Copoly(alpha-alkyl-beta,L-aspartate)s containing n-octadecyl and n-butyl side groups at different ratios were prepared by anionic ring-opening polymerization of the corresponding optically pure (S)-4-alkoxycarbonyl-2-azetidinones. Random copolymers were obtained by polymerization of comonomer mixtures. Diblock copolymers were achieved by sequential copolymerization using the living poly(alpha-n-octadecyl-beta,L-aspartate) block to initiate the polymerization of (s)-4-n-butoxycarbonyl-2-azetidinone as a second block. Composition and sequence distribution were characterized by NMR with the help of a model copoly(beta,L-aspartate) made of alpha-n-dodecyl and alpha-benzyl beta,L-aspartate units. All the copolymers were found to adopt the layered structure made of 13/4 helices described previously for comb-like poly(alpha-n-alkyl-beta,L-aspartate) homopolymers. Copolymers containing at least 50% of n-octadecyl side groups have these groups crystallized in an interlayer microphase and aligned normal to the main helical chain. Melting of the paraffinic crystallites happened within the 40-60 degrees C temperature range with formation of a liquid-crystal phase in which side chains are molten but retain the alignment of the low temperature phase. Different from what is known to happen to poly(alpha-n-octadecyl-beta,L-aspartate), no indications on the occurrence of a second structural transition were observed at higher temperatures.