A series of well-defined dendrimer-like star-branched polystyrenes (PS)s has been synthesized by developing a new iterative methodology based on "arm-first" divergent approach. In the methodology, the following three reaction steps are needed for the entire iterative synthetic sequence: (1) a linking reaction or alpha-3-(tert-butyldimethylsilyloxy)propyl- (TBDMSOP-) functionalized polystyrylithium end-capped with 1,1-diphenylethylene with either a core compound with four benzyl bromide (BnBr) functions or chain-end-BnBr-functionalized PS, (2) a transformation reaction of the terminal TBDMSOP group into 3-bromopropyl group, and (3)an introduction reaction of two BnBr functions via the 3-bromopropyl group. The synthetic sequence has been repeated five times to successfully synthesize dendrimer-like star-branched (PS)s up to the fifth-generation (5G). The final 5G polymer was 1.88 x 10(6) in M-w value (M-w/M-n = 1.05) consisting of 124 PS branch segments. By using alpha-functionalized living PMMA with two 3-tert-butyldimethylsilyloxymethylphenyl groups convertible to BnBr functions in the iterative process of the new methodology, two kinds of the 3G dendrimer-like star-branched block copolymers composed of PS, PM MA, I'S and PMMA, PS, PMMA introduced at the 1G, 2G, and 3G generations, respectively, have also been successfully synthesized. The resulting polymers all herein synthesized were observed to have precisely controlled molecular weights and compositions and narrow molecular weight distributions (M-w/M-n <= 1.05). Their expected and well-defined Structures and low degrees of homogeneity were guaranteed by agreement of both observed and calculated molecular weights of the Final polymers obtained at all generation stages.