Diblock copolymers of ethylene oxide and 1,2-butylene oxide, E30Bn, with constant E-block length of 30 units and various B-block lengths (n = 3-30) were investigated, in parallel with a series of homopoly(oxybutylene)s of similar to B-block lengths, using broad-band dielectric relaxation spectroscopy (10(-2)-10(9) Hz). The normal mode relaxation process due to reorientation of the end-to-end vector and the main (segmental) process caused by local chain motions, exhibited by the B-blocks in the copolymers and by the homopoly(oxybutylene), were studied in comparison to each other. The dynamics of the free chains in the liquid homopolymers is described more appropriately by the Rouse model, whereas the B-blocks in the crystallized copolymers exhibit significantly different dynamics. The results show that the B-blocks in the copolymers, constrained between lamellar crystals created by E-blocks, are more oriented and expanded, as compared to the chain conformation of the homopolymers. Comparative study of normal mode and main relaxations reveals, only for the homopolymers, a correlation length xi for the main process on the order of 1-2 nm at temperatures close to the glass transition temperature, T-g.