Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2000-05-26
2001-07-17
Teskin, Fred (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S086000, C526S228000, C526S232100, C526S346000, C521S056000, C521S060000, C521S146000
Reexamination Certificate
active
06262193
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a process for the preparation of polyvinylarene polymer particles. More specifically, the present invention relates to a process for the preparation of polyvinylarene polymer particles, wherein the polymerization reaction is started at a relatively high temperature. This process allows for short batch cycle times, a reduced need of energy and allows for particles having advantageous median particle sizes and particle size distributions. Vinylarene throughout this patent document means an aromatic compound to which at least one vinyl group is attached.
BACKGROUND OF THE INVENTION
Polyvinylarene polymer particles are well known in the art. An example of such particles is polystyrene. Polystyrene is prepared on a commercial scale by suspension polymerization.
EP-B-405 324 discloses such a suspension polymerization process. According to this document, styrene monomers are suspended at room temperature in an aqueous phase together with a suitable initiator and customary stabilizers and additives. Initiation of the polymerization is caused by heating the polymerization batch from room temperature to 80 to 90° C. within 2 hours. Subsequently, the temperature is gradually increased to a temperature in the range of 120 to 130° C.
The process disclosed in EP-B-405 324 has the disadvantage that it requires a high energy input. Namely, each new polymerization batch requires mixing of the components at room temperature and subsequent heating to 80 to 90° C.
In addition, Applicant has found that the process of EP-B-405 324 results in particles with a relatively small median particle size, which makes these particles less suitable for certain applications such as insulation applications, drainage applications and sit bags.
Furthermore, Applicant has found that the process of EP-B-405 324 leads to particles having a relatively broad particle size distribution. This is undesirable, since polyvinylarene polymer particles in a particular desired size range should be formed in an adequate amount. The occurrence of oversized or undersized grains should be as small as possible, i.e. the particle size distribution should be narrow.
SUMMARY OF THE INVENTION
It was an object of the present invention to provide a suspension polymerization process for the preparation of polyvinylarene polymer particles which does not yield the above mentioned disadvantages.
Surprisingly, it was found that this object can be achieved in a suspension polymerization process wherein the initiator is added to the polymerization mixture at a temperature above 50° C.
Accordingly, the present invention relates to a process for the preparation of polyvinylarene polymer particles by suspension polymerization, wherein:
(a) vinylarene monomers are suspended in an aqueous medium to yield a suspension;
(b) the temperature of the suspension is adjusted to a temperature above 50° C., at which temperature an initiator is added;
(c) subsequently, the reaction temperature is increased by 5 to 30° C. per hour until a temperature of at least 120° C. has been reached; and
(d) the temperature is retained at a temperature of at least 120° C. until the polymerization is complete.
In the process of the present invention there is no need to admix the vinylarene monomer and initiator at room temperature and heat the resulting mixture all the way to 80 to 90° C. The vinylarene monomers can be suspended in an aqueous medium which already has a relatively high temperature. Apart from shorter batch cycle times, this also results in a gain in energy. Furthermore, polymer particles resulting from this process have advantageous particle sizes for particular applications and have a narrow particle size distribution.
Suitable vinylarene monomers to be used in the present process are well known in the art and can suitably be selected from styrene, &agr;-methylstyrene, p-methylstyrene, chlorostyrene, dimethylstyrene, vinyltoluene and similar styrenic derivatives. Preferably, the vinylarene is styrene.
The polyvinylarene polymer resulting from the process according to the invention preferably is a polymer containing at least 50% by weight of styrene. Optionally, the polymer contains further co-monomers such as other vinylarene monomers, butadiene, acrylonitril, acrylic acid, methacrylic acid and esters of (meth)acrylic acid with alcohol compounds having 1-10 carbon atoms such as methyl methacrylate. Preferably, the polyvinylarene is polystyrene.
