Triggering effect caused by elemental sulfur as a mean to reduce the polymerization temperature of benzoxazine monomers

Abstract

Mixtures of different benzoxazine resins and elemental sulfur (S8) are prepared and then reacted at 120 °C, below the temperature for radical formation of sulfur, triggering the reduction of the polymerization temperature.

Sulfur Radical Transfer and Coupling Reaction to Benzoxazine Groups: A New Reaction Route for Preparation of Polymeric Materials Using Elemental Sulfur as a Feedstock

“…Meanwhile, the new peak appearing at 3360 cm −1 corresponds to the absorption of the phenolic OH generated from the ring‐opening reaction of the benzoxazine rings. The ring opening of benzoxazine rings occurs at a relatively low temperature (170 °C), which is similar to previous reports . Moreover, notably, an absorption peak at approximately 653 cm −1 appears in the FTIR spectra recorded from the sample taken after 6 min of reaction, indicating the formation of CS linkages in the reaction system.…”

“…It is noteworthy that the acidic medium associated with the formation of the H 2 S byproduct has been shown to catalyze benzoxazine polymerization . Moreover, Ishida and co‐workers demonstrated that elemental S 8 can effectively trigger the formation of Schiff bases from benzoxazine rings since sulfur radicals did not form at the studied temperature (120 °C) because it was lower than the floor temperature of S 8 ring opening. The phenol groups of the formed Schiff bases reduce the polymerization temperature of the benzoxazine compounds.…”

“…The phenol groups of the formed Schiff bases reduce the polymerization temperature of the benzoxazine compounds. Prior studies have shown that sulfur can reduce the temperature required for benzoxazine ring opening reactions, [16][17][18][19]27] the reaction between benzoxazine and sulfur (or sulfur radical), and the radical transfer mechanism have not been reported in these studies. In this work, SRTC reaction to benzoxazine groups has been demonstrated as a new reaction route for preparation of polymeric materials using elemental sulfur as a feedstock.…”

“…[16][17][18][19] It is noteworthy that the acidic medium associated with the formation of the H 2 S byproduct has been shown to catalyze benzoxazine polymerization. [16] Moreover, Ishida and co-workers [27] demonstrated that elemental S 8 can…”

Cardanol Benzoxazines: A Versatile Monomer with Advancing Applications

“…It is reported that Bz monomers possess radical transfer agent characteristics and assist sulfur radical transfer and coupling reactions between S 8 and organic compounds . Elemental S 8 trigger the formation of intermediate Schiff bases from benzoxazine rings at 120 °C suggesting occurrence of benzoxazine ring‐opening reaction. The liberation of H 2 S gas by co‐reaction of benzoxazine with S 8 was also demonstrated .…”