Iso- and Syndio-Selective ROMP of Norbornene and Tetracyclododecene: Effects of Tacticity Control on the Hydrogenated Ring-Opened Poly(cycloolefin)s

Abstract

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%: Tm = 130–136 °C, ΔH = 60–75 J/g, wc = 0.55–0.70) was close to that of conventional atactic one (meso/racemo = 50/50: Tm = 145–150 °C, ΔH = 65–70 J/g, wc = 0.65). On the contrary, isotactic hydrogenated poly(NB) was characterized by a remarkably unique crystalline nature such as high melting points (isotacticity > 90%: Tm = 160–180 °C, ΔH = 50–90 J/g, wc = 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 (Tm = 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 (Tm > 350 °C, wc = 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%; Tm = 270 °C and isotacticity > 95%; Tm = 295 °C, respectively).