Exfoliated modified syndiotactic polystyrene/montmorillonite nanocomposite was synthesized by a solution intercalation method. Nitroxide-mediated radical polymerization (NMRP) and atom transfer radical polymerization (ATRP) were used for the first time to prepare graft and block copolymers using α-phenyl chloro acetylated syndiotactic polystyrene (α-ph-ch-sPS) as a backbone and polystyrene (PS), poly(p-methylstyrene) (PMS) and poly(methyl metacrylate) (PMMA) as a branches. Firstly, 1-hydroxy 2,2,6,6-tetramethyl-1-piperidinyloxyl (TEMPO) was coupled with α-ph-ch-sPS. The controlled graft and block copolymerization of styrene and p-methylstyrene monomers onto the syndiotactic polystyrene (sPS) backbone were initiated by the sPS and sPS-g-PS carrying TEMPO groups as a macroinitiators, respectively. Thereafter, N-boromosuccinimide (NBS) was used to introduce bromine to the benzylic positions of the copolymer. This multicentre macroinitiator was used to prepare the [sPS-g-(PS-b-PMS)]-g-PMMA copolymer using the ATRP technique in the presence of the CuBr/Bpy catalyst system. Organophilic montmorillonite (O-MMT) was obtained after being treated with hexadecyl trimethyl ammonium chloride salt by an ion-exchange process. Finally, [sPS-g-(PS-b-PMS)]-g-PMMA/O-MMT nanocomposite was prepared by a solution intercalation method. The exfoliated structure of the nanocomposite was probed by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Compared to pure [sPS-g-(PS-b-PMS)]-g-PMMA, the nanocomposite showed a much higher decomposition temperature and higher glass transition temperature (Tg).