Abstract
A range of well-defined, sparsely grafted, comblike linear poly(ethylene imine)/poly(2-ethyl-2-oxazoline) (LPEI-comb-PEtOx) and comblike linear poly(ethylene imine)/linear poly(ethylene imine) (LPEI-comb-LPEI) polymers with various degrees of polymerization of both main and side chains were prepared. Their aqueous solution properties were investigated by means of dynamic light scattering (DLS) and small-angle neutron scattering (SANS) over a temperature range of 25–65 °C. For LPEI-comb-LPEI polymers the particle distributions were mono-, bi-, or trimodal depending upon the temperature and/or polymer composition. The particles tended to decrease in size upon heating due to the weakening of intra- and interchain hydrogen bonds between −NH groups of the polymers and also with water molecules. However, the aggregates formed from the LPEI-comb-LPEI polymers featuring longer main chains, shorter branches, and lower grafting densities were more resistant to heat-induced disassociation. LPEI-comb-PEtOx particles featured smoother temperature variations of hydrodynamic radius and typically bimodal distributions. The shape and structure of the small LPEI-comb-PEtOx aggregates (average radius 6 nm) as well as their temperature evolution were studied by SANS. A variety of structures were observed, depending upon the polymer composition. The LPEI-comb-PEtOx polymers with low grafting densities and short branches formed elongated aggregates, whereas particles of spherical core–shell structure were observed for the more densely grafted polymer with longer branches. Spherical or rodlike aggregates were monitored in LPEI-comb-LPEI aqueous solutions.
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