Low molecular weight alkenyl aromatic polymer foam

Details Low molecular weight alkenyl aromatic polymer foam Low molecular weight alkenyl aromatic polymer foam

1996-03-12

1997-11-18

Foelak, Morton

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Cellular products or processes of preparing a cellular...

521 97, 521146, C08J 908

Patent

active

056888325

DESCRIPTION:

BRIEF SUMMARY
The present application, International Publication No. WO 95/10560, published on 20 Apr. 1995, is a continuation-in-part of U.S. Ser. No. 08/137,234, filed 14 Oct. 1993, abandoned.
This invention relates to a low molecular weight alkenyl aromatic polymer foam structure having desirable physical properties. Further, the invention relates to a process for making such foam structures with an inorganic blowing agent.
Alkenyl aromatic polymer foam structures heretofore have been made with organic blowing agents. Such agents include aliphatic hydrocarbons, chlorocarbons, chlorofluorocarbons, and hydrofluorocarbons. The use of some of these agents has been criticized for potential ozone depletion and other environmental effects.
Due to present environmental concerns over organic blowing agents, it is desirable to make alkenyl aromatic polymer foam structures with an inorganic blowing agent such as carbon dioxide, nitrogen, argon, air, and helium.
A problem with using inorganic blowing agents for alkenyl aromatic polymer foam structures is their relatively low solubility in melts of the alkenyl aromatic polymer. The low solubility results in high system pressure, which results in high pressure drop and high die pressure. Lowering pressure drop and die pressure would save energy costs and reduce the pressure duty requirements for process equipment.
One means of reducing operating pressures in making foam structures is to employ low molecular weight alkenyl aromatic polymers. Such low molecular weight polymers typically have a weight average molecular weight of 100,000 to 165,000 according to size exclusion chromotography (SEC). Polymers commonly employed in making commercial foam structures typically have a weight average molecular weight of 200,000 to 300:000 according to SEC. The processing advantages of the low molecular weight polymers include potentially lower operating and foaming temperatures and lower operating pressures and pressure drops.
A problem with using low molecular weight alkenyl aromatic polymers is the relatively low mechanical strength observed in foam structures made with some conventional organic blowing agents. Typically, as number average molecular weight decreases, the glass transition temperature decreases. A relatively low glass transition temperature usually makes the foam more brittle, which affects the mechanical strength of the foam structure in certain applications. The problem of mechanical strength is particularly apparent in relatively low temperature applications such as in refrigeration insulation or relatively high temperature applications such as in roof insulation. The reduction in mechanical strength also becomes apparent in large cell (greater than 0.8 millimeter) foam structures, such as those used in buoyancy applications and decorative and craft applications.
it would be desirable to make foam structures with low molecular weight alkenyl aromatic polymers yet maintain levels of mechanical strength typically observed with high molecular weight polymers. It would be further desirable to make such foam structures that exhibit desirable mechanical strength in a variety of applications and temperature environments.
According to the present invention, there is an alkenyl aromatic polymer foam structure comprising an alkenyl aromatic polymer material and a blowing agent. The alkenyl aromatic polymer material comprises greater than 50 percent by weight alkenyl aromatic monomeric units. The polymer material comprises an alkenyl aromatic polymer having a weight average molecular weight of 100,000 to 165,000 according to SEC. The blowing agent comprises 50 percent or more by weight of an inorganic blowing agent based upon the total weight of the blowing agent. A preferred blowing agent is carbon dioxide. Surprisingly, the foam structure has mechanical properties at levels which may correspond to those of foam structures of higher molecular weight blown with conventional organic blowing agents.
Further according to the present invention, there is a foamable alkenyl aromatic polymer

REFERENCES:
patent: 4513105 (1985-04-01), Hahn et al.
patent: 4525484 (1985-06-01), Hahn et al.
patent: 4528221 (1985-07-01), Komatsuzaki et al.
patent: 5250577 (1993-10-01), Welsh
patent: 5286429 (1994-02-01), Blythe et al.

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