Pyranyl foams

Pyranyl monomers have at least two double bonds, producing polymeric foams that are crosslinked, thermosetting and temperature-resistant. These foams were developed by Canadian Industries, Ltd. (1-5), and in part by ICI America, Inc. (7), but the foams have not been commercialized. The reason for this is not clear, but may be due to the fact that pyranyl monomers were not cost effective in comparison with polyurethane foams. However, the technology developed for the foams could be applied for preparing other types of foams from different vinyl monomers. 

Pyranyl foams are prepared by the cationic polymerization of pyranyl monomers in the presence of a catalyst and a surfactant. The pyranyl monomers are prepared via acrolein and acrolein dimer. 

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Among promising oligomeric foams one should also mention 2-pyranyl foams for a discussion of the chemistry, technology and properties of these materials see Finally, several works concerned with the preparation of foams from cumaron-indene and aniline-formaldehyde oligomers have been reported ... 

Polyisocyanurate foams, polyurea foams and phenolic foams are growing rapidly in recent years. Urea-formaldehyde foams disappeared recently from the U.S. market. Rubber foams and pyranyl foams are no longer available in the worldwide market. 

Surfactants. Silicone surfactants, which are used in rigid urethane foams, can be used as surfactants for pyranyl foam jn-eparation. The silicone surfactants are block copolymers of polydimethylsiloxane-polyoxyalkylene ether in either linear or pendant structures. 

Comparative tests between free-rise urethane and pyranyl foams indicate that the total pressures obtained are similar, but that the rate of pressure build-up and pressure dissipation are faster with the pyranyl systems. This property allows short jig-dweU times. Freezer cabinets varying in storage capacity from 7 to 30 ft, have been insulated completely satisfactorily with pyranyl foam (1). 

In rigid urethane foams, the cell shapes are elliptical like eggs, and, therefore, the compressive strengths in the direction perpendicular to foam rise is smaller than the direction parallel to foam rise. Therefore, if urethane foams are required to have the same compressive strength as pyranyl foams in the direction perpendicular to foam rise (i.e., compressive strength in the direction vertical to the panel substrate) urethane foams must have foam densities greater than those of pyranyl foams. Adhesion of pyranyl foams to various substrates, e.g., steel, phosphated steel, stainless steel and aluminum, as well as paper and wood, is very good. 

Thermal Conductivity. The thermal conductivity of pyranyl foams is almost equal to that of rigid. urethane foams. Figure 48 shows the thermal conductivity of a pyranyl foam having an overall density of 2.2 pcf. The foam was cut from a freezer mock-up, and the K-factors... 

Dimensional Stability. The dimensional changes of a pyranyl foam after a 28-day test period are shown in Table 34. 

Thermal Stability. Pyranyl foams are crosslinked aromatic polymers, and, therefore, their thermal stability is good in comparison with polyurethane foams. The maximum service temperature for low-density pyranyl foams is 135°C (275 F), but higher temperatures are possible for short periods. The minimum temperature to which the foam has been subjected is -78°C (-108 F) (1). 

Chemical Resistance. Table 35 shows some of the chemical resistance properties of pyranyl foams. The table shows that pyranyl foams are stable in polar and non-polar solvents. 

It has been proved that pyranyl foams can be used for pour-in-place applications in household refrigerators and deep freezers. Furthermore, because of their high thermal stability the foams can withstand inunersion in molten asphalt at 205°C (400°Q. This jn-operty makes possible applications to roof insulation with molten asphalt as a water-I otecting layer. Another possible application is the baking of the enamel finish on freezer cabinets after the foam insulation has been applied. The foaming reaction is very fast, and, therefore, spraying of the foams onto out-door tanks and pipes is possible. 

Pyranyl foam n. A type of rigid, pour-inplace, thermosetting foam similar to a polyurethane foam, but with superior resistance to high temperatures, it is formed in the same maimer as polyurethane foams, using as the monomer a pyranyl (radical) derived from polypropylene by heating and oxidation to form an Acrolein dimmer, which ultimately forms the pyranyl. 

Pyranyl Foam n A type of rigid, pour-in-place, thermosetting foam similar to a polyurethane foam, but with superior resistance to high temperatures. It is formed in... 

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