Influence of sodium dodecyl sulfate on the phase transition of thermoresponsive hyperbranched polymer in water

The influence of sodium dodecyl sulfate (SDS) on the cloud point temperature (T _cp) of the aqueous solution of thermoresponsive hyperbranched polyethylenimine derivative HPEI-IBAm was studied systematically. When pH was below 8.5, HPEI-IBAm was positively-charged. Initially, the T _cp of HPEI-IBAm decreased significantly, followed by an obvious increase with the increase of SDS concentration. The lower the pH was, the higher the SDS concentration was required to achieve the minimum T _cp. When pH was above 8.5, HPEI-IBAm was neutral and raising the SDS concentration led to the gradual increase of T _cp. Compared to linear poly(N-isopropyl acrylamide) (PNIPAm), the T _cp of the current hyperbranched HPEI-IBAm was more sensitive to SDS. The thermoresponsive HPEI-IBAm/SDS complex was used as host to accommodate the non-polar pyrene in water. The lowest SDS concentration for effectively enhancing the solubility of pyrene in water was around 6.4 mmol·L^-1. When HPEI-IBAm was present, the SDS concentration threshhold was decreased to about 0.31 mmol·L^-1. Fluorescence technique with pyrene as the hydrophobic probe demonstrated that the SDS concentration of 7.2 mmol·L^-1 was required to form the hydrophobic domain to accommodate pyrene guests without HPEI-IBAm, while only 0.2 mmol·L^-1 of SDS was required in the presence of HPEI-IBAm.