Using self‐synthesized aminopropyl‐terminated polydimethylsiloxane to toughen epoxy resin: The role of molecular weight of polydimethylsiloxane

Aminopropyl‐terminated polydimethylsiloxane (APDMS) with different molecular weights ( M¯n) were synthesized by 1,3‐bis(3‐aminopropyl)‐1,1,3,3‐tetramethyldisiloxane (BADS) and dimethylcyclosiloxane (Dn). Fourier‐transform infrared shows the increase in APDMS Mn and the decrease in NH2 content in the products with the increasing ratio of Dn/BADS. 1H NMR further confirmed the conclusion obtained by Fourier‐transform infrared spectra, and the APDMS Mn resulted from 1H NMR were 1,106 (APDMS1), 1,987 (APDMS2), 2,690 (APDMS3), and 4,313 (APDMS4) g/mol. These APDMS were then blended with the epoxy resin (diglycidyl ether of bisphenol A) system to improve its toughness. Mechanical tests revealed that the impact strength of the epoxy resin was improved by APDMS1 and APDMS2, which has lower Mn. The toughening effect decreased when APDMS4 was used. It was suggested that the APDMS with high Mn was easier to agglomerate, which in turn resulted in lower toughening efficiency. This was also confirmed by scanning electron microscopy results. J. VINYL ADDIT. TECHNOL., 23:305–311, 2017. © 2015 Society of Plastics Engineers