Thermal behaviour of H-bonded interpolymer complexes based on polymers with acrylamide or lactame groups and poly(acrylic acid): Influence of N-alkyl and α-methyl substitutions

The influence of the N-alkyl or α-methyl substitutions on thermal properties of H-bonded interpolymer complexes formed with polyacrylamides or polymers with lactame groups and poly(acrylic acid) was studied. Poly(N-isopropylacrylamide) has been chosen as a reference in order to compare the effect of the complexation with poly(acrylic acid) in their thermal behaviour. First, the linear polyacrylamides were analysed, poly(N-isopropylacrylamide), poly(N-tert-butylacrylamide), poly(N-diethyacrylamide) and poly(N-isopropylmethacrylamide). Second, two polymers with lactame groups were studied, poly(N-vinylpyrrolidone) and poly(N-vinylcaprolactam). Finally, poly(N-isobutyramide), a structural isomer of poly(N-isopropylacrylamide) was considered. The glass transition temperature and the thermal stability of these complexes have been studied. The study has denoted that the α-methyl substitution allows more stable and strong hydrogen bonding, which was confirmed by a high glass transition temperature and a good thermal stability.