From nano to the macro: tuning hierarchical aggregation of thermoresponsive PEG/PCL-based polyurethanes via molar mass/composition control

Abstract

Amphiphilic hyperbranched polyurethanes (HPUs) based on PEG and PCL are promising for several biomedical applications. However, the lack of control over the molar mass and composition hinders a deep understanding of the aqueous self-assembly of HPUs. In this paper, the control over the HPU molar mass and composition was provided by dynamic urea bond-mediated polymerization (DUBMP), enabling a careful evaluation of their aqueous self-assembly by 1H NMR, DLS, and Cryo-TEM. HPUs containing a single PCL block per chain self-assemble into nanoaggregates (Rh ≈ 10 nm) in water up to its cloud-point temperature (Tcp) of 34 °C. On the other hand, HPUs with more than one PCL block per chain self-assemble into nanoaggregates and their clusters below Tcp. In this case, the solution behavior can be tuned by the HPU molar mass. Increasing overline{{mathrm{M} }_{mathrm{w}}} from 4 to 19 kDa, HPUs of similar composition can form colloidally stable cluster suspensions (overline{{mathrm{M} }_{mathrm{w}}} = 4 kDa) and phase separate into a denser liquid aggregate–cluster phase (overline{{mathrm{M} }_{mathrm{w}}} = 7 kDa) or into a highly viscous aggregate-network phase (overline{{mathrm{M} }_{mathrm{w}}} = 19 kDa). This type of control over the hierarchical aggregation of HPUs was reported for the first time and is interesting for biomedical applications.Graphical abstractThe control of amphiphilic branched PU molar mass and architechture via isocyanate reversible deactivation provided the control over its aqueous phase behavior, tuning it from micelles to micelle-networks