Poly(styrene-co-N-maleimide) (NMI) copolymers were obtained from reactive extrusion experiments of poly(styrene-co-maleic anhydride) (SMA) with ammonia in small reaction times (2 min). As a result of this modification, materials with relatively high glass-transition temperatures have been obtained compared to the starting material, and this is believed to result mainly from hydrogen bonding between the maleimide groups. Qualitative and quantitative evidence has been obtained from an FTIR study performed on NMI-14 containing 14 wt % maleimide groups. This investigation revealed hydrogen bonding between the NH and carbonyl groups of the maleimide groups. A systematic FTIR spectroscopic study of the blend system consisting of NMI-14 and poly(styrene-co-2-vinylpyridine) (SPVP) was also performed. Direct evidence of hydrogen bonding involving the NH groups of NMI-14 and the nitrogen of the pyridine group in SPVP is presented.