In the first Chapter, Polyhomologation, a powerful technique to synthesize well-defined, perfectly linear, polyethylenes with controllable molecular weight, topology and low polydispersity, is presented in the first Chapter. In this Chapter is also discussed the combination of polyhomologation with other polymerization techniques such as Ring Opening Polymerization, ROP, Atom Transfer Radical Polymerization, ATRP, as well as with chlorosilane linking chemistry towards well-defined polyethylene-based macromolecular architectures. In the second Chapter, α,ω-dihydroxy-polyethylene was synthesized by the polyhomologation of dimethylsulfoxonium methylide with 9-thexyl-9-BBN (9-BNN: 9-borabicyclo[3.3.1]nonane), a novel difunctional initiator produced from 9-BBN and 2,3-dimethylbut-2-ene with two active and one blocked sites, followed by hydrolysis/oxidation. The terminal hydroxy groups were used either directly as initiators, in the presence of 1-tertbutyl-2,2,4,4,4-pentakis(dimethylamino)-2λ5,4λ5-catenadi(phosphazene) (t-BuP2), for the ring opening polymerization of ε-caprolactone, ε-CL, in order to afford polycaprolactone-b-polyethylene-b-polycaprolactone (PCL-b-PE-b-PCL) or after transformation to ATRP initiating sites in order to polymerize styrene and produce polystyrene-b-polyethylene-b-polystyrene (PSt-b-PE-b-PSt) triblock copolymers. Molecular characterization by 11B, 13C and 1H NMR as well as FTIR, and high-temperature GPC (HT-GPC) confirmed the well-defined nature of the synthesized new difunctional initiator and triblock copolymers. Differential scanning calorimetry was used to determine the melting points and degree of crystallinity of PE and PCL. In the third Chapter, a novel triallylborane initiator was synthesized and used to afford α-allyl-ω-hydroxy-polyethylene by polyhomologation of dimethylsulfoxonium methylide. The α-allyl-ω-hydroxy-polyethylene was then used as a macroinitiator (OH group) for the ROP of ε-CL and LLA to afford well-defined triblock terpolymer of polylactide-b-polyethylene-b-polycaprolactone (PLLA-b-PE-b-PCL). The characterization of all intermediate and final products by 1H NMR, FTIR, and HT-GPC, verified the well-defined nature of the triblock terpolymer. In the fourth Chapter, polyethylene (PE)-based 3- and 4-miktoarm star [PE(PCL)2, PE(PCL)3], as well as H-type [(PCL)2PE(PCL)2] block copolymers (PCL: polycaprolactone), were synthesized by combining polyhomologation, chlorosilane chemistry, and Ring Opening Polymerization (ROP). For the synthesis of miktoarm stars, a hydroxyl-terminated PE-OH, prepared by polyhomologation of dimethylsulfoxonium methylide with a monofunctional boron initiator, reacted with either chloromethyl(methyl)dimethoxysilane or chloromethyltrimethoxysilane. After the hydrolysis of the methoxysilane groups, the produced difunctional or trifunctional macroinitiators were used for the ROP of ε-caprolactone, in the presence of 1-tert-butyl-2,2,4,4,4-pentakis(dimethylamino)-2λ5,4λ5-catenadi(phosphazene)(t-BuP2). The H-type block copolymers were synthesized using the same strategy but with a difunctional polyhomologation initiator. All intermediates and final products were characterized by HT-GPC, 1H NMR, and FTIR analysis. The thermal properties of the PE precursors and final products were studied by DSC and TGA. In the fifth Chapter, the self-assembly properties of the amphiphilic linear block copolymer PE-b-PCL and 3-miktoarm star copolymers (PE-b-PCL2) were studied in THF, a selective solvent for PCL, by Dynamic Light Scattering (DLS), Transmission Electron Microscopy (TEM) and Atomic Force Microscope (AFM). All the above findings presented in this dissertation emphasize the utility of polyhomologation for the synthesis of well-defined polyethylene-based complex macromolecular architectures, which is practically impossible through another kind of polymerization, including the catalytic polymerization of ethylene. In the sixth Chapter, the summary of the thesis and some consideration on the subjects of future work are given.

Silica nanoparticles (SiO2 NPs) were prepared and functionalized with polyethylene (PE@SiO2 NPs) using the surface-initiated polyhomologation (SI polyhomologation) technique. Polyolefin nanocomposites were fabricated later by melt mixing of different ratios of the as-prepared SiO2 NPs and PE@SiO2 NPs with linear low-density polyethylene (LLDPE) and low-density polyethylene (LDPE) matrices. Firstly, SiO2 NPs were modified with different alkoxysilane ligands, dichloro(divinyl)silane (DCDVS), allyl trimethoxysilane (ATMS), and vinyl triethoxylsilane (VTES). Subsequently, thexylborane, an initiator for SI polyhomologation, was immobilized to the modified surface of SiO2 NPs through hydroboration reactions. Polyhomologation was then allowed to proceed by adding monomer solution to form polyethylene brushes covalently bonded to the surface of the NPs. Physicochemical characterization had confirmed the morphology, chemical structure, and thermal stability for each step of modification reactions. LLDPE and LDPE nanocomposites were prepared by extrusion with SiO2 NPs and PE@SiO2 NPs as nanofillers. Finally, tensile tests and morphological SEM-based analyses are presented to discuss the influence of the grafted PE on both the dispersion of the fillers and the mechanical properties of the filler/matrix interphase.

