Synthesis and properties of polynorbornenes bearing oligomeric siloxane pendant groups

The ring-opening metathesis polymerization (ROMP) of norbornene derivatives 1–5 bearing oligomeric siloxane pendant groups was carried out with Grubbs 1st and 2nd generation, and Grubbs–Hoveyda ruthenium (Ru) catalysts. Monomer 1 gave high-molecular-weight polymers (Mn ca. 27 000–180 000) in high yields (80–100%). Monomers 2–5 also polymerized with Ru carbene catalysts to give high-molecular-weight polymers (Mn ca. 34 000–240 000) in high yields (66–100%). The onset temperatures of weight loss (T0) of the polymers were 180–250 °C. The glass transition temperatures (Tgs) of poly(1) and poly(2) bearing branched siloxane linkages were near or higher than room temperature (27 and 101 °C). Meanwhile, the Tgs of poly(3)–poly(5) bearing linear siloxane linkages were much lower (−115 to −23 °C), and decreased with increasing length of the siloxane linkages. Poly(1) and poly(2) were hydrogenated completely, which was confirmed by 1H NMR spectroscopy. The free-standing membranes of poly(1) and poly(2) showed high gas permeability; especially poly(2) is the most permeable to various gases among ROMP–polynorbornene derivatives reported so far.