Hybrid block copolymers amylose-block-polystyrene were synthesized by covalent attachment of maltoheptaose derivatives to end-functionalized polystyrene and subsequent enzymatic grafting from polymerization. The maltoheptaose derivatives were attached by reductive amination or hydrosilation to amino- or SiH-terminated polystyrene (synthesized by anionic polymerization), respectively. The enzymatic polymerization could be started even though the primer-modified polystyrenes were insoluble in the medium of polymerization, i.e., citrate buffer. The polymerization kinetics show an interesting dependence on the molecular weight of polystyrene due to the micellar structure of the primer in water.