Critical evaluation of the microwave effect on radical (Co)polymerizations

Critical evaluations of the microwave effect on initiation, propagation, and termination during conventional radical polymerizations (RPs) of methyl methacrylate (MMA) and random copolymerization of styrene (St) with (meth)acrylates are examined by comparing microwave heating (MWH) and conventional heating (CH). Poly(methyl methacrylate) with similar $ \overline M-{\rm n} $, $ \overline M-{\rm w} $/$ \overline M-{\rm n} $, and conversion are obtained under precisely controlled temperature, indicating very small changes of propagation rate constant. Rate enhancement in the absence of precise temperature control is mostly due to the higher reaction temperature of the reaction mixture than the apparent value indicated on display. Rates of initiator decomposition under well-controlled temperature are essentially the same for MWH and CH. Using precise temperature control, a critical evaluation of the microwave effect on initiation, propagation, and termination during conventional radical polymerizations is examined. Comparison of microwave heating (MWH) and conventional heating (CH) suggests that MWH has a minor influence on k _d, k _p/k _t, and comonomer reactivity.