Abstract: The solid and solution spectra of the soft segment of styrene-dimethyl sil-oxane block copolymeri, are studied by ¹³C and ²⁹Si NMR spectroscopy and their spin-lattice relaxation times(T₁) are determined.It is found that in CDCl₃ solution the T₁s of the main chain ²⁹Si and the pendant methyl group ¹³C are toth longer than the homopoly dimethylsiloxane, but they are identical with the homopolymer in the bulk state,It is known that the spin-lattice relaxation of high polymers is mainly dominated by dipole-dipole interactions. There isa clear two-phase strucre, Therefore, the mode of motion is essentially the same in block and in homopolymers CDCl₃ is a good solvent for polystyrene and polydimethylsiloxane. In CDCl₃ solution there is a mutual effect between the hard and the soft segmental motion no longer resembles that of the homopolymer.Therefore, the correlation time of the segmental motion of the block copolymer is shorter and T₁ is much longer.