Abstract
The crystal structures of highly crystalline isotactic and syndiotactic hydrogenated poly(norbornene)s [H-poly(NB)s], synthesized by the stereospecific ring-opening metathesis polymerizations of norbornene followed by complete hydrogenation, have been determined for the first time on the basis of the X-ray diffraction data analyses. The similarity and difference of the chain conformation and the chain packing mode in the crystal lattice have been clarified among the three kinds of H-poly(NB) samples (syndiotactic, isotactic, and atactic species). The molecular chains were found to take essentially the planar zigzag conformation at room temperature with slight torsional angle fluctuations around the skeletal C–C bonds. The cyclopentylene rings were found to protrude from the plane of the skeletal polymer chain in various different ways depending on the tacticity, resulting in the difference of the whole shape of the chains and then the difference of the chain packing structure. The melting point was found to be different depending on the tacticity: 178, 148, and 134 °C for the isotactic, atactic, and syndiotactic H-poly(NB)s, respectively. The difference in the thermal behavior has been discussed qualitatively on the basis of these structural pieces of information.
Highlights
Hydrogenated ring-opened poly(cycloolefin)s have been attracting intensive interest from academia and industry because of their superior properties such as optical properties, heat resistance, moisture resistance, chemical resistance, and electric property.[1,2] In particular, the stereospecific ringopening metathesis polymerization (ROMP) of cycloolefins has been studied well in the past decade
Its basic structure is an alternate arrangement of a cyclopentylene ring and an ethylene unit along the chain, but several types of different regularities are existent in their stereostructure
The syndiotactic and isotactic H-poly(NB)s are new polymer species, which were successfully synthesized by developing the new catalysts as already reported.[8]
Summary
Hydrogenated ring-opened poly(cycloolefin)s have been attracting intensive interest from academia and industry because of their superior properties such as optical properties, heat resistance, moisture resistance, chemical resistance, and electric property.[1,2] In particular, the stereospecific ringopening metathesis polymerization (ROMP) of cycloolefins has been studied well in the past decade. The similar behavior was reported for the H-poly(DCP) sample, where the Tm of the isotactic species 293 °C is higher than that of the syndiotactic one, 270 °C.3,4 The difference of the melting temperatures between the three types of polymers is originated from the difference of the stereoregularity and so the difference in the crystal structure, as will be described in a later section.
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