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Free radical reactions, carried out in polymer melts, have become a popular method of chemically modifying polyolefins. The elementary free-radical reactions which are relevant in the chemical modification of polyolefins at high temperatures in extruders, such as chain transfer to polymer via primary and polymer radicals, /3-scission, double bond addition and bimolecular termination, affect chain scission, long chain branching, crosslinking and grafting. This brief review will discuss some of the work focused on the kinetics and mathematical modelling of these reactions. ~ ~~Les reactions de radicaux libres, effectutes dans les mklanges de polymtres, sont devenues des methodes rkpandues pour modifier chimiquement les pol yolkfines. Les reactions de radicaux libres ClCmentaires qui sont importantes dans la modification chimique des polyolkfines a des tempkratures Clevees dans les extrudeuses, telles que le transfert de chaine vers le polymtre via des radicaux primaires et de polymtres, la /3-scission, I'addition des doubles liens et la terminaison bimoliculaire, influent sur la scission de chaine, le branchement de chaines longues, la rkticulation et le greffage. Nous examinerons brievement certains des travaux portant en particulier sur la modelisation cinetique et mathkmatique de ces reactions.

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Free radical copolymerization in high-pressure autoclave reactors is studied by developing a mathematical model. Kinetic mechanisms to describe the polymerization rate, molecular weight averages, branching frequencies, as well as copolymer composition are presented. Two phase kinetics due to polymer-monomer solubilities in the reaction mixture are taken into account. Gel formation from cross-linking reactions is also analyzed. A mixing model is developed to represent the stirring effect inside the reactor. The mathematical model is implemented as a computer program to simulate commercial autoclave reactors. PID control equations are used to maintain operation at the unstable steady state. A sensitivity study is performed on the mixing model parameters and on some of the kinetic parameters and the model is compared to rate data from commercial reactors.

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