The present work examines an in-situ NMR technique for the copolymerization of methyl methacrylate (MMA) and diallyl dimethylammonium chloride (DADMAC). The copolymer poly(MMA-co-DADMAC) contains monomers of significantly different polarities, making it challenging to measure DADMAC incorporation. The conventional technique for accurate measurement of monomer reactivity ratios in copolymers is time consuming, requiring a large number of experiments, in addition to being challenging for isolation/analysis of formed copolymers from this heterogeneous polymerization. The results show that the reactivity ratios were insensitive to temperatures between 60 and 80 degrees C, while the reactivity ratios of MMA were found to be much higher than that of DADMAC. The results were comparable to those obtained by the conventional technique. Due to the heterogeneous nature, the measured reactivity ratios are considered as apparent reactivity ratios but important for modifying poly(methyl methacrylate) with DADMAC by copolymerization, enabling design and development of copolymers with desired composition for specific end-use applications.