Thermal curing and degradation behaviour of silicon-containing arylacetylene resins

Silicon-containing aryacetylene resins (PSAs) have already shown potential application as heat-resistant materials due to their excellent thermal stability. The formation and degradation of structures in cured PSAs are very important to evaluate the thermal properties during their applications. Herein, the thermal curing and degradation behavior of PSAs with different substituents were investigated by DSC, FT-IR, Py-GC-MS, TGA and TG-GC-MS. DSC and FT-IR analysis reveals that the curing reaction is dominated by the crosslinking reaction of CCH and SiCC, meanwhile, the reactive substituents (such as SiH and SiCHCH2) could promote the CCH and SiCC reaction with higher conversion. Py-GC-MS was used to detect the pyrolysis products at 650 °C and 750 °C, respectively, and the results could provide important information about the curing reaction and structures of cured PSAs. The curing reaction of PSAs mainly contains cyclotrimerization and Diels-Alder reaction of CCH and SiCC, and some addition reaction to form polyene structure. The main structures in cured PSAs contain a lot of phenyl rings, some aromatic fused rings and a little of polyene structure, moreover, their contents in cured PSAs are dependent on the substituents of the precursors. The TGA results show that the substituents of SiH and SiCHCH2 can effectively improve the crosslinking index of the cured PSA-H and PSA-V, and endow them with better thermal stability. Additionally, the degradation behavior of cured PSAs have been well studied by TG-GC-MS. When the temperature is 400 °C, the SiCH3 and some aliphatic structure begin to degrade and form CH4, and with the temperature increasing to 500 °C, the unsaturated and aliphatic structures decompose into C2H4 and C2H6, and after 600 °C, the aromatic rings and fused rings in cured PSAs are dehydrogenated and release H2. In addition, the content of the degradation products and their forming temperature are also related with the substituents.