Graft copolymers with poly(vinyl acetate) (PVAc) backbones and poly(dimethylsiloxane) (PDMS) or poly(styrene) (PS) branches have been synthesized and their bulk nanophase-separation behaviors characterized. The PDMS and PS branches were prepared by anionic polymerization of hexamethylcyclotrisiloxane (D3) and styrene, respectively, followed by termination with chlorodimethylvinylsilane. Radical copolymerization of vinyl acetate with the vinyl terminus of these macromonomers yielded the PVAc-g-PDMS (1) and PVAc-g-PS (2a-d) graft copolymers. The branch repeat units of the copolymers were varied between 19 and 41 mol%. The graft copolymers were predicted to be moderately to strongly nanophase-segregated systems at room temperature by estimating the Flory-Huggins interaction parameters (chi) for the polymer segments. Thermal analyses revealed two glass transition temperatures for the PVAc and PDMS or PS polymer segments of the annealed samples, indicating that the polymer segments were locally phase-separated in the bulk phase. Transmission electron micrographs confirmed the presence of nanophase-separated PDMS- or PS-rich domains imbedded in a PVAc matrix.