This dataset contains source data obtained during research under the project OPUS-26 2023/51/B/ST8/00775 "Development of a new approach to the production and compatibility of polyester blends using hybrid organic–inorganic additives", relating to research results described in the publication "Crystallization behavior and thermal properties of octa-phenyl-substituted silsesquioxane-modified polylactide (PLA)", DOI: 10.1007/s10853-024-10328-w As part of the research work carried out, measurements were carried out using the following methods: - differential scanning calorimetry DSC | abbreviation: DSC- polarized light microscopy POM | abbreviation: POM- DSC thermogravimetry | abbreviation: TGA- spherulite growth ratio calculated on the basis of microscopic images | abbreviation: SGR- Energy Dispersive X-ray Spectroscopy used for mapping of Si | abbreviation: EDS- solvent-based viscometric analysis | abbreviation: GLL- dynamic thermomechanical analysis | abbreviation: DMA The nomenclature and samples assignment corresponding to the content of octa-phenyl-substituted silsesquioxane (phSQ) used as a modifier of polylactide (PLA), presented in SCHEME_phSQ.tif file, were used. The database designation refers to the phSQ concentration (0.5%, 1%, 2%, 5%), and in that case, it is abbreviated as the filler content. Polymer not modified with filler is marked as PLA. Thermogravimetric measurements were carried out in nitrogen, which was additionally described in the sample designation. DSC and POM analyses were made in isothermal (ISO) and nonisothermal (NONISO) modes. As part of the file assignment for the NONISO series (POM, DSC), the heating/cooling rate of 10 °C min-1 was specified, while for the ISO series, the isothermal step temperatures of 130 °C, 135 °C, and 140 °C were presented. For microscopic images (POM, EDS), the file name also includes information about the magnification (10x or 5000x). File markings consist of:measurement type_material name_measurement vatiant_temperature or heating/cooling rate variant_magnification or atmosphere type