Polymerization of Substituted Acetylenes Using Well-Defined Rhodium Complex Catalyst. Chirality Transfer and Amplification in Chiral-Chiral Block and Random Copolymers

Block and random copolymers are synthesized by the copolymerization of N-tert-butoxycarbonyl--valine 4-ethynylanilide (1L) and N-tert-butoxycarbonyl-d-valine 4-ethynylanilide (1D) using [(nbd)Rh{C(Ph) = CPh2}(PPh3)]/PPh3 as a catalyst. The size exclusion chromatography (SEC) peaks show narrow polydispersities from the first stage polymerization to the second one in the block copolymerization. Poly(1L(25)-ran-1D(25)) exhibits no circular dichroism (CD) signal, while poly(1L(25))-block-poly(1D(25)) exhibits weak CD signals with the same sign as those of poly(1L(50)), suggesting the occurrence of chirality transfer from the poly(1L) block to poly(1D) block. The relationship between the |g| values and 1L/1D contents of the block copolymers becomes almost linear at the region of each unit larger than 60%. On the other hand, the relationship between these two factors of the random copolymers is convex upward.