Mechanism and Kinetics of the Spontaneous Thermal Copolymerization of Styrene/Maleic Anhydride. Experimental and Simulation Studies in the Presence of 4-oxo-TEMPO

The mechanism and kinetics of the spontaneous copolymerization of styrene (S) and maleic anhydride (MA) in the presence of 4‐oxo‐TEMPO nitroxide (N) were studied. Experiments were performed at 125 °C varying the S/MA and the N/S ratios and the evolution of conversion was measured by dilatometry up to 20% conversion. Clean induction periods or severe retardation in the initial stage of the reaction were observed. From a proposed kinetic mechanism a mathematical model was built, which was used for fitting the relevant kinetic constants for the self‐initiation steps, and the ratio ${{\bar {k}_{\rm p} } \mathord{\left/ {\vphantom {{\bar {k}_{\rm p} } {\bar {k}_{\rm t}^{{1 \mathord{\left/ {\vphantom {1 2}} \right. \kern-\nulldelimiterspace} 2}} }}} \right. \kern-\nulldelimiterspace} {\bar {k}_{\rm t}^{{1 \mathord{\left/ {\vphantom {1 2}} \right. \kern-\nulldelimiterspace} 2}} }}$. The model performs well in certain concentration regimes, but it remains a challenge to completely understand this complex system in other concentration regimes. Induction period experiments for the spontaneous copolymerization of styrene and maleic anhydride in the presence of 4‐oxo‐TEMPO at 125 °C allowed the separation of the self‐initiation from the propagation/termination steps. With the aid of a kinetic and mathematical model the relevant kinetic constants for the self‐initiation steps and the ratio $\bar{k}_{\rm p}/\bar{k}_{\rm t}^{1/2}$ for this system are estimated for the first time.