Synthesis and characterization of novel vinyl copolymers containing N-vinylphthalimide: Comonomers reactivity ratios and thermal stability

N-Vinylphthalimide (NVPh) was copolymerized with p-methylstyrene (PMS), p-methoxystyrene (PMOS) and p-chlorostyrene (PCIS) at 60 degrees C, with 2,2'-azo-bis-isobutyronitrile as an initiator. Copolymer composition was determined by elemental analysis in case of the N-vinylphthalimide and p-methylstyrene comonomer pair, whereas proton nuclear magnetic resonance was used for the analysis of the two other copolymers. The reactivity ratios for each comonomer pair were estimated by the classical Fineman-Ross and Kelen-Tudos linear techniques. These data showed that N-vinylphthalimide was less reactive in all the cases and that the comonomer distribution, that was basically random in the poly(N-vinylphthalimide-co-p-methylstyrene) and poly(N-vinylphthalimide-co-p-chlorostyrene) copolymers, was rather alternate in the third poly(N-vinylphthalimide-co-p-methoxystyrene) copolymer. The difference observed in the reactivity ratios was discussed in reference to the structure of the comonomer units and the parent radicals. The thermal properties of the copolymers and model homopolymers were investigated by differential scanning calorimetry and thermogravimetric analysis.