The crystal–crystal transition in hydrogenated ring‐opened polynorbornenes: Tacticity, crystal thickening, and alignment

Abstract

AbstractAt a temperature Tcc well below its melting point Tm, hydrogenated ring‐opened polynorbornene (hPN) is known to exhibit a crystal–crystal transition; above Tcc, the hPN chains are rotationally disordered. This transition is examined in a series of hPNs polymerized with different Mo‐ and Ru‐based catalysts, each of which imparts a slightly different tacticity to the polymer. Tcc is found to correlate well with the ratio of meso to racemo dyads (m:r); small changes in m:r (from 0.8 to 1.1) are sufficient to raise Tcc by nearly 20 °C. For the homogeneous Mo‐based “Schrock‐type” catalyst examined, such a change in m:r is easily achieved by simply adding the reversibly binding ligand trimethylphosphine during polymerization. Tcc approaches Tm with increasing m:r, indicating that r dyads stabilize the rotationally disordered structure. When heated above Tcc, hPN crystals thicken at a rate much greater than conventional three‐dimensionally ordered crystals, but below the rates shown by the two‐dimensional hexagonal (columnar) phase formed by some polymers, reflecting the intermediate level of order and chain mobility present in the high‐temperature hPN crystal phase. Solid‐state processing of hPN between Tcc and Tm yields highly aligned macroscopic specimens. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010