Phase diagrams of blends of poly(ethylene oxide) (PEO)/diacrylate (DA) monomer have been established by means of differential scanning calorimetry and optical microscopy. A phase field theory based on the combination of the phase field free e energy of crystal solidification and the Flory-Huggins theory for liquid-liquid phase separation has been developed that is capable of predicting various coexistence regions of the binary crystalline PEO/DA blends, viz., isotropic (I), the coexistence of crystal + liquid (Cr-1 + I), crystal + crystal (Cr-1 + Cr-2), and the single phase crystal (Cr) regions. These aforementioned coexistence regions have been further verified experimentally by probing the spatiotemporal emergence of crystalline structure and phase morphology. Guided by these established phase diagrams of the PEO/diacrylate blends, photopolymerization-induced crystallization experiments have been carried out at the isotropic temperatures slightly above the depressed melting points of PEO crystals. Of particular interest is the development of spherulites in the continuum of isotropic in the crystal + liquid coexistence region, whereas viscous fingering (or fractal growth) occurs during photopolymerization at a higher temperature, showing phase-separated domains within these advancing viscous fingering structures.