Post-Polymerization Crosslinked Polyurethane Shape Memory Polymers

Novel urethane post-polymerization curable shape memory polymers (SMPs) have been synthesized and characterized. Several series of linear, olefinic urethane polymers were made from 2-butene-1,4-diol, other saturated diols, and various aliphatic diisocyanates. These thermoplastics were melt-processed into desired geometries and thermally crosslinked at 200 degrees C or radiation crosslinked at 50 kGy. The SMPs were characterized by solvent swelling and extraction, differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), tensile testing, and qualitative shape recovery analysis. Swelling and DMA results provided concrete evidence of chemical crosslinking, and further characterization revealed that the urethanes had outstanding mechanical properties. Key properties include tailorable transitions between 25 and 80 degrees C, tailorable rubbery moduli between 0.2 and 4.2 MPa, recoverable strains approaching 100%, failure strains of over 500% at T(g), and qualitative shape recovery times of less than 12 s at body temperature (37 degrees C). Because of its outstanding thermo-mechanical properties, one polyurethane was selected for implementation in the design of a complex medical device. We believe that these new post-polymerization crosslinkable urethane SMPs are an industrially relevant class of highly processable shape memory materials. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 121: 144-153, 2011