Characteristic events in free radical polymerization of lower n-alkyl methacrylates

Abstract

It is well known that the free radical bulk polymerization of lower n-alkyl methacrylate is characterized by autoacceleration after definite conversions of the monomers. The conversion vs. time curves of polymerization have a typical `S' shape. There are several characteristic points in these curves: the onset of autoacceleration (point M), the maximum in the polymerization rate (point S) and the end of the polymerization (point K). We have observed points P and R (maximum and minimum of autoacceleration) as inflection points in the derived polymerization rate vs. time curve. In this work, the free radical bulk polymerizations of methyl, ethyl and butyl methacrylate were investigated by differential scanning calorimetry. The effects of the polymerization temperature and the alkyl group length in the esters on the monomer conversions at the points M, P, S, R and K were studied. By regression analysis of the experimental results, relations were developed with which it is possible to predict the positions of the characteristic points, depending on the polymerization temperature and the alkyl group length.