Tapered Block Copolymers Containing Ethylene and a Functionalized Comonomer

We report the synthesis of tapered block copolymers of ethylene with 5-norbornen-2-yl acetate (1) by the nickel catalyst system [N-(2,6-diisopropylphenyl)-2-(2,6-diisopropylphenylimino)propanamide] Ni(η-CH2Ph)(PMe3) (2) and Ni(COD)2 (bis(1,4-cyclooctadiene)nickel). This technique utilizes a one-pot semibatch copolymerization in which ethylene is continuously added while 1 is depleted by incorporation into the polymer chain. The simplicity of this technique allows the construction of a polymer library, which enabled us to study the effect of polymer composition and chain length on solid-state morphology and mechanical and thermal properties. From these studies we were able to derive a profile relating the probability of 1 insertion vs degree of polymerization (X n ). Under proper experimental conditions, these tapered polymers form ordered microphase-separated morphologies where the phase morphology is modulated by the polymer chain length. The percent crystallinity and storage modulus of the polymers were found to be chain length dependent.