Synthesis And Characterization Of Nonlinear Architectures Polymers Via Controlled/Living Polymerization

Several recent conceptual advances, which take advantage of the design criteria and practical techniques of molecular-level control in organic chemistry, allow preparation of well-defined polymers and nanostructured materials. Two trends are clear: the realization that synthesis of complex macromolecules poses major challenges and opportunities and the expectation that such materials will exhibit distinctive properties and functions. Polymer synthesis methods now being developed to yield well-defined synthetic macromolecules that are capable of mimicking many of the features of proteins (for example, three-dimensional folded structure) and other natural materials. These macromolecules have far-reaching potential for the study of molecular-level behavior at interfaces, in thin films, and in solution, while also enabling the development of encapsulation, drug-delivery, and nanoscale imprint-patterning technologies.Although the promise of accurately controlling chemical structure and functionality at the macromolecular level is considerable, it should be realized that it is not a simple process of transferring synthetic techniques directly from organic chemistry to polymer synthesis. Rather, because of the distinctive features of macromolecules compared with small molecules (e.g., number of functional groups, molecular weight distribution, and purification techniques), the elucidation of polymer synthesis protocols that proceed with structural fidelity and high levels of functional group compatibility is a grand challenge.Recently, however, several polymerization systems have been developed that offer much better control. In a living radical polymerization (LRP), each molecule of catalyst promotes rapid initiation and then stabilizes the growing chain to prevent branching or termination. Thus, different types of monomer can be added to the reaction consecutively, leading to polymers with well-defined blocks that vary in structure and function.The discovery of simple and powerful approaches to polymerization reactions, which are not limited by the presence of additional functional groups and provide accurate molecular weights and narrow molecular weight distributions, allows nonspecialists access to well-defined materials, previously the domain of a select few. Moreover, the increased tolerance of functional groups for these new polymerization processes offers opportunities for combining different fields of chemistry and the construction of macromolecules with a hierarchical arrangement of functional groups and branches.Depending on the matter of end groups per macromolecule as well as macroinitiator, the telechelic polymers can be used as precursors to form various types of block copolymers, e.g., AB, ABA, as well as sophisticated star or radical block copolymers. With the advent of this method, during the past decade, the design and realisation of well-defined and functional polymer architectures have attracted considerable attention. The newly designed polymer architectures determine the different properties of polymers with versatile applications in various fields like drug delivery and controlled release, molecular devices for sensors, switchable and signal transducing, microphase separation in bulk, sol-gel states, interfaces and surfaces, the phenomenal changes in bulk behaviors, phase structures, morphologies and others.The amphiphilic block copolymers with sophisticated structures play important role in this direction. For example, amphiphilic block copolymers: PS-b-PEO and PS-b-PAA can self-assemble to form vesicles with spherical, cylindrical, and vesicular morphologies in aqueous medium. Water-dispersible polymeric vesicles are more durable than conventional liposomes and hence those are promising nanosized vehicles for the protection and delivery of water-soluble drugs and proteins. Micellar self-assembly techniques have attracted increasing attention to prepare block copolymer vesicles which avoid solvents, such as film rehydration (film swelling), bulk swelling, and electroformation.In many cases, specific applications are driving areas of research. For targeted drug delivery and/or diagnostic agents, precisely defined macromolecules and nanoscale objects are needed and will require multiple functional groups for drug payload, cell targeting, delivery, and tracking. Other diverse fields, such as microelectronics, where the drive is to develop G50-nm feature sizes, require polymers with accurate control over their length, dispersity, and functionality not only for traditional photolithography but also for alternative nanopatterning techniques. An excellent example is the enabling influence of functionalized block and random copolymers, prepared by LRP, on selfassembling block copolymer template strategies. This synergy and molecular-level focus will be matched by a closer connection between nanotechnology and organic/polymer chemistry. The controlled manipulation of nanoscale objects and patterns by predictable changes in polymer structure is a potent concept that is only beginning to be exploited.The well-defined and complex macromolecular architectures of polymers are synthesized by various methods like living anionic polymerization, living cationic polymerization, and controlled/living