Abstract: “Chain walking” catalytic polymerization CWCP is a powerful tool for the one-pot synthesis of a unique class of hyperbranched polyethylene (HBPE)-based macromolecules with controllable molecular weight, topology, and composition. This dissertation focuses on new synthetic routes leading to HBPE-based macromolecular architectures by combining CWCP technique with ring opening polymerization (ROP), atom–transfer radical polymerization (ATRP), and “click” chemistry. Taking advantage of end-functionalized HBPE, and a new ethynyl-soketal star-shaped compound, we were able to synthesize different types of the HBPE-based architectures including hyperbranched-on-hyperbranched core-shell nanostructures, and miktoarm-star-HBPE-based block copolymers. The first part of the dissertation provides a general introduction to well-defined polyethylenes with different macromolecule architectures synthesized either for academic or industrial purposes.
In the second part, HBPE with different topologies was synthesized by CWCP, using α-diimine Pd (II) catalyst. The effect of the temperature and pressure on the catalyst activity and polymer properties, including branch content, molecular weight, distribution, and thermal properties was studied. Two series of samples were synthesized: a) serial samples A under pressures of 1, 5, and 27 atm at 5˚C, and b) serial samples B at temperatures of 5, 15, and 35 ˚C under 5 atm.
Well-defined HBPE-based core diblock copolymers with predictable amphiphilic properties are studied in the third part of the project. Hyperbranched polyethylene-b-poly(N-isopropylacrylamide), HBPE-b-PNIPAM, and hyperbranched polyethylene-b-poly(solketal acrylate), HBPE-b-PSA, were successfully synthesized by combining CWCP and ATRP. The synthetic methodology includes the following steps; a) synthesis of multifunctional hyperbranched polyethylene initiators (HBPE-MI) by direct copolymerization of ethylene with 2-(2-bromoisobutyryloxy)ethyl acrylate (BIEA) in the presence of a α-diimine Pd(II) catalyst, and b) ATRP using the α-bromoester groups (HBPE-MI) as initiation sites.
In the fourth part, a well-defined 3-miktoarm star copolymer 3μ-HBPE(PCL)2 (HBPE: hyperbranched polyethylene, PCL: poly(ε-caprolactone) was synthesized by combining CWCP, ROP, and “click” chemistry. The synthetic methodology includes the following steps: a) synthesis of azido-functionalized hyperbranched polyethylene HBPE-N3 by CWCP of ethylene with the α-diimine Pd(II) catalyst, followed by quenching with an excess of 4-vinylbenzyl chloride and transformation of –Cl to the azido group with sodium azide, b) synthesis of in-chain ethynyl-functionalized poly(ε-caprolactone), (PCL)2-C CH by ROP of ε-CL with ethynyl-functionalized solketal [3-(prop-2-yn-1-yloxy) propane-1,2-diol] as a bifunctional initiator, in the presence of P2-t-Bu phosphazene super base, and c) “clicking” HBPE-N3 and (PCL)2-C CH using the copper(I)-catalyzed alkyne–azide cycloaddition, CuAAC.
The fifth part illustrates the self-assembly behavior of the HBPE-based block copolymers of PNIPAM, and PCL, at room temperature in water and a petroleum ether-selective solvent, respectively. The synthesized copolymers HBPE-b-NIPAM and 3μ-HBPE(PCL)2 revealed either core-shell nanostructure in vesicles or worms and worm-likes branches, as confirmed by combining dynamic light scattering, DLS, transmission electron microscopy, TEM, and atomic force spectroscopy, AFM.
All the findings presented in this dissertation emphasize the utility of "living" CWCP to synthesize end-functionalized HBPE, and new star-shaped HBPE-based complex architectures. Proton nuclear magnetic resonance spectroscopy, 1H NMR, gel permeation chromatography, GPC, and Fourier transform infrared, FT-IR, spectroscopy analyses were used to determine the branching content, molecular weight, and distribution, whereas differential scanning calorimetry, DSC, and thermogravimetric analysis, TGA, were used to record the melting temperature and to study the thermal stability of the resultant polymers, respectively.
The summary and future work concerning synthesis of HBPE-based materials with predictable properties and applications are discussed in the sixth part.