AbstractSoluble copolymers of a series of (N‐maleimido phenoxy) silane monomers with styrene (St) were synthesized by radical polymerization in toluene using 2,2′‐azobisisobutyronitrile as initiator. The comonomer reactivity ratios were calculated by the conventional Fineman–Ross and Kelen–Tüdos methods and a nonlinear least‐squares Tidwell–Mortimer method. The glass transition temperatures (Tg's) and thermal degradation of copolymers were determined by differential scanning calorimetric and thermogravimetric analysis methods respectively. The introduction of silane side‐chain into maleimide (MI) monomers changed the comonomer reactivity ratio with styrene from an alternating to azeotropic copolymerization. The curves of Tg's versus the different compositions of the synthesized St‐MI copolymers (mentioned earlier) matched a modified Johnston's equation as increasing the effect of weight ratio on alternating segment, and exhibited an S‐shaped curve of deviation in comparison with the Fox's equation. The MI segments within these copolymers exhibited a good compatibility, and the thermal stability and flame retardancy of polystyrene could be enhanced simultaneously via the introduction of silicon‐containing MI. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102:3369–3375, 2006