Instabilities in free radical polymerization

The rheokinetics of bulk free radical polymerization has so far been invest igated only at low degrees of conversion, where the system may be considere d as Newtonian. In that case the rheokinetic equations can be linearized, y ielding a simplified expression of the viscosity increase as a function of time during polymerization. In this paper we extend the rheokinetic approac h to the study of bulk free radical polymerization at high degrees of conve rsion, where the rheokinetic equations may not be linearized and the system must be considered as non-Newtonian. Moreover, the occurrence of the so-ca lled gel effect complicates the nonlinearity of the rheokinetic problem eve n more. The rheokinetic experiments performed show that the gel effect is reduced w hen the polymerization is performed at high shear rates. At very high degre es of conversion an onset of irregularities in the viscosity measurements w as noticed. Possible explanations for these irregularities are discussed.