A general model describing molecular weight distribution and branching indices in copolymerizations demonstrated by the high-pressure free-radical copolymerization of ethene and methyl acrylate

A general copolymerization model is developed which incorporates various tr ansfer reactions, like transfer to polymer and backbiting, and scission rea ctions. The potential of the model is investigated using the simulation pac kage PREDIC(R) by performing a number of sensitivity analyses. The main foc us of this work is directed toward the development of experimental strategi es for,deriving proper kinetic parameters based on simulation;calculations. To provide a broad base for general application the model is designed for investigating fundamental aspects as well as providing the potential for us e in technical production. This would mean dealing with complex reactor ope ration modes and dealing with multiple broad species distributions. At thes e simulations the high-pressure free-radical copolymerization of ethene CE) with methyl acrylate (MA) is used. This complex fluid-phase copolymerizati on system features all elementary reaction steps being discussed to occur a t free-radical (co-polymerizations at the moment and is therefore self-sugg esting for such investigations. The experimental strategy derived from the simulation study is verified by two experimental examples of E-MA copolymer s both containing 15 mol-% methyl acrylate synthesized at 150 degreesC and 2000 bar featuring 22 mol-% and 32 mol-% acrylate conversion. It becomes ob vious that the kinetic model is capable of well describing experimental mol ecular weight distributions and branching indices by one set of kinetic par ameters. Successful experimental design and description of data demonstrate the usefulness of modeling for kinetic investigations. Moreover, they are the justification for a future application of models following strategies b eing proposed in this contribution for other copolymerization systems and m ore complex copolymerization applications. In this model the coupled implem entation of the transfer to poly-mer and p-scission reaction is applied for the first time in copolymerizations (this description is close to the real process). Also the design of an experimental strategy showing singular sen sitivities on the determination of rate coefficients for branching and scis sion in copolymerizations, is presented for the first time. An assumption t hat has still to be made within this model is the treatment of p-scission a cting on a linear chain. However, as long as a macromolecule is not multipl y long-chain branched there is no error introduced into modeling using this approximation.