| 摘要 |
The invention described herein pertain generally to at least semi-rigid polyurethane foams which cure upon exposure to moisture and which contain major amounts of non-ozone depleting hydrofluorocarbon gas. The foams additionally contain a diisocyanate, preferably, 4,4'-diphenylmethane diusocyanate (MDI) and optionally including higher oligomers of MDI (polymeric MDI) in addition to at least two polyols of different molecular weights, e.g., as measured by number average molecular weight, preferably a polyester or polyether polyol, more preferably a polyalkylene polyol. The at least two polyols have a difference in molecular weight which is greater than or equal to 10%, preferably greater than or equal to 20%, more preferably greater than or equal to 35%, and most preferably greater than or equal to 50%, said number average molecular weight of the higher molecular weight polyol being no greater than approximately 4,000. Alternatively, a first of said at least two polyols having a number average molecular weight ranging from approximately 400 to 2000, and a second of said at least two polyols having a number average molecular weight ranging from approximately 800 to 4000 wherein a molecular weight of said second polyol is always greater than a molecular weight of said first polyol, and at least one catalyst.
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