Soluble copolymers of a series of (N-male-imido 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-Tudos methods and a nonlinear least-squares Tidwell-Mortimer method. The glass transition temperatures (T-g'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 T-g'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. (c) 2006 Wiley Periodicals, Inc.