The structure and the associated dynamics of a series of poly(?-benzyl-L-glutamate)-b-poly(dimethyl siloxane)-b-poly(?-benzyl-L-glutamate) (PBLG-b-PDMS-b-PBLG) triblock copolymers were investigated using small- and wide-angle X-ray scattering, NMR, transmission electron microscopy, and dielectric spectroscopy, respectively. The structural analysis revealed phase separation in the case of the longer blocks with defected ?-helical segments embedded within the block copolymer nanodomains. The ?-helical persistence length was found to depend on the degree of segregation; thermodynamic confinement and chain stretching results in the partial annihilation of helical defects. © 2006 American Chemical Society.