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 center dot L-1. When HPEI-IBAm was present, the SDS concentration threshhold was decreased to about 0.31 mmol center dot L-1. Fluorescence technique with pyrene as the hydrophobic probe demonstrated that the SDS concentration of 7.2 mmol center dot L-1 was required to form the hydrophobic domain to accommodate pyrene guests without HPEI-IBAm, while only 0.2 mmol center dot L-1 of SDS was required in the presence of HPEI-IBAm.