We report on the synthesis of a series of second-generation hyperbranched polyesters with a variable composition of alkyl-terminated groups. We observed that the chemical modification of the hyperbranched cores by substituting a controlled fraction of the terminal hydroxyl groups with hydrophobic alkyl chains is an effective method for a controlling amphiphilic balance of hyperbranched cores with a degree of branching of 50%. Even for imperfect cores, the chemical reaction of hydroxyl groups alkyl tails was very efficient. In fact, the number of attached alkyl tails was fairly close to the theoretical value based on the assumption that all targeted hydroxyl groups were available for the reaction despite their different interior/exterior location. Detailed microstructural analysis of the structure revealed that organized monolayers could be formed at the air-water interface if the number of alkyl tails was higher than two per core. Similar to regular dendrimers, the alkyl tails of hyperbranched molecules at high surface pressure form intramonolayer ordering of the quasi-hexagonal type. However, higher defectness and irregularities of the hyperbranched cores are responsible for poor intralayer ordering of alkyl tails in comparison with regular dendrimers. At high surface pressure, the alkyl tails became arranged in an up-right orientation. The highly water-swollen state of the hyperbranched cores of prolate shape and the partially submerged and standing-off alkyl tails is a characteristic of hyperbranched molecules with fewer alkyl chains in condensed monolayer state at the air-water interface. The core structure is transformed into the oblate, flattened state with preservation of standing-off orientation of the alkyl tails for hyperbranched molecules with crowded outer shells.

The interfacial behavior of third and fourth generations of hyperbranched polyesters (HBP3 and HBP4) with 32 and 64 hydroxyl-terminal groups was studied with scanning probe microscopy. The molecular adsorption on a bare silicon surface of both hyperbranched polymers was described in the terms of the Langmuir isotherm. A higher adsorption amount under an identical adsorption condition was found for lower generation HPB3. The shape of HBP3 molecules within an adsorbed layer evolved from a pancake with a thickness less than 1 nm for very low surface coverage to densely packed wormlike bilayer structures with a thickness of about 3 nm for the highest surface coverage. The molecules of the fourth generation, HBP4, hold a stable, close-to-spherical shape with a diameter of 2.5 nm throughout the entire range of surface coverage including both dense monolayers and isolated molecules. High intramolecular flexibility of HBP3 molecules as compared with constrained mobility of bulkier branches of HBP4 is considered to be responsible for different surface behavior.