The Dow Chemical Company

Brian D Dalke

Eugene R Moore

Michael T Malanga

Gary C Welsh

Eric K Lee

Rudolph Lindsey, Jr

Gary M Poindexter

An improved polystyrene foam having less corrugation is disclosed which uses carbon dioxide as the blowing agent and 1-30 weight percent endothermic agent, such as water, with the weight based on the total carbon dioxide blowing agent and endothermic agent weight. This combination of carbon dioxide and endothermic agent decreases the corrugation of the thermoplastic foam, while just slightly increasing density, when the process parameters, including throughput, are equivalent to using only carbon dioxide. The process an also allow an increased foaming temperature and greater process throughput of an equivalent density thermoplastic foam at approximately equivalent corrugation levels when compared to the use of only using only carbon dioxide.

Polystyrene foam and a process for making the same

The specification discloses a monovinylidene aromatic polymer having a molecular weight of at least 50,000 and an extremely narrow molecular weight distribution of less than 1.5, preferably with at least 80% by weight of the polymer having a molecular weight within plus or minus 30% of the weight average molecular weight. This polymer is produced through anionic polymerization of a pure feed stock which is first cooled to a temperature at which an anionic initiator preferentially reacts with impurities present in the feed stock and initiates the polymerization reaction but does not substantially propagate styrene polymerization. The initiator is uniformly dispersed into the feed stock while maintaining it at the lower temperature and the feed stock temperature is subsequently increased to a temperature at which polymerization of the sytrene proceeds normally. The resulting polymer is especially well adapted to injection molding in that exceptional strength properties are achieved in combination with good processability, e.g., melt flow rate.

Anionic polymerization of purified monovinylidene aromatic monomer feed

The specification discloses a method for assuring consistent and, if desired, increased melt flow rate in a vinyl aromatic based polymer by controlling the degree of absorption of carbon dioxide, oxygen and/or argon for a substantial period of time immediately prior to introduction of the polymer into a molding machine.

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Midland, MI, United States of America

Brian D Dalke