Synthesis, characterization and thermal degradation kinetics of azomethine-based halogen-free flame-retardant polyphosphonates

Abstract

In this study, azomethine polyphosphonates were synthesized by solution polycondensation of phenylphosphonic dichloride with various azomethine diols such as [4-(4-hydroxy phenyl) iminomethyl] phenol, [(4-(4-hydroxy-3-methoxy phenyl) iminomethyl)] phenol and [4-(4-hydroxy-3-ethoxy phenyl) iminomethyl] phenol using triethylamine catalyst at ambient temperature. The structure of the synthesized polymers was confirmed by Fourier transform infrared and 1H-, 13C- and 31P- nuclear magnetic resonance spectroscopic techniques. Thermal properties of the polymers were studied by thermogravimetric analysis (TGA) and differential scanning calorimetry under nitrogen atmosphere. The TGA data showed that the synthesized polyphosphonates produce high char yield at 600°C due to the presence of phosphorous atom in the polymer chain and hence have good flame-retardant properties. One of the synthesized polyphosphonate was blended with commercial diglycidyl ether of bisphenol-A (DGEBA) resin in various weight percentage and cured with commercial curing agent triethylene tetramine (TETA). The polyphosphonates-blended epoxy thermosets have tensile strength in the range of 5–41 MPa and the percentage of elongation at breaks was 4–18. It was found that the incorporation of polyphosphonates into epoxy thermoset decreased the tensile strength from 41 MPa to 5 MPa, whereas the elongation at break value increased with increase in the weight percentage of polyphosphonate. The influence of polyphosphonates on the flame retardancy of blended thermosets was examined by limiting oxygen index (LOI) and vertical burning (UL-94) tests and found that the polymer samples achieved an increased UL-94 rating and the LOI values were in the range of 24–26. Broido and Horowitz–Metzger methods have been used to study the thermal degradation kinetic parameters.

Investigation on mechanical, thermal, and flame retardant properties of particulate SiO2 reinforced cardanol based composites

“…This reveals that crosslinking ability was reduced by the increase in silica‐silica interaction led to the aggregation of SiO 2 particle. It was reported that poor adhesion of polymer‐filler interaction expected to decrease the elongation properties slowly with aggregation of filler reinforcement …”

“…This is reflected in decreased thermo mechanical properties of thermosetting polymers. In order to overcome the existing drawbacks in developing bio‐based thermosetting polymers, the crosslinking ability was improved by incorporation of rigid high strength particulate inorganic fillers which could modify the inherent physical and mechanical properties . Recently, some research have been proceeded with nano sized inorganic fillers, which are expensive, to improve the physical and mechanical properties of polymers.…”

“… Most of the researchers have worked with wide scope in various applications field by incorporating fillers such as micro/nanosized SiO 2 , glass powder, Al 2 O 3, Mg(OH) 2 and CaCO 3 particles and carbon nanotubes . It was noted in the literature that the micro to nanosized and other forms of silica play an important role in modifying the thermal stability and physical properties of polymeric materials and exhibit extended applications in most of the high performance engineering product sectors.…”

Polyphosphonates as ionic conducting polymers

“…Polyethylene oxides have been widely studied as SPEs, and polyphosphonates derived from tetraethylene glycol, which have similar cation binding groups, may exhibit similar cation binding abilities. In addition, it may be possible to tune the cation binding abilities of the polyphosphonates derived from tetraethylene glycol by the appropriate choice of R and X groups 14–17 . Further, similar phosphorus‐containing polymers are typically flame‐resistant.…”

“…In addition, it may be possible to tune the cation binding abilities of the polyphosphonates derived from tetraethylene glycol by the appropriate choice of R and X groups. [14][15][16][17] Further, similar phosphorus-containing polymers are typically flame-resistant. Finally, the presence of 31 P nuclei in the polymer backbone should allow 31 P{ 1 H} NMR spectroscopy to be used to probe the cation binding and its effect on the polymer microstructure.…”