Dynamic viscoelastic properties of bulk free radical polymerizing systems under near-isothermal and non-isothermal conditions

Abstract

Dynamic viscoelastic moduli of an example polymerizing system namely the free radical bulk polymerization of methyl methacrylate (MMA), is studied using a Haake® rheometer-reactor assembly and an adapted Haake® HV-DIN cup-and-bob assembly. A series of experiments on the bulk polymerization of MMA under different temperature histories (isothermal, step-increase and step-decrease) and at two different initiator [2, 2'-azoisobutyronitrile (AIBN)] concentrations, have been carried out. The data on the storage modulus, G', the loss modulus, G'', and the phase shift, δ, are measured during the course of polymerization, well into the gel effect region. A new correlation is developed for these properties. The kinetic model and the correlation for the zero-shear viscosity, presented in our earlier studies, are used in this generalized correlation. The correlation so developed is observed to represent experimental data quite well for a variety of temperature histories. The characteristic relaxation time, τi, representing the bulk polymerization of MMA is observed to be larger than the Rouse value, τR, by a factor of about seven. The findings are observed to be in agreement with several other studies for entangled non-polymerizing systems.