Synthesis and properties of 4-arm star-shaped amphiphilic macromolecules

Abstract

<p>The major goal of this research was to understand the role of number of branching molecular weight and hydrophilic balance of chains segments on star polymer morphology. The present work was focused on synthesis of linear and star-shaped macromolecules with specific topology, using different types of polymerization methods, such as anionic and atom transfer radical polymerization (ATRP). After synthesis of a series of amphiphilic star macromolecules, the chemical composition of the polymers was confirmed by nuclear magnetic resonance (NMR), Fourier transform infra-red (FTIR) spectroscopy, and gel permeation chromatography (GPC). Then, the physical properties of the polymers were analyzed by differential scanning calorimetry (DSC) and X-ray diffraction techniques. X-ray data showed that the degree of crystallinity decreased for PEO star homopolymer. It was due to a junction of the branches of the star polymers. For heteroarmed PEO[subscript n]-b-PS[subscript m], where n+m=4, star polymers, the degree of crystallinity depends not only on architecture, but also on a ratio of PEO and PS segments. Finally, the behavior of the amphiphilic macromolecules at the air/water interface and on a solid surface was characterized by atomic force microscopy (AFM). As observed, all amphiphilic star polymers formed stable monolayers at the air/water interface, which later can be successfully transferred on a silicon substrate. The amphiphilic star polymers spontaneously aggregated after spreading the polymer solution on the surface of water. At the small surface pressure, the amphiphilic star polymers form monolayers with circular micellar structures. In the case of PEO-b-PS3 star polymer with higher content of PEO, the aggregates move closer together without increase in size with increasing surface pressure until layer collapsed. The PEO-b-PS3 star polymer with lower PEO content, aggregates are collapse in lamellar structures when surface pressure reached 5 mN/m. Also, the specific kind of star polymer, containing alkyl terminated hydrophilic hyperbranched core, was synthesized. AFM studies were applied to determine the role of amphiphilic core-shell balance on the aggregation of the polymer in the monolayer at the interface.</p>