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An experimental setup, making use of a Flash DSC 1 prototype, is presented in which materials can be studied simultaneously by fast scanning calorimetry (FSC) and synchrotron wide angle X-ray diffraction (WAXD). Accumulation of multiple, identical measurements results in high quality, millisecond WAXD patterns. Patterns at every degree during the crystallization and melting of high density polyethylene at FSC typical scanning rates from 20 up to 200 °C s(-1) are discussed in terms of the temperature and scanning rate dependent material crystallinities and crystal densities. Interestingly, the combined approach reveals FSC thermal lag issues, for which can be corrected. For polyamide 11, isothermal solidification at high supercooling yields a mesomorphic phase in less than a second, whereas at very low supercooling crystals are obtained. At intermediate supercooling, mixtures of mesomorphic and crystalline material are generated at a ratio proportional to the supercooling. This ratio is constant over the isothermal solidification time.

The non-isothermal and isothermal crystallization of polyamide 11 (PA11), polyamide 12 (PA12), and their random copolymers was studied over the entire temperature range between the glass transition temperature and the high temperature melting point, using differential scanning calorimetry (DSC) and fast scanning calorimetry (FSC). The DSC and FSC thermal behavior was translated into structural evolutions, relying on earlier gathered X-ray based structural information and theoretical calculations. At low supercooling, the thermal behavior of the copolymers is typical for eutectic systems, involving monomeric segregation and crystallization into separate PA11 and PA12 crystals. Depending on the copolymer composition and the supercooling, the crystals are 4, 5, or 6 monomeric units thick. At very high supercooling, the PA11 and PA12 sequences cocrystallize into mesomorphic solid solutions with isodimorphic characteristics. At intermediate supercooling, the FSC heating traces following isothermal crystallization suggest that crystallization involves the simultaneous, isokinetic production of crystalline and mesomorphic patches. In this temperature range, lamellar crystals are 3 monomeric units thick throughout.