Thermal characteristics and flame retardance behavior of phosphoric acid-containing poly(methacrylates) synthesized by RAFT polymerization

The RAFT polymerization of strongly acidic, cross-linkable ethylene glycol methacrylate phosphate (EGMP) is described without protecting the acidic groups, with applications towards fire retardant polymers. After achieving the optimized polymerization conditions, we synthesized organo-soluble phosphoric acid-containing copolymers with methyl methacrylate (MMA) and bio-based isobornyl methacrylate (IBMA) with M-n in the range of 7.2-9.5 kg mol(-1) and relatively low dispersities of 1.40-1.55. Additionally, we showed that it was possible to reinitiate RAFT polymerization from a P(EGMP)-rich macro-chain transfer agent with MMA and IBMA. DSC revealed T-g depression of copolymers as a function of EGMP concentration, which shows the plasticizing effect of EGMP. Rheology revealed cross-liking behavior of HEMAP-rich samples at 120 degrees C. Thermogravimetric analysis (TGA) showed a one-step decomposition for PMMA and a two-step decomposition for PIBMA copolymers. In addition, the incorporation of 28 mol% EGMP slowed down the decomposition rate, improved the decomposition temperature (T-d) by 41 degrees C, and notably increased the limiting oxygen index (LOI) from similar to 17.6 to over 24. Among all samples, the EGMP-rich polymer (F-EGMP = 0.71, F-MMA = 0.29) exhibited prominent flame retardancy with the highest LOI value of 34. This result is invariably due to the strong acidity of phosphoric acid groups which notably leads to interesting flame retardancy properties.