Solid-state thermal stability and degradation of a family of poly(N-isopropylacrylamide-co-hydroxymethylacrylamide) copolymers

There is widespread interest in responsive polymers that show cloud point behavior but little attention is paid to their solid state thermal properties. To manufacture products based on such polymers it may be necessary to subject them to high temperatures hence it is important to investigate their thermal behavior. In this study we characterized a family of poly(N iso propylacrylamide co-hydroxymethylacrylamide) copolymers Although poly(N isopropylacrylamide) shows very high thermal stability (up to 360 C) introduction of hydroxy side chains leads to a significant reduction in stability and new degradation processes become apparent. Thermogravimetric analysis and fourier transform infrared spectroscopy (FT IA) indicate that the first degradation process involves a chemical dehydration step (110-240 degrees C) supported by the nonreversing heat flow response in modulated temperature differential scanning calonmetry. Water loss scales with the fraction of hydroxy monomer in the copolymer. Glass transition temperatures (T-g) are higher than the temperatures causing dehydration hence these values relate to newly formed copolymer structures produced by con trolled heating under nitrogen. Fourier transform Raman (FT Raman) spectra suggest that this transition involves imine for mation The Tg increases as the fraction of hydroxy groups in the original copolymer increases. Further heating leads to deg radation and mass loss and more complex changes in the FT IR spectra consistent with formation of unsaturated species