Thermal degradation of polymethylsilsesquioxane and microstructure of the derived glasses

The present work aims to elucidate the physicochemical factors determining the microstructure of Si–O–C glasses derived from a polymethylsilsesquioxane powder pyrolyzed at 200–1300 °C in helium atmosphere. The pyrolysis behavior of the powder was studied by thermogravimetry coupled with mass spectrometry. The chemical composition of the glasses was determined by elemental analysis while the microstructure was studied by optical microscopy combined with scanning and transmission electron microscopy. The degradation of the polymer proceeds by a three-stage decomposition characterized by different mass losses as well as by different amount and type of evolved gaseous species. The derived glasses contain networks of pores and bubbles with diameters more than 0.1 mm. The increasing thermal treatment of the polymer above 200 °C does not lead to the disappearance of macropores. Micrometer-sized amorphous filaments are observed in porous interiors. A formation mechanism of pores and filaments is proposed. Polymer swelling accompanied by pore coagulation and gas release is believed to be responsible for the spatial separation of oligomers forming filaments.