Synthesis and thermal characterization of chemically modified cardanol polymers

Cardanol was functionalised to incorporate elements such as phosphorus and bromine and polymerised with formaldehyde or hexamethylenetetramine (HMTA) to get flame retardant polymers. Thus, monocardanyl phosphoric acid (MCPA), its bromoderivative (BrMCPA), and their formaldehyde condensates (MCPAF and BrMCPAF) and cross‐linked polymers were prepared and characterized by IR, NMR, and GPC. Flammability and thermal stability of these polymers were evaluated by LOI and TGA, respectively, and compared with those of conventional cardanol‐formaldehyde (CF) resin and its bromoderivative. TGA of MCPAF showed that although it is initially less stable than that of CF, its stability increases above 500°C over that of CF. Char yields of MCPAF and BrMCPAF are 21 and 27, respectively, and corresponding LOI values are 27 and 49. The present data do not support any synergism nor any additive effect between phosphorus and bromine, but a positive interaction between them is indicated with phosphorus mainly contributing in the condensed phase and bromine in the vapour phase mechanism. The activation energies in the range 20–30 kcal/mol for MCPAF suggest an ionic mechanism for its decomposition, whereas mainly a free radical type of decomposition is inferred for BrMCPAF with an activation energy in the range of 35–50 kcal/mol.