Thermoplastic elastomers (TPEs) are typically ABA triblock copolymers made up of a rubbery midblock (B) and glassy endblocks (A).  If instead the hard segments were crystalline, microphase separation could be driven by crystallization from a lower-viscosity single-phase melt, while the crystalline endblocks would simultaneously confer properties such as solvent resistance. We use living ring-opening metathesis polymerization and subsequent hydrogenation to synthesize TPEs consisting of crystalline hydrogenated polynorbornene (hPN), rubbery hydrogenated poly(5-hexylnorbornene) (hPHN), and glassy hydrogenated polymethyltetracyclododecene (hPMTD).  By suitable control of the block lengths, we achieve a single-phase melt in a symmetric pentablock TPE with the architecture hPN-hPMTD-hPHN-hPMTD-hPN, where microphase separation is driven by crystallization.  When the hPN block crystallizes, the attached hPMTD block forms a glassy layer surrounding the crystals, limiting their lateral growth.  The resulting pentablock TPE is insoluble at room temperature due to the hPN crystallinity; has an easily processed single-phase melt; and possesses composite crystalline/glassy hard domains that impart good TPE behavior to the material, with only modest permanent set.

Thermoplastic elastomers with composite crystalline/glassy hard domains

239th National Meeting (2010)

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