Study of Spontaneous Polymerisation Inhibition

Spontaneous polymerisation is an unwanted reaction, prevented by inhibitor molecules. In order to observe the inhibition of spontaneous polymerisation by different molecules, a small scale dilatometry experiment was developed. This was used to screen structurally related molecules to 2-nitrophenol to determine what structural features give rise to inhibition properties. Compounds with an intramolecular hydrogen bond demonstrated more efficient inhibition of polymerisation. The product mixture of styrene inhibited by 2-nitrophenol was analysed to determine the reaction pathway. Column chromatography, MS and NMR were used to determine the structure of two intermediates, 2-aminophenol and a compound derived from a Diels Alder styrene initiator and 2-nitrophenol. The proposed intermediate, 2-nitrosophenol, was synthesised and its stability in styrene was determined. The products of reaction between 2-nitrosophenol and styrene at room temperature were proposed by comparing results with the reaction between styrene and nitrosobenzene. The main product of the inhibition by 2-nitrosophenol, was also determined to be 2-aminophenol, suggesting that 2-aminophenol formed from inhibition by 2-nitrophenol goes via 2-nitrosophenol. Other intermediates and products identified were also screened in the dilatometry setup. They show inhibition properties at high concentration, but at more realistic concentrations, they did not inhibit styrene polymerisation. An overall mechanism for the inhibition of styrene polymerisation by 2-nitrophenol, was proposed based on the data obtained.