Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Cellular products or processes of preparing a cellular...
Patent
1995-08-02
1997-04-01
Foelak, Morton
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Cellular products or processes of preparing a cellular...
521 59, C08J 918
Patent
active
056166249
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a process for the preparation of bead-form expandable styrene polymers (EPSs) having improved expandability by polymerizing styrene, if desired in the presence of further comonomers, in aqueous suspension in the presence of a molecular colloid and a small amount of at least one unsaturated carboxylic acid or a water-soluble salt thereof.
Foams based on styrene polymers have achieved considerable industrial importance as thermal insulation and packaging materials. They are produced on an industrial scale by first preparing expandable styrene polymers by suspension polymerization of styrene in the presence of a blowing agent, expanding these polymers to foam particles by heating, and subsequently welding the particles in molds to give moldings.
This suspension polymerization is carried out in the presence of suspension stabilizers and conventional styrene-soluble polymerization catalysts.
The suspension stabilizers employed are usually, in addition to so-called Pickering stabilizers, in particular molecular colloids, such as polyvinyl alcohols, hydroxyethylcellulose or polyvinylpyrrolidone.
An important property for industrial utilization of the blowing agent-containing EPS beads produced in this way is the expansion capacity, a differentiation being made here between the expansion rate and the minimum achievable bulk density.
In order to achieve very low bulk densities and a high expansion rate, the patent literature gives various methods which, without exception, are aimed at improving the flow properties of the polymer matrix in the plastic state.
In addition to targeted modeling of the molecular weight distribution by means of conventional molecular weight regulators, for example tert-dodecyl mercaptan or DMS (dimeric .alpha.-methylstyrene) (cf. EP-B-106 129), intentional branching of the molecular units by means of difunctional or polyfunctional monomers, for example butanediol disacrylate, is also known here.
Expandable styrene polymers prepared by suspension polymerization have a certain internal water content immediately after the polymerization.
High internal water contents occur, in particular, in flame-resistant, expandable styrene polymers containing, as flameproofing agents, organobromine compounds, such as hexabromocyclododecane.
It is an object of the present invention to provide a process for the preparation of bead-form expandable styrene polymers having improved expandability in which targeted modeling of the molecular weight distribution is unnecessary. It is a further object of the present invention to provide a process for the preparation of bead-form expandable styrene polymers in which the drying of the expandable styrene polymer beads which still contain water after the suspension polymerization can be carried out more rapidly.
We have found that this object is achieved by a process for the preparation of bead-form expandable styrene polymers by polymerizing styrene, if desired in the presence of further comonomers, in aqueous suspension in the presence of organic molecular colloids as suspension stabilizers and conventional styrene-soluble polymerization catalysts and with addition of a blowing agent and, if desired, conventional additives in effective amounts, wherein the aqueous suspension contains at least one olefinically unsaturated carboxylic acid or a water-soluble salt thereof in an amount, based on the organic phase, of from 0.002 to 0.3% by weight of carboxylate anions.
U.S. Pat. No. 3,755,282 describes the suspension polymerization of vinyl aromatic monomers in the presence of from 0.2 to 1% by weight, based on the monomer, of a phosphate suspending agent (for example magnesium phosphate) and an .alpha.,.beta.-unsaturated carboxylic acid as the only extender. For the purpose of the present invention, extenders are taken to mean compounds which increase the suspension-stabilizing action of the finely divided phosphate. The process gives large, virtually spherical beads having a low bead-size distribution. Examples of .alpha.,.beta.-unsaturat
REFERENCES:
patent: 3755282 (1973-08-01), Wright
Hahn Klaus
Naegele Dieter
Scherzer Dietrich
Witt Michael
BASF - Aktiengesellschaft
Foelak Morton
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