Polyethylene (PE) is produced in a huge scale globally and has plenty of desirable properties. It is used in coating, packaging, and artificial joint replacements. The growing need for high performance polyethylene led to the development of new catalysts, monomers and polymerizations. The synthesis of polymethylene (equivalent to polyethylene) by living polyhomologation opened the way to well-defined polymethylenes-based polymeric materials with controlled structure, molecular weight and narrow polydispersity. Such model polymers are substantial to study the structure-properties relationships. This research presents a new strategy based on the in situ formation of B-thexyl-silaboracyclic serving as initiating sites for the polyhomologation of dimethylsulfoxonium methylide. Combination with metal-free ring-opening polymerization (ROP) of ɛ-caprolactone (CL) and atom transfer radical polymerization (ATRP) of styrene led to three polymethylene-based 3-miktoarm stars copolymers PCL(PM-OH)2, Br-PCL(PM-OH)2 and PS(PM-OH)2.

Polyhomologation is a powerful method to prepare polyethylene-based materials with controlled molecular weight, topology and composition. This dissertation focuses on the discovery of new synthetic routes to prepare polyethylene-based macromolecular architectures by combining polyhomologation with highly orthogonal and efficient linking reactions such as Diels Alder, copper-catalyzed azide-alkyne cycloaddition (CuAAC), and Glaser. Taking advantage of functionalized polyhomologation initiators, as well as of the efficient coupling chemistry, we were able to synthesize various types of polymethylene (polyethylene)-based materials with complex architectures including linear co/terpolymers, graft terpolymers, and tadpole copolymers. In the first project, a facile synthetic route towards well-defined polymethylene-based co/terpolymers, by combining the anthracene/maleimide Diels–Alder reaction with polyhomologation, is presented. For the synthesis of diblock copolymers the following approach was applied: (a) synthesis of α-anthracene-ω-hydroxy-polymethylene by polyhomologation using tri (9 anthracene-methyl propyl ether) borane as the initiator, (b) synthesis of furan-protected-maleimide-terminated poly(ε-caprolactone) or polyethylene glycol and (c) Diels–Alder reaction between anthracene and maleimide-terminated polymers. In the case of triblock terpolymers, the α-anthracene-ω-hydroxy polymethylene was used as a macroinitiator for the ring-opening polymerization of D, L-lactide to afford an anthracene-terminated PM-b-PLA copolymer, followed by the Diels–Alder reaction with furan-protected maleimide-terminated poly (ε-caprolactone) or polyethylene glycol to give the triblock terpolymers. The synthetic methodology is general and potentially applicable to a range of polymers. The coupling reaction applied in the second project of this dissertation was copper-catalyzed “click” cycloaddition of azides and alkynes (CuAAC). Novel well-defined polyethylene-based graft terpolymers were synthesized via the “grafting onto” strategy by combining nitroxide-mediated radical polymerization (NMP), polyhomologation and copper(I)-catalyzed azide–alkyne cycloaddition (CuAAC). Three steps were involved in this approach: (a) synthesis of alkyne-terminated polyethylene-b-poly(ε-caprolactone) (PE-b-PCL-alkyne) block copolymers (branches) by esterification of PE-b-PCL-OH with 4-pentynoic acid; the PE-b-PCL-OH was obtained by polyhomologation of dimethylsulfoxonium methylide to afford PE-OH, followed by ring opening polymerization of ε-caprolactone using PE-OH as a macroinitiator (b) synthesis of random copolymers of styrene (St) and 4-chloromethylstyrene (4-CMS) with various CMS contents, by nitroxide-mediated radical copolymerization (NMP), and conversion of chloride to azide groups by reaction with sodium azide (NaN3) (backbone) and (c) “click” linking reaction to afford the PE-based graft terpolymers. This method opens up new routes for the creation of polyethylene-based graft terpolymers by a combination of polyhomologation, NMP and CuAAC. The third project deals with the synthesis of polyethylene-based tadpole copolymer (c-PE)-b-PSt. Cyclic polymers represent a class of understudied polymer architecture mainly due to the synthetic challenges. Within this dissertation, a new method was reported for the synthesis of cyclic polymers in exceptionally high purity and yield. The main approaches to synthesize macrocycles are based on the end-to-end ring-closure (coupling) of homo difunctional linear precursors under high dilution. Our process relies on the preparation of well-defined linear α, ω-dihydroxy polyethylene and a bromide group at the middle of the chain through polyhomologation of ylide using functionalized initiator, followed by ATRP of styrene monomer. The two hydroxyl groups were transformed into alkyne groups, via esterification reaction, followed by Glaser reaction between terminal alkynes to afford the tadpole-shaped copolymers with PE ring and PSt tail. In Our PhD research, we also studied the self-assembly properties of the amphiphilic copolymers PM-b-PEG in aqueous solution by DLS, Cryo-TEM, and AFM. Furthermore, the critical micelle concentration (CMC) was estimated from the intensity of the pyrene emissions by the fluorescence technique. All the findings presented in this dissertation are emphasizing the utility of polyhomologation for the synthesis of well-defined polyethylene-based complex macromolecular architectures, almost impossible through other kind of polymerization including the catalytic polymerization of ethylene.