Methyl-silsesquioxane (MSQ) precursors are used to create complex SiOC or SiO structures through pyrolysis in an inert atmosphere or air employing additive manufacturing techniques. Material extrusion based additive manufacturing (MEX-AM) as a thermoplastic shaping method uses heat treatment in air to produce MSQ-based parts. MSQ's high formability and low processing temperatures make it desirable for MEX-AM. Using this technique, heat treatment in air is vital. The presence of oxygen in full burnout of the organic thermoplastic binder via oxidation reactions and pyrolysis of MSQ to achieve pure oxide ceramic (e.g. SiO2) is essential. Furthermore, the fabrication of bulk structures by MEX-AM requires an optimum debinding program with different heating rates and dwell times to remove each organic component gradually. This way, sudden organics removal will not damage the final desired shape. Although there are quite interesting results published on the synthesis of complex and novel polymer derived ceramics (PDCs), the impact of heating rate and atmosphere on the yielded residue has yet to be explored. This study examined the crosslinking and pyrolysis behavior of SILRES MK, a methyl-silsesquioxane with a yield of 82wt% after pyrolysis, using air, nitrogen, and argon up to 800°C and different heating rates. Complementary techniques such as thermogravimetric analysis (TG) and Fourier-transformed infrared spectroscopy (FT-IR) were employed. Results showed that lower yield below the heating rate of 2K/min – 69.1 and 75.0% using 0.3 and 0.6K/min heating rates, respectively – occurs. The lower the heating rate, the higher the chance of yet unlinked molecules to evaporate and escape from the structure. Heating MK up to 800°C, gaseous species released from MK were analyzed by gas chromatography–mass spectrometry (GC-MS). In addition, 3:2 mullite ceramics were produced using a homogenous mixture of MK, γ-Al2O3, MgO and a thermoplastic binder system heated with low and high heating rates to investigate its effect on the final mullite purity. Based on XRD and XRF results, change in the yield of MK alters the stoichiometric ratio of the final product and causes corundum impurities. Finally, TG results indicated that crosslinking MK prior to pyrolysis heat treatment could prevent the escape of oligomers regardless of the heating rate (a yield of 82wt% can be expected) and leads to pure mullite formation at 1600°C.