Isospecific and syndioselective ring-opening metathesis polymerizations (ROMP) of norbornene (NB) and tetracyclododecene (TCD), as well as their tactic (and atactic) hydrogenated ring-opened polymer products have been thoroughly investigated for the first time. In the case of NB polymerization, cis-isospecific ROMPs of NB were achieved with Mo(O)(rac-5,5′,6,6′-Me4-3,3′-t-Bu2-biphenolate)2-based catalyst (cis = 100%, isotacticity =100%). Cis-syndioselective ROMPs of NB proceeded in the presence of W(NPh)Cl4·Et2O- and W(N-2,6Me2Ph)Cl4·Et2O-based catalysts (cis = 90%, syndiotacticity =90%). Hydrogenated poly(NB)s exhibited high crystallinity irrespective of their stereostructures. The crystalline nature of syndiotactic hydrogenated poly(NB) (syndiotacticity = 90%: T m = 130–136 °C, ΔH = 60–75 J/g, w c = 0.55–0.70) was close to that of conventional atactic one (meso/racemo = 50/50: T m = 145–150 °C, ΔH = 65–70 J/g, w c = 0.65). On the contrary, isotactic hydrogenated poly(NB) was characterized by a remarkably unique crystalline nature such as high melting points (isotacticity > 90%: T m = 160–180 °C, ΔH = 50–90 J/g, w c = 0.50–0.65). In the case of TCD polymerization, W(NPh)Cl4·Et2O-based catalyst introduced cis-syndioselective ROMP of TCD (cis = 90%, syndiotacticity = 86%). Syndiotactic hydrogenated poly(TCD) obtaining from W(NPh)Cl4·Et2O-based catalyst was entirely amorphous and soluble in ordinary organic solvents. On the other hand, atactic hydrogenated poly(TCD) showed poor solubility and semicrystallinity (T m = 290 °C, ΔH < 10 J/g). In addition, Mo(O)(rac-5,5′,6,6′-Me4-3,3′-t-Bu2-biphenolate)2-based catalyst provided all-cis poly(TCD), of which hydrogenated product was completely insoluble and highly crystalline (T m > 350 °C, w c = 0.65). These tendencies are in significant contrast to those of the hydrogenated poly(endo-dicyclopentadiene)s, wherein atactic polymer is amorphous and both tactic polymers are crystalline (syndiotacticity = 90%; T m = 270 °C and isotacticity > 95%; T m = 295 °C, respectively).

Novel molybdenum-and tungsten-based catalysts induced stereospecific ring-opening metathesis polymerization (ROMP) of cycloolefins to produce a new class of crystalline polymers. Various monomeric molybdenum(VI) and tungsten(VI) complexes of the general formula M()O)(O-Ar) 4 (M ) Mo or W;(O-Ar)4 is two biphenolate or four phenolate ligands) were prepared. These catalysts exhibited moderate ROMP activity in the presence of cocatalyst such as n-BuLi and Et3Al. The molybdenum and tungsten complexes bearing substituted biphenolate ligands such as oxomolybdenum(VI) bis(racemic-5,5′,6,6′-tertamethyl-3,3′-di-tert-butyl-1,1′-biphenyl-2,2′-diolate) promoted cis and isospecific ROMP of endodicyclopentadiene (cis > 90% and meso > 95%). The novel ternary and quarternary catalysts such as MoOCl 4-biphenolate-n-BuLi (1:2:2) were developed as a new useful methodology to control the stereoselectivity of the ROMP. Hydrogenation of the cis-isotactic poly(endo-dicyclopentadiene)s and poly-(norbornene)s provided novel crystalline polymers with high melting points (295 °C, ∆H ) 50 J/g; 175 °C, ∆H ) 60 J/g, respectively), which can be regarded as a new class of crystalline polymers.

Properties of the tactic and atactic hydrogenated ring-opened poly(endo-dicyclopentadiene)s and features of the tungsten imido/phenolate-catalyzed stereoselective ring-opening metathesis polymerizations (ROMP) were studied. Several tungsten(VI) imido phenolate complexes were synthesized and exhibited moderate ROMP activity in the presence of n-BuLi. W(dNPh)((R)-(+)-5,5′,6,6′-Me 4 -3,3′-t-Bu 2 -biphenolate) 2 was found to be effective for cis-, isoselective ROMP of endo-dicyclopentadiene (DCPD), while W(dNPh)Cl 4 ‚Et 2 O promoted cis-, syndioselective ROMP. On the other hand, W(dNPh)(2,6-Me 2 -phenolate) 4 provided atactic poly(DCPD). Isotactic, atactic, and syndiotactic hydrogenated ring-opened poly(DCPD)s were characterized well by various methods for the first time. Both tactic polymers were shown to be crystalline polymers by means of DSC, WAXD, and TEM measurements. In contrast, atactic poly(DCPD) was an amorphous polymer. The crystallization rate of the syndiotactic hydrogenated poly(DCPD) was significantly higher than that of the isotactic polymer.

The crystal structures of highly crystalline isotactic and syndiotactic hydrogenated poly(norbornene)s [Hpoly(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.

Stereoregularity significantly influences the crystallization, mechanical, and thermal properties of polymers. In this work, we investigate crystallization behaviors and molecular dynamics of atactic (a)-, isotactic (i)-, and syndiotactic (s)hydrogenated poly(norbornene) (hPNB)s by using small-angle X-ray scattering and solid-state (ss) NMR. a-hPNB exhibits a much higher crystallinity (Φ c ) (82%) and long period (L) (80 nm) than i-and s-hPNB (50−55% and 17−21 nm). Moreover, in the s-hPNB crystalline region, chain dynamics is not thermally activated up to the melting temperature (T m ), while in the crystalline regions of i-and a-hPNB, small amplitude motions occur in a slow dynamic regime of 10 −2 −10 2 s. The molecular dynamics follows Arrhenius behavior in a-hPNB up to the crystal−crystal transition temperature (T cc ), while these dynamics are surprisingly saturated in i-hPNB under these conditions. Temperature dependence of the molecular dynamics leads to different crystal−crystal transitions between i-and a-hPNBs: i-hPNB changes the trans conformation to the gauche one due to the localized bond rotations where chain dynamics is restricted, whereas a-hPNB keeps a nearly trans conformation and conducts fast chain dynamics due to the amplified C−C bond rotations in the high-temperature phase. Such fast chain dynamics leads to unique crystallization behaviors of hPNB, specifically in the atactic configuration due to configurational disorder coupled with conformational flexibility.