Cyclopentadienyl Nickel and Palladium Complexes/Activator System for the Vinyl‐Type Copolymerization of Norbornene with Norbornene Carboxylic Acid Esters: Control of Polymer Solubility and Glass Transition Temperature

Summary: In non‐polar solvents such as toluene, Cp‐Ni and ‐Pd complexes (Cp =  η 5 ‐C 5 H 5 ) with appropriate activators have been found to induce the addition polymerization of norbornene in excellent yields, for example (Cp)Pd(allyl)/[Ph 3 C][B(C 6 F 5 ) 4 ] gave 105 120 kg‐polymer/cat‐mol · h at room temperature. While the Cp‐Pd system was not suitable in the presence of ester‐substituted norbornenes, the Cp‐Ni system, for example (Cp)Ni(Cl)(PPh 3 )/AlMe 3 /B(C 6 F 5 ) 3 can copolymerize norbornene with 5‐norbornene‐2‐carboxylic acid methyl ester in toluene to give high yields (up to 68% in 2 h at room temperature) of copolymer with variable contents of the methyl ester monomer unit (17.4–60.7 mol‐%). These copolymers have high molecular weights ( $\overline M _{\rm n}$  = 234 100–109 500) and narrow molecular weight distributions ( $\overline M _{\rm w} /\overline M _{\rm n}$  = 1.78–1.89). In addition, they are soluble in common organic solvents giving flexible and transparent films on casting, that show very high T g in the range of 352.8 to 316.0 °C. The same Ni‐catalyst system can also copolymerize norbornene derivatives with bulky substituents, i.e., 2‐butyl‐5‐norbornene and 5‐norbornene‐2‐carboxylic acid butyl ester. The T g of these copolymers are lower (294.9–267.3 °C) than the methyl ester‐based copolymers, demonstrating that the T g of the polynorbornene copolymer film can be tailored simply by changing the alkyl group of the monomer to within the range of 352 to 267 °C.Figure showing the addition polymerization of norbornene using Cp‐Ni complex with appropriate activators.