A pioneering class of proccessable thermoplastic/thermosetting crossover polymers made of commercially available chemicals has been developed. The striking feature of this class of polymers is its inherently low viscosity at room temperature that facilitates the processability. The polymers have been synthesized from the polycondensation reaction of bisphenol A, formaldehyde, and amine-terminated poly(ether diamine). The structure of the polymers has been confirmed by proton nuclear magnetic resonance spectroscopy (H-1 NMR) and Fourier transform infrared spectroscopy (FTIR). The polymers are cross-linked via thermal treatment to produce tough and flexible thermosetting materials without using any external initiators, accelerators, catalysts, or reactive diluents. Differential scanning calorimetry (DSC) and FTIR are used to study cross-linking behavior of these polymers. Atomic force microscopy (AFM) has been employed to study the phase behavior of the cross-linked polymers as a function of poly(ether diamine) chain length and wettability. Thermal properties of the cross-linked polymers have been studied by dynamic mechanical analysis (DMA) and thermogravimetric analysis (TGA).