Novel self-promoted phthalonitrile monomer with siloxane segments: synthesis, curing kinetics, and thermal properties

Abstract

A new kind of autocatalytic phthalonitrile monomer (PN) containing siloxane segments and secondary amino groups (TSOP) was synthesized from bisphenol compound and 4-nitrophthalonitrile using K₂CO₃ as a catalyst. Bisphenol was a reducing agent with a Schiff base containing secondary amine groups produced by the condensation reaction of 1,3-bis(3-amino-propyl)-1,1,3,3-tetra-methyl disiloxane and vanillin. The curing behaviors, kinetics, and thermal and thermomechanical characteristics of the TSOP monomer and its polymer (poly(TSOP)) were analyzed by torque rheometry, differential scanning calorimetry (DSC), Fourier transformation infrared spectroscopy (FTIR), thermogravity analysis (TGA), and dynamic thermal mechanical analysis (DMA), respectively. The non-isothermal curing kinetics results indicated that the cyano addition polymerization of the TSOP monomer was a self-catalytic reaction. The active hydrogen atoms from the secondary amino groups in the TSOP monomer could accelerate the crosslinking polymerization reaction of cyano groups, producing a decline in the curing temperature and a rise in the curing rate. Meanwhile, the TSOP monomer had a low melting temperature (77 °C) and a wide process window (110 °C) due to the introduction of flexible siloxane segments. The poly(TSOP) having phthalocyanine and a triazine ring exhibited a higher glass transition temperature (T_g) of 348 °C and good thermal stability.