The Trommsdorff effect under shear and bulk polymerization of methyl methacrylate via reactive extrusion

[Display omitted] •The Trommsdorff effect was weakened and postponed under higher shear rate.•Increasing shear rate significantly enhanced the chain initiation rate(Ri)•The Trommsdorff effect occurred at a critical viscosity about 1000 ± 100 Pa·s.•The Trommsdorff effect was effectively utilized during reactive extrusion of PMMA. In this study, a concentric-cylinder and double-walled reactor accurately controlling shear rates was established to conduct the free radical bulk polymerization of methyl methacrylate, and the kinetics of Trommsdorff effect under constant shear was investigated. The results showed that increasing shear rate significantly enhanced the termination rate constant (kt), and thus effectively weakened and postponed the Trommsdorff effect. However, the polymerization rate during the “quasi-steady state” was almost not affected by shear rate. Differing from the classical theory, the chain initiation rate (Ri) also increased with shear rate, which was due to the improving initiation efficiency of polymerization reaction. On the other hand, it was found that the critical viscosity when Trommsdorff effect occurred was about 1000 ± 100 Pa·s, independent of shear rates, temperatures and initiator concentrations. Based on utilizing the Trommsdorff effect, polymethyl methacrylate (PMMA) was further synthesized via reactive extrusion, with superior performance comparing to commercial product.