High conversion free‐radical suspension polymerization: End groups in poly(methyl methacrylate) and their influence on the thermal stability

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Abstract
Suspension free‐radical polymerization of vinyl monomers, carried out in the presence of alkyl mercaptans as chain‐transfer agents, is analyzed. A model which accounts for the development with conversion of the polymer weight fractions having particularly tagged end groups, namely sulfur‐containing and unsaturated end groups, is presented. The best current theories for diffusion‐controlled polymerizations are included in the model. The sulfur content of poly(methyl methacrylate), determined as a function of conversion by a microcoulometric method, is in good agreement with the values predicted from polymerization kinetics. The rate of weight loss of the produced polymers is then related to the content of the unsaturated end groups. By comparing experimental thermal stability indexes (from thermogravimetry and isothermal heating experiments) to calculated polymer weight fractions, it is shown that the thermal stability of poly(methyl methacrylate) produced in the presence of alkyl mercaptans approximately depends on the square of the weight fraction of the polymer chains with an unsaturated end group.

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