tert-amylperoxy)cyclohexane.

26. The polymerization process as claimed in claim 16, comprising the addition of a blowing agent, during stage a), before stage b), during stage b) and/or after stage b).

27. The polymerization process as claimed in claim 16, wherein the aqueous suspension does not comprise OO-t-butyl O-(2-ethylhexyl) monoperoxycarbonate.

28. The polymerization process as claimed in claim 16, wherein the hemiperoxyacetal content is of between 0.05% and 3% by weight, with respect to the weight of the styrene monomers.

29. The polymerization process as claimed in claim 16, wherein at least 80% by weight, of the organic peroxide is added to the aqueous suspension comprising the styrene monomers before stage a).

30. The polymerization process as claimed in claim 16, wherein the aqueous suspension as defined above comprises an athermanous filler.

Description

EXAMPLES

[0084] In all the examples below, the molecular weight of the product obtained is measured by the method of size exclusion chromatography (SEC) with polystyrene standards.

Example 1: Synthesis of 1-methoxy-1-(t-amylperoxy)cyclohexane (TAPMC)

[0085] A mixture of t-amyl hydroperoxide (TAHP), cyclohexanone and methanol is treated with 70% sulfuric acid at a temperature of between −6° C. and -4° C. In fifteen minutes, an equilibrium mixture of 1-methoxy-1-(t -amylperoxy)cyclohexane, 1,1-di(t-amylperoxy)cyclohexane and unreacted starting materials, cyclohexanone and TAHP, is formed. A small amount (approximately 2%) of cyclohexanone dimethyl ketal (CDMK) is also obtained in the reaction mixture. The reaction mixture is treated with cold water and then the aqueous phase is separated from the organic phase, which is purified by rinsing.

Example 2: (Comparative) BPO/TBEC

[0086] 680 g of deionized water with 1.6 g of tricalcium phosphate and 0.027 g of sodium dodecylbenzenesulfonate are added at ambient temperature and with stirring to a 2 liter glass reactor of Büchi type which is resistant to the pressure of 8 bars and which is equipped with a jacket and with specific stirring (stirrer having 3 blades on two levels). 320 g of non-destabilized styrene monomer with 1.44 g of 75% benzoyl peroxide (BPO), sold under the grade name Luperox® A75 by Arkema, and 0.42 g of OO-t-butyl O-2-ethylhexyl monoperoxycarbonate (TBEC), sold under the Luperox® TBEC brand by Arkema, are subsequently added, still with stirring. The reactor is then closed and placed under nitrogen at a pressure between 1.8 and 2 bars. This suspension is subsequently brought to 90° C. over 52 minutes and then maintained at this temperature for 4 hours for the first stationary phase of polymerization. The reaction medium is subsequently heated to 130° C. in 42 minutes and then maintained at this temperature for 2 hours. In this example, the first stationary phase of conversion is essentially provided by the BPO, while the second stationary phase, called the finishing stationary phase of conversion, employs essentially the TBEC. The reaction medium is subsequently rapidly cooled in half an hour in order to make possible the emptying of the reactor in the vicinity of 50° C. After filtration and drying overnight at 50° C., a product is obtained in the form of uniform particles with a diameter of less than 1.4 mm exhibiting a weight-average molecular weight (Mw) of 185 700 g/mol, for a polydispersity of 2.48 and containing 385 ppm of residual styrene monomer.

Example 3: (Invention) TAPMC Sole Initiator for Conversion of the Styrene

[0087] 680 g of deionized water with 1.6 g of tricalcium phosphate and 0.029 g of sodium dodecylbenzenesulfonate are added at ambient temperature and with stirring to a reactor identical to that of example 2. 320 g of styrene monomer with 1.76 g of 1-methoxy-1-(tert-amylperoxy)cyclohexane (TAPMC) are subsequently added, still with stirring. This suspension is subsequently brought to 90° C. in 52 minutes. The reactor is then left open and the temperature maintained for 2 h 30 at this temperature for the first stationary phase of polymerization. The reactor is subsequently closed and placed under nitrogen at a pressure between 1.8 and 2 bars. The reaction medium is subsequently heated to 115° C. in 42 minutes and then maintained at this temperature for 2.5 hours. The reaction medium is subsequently rapidly cooled in half an hour in order to make possible the emptying of the reactor in the vicinity of 50° C. In this example, the two stationary phases of conversion are provided by the TAPMC. After filtration and drying of the particles overnight at 50° C., a product is obtained in the form of uniform particles with a diameter of less than 1.4 mm, exhibiting a weight-average molecular weight (Mw) of 190 700 g/mol, for a polydispersity of 2.37 and containing 990 ppm of residual styrene monomer, which value can be considered as satisfying the limiting value of 1000 ppm accepted by the profession (see the document U.S. Pat. No. 6,608,150).

[0088] According to this example, it is seen that, despite a first stationary phase temperature 15° C. lower than the half-life temperature for 1 h of the TAPMC (i.e., 90° C. versus 105° C.), the conversion at the end of the cycle remains virtually total and the fundamental characteristics of the resin are preserved. No loss of suspension was observed in the repetition of this example.

[0089] The invention makes it possible to reduce the duration of the overall cycle compared to conventional BPO/TBEC conditions.