The vinylarene monomers are suspended in an aqueous medium to yield a suspension. The volume ratio between the organic phase and aqueous medium may vary between wide ranges, as will be appreciated by a person skilled in the art. Suitable volume ratios include 1:3 to 4:3. The optimal ratio is determined by economic considerations. Preferably, a ratio of 1:1 is used.
The suspension suitably contains one or more conventional stabilizing agents, such as poly(vinyl alcohol), gelatine, agar, sodium salt of polyacrylic acid and polymethacrylic acid, polyethylene glycol, hydroxyethyl or hydroxymethyl cellulose, carboxy methyl cellulose, methyl cellulose, polyvinyl pyrrolidine, polyacrylamide, copolymer of styrene and maleic acid, preferably in a molar ratio of between 2:1 and 1:2, ethylene glycol or combinations thereof, sodium dodecyl-sulphonate, alkali metal salts of fatty acids, water soluble persulphates (sodium persulphate, potassium persulphate) or sodium bisulphites. Further, it is possible to use inorganic stabilizers such as alumina, bentonite, magnesium silicate or phosphates, like tricalciumphosphate and/or disodiumhydrogen phosphate, optionally in combination with any of the stabilizing compounds mentioned earlier. The amount of stabilizer may suitably vary from 0.1 to 0.9% weight, based on the weight of the aqueous medium.
After the vinylarene monomers have been suspended in the aqueous phase, the temperature of the suspension is adjusted to a temperature above 50° C. Preferably, the temperature is adjusted to from 70 to 95° C., more preferably to from 80 to 90° C.
When a temperature of above 50° C. has been reached, an initiator is added. Typically, the initiator to be added is a radical initiator having a half-life of one hour in benzene at 70 to 110° C., preferably at 80 to 100° C. In particular, the radical initiator is a peroxide compound having these half-life values. Suitable radical initiators for use are tert-amylperoxy-pivalate, di(2,4-dichlorobenzoyl)peroxide, tert-butylperoxy-pivalate, di(3,5,5-trimethyl-hexanoyl)peroxide, didecanoyl-peroxide, di-lauroylperoxide, di(2-methylbenzoyl)peroxide, 2,5-dimethyl-2,5-di(2-ethylhexanoyl)hexane, di(4-methylbenzoyl)peroxide, dibenzoyl-peroxide, tert-amylperoxy-2-ethylhexanoate, tert-butylperoxy-2-ethylhexanoate, tert-butylperoxy-isobutyrate, tert-butyl-monoperoxy-maleate. Preferably, dibenzoyl-peroxide used. The skilled person will understand that at different temperature levels different initiators may be used in accordance with the half-lives of the initiator.
If desired, a radical initiator having a half-life of one hour in benzene at higher temperatures, e.g. 110-135° C. may be used in addition to the initiators mentioned in the previous paragraph. Examples of such initiators are 1,1-di(tert-butylperoxy)-3,3,5-trimethylcyclohexane, 1,1-di(tert-butylperoxy)cyclohexane, tert-butyl perbenzoate, 2,2-di(tert-butylperoxy)butane, tert-butylperoxy-isopropylcarbonate, tert-butylperoxy-acetate, tert-amylperoxy-benzoate, tert-butylperoxy-benzoate, n-butyl-4,4-di(tert-butylperoxy)valerate, tert-butylperoxy-(2-ethylhexyl)carbonate, dicumylperoxide. Preferably, tert-butyl perbenzoate, tert-butylperoxy-isopropylcarbonate, tert-butylperoxy-(2-ethylhexyl)carbonate and/or dicumylperoxide are used.
The amount of initiator to be added typically varies in the range of 0.05 to 1.0% by weight, based on the amount of vinylarene monomer.
When the initiator has been added to the suspension, the reaction temperature is increased by 5 to 30° C. per hour until a temperature of at least 120° C. has been reached. Preferably, the temp
Poppelaars Adrianus Cornelis
Zijderveld Johannes Maria
Johnson Kenneth H.
NOVA Chemicals (International ) S.A.
Teskin Fred
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