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

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Abstract

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-isopropylacrylamide-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-IR) indicate that the first degradation process involves a chemical dehydration step (110–240 °C), supported by the nonreversing heat flow response in modulated temperature differential scanning calorimetry. Water loss scales with the fraction of hydroxy monomer in the copolymer. Glass transition temperatures (Tg) are higher than the temperatures causing dehydration; hence, these values relate to newly-formed copolymer structures produced by controlled heating under nitrogen. Fourier transform-Raman (FT-Raman) spectra suggest that this transition involves imine formation. The Tg increases as the fraction of hydroxy groups in the original copolymer increases. Further heating leads to degradation and mass loss, and more complex changes in the FT-IR spectra, consistent with formation of unsaturated species. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010

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