Poly(L‐valine). Conformational dependence on the degree of polymerization: Infrared studies

Abstract The infrared spectra of poly( L ‐valine)'s with varying degrees of polymerization have been investigated, as well as copolymers of L ‐alanine and L ‐valine. The spectra of nujol mulls of various molecular‐weight poly( L ‐valine)'s, isolated directly from the polymerization media, as well as spectra of these same samples after treatment with strong acid, are recorded. In the 700–250‐cm −1 region, bands at 543 and 414 cm −1 are found to increase with increasing degree of polymerization in the nujol mulls, but are missing in the acid‐treated samples. These bands are assigned to the L ‐valine residues with an β‐helixlike local conformation. It is inferred that the polymerization proceeds initially in the β form, and after a critical degree of polymerization the chains adopt an appreciable amount of an α‐helixlike local conformation.