Well-defined poly(tert-butyl methacrylate)-graft-poly (dimethylsiloxane) (PtBuMA-g-PDMS) graft copolymers were synthesized via reversible addition-fragmentation chain transfer (RAFT) copolymerization of methacryloyl-terminated poly (dimethylsiloxane) (PDMS-MA) with tert-butyl methacrylate (tBuMA) in ethyl ace.:ate, using 2,2'-azobis(isobutyronitrile) (AIBN) as the initiator and 2-cyanoprop-2-yl dithiobenzoate as the RAFT agent. The RAFT statistical copolymerization of PDMS-MA with tBuMA is shown to be azeotropic and the obtained PtBuMA-g-PDMS graft copolymers have homogeneously distributed brancies because of the similar reactivity of monomers (r(tBuMA) approximate to r(PDMS-MA) approximate to 1). By the RAFT block copolymerization of PDMS-MA with tBuMA, moreover, narrow molecular weight distribution (M-w/M-n, < 1.3) PtBuMA-g-PDMS graft copolymers with gradient or blocky branch spacing were synthesized. The graft copolymers exhibit the glass transitions corresponding to the PDMS and PtBuMA phase, respectively. However, the arrangement of monomer units in copolymer chains and the length of PtBuMA moieties have important effects on the thermal behavior of PtBuMA-g-PDMS graft copolymers. (C) 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49: 1483-1493, 2011