Abstract A series of copolymers containing different ratios of methyl methacrylate and 2-(dimethylamino)ethyl methacrylate has been synthesised by conventional free radical polymerisation. These copolymers have been converted into a series of novel salts by reaction with the acid monomers, methacrylic acid, methacryloyloxyethyl phosphate and vinyl phosphonic acid. The copolymers and the corresponding salts have been characterised fully by a range of spectroscopic and thermal analysis techniques. The nature of the salt has a characteristic effect on the thermal degradation of the polymer. The presence of the phosphorus monomers leads to formation of residual char, even at temperatures as high as 1000 °C.