their molecular weight distribution (MWD) and chemical composition distribution (CCD) that depend on copolymerization conditions and catalyst type. [ 1 ] Polymers with narrow MWDs can be synthesized with single-site-type metallocene catalysts. [ 2 ] A combination of two metallocene catalysts can be used to control polyolefi n structures with versatility and fl exibility. [3][4][5][6] Polymerization kinetics models for ethylene/1-olefi n copolymerization with two metallocenes are expressed as a system of ordinary differential or algebraic equations. These model can be used to estimate chain microstructures from a specifi c set of polymerization conditions; [ 7 ] they cannot, however, be used to determine polymerization conditions to yield desired microstructures because these models cannot be inverted.Artifi cial neural networks (ANNs) can be used to solve highly nonlinear problems. ANNs mimic the pattern recognition process of neural systems by learning from examples. Only input and output datasets are used in ANNs-phenomenological models for the process Two artifi cial neural network models (forward and inverse) are developed to describe ethylene/1olefi n copolymerization with a catalyst having two site types using training and testing datasets obtained from a polymerization kinetic model. The forward model is applied to predict the molecular weight and chemical composition distributions of the polymer from a set of polymerization conditions, such as ethylene concentration, 1-olefi n concentration, cocatalyst concentration, hydrogen concentration, and polymerization temperature. The results of the forward model agree well with those from the kinetic model. The inverse model is applied to determine the polymerization conditions to produce polymers with desired microstructures. Although the inverse model generates multiple solutions for the general case, unique solutions are obtained when one of the three key process parameters (ethylene concentration, 1-olefi n concentration, and polymerization temperature) is kept constant. The proposed model can be used as an effi cient tool to design materials from a set of polymerization conditions.