Functional benzoxazines containing ammonium salt of carboxylic acid: Synthesis and highly activated thermally induced ring-opening polymerization

Review on the Accelerated and Low-Temperature Polymerization of Benzoxazine Resins: Addition Polymerizable Sustainable Polymers

Due to their outstanding and versatile properties, polybenzoxazines have quickly occupied a great niche of applications. Developing the ability to polymerize benzoxazine resin at lower temperatures than the current capability is essential in taking advantage of these exceptional properties and remains to be most challenging subject in the field. The current review is classified into several parts to achieve this goal. In this review, fundamentals on the synthesis and evolution of structure, which led to classification of PBz in different generations, are discussed. Classifications of PBzs are defined depending on building block as well as how structure is evolved and property obtained. Progress on the utility of biobased feedstocks from various bio-/waste-mass is also discussed and compared, wherever possible. The second part of review discusses the probable polymerization mechanism proposed for the ring-opening reactions. This is complementary to the third section, where the effect of catalysts/initiators has on triggering polymerization at low temperature is discussed extensively. The role of additional functionalities in influencing the temperature of polymerization is also discussed. There has been a shift in paradigm beyond the lowering of ring-opening polymerization (ROP) temperature and other areas of interest, such as adaptation of molecular functionality with simultaneous improvement of properties.

In(NO3)3 catalyzed curing reaction of benzoxazine

Benzoxazine is a new kind of thermoset resin with excellent properties, but it suffers from high curing temperature and low char yield in the presence of catalyst without halogen. In(NO3)3 was herein used for the first time to efficiently catalyze the curing reaction of benzoxazine and to elevate the char yield at 800°C. The reaction of benzoxazine was catalyzed by In(NO3)3 after stirring at 35°C for 300 min, and the initial curing temperature decreased to 151°C. Polybenzoxazine/In(NO3)3 showed higher thermal stability and char yield at 800°C (increased by 7.5%) compared with those of polybenzoxazine. The possible pathway of coordination bonding between In3+ and benzoxazine was proposed. In the cross-linking process, two different structures, that is, the N, O-acetal bridge structure and arylamine Mannich bridge structure formed at 35°C, both existed, which ultimately affected the thermal stability of the cured product.

Catalytic effect of trifluoroacetamido group on thermally induced ring-opening polymerization of 1,3-benzoxazine and formation of arylamine Mannich bridge structure

The autocatalytic ring-opening polymerization behavior of trifluoroacetamido group containing benzoxazine (FBA) is reported and its curing process was monitored by in situ proton nuclear magnetic resonance and Fourier transform infrared spectra analysis. The ring-opening polymerization temperature of FBA is significantly lower than that of typical 1,3-benzoxazine (BA), which can be attributed to higher stability of benzoxazine zwitterionic ion intermediate due to strong electron-withdrawing effect of trifluoroacetamido substituent. Arylamine Mannich bridge structure is found to form during polymerization, thereby enhancing the thermal stability of FBA homopolymer (poly-FBA). Differential scanning calorimetric analysis indicates that FBA effectively catalyzes the copolymerization of FBA and BA monomers at a temperature even lower than the polymerization temperature of pure FBA monomer, and the resultant copolymer exhibits higher glass transition temperature than either FBA or BA homopolymer, indicating promising possibility of FBA as reactive comonomer of polybenzoxazine systems for curing acceleration and performance improvement.