A comprehensive dynamic model for high-pressure tubular LDPE (low-density polyethylene) reactors (HPTLR) is presented. The model is capable of predicting molecular weight distribution (MWD) characteristics of the polymer and the influence of process conditions on the same. The physico-chemical phenomena considered in the model include polymerization kinetics, monomer (ethylene) decomposition kinetics, turbulent micromixing and heat transfer. A two-environment (2E) model is used to describe micromixing following the approach proposed originally by Fox (1998). Since the model considers the effect of ethylene decomposition on the dynamic behavior of the reactor, dynamic changes in the process conditions leading to ethylene decomposition (decomp) and reactor runaway are studied. Furthermore, a consistent dynamic model for pressure-pulsing due to kick-valve operation (Zabisky, 1992) has been included, making the model more relevant to plant operations. Model parameters have been fit to plant data in order to satisfactorily emulate plant behavior. The model can thus be reliably used in off-line studies and should prove to be an effective tool to the plant engineer in making critical operational decisions.