Institute of Polymer Science & Engineering, Department of Chemical Engineering, Tsinghua University, Beijing 100084, China
￼Nucleation is a fundamental step of polymer crystallization and the mechanism is not fully understood yet . Classical nucleation theory based on the capillary approximation has achieved success in the field of polymer crystallization; however, there are still some open questions remained: (1) Which pathway is chosen for nuclei formation of polymer lamellar crystals, stem by stem or cluster by cluster? (2) How to describe the many intermediate states during nucleation? In this work, we propose a microscopic kinetics model without the prerequisite thermodynamics parameters. In our new model, crystal nucleation is considered as a series of elementary processes: attaching and detaching of units. Correlation factors were introduced to describe the variation of the rate constants to attach and detach a unit with the cluster size. Via the microscopic kinetics, we can determine the equivalent thermodynamics parameters and simulate the time evolution of cluster size distribution . Application of the new model to some polymers will be given. The critical size of nuclei in poly(butylene succinate) during crystallization and melting will be estimated. The model describes nucleation of small molecules and polymer chains in a unified view, which we believe can be applied to other kinetic processes far from equilibrium.