Structure–property relationships and nanofiller‐induced hydro‐anti‐plasticization in polyhydroxyurethane/<scp>POSS</scp> hybrid composites

Abstract Non‐isocyanate polyhydroxyurethanes/polyhedral oligomeric silsesquioxane (PHU/POSS) hybrid composites are prepared by in situ physical introduction of octa(3‐hydroxy‐3‐ethylbutyldimethylsiloxy) POSS into a linear non‐isocyanate polyhydroxyurethane matrix. The amorphous nature of the matrix is retained in the composites and no POSS crystals are observed. Thermal and mechanical properties are studied along with water‐polymer interactions and are discussed in terms of structure‐properties relationships. POSS has only minimal effect on thermal stability. Composite materials with up to 2 wt% POSS exhibit an increased rubbery modulus. The glass transition temperature of the composite materials increases up to 2 wt% loading and decreases at higher POSS content. Water‐polymer interactions are studied in a broad range of relative humidity (0–0.97). Materials exhibit a relatively high water absorption, which is enhanced by POSS at low concentrations. Moisture sorption isotherms are discussed in terms of the Guggenheim‐Anderson‐de Boer model. The study of molecular mobility of hydrated systems by differential scanning calorimetry reveals a peculiar POSS‐induced antiplasticization in PHU/POSS blends at 10–20 wt% water uptake, possibly due to the formation of POSS‐centered water clusters.