Influence of aliphatic acids on the phase transition of thermoresponsive hyperbranched polymer

Abstract The influence of aliphatic acids on the phase transition temperature of thermoresponsive hyperbranched polyethylenimine possessing a large amount of isobutyramide and amine groups (HPEI-IBAm) was studied systematically. Nine saturated aliphatic acids including formic acid (C1), acetic acid (C2), n-pentanoic acid (n-C5), trimethylacetic acid (t-C5), hexanoic acid (C6), octanoic acid (C8), decanoic acid (C10), dodecanoic acid (C12) and hexadecanoic acid (C16) were used to measure their effects on the cloud point temperature ( T cp ) of HPEI-IBAm in a mixture of H 2 O/DMF ( v / v  = 9:1). For comparison, the effect of these aliphatic acids on the traditional thermoresponsive linear poly(2-dimethylaminoethyl methacrylate) (PDMAEMA) and poly(N-isopropyl acrylamide) (PNIPAm) was also studied. The influence of aliphatic acids on different thermoresponsive polymers was different. The aliphatic acids with shorter carbon chains ( C  ≤ 8) increased the T cp of HPEI-IBAm, and those with long hydrocarbon chains ( C  > 8) depressed the T cp . Moreover, the effect of aliphatic acids with C  ≤ 5 was similar, even though their configurations might be different. The specific ranking of aliphatic acids in raising the T cp of HPEI-IBAm was as follows: C1 ～ C2 ～ n-C5 ～ t-C5 > C6 > C8 > C10 > C12 ～ C16. With respect of the linear PDMAEMA, all the aliphatic acids employed elevated its T cp . The specific ranking of aliphatic acids in raising the T cp of linear PDMAEMA was similar to that for dendritic HPEI-IBAm, but with a minor difference: C1 ～ C2 ～ n-C5 ～ t-C5 > C6 > C8 > C10 > C12 > C16. In the case of the linear PNIPAM, the aliphatic acids with C  ≤ 6 had almost no influence on the T cp . Raising the carbon number to be 8 or higher leads to the obvious T cp depression. The different effect of aliphatic acids on the phase transition of these thermoresponsive polymers was discussed, and it was mainly attributed to their structural and topological difference.