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A new multi-variable-measurement approach for characterizing and correlating the nanoscale and microscale morphology of crystal-amorphous polymer blends with melt-phase behavior is described. A vertical small-angle light scattering (SALS) instrument optimized for examining the scattering and light transmitted from structures ranging from 0.5 to 50 m, thereby spanning the size range characteristic of the initial-to-late stages of thermal-phase transitions (e.g., melt-phase separation and crystallization) in crystal-amorphous polymer blends, was constructed. The SALS instrument was interfaced with differential scanning calorimetry (DSC), and simultaneous SALS/DSC/transmission measurements were performed. We show that the measurement of transmitted light and SALS under H V (cross-polarized) optical alignments during melting can be used to reliably measure the thermodynamic (e.g., crystal melting and melt-phase separation temperatures) and structural variables (e.g., crystalline fraction within the superstructures and volume fraction of superstructures) necessary for describing the multiphase behavior of crystal-amorphous blends in one combined measurement. We also evaluate the orientation correlations of crystalline volume elements within the superstructures. Our results indicate that simultaneous measurement of transmitted light can provide a reliable estimate of the total scattering from density and orientation fluctuations and the melt-phase separation temperature of polymer blends. For solution-cast poly(⑀-caprolactone)/poly(D,L-lactic acid) blends, our multivariable measurements during melting provide the parameters necessary to generate a crystal-liquid and liquid-liquid phase diagram and characterize the solidstate morphology. This opens up the challenge to explore use of our vertical SALS instrument as a rapid and convenient method for developing structure-property relationships for crystal-amorphous polymer blends.