In the face of impending CFC elimination, a large variety of low-boiling alternate blowing agents have come under scrutiny for use in rigid foam insulation applications. The permeability of both the alternate blowing agent and atmospheric gases through the rigid foam thermoset polymer contributes to the rate at which the k -factor of the resulting foam deteriorates.In this study, a compression molding method for synthesizing polymer films from polyurethane formulation components (a variety of diols with pure and polymeric methylenediphenyl diisocyanate) was developed and utilized to produce films containing distinct structural features. The permeabilities of the films to oxygen and carbon dioxide were then determined using a diffusion cell combined with either an infrared or coulombic detector.The effects on permeability of structural features such as diol molecular weight, alkylene oxide repeat unit, and isocyanate functionality are presented. Structural features determined to promote improved barrier performance in polymer films have been incorporated into a fully formulated foam system. Foam permeability and k -factor aging comparisons were then made which demonstrate the improved foam barrier performance. The resulting structure/permeability correlations derived from these experiments will be useful in designing rigid foam polymers for use in alternate blowing agent applications.

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The decreased emphasis on the use of CFC blowing agents for rigid foam has placed a greater demand on the performance of the polymer in the foam. One area where higher performance is needed is in permeability. In order for non-CFC foam to retain its insulation performance the permeation of low k-factor blowing agent out of the foam and the permeation of high k-factor air into the foam must be minimized. This paper will present data on several new types of polyols which have been designed specifically to give lower permeability than conventional rigid foam polyols. Data on the permeability of both air and carbon dioxide for these polyols was developed on both compression molded thermoset polymer films and foam samples. These polyols gave significant improvement in both carbondioxide retention and air exclusion which lead to improved k-factor aging in the foam samples.

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