AbstractA low molecular weight prepolymer with reactive end groups was annealed at temperatures between 200 and 245°C to obtain kinetic parameters for solid‐state polymerization of poly(ethylene naphthalate) (PEN). An equation was developed to describe the relationships among time, temperature, and final molecular weight for PEN. The intrinsic viscosity and melting point during polymerization were used to monitor the molecular weight and the thermal stability of the resulting resins. The effect of moisture concentration on solid‐state polymerization was also investigated. Hydrolytic degradation caused initial reductions of the molecular weight if prepolymers were solid‐stated without being dried. With increased exposure to solid‐state conditions, however, the hydrolytically degraded resin dried and repolymerized at rates similar to those samples that had undergone hydrolysis. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2055–2061, 2001