Preparation of Flexible, Self-Extinguishing Silicone Foams

Flexible, self-extinguishing silicone foams (SFs) with a relatively low density (0.25-0.45 g/cm(3)) were obtained from a mixture of alpha,omega-(dihydroxy) poly-dimethylsiloxanes, water, flame retardants (melamine and/or expanded graphite), and polyisocyanates [poly(diphenylmethane isocyanate)]. These compositions were crosslinked at room temperature with branched poly-methylhydrosiloxanes with the structure (MeSiO1.5)(3) (MeHSiO)(102)(Me3SiO0.5)(5) in the presence of tin octoate as a catalyst. The SFs were modified by the addition of linear or graft carbofunctional polysiloxanes containing gamma-hydroxypropyl groups. Only the SFs prepared by means of a dehydrocondensation reaction had a good homogeneity of pores, whereas the foams formed with two kinds of blowing agents (hydrogen and carbon dioxide, generated in the reaction of water with isocyanate groups) had lower densities but a poor homogeneity of pores. Unmodified SFs showed a tensile strength of 20 kPa or less, whereas the foams formed with the addition of poly(diphenylmethane isocyanate) and water had a tensile strength of 23-25 kPa. The SFs with 15 and 30% contents of melamine or expanded graphite had tensile strengths in the ranges 38-45 and 51-54 kPa, respectively. All of the prepared SFs were combustible materials. The SFs without the addition of flame retardants had a limiting oxygen index of approximately 21%, whereas the SFs with a 30% content of fire retardant had self-extinguishing properties and a limited oxygen index of 41-43%. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 119: 1696-1703, 2011