Covalent organic frameworks (COFs) are crystalline porous materials linked by dynamic covalent bonds. Dynamic chemistries enable the transformation of an initially amorphous network into a porous and crystalline COF. While dynamic chemistries have been leveraged to realize transformations between different types of COFs, including transformations from two-dimensional (2D) to three-dimensional (3D) COFs and insertion of different linking groups, the transformation of linear polymers into COFs has not yet been reported. Herein, we demonstrate an approach to transform linear imine-linked polymers into ketone-linked COFs through a linker replacement strategy with triformylphloroglucinol (TPG). TPG first reacts through dynamic chemistry to replace linkers in the linear polymers and then undergoes irreversible tautomerism to produce ketone linkages. We have analyzed the time-dependent transformation from the linear polymer into COF through powder X-ray diffraction, Fourier-transform infrared spectroscopy (FT-IR), and scanning electron microscopy (SEM) to understand the transition and substitution mechanisms. This work demonstrates another route to produce COFs through sequential reversible and irreversible chemistries and provides a potential approach to synthesizing COFs through the solution processing of linear polymers followed by transformation into the desired COF structure.