Synthesis and characterization of organosiloxane modified segmented polyether polyurethanes

Segmented polyurethanes derived from a 1000 (M) over bar(n), hydroxyl terminated polytetramethylene oxide soft segment, 4,4'-methylene diphenyl diisocyanate. MDI, and 1,4-butanediol were modified with a 1200 (M) over bar(n) secondary aminoalkyl functional polydimethylsiloxane (PDMS) oligomer via solution polymerization in tetrahydrofuran (THF)/dimethylacetamide (DMAC). Various compositions were studied using FTIR and NMR spectroscopy, thermal analysis, quantitative size exclusion chromatography (SEC), cone calorimetry, transmission electron microscopy, XPS and mechanical testing. The results suggest that, with as little as 15% of the polydimethylsiloxane one may reduce the cone calorimetry heat release rate by a factor of about 2/3 and hence improve fire resistance, while maintaining mechanical behavior. It is suggested that the low surface energy characteristics of PDMS promote migration to the air-polymer interface to form a predominately PDMS enriched surface. The latter is oxidized at elevated temperatures in air to a silicate-like material and this serves as a protective layer, which further reduces burning of the underlying polyurethane. Dynamic mechanical behavior and electron microscopy suggest that a complex mutiphase structure is produced, particularly at low PDMS weight fractions. (C) 2000 Elsevier Science Ltd. All rights reserved.