Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Patent
1998-01-29
1999-05-18
Foelak, Morton
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Cellular products or processes of preparing a cellular...
521 58, 521 59, 521 60, C08J9/16;9/18;9/20
Patent
active
059050969
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a continuous process for the preparation of expandable styrene polymers.
Expandable particles of styrene polymers (EPS) have been known for some time and have been described many times in the literature.
Such products are usually prepared by suspension polymerization, in which the organic phase containing the monomers and, if used, the initiators and further organic auxiliaries is distributed and polymerized in an aqueous phase in the form of droplets. The blowing agent, usually a low-boiling hydrocarbon, is usually added during the polymerization or in a subsequent step.
JP-A-82-10,610 describes a two-step batch process in which bulk polymerization of the styrene in a stirred reactor is followed by suspension polymerization. This method gives a narrow bead-size distribution of the polymer.
However, the conventional batch processes for the preparation of EPS have the typical disadvantages of this method: there are quality variations between the individual batches, and the process is labor-intensive.
In addition, the batch method is also unfavorable for the preparation of EPS from the energetic point of view. In spite of the exothermic character of the reaction, energy is required at the beginning to heat the reaction mixture and to initiate the polymerization.
Processes for the continuous polymerization of vinyl monomers in bulk or suspension or in a combination thereof are also known.
For example, U.S. Pat. No. 2,566,567 describes a process for the preparation of polystyrene beads in which styrene is prepolymerized in bulk to a conversion of about 70%, and the prepolymer is cooled and granulated. The granules are then suspended in a viscous aqueous solution, and the polymerization is then completed in a continuous tower reactor.
SU-A-412 919 describes a continuous process for the preparation of polystyrene particles in which the styrene is first polymerized to a conversion of 30-40%, suspended in aqueous solution and polymerized in a series of 4 to 6 reactors separated by confuser/diffuser bushes.
However, these processes are not suitable for the preparation of styrene polymers containing blowing agents, since firstly the presence of a blowing agent reduces the stability of the beads, so that coalescence in the aqueous suspension must be expected, and secondly addition of the blowing agent means that the process must be carried out under superatmospheric pressure. In addition, the process of SU-A-412 919 has the further disadvantage that the polymer obtained has a relatively high residual styrene content which is unacceptable for polystyrene foams.
It is an object of the present invention to develop a continuous process for the preparation of EPS which is simple to carry out and gives beads having a narrow bead-size distribution and a low residual styrene content.
We have found that, surprisingly, this object is achieved by a process for the continuous preparation of expandable styrene polymer particles which comprises presence of suspension stabilizers, and a residual styrene content of less than 2000 ppm, steps.
JP-A 57 010 610 and JP-A 60 206 846 describe the preparation of expandable polymers of styrene or .alpha.-methylstyrene in which, in a first step, the polymerization is carried out to completion in aqueous suspension in the presence of suspension stabilizers. There is no mention in either case of carrying out the two-step process continuously.
For the purposes of the present invention, styrene polymers are polystyrene or copolymers of styrene containing up to 50% by weight, based on the copolymer, of at least one further olefinically unsaturated monomer.
Examples of suitable comonomers are .alpha.-methylstyrene, ring-halogenated styrenes, ring-alkylated styrenes, acrylonitrile, esters of acrylic or methacrylic acid with alcohols having 1 to 8 carbon atoms, N-vinylcarbazole, maleic acid and maleic anhydride. The styrene polymer advantageously contains a small amount of a copolymerized branching agent, ie. a compound containing more than one, preferably 2, double b
REFERENCES:
patent: 2566567 (1951-09-01), Hutchinson et al.
patent: 5043404 (1991-08-01), Mahabadi et al.
Baumgartel Michael
Dembek Gerhard
Hahn Klaus
Holoch Jan
Husemann Wolfram
BASF - Aktiengesellschaft
Foelak Morton
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