radical polymerization, namely, atom transfer radical polymerization, nitroxide-mediated polymerization, and reversible addition-fragmentation chain transfer polymerization. The methods provided powerful tools to synthesize star-shaped, star-branched, comb-like, dendrimer-like, exact graft polymers (π-shaped, H-shaped, super H-shaped). In general, those copolymers are synthesized by living ionic polymerization method. Besides these, some combinations of those methodologies like living anionic and cationic polymerization, and controlled and living radical polymerizations have recently been widely used to prepare some complex polymers.Combinations of living anionic/cationic polymerization with other controlled/living polymerization methods allow for functionalization of the monomer units and termini through orthogonal chemistry to yield more predictable macromolecular architectures and complex polymers for target specific applications.A new asymmetric H-shaped block copolymer (PS)2-PEO-(PMMA)2 has been designed and successfully synthesized by the combination of atom transfer radical polymerization and living anionic polymerization. The synthesized 2,2-dichloro acetate-ethylene glycol (DCAG) was used to initiate the polymerization of styrene by ATRP to yield a symmetric homopolymer (Cl-PS)2-CHCOOCH2CH2OH with an active hydroxyl group. The chlorine was removed to yield the (PS)2-CHCOOCH2CH2OH ((PS)2-OH). The hydroxyl group of the (PS)2-OH, which is an active species of the living anionic polymerization, was used to initiate ethylene oxide by living anionic polymerization via DPMK to yield (PS)2-PEO-OH. The (PS)2-PEO-OH was reacted with the 2,2-dichloro acetyl chloride to yield (PS)2-PEO-OCCHCl2 ((PS)2-PEO-DCA). The asymmetric H-shaped block polymer (PS)2-PEO-(PMMA)2 was prepared via ATRP of MMA at 130°C using (PS)2-PEO-DCA as initiator and CuCl/bPy as the catalyst system. The architectures of the asymmetric H-shaped block copolymers, (PS)2-PEO-(PMMA)2, were confirmed by 1H NMR, GPC and FT-IR.A novel fluorescent dye labeled H-shaped block copolymer, (PMMA-dye-PS)2-PEO-(PS-dye- PMMA)2, is synthesized by the combination of atom transfer radical polymerization (ATRP) and anionic polymerization (AP). To obtain the designated structure of the copolymer, a macroinitiator, 2,2-dichloro acetyl-PEO-2,2-dichloro acetyl (DCA-PEO-DCA), was prepared from DCAC and poly(ethylene oxide). The copolymer was characterized by 1H NMR, GPC and fluorescence spectroscopy. The functionalization of the monomer units in the form of macroinitiators in an orthogonal fashion yields more predictable macromolecular architectures and complex polymers. As a result of fact, a new王-shaped amphiphilic block copolymer: (PMMA)2-PEO-(PS)2-PEO-(PMMA)2 has been designed and successfully synthesized by the combination of atom transfer radical polymerization and living anionic polymerization. The synthesis of Meso-2,3-dibromosuccinic acid acetate-diethylene glycol (DBSDG) was used to initiate the polymerization of styrene via ATRP to yield the linear (HO)2-PS2 with two active hydroxyl groups by living anionic polymerization via DPMK to initiate the polymerization of ethylene oxide. Afterwards, the synthesis of miktoarms-4 amphiphilic block copolymer (HO-PEO)2-PS2 was esterified with 2,2-dichloro acetyl chloride to form a macroinitiator that initiates the polymerization of MMA via ATRP to prepare the王-shaped amphiphilic block copolymer. The polymers were characterized by GPC and 1H NMR spectroscopy.A new initiator for atom transfer radical polymerization, (Cl2HCCOOCH2)4-C (TeDCAP), has been designed and successfully synthesized. The initiator was used to initiate the polymerization of styrene via atom transfer radical polymerization to yield an eight-Arm polystyrene with functional end-group chlorides. The different polymers could be prepared via ATRP of different monomers at 130°C using TeDCAP/CuCl/bPy as the initiating system. The initiator and eight-Armed polymer were characterized by means of 1H NMR, FT-IR and GPC.A new initiator for atom transfer radical polymerization, (Cl2HCCOO)3-C6H3, (TrDCAP), has been designed and successfully synthesized. The 6-Arm PS was synthesized by that ATRP of styrene was carried out using TrDCAP as hexafunctional initiator and the CuCl/bPy catalyst at 130°C in 30% THF via Core-First strategy. The 6-Arm PS-AAP was synthesized by nucleophilic substitution polymerization of 6-Arm PS and 4-anisidine azomethine-4'-phenol (AAP).The initiator and the architectures of the 6-Arm PS were confirmed by 1H NMR, FT-IR, UV-vis and GPC.The functionalization of the monomer units in the form of macroinitiators in an orthogonal fashion yields more predictable macromolecular architectures and complex polymers. As a result of fact, a novel star comb-like block copolymer 4-Arm poly[styrene-ran-4-vinylbenzyl-g-(pMMA)]has been designed and successfully synthesized by the combination of reversible addition-fragmentation chain transfer polymerization and atom transfer radical polymerization. The effect of steric hindrance in Grafting From technique has been studied. The polymers were full characterized by GPC, 1H NMR spectroscopy and 13C NMR spectroscopy. To obtain the star comb-like architectures of the copolymer a series of initiators/macroinitiators were prepared and analyzed with the above mentioned analytical techniques.