A generalized multiscale modeling framework is described for the digital simulation of a high-pressure low-density polyethylene (LDPE) tubular reactor. According to the proposed modeling approach, various models describing the complex physical and chemical phenomena at different length and time scales are linked together to assess the effects of reactor operating conditions on the molecular and rheological behavior of LDPE. The molecular properties of LDPE are determined by employing a comprehensive kinetic scheme. On the basis of the postulated kinetic mechanism, detailed population balance equations (PBEs) are derived describing the conservation of the various macromolecular polymer chains. A review of the potential methods for solving the governing PBEs is presented. In addition, a novel kinetic/topology Monte Carlo method to calculate the molecular and topological properties of the highly branched polymer chains and an advanced rheological model for the calculation of the viscoelastic properties of branched polymers in terms of their respective molecular and topological properties